gear cutting_tools ( hobbing, seration , milling etc )

Leitz Metalworking Technology Group

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Gear Cutting Tools• Hobbing• Gear Milling

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Belgien/BelgiumSA LMT Fette NVIndustrieweg 15 B21850 GrimbergenFon +32-2/2 51 12 36Fax +32-2/2 51 74 89

Brasilien/BrazilLMT Böhlerit LTDA.Rua André de Leão 155 Bloco ACEP: 04672-030Socorro-Santo AmaroSão PauloFon +55/11 55 46 07 55Fax +55/11 55 46 04 [email protected]

ChinaLeitz Tooling Systems(Nanjing) Co. Ltd.Division LMTNo. 81, Zhong Xin RoadJiangning Development ZoneNanjing 211100Fon +86-25/2 10 31 11Fax +86-25/2 10 63 [email protected]

Deutschland/GermanyLMT Deutschland GmbHHeidenheimer Straße 84D-73447 Oberkochen Tel. +49 (0) 73 64/95 79-0Fax +49 (0) 73 64/95 79-80 00E-mail: [email protected]: www.LMT-tools.de

www.LMT-tools.com

England/United Kingdom LMT Fette LimitedLongfordCoventry 304 Bedworth RoadWarwickshire CV6 6LAFon +44 24 76 36 97 70Fax +44 24 76 36 97 [email protected]

Frankreich/FranceLMT FETTEParc d’Affaires Silic-Bâtiment M216 Avenue du QuébecVillebon sur YvetteBoite Postale 76191963 Courtabœf CedexFon +33-1/69 18 94-00Fax +33-1/69 18 [email protected]

Belin Yvon S.A.F-01590 Lavancia, FrankreichTel. +33 (0) 4 74 75 89 89Fax +33 (0) 4 74 75 89 90E-mail: [email protected]: www.belin-y.com

Bilz Werkzeugfabrik GmbH & Co. KGVogelsangstraße 8 D-73760 Ostfildern, DeutschlandTel. +49 (0) 711 3 48 01-0Fax +49 (0) 711 3 48 12 56E-mail: [email protected]: www.bilz.de

Boehlerit GmbH & Co. KGWerk VI-StraßeDeuchendorf A-8605 Kapfenberg, ÖsterreichTel. +43 (0) 38 62 300-0Fax +43 (0) 38 62 300-793E-mail: [email protected]: www.boehlerit.com

Fette GmbHGrabauer Str. 24D-21493 Schwarzenbek, DeutschlandTel. +49 (0) 41 51 12-0Fax +49 (0) 41 51 37 97E-mail: [email protected]: www.fette.com

Kieninger GmbHAn den Stegmatten 7 D-77933 Lahr, DeutschlandTel. +49 (0) 7821 943-0Fax +49 (0) 7821 943-213E-mail: [email protected]: www.kieninger.de

Onsrud Cutter LP800 Liberty Drive Libertyville, Illinois 60048, USATel. +1 (847) 362-1560Fax +1 (847) 362-5028E-mail: [email protected]: www.onsrud.com

Indien/IndiaLMT Fette India Pvt. Ltd. 29, II Main RoadGandhinagar, AdyarChennai 600 020Fon +91-44/24 405 136 / 137Fax +91-44/24 405 [email protected]

Mexiko/MexicoLMT Boehlerit S.A. de C.V.Matias Romero No. 1359Col. Letran Valle03650 Mexico D.F.Fon +52 (55) 56 05 82 77Fax +52 (55) 56 05 85 [email protected]

Österreich/AustriaFETTE PräzisionswerkzeugeHandelsgesellschaft mbHRodlergasse 51190 WienFon +43-1/3 68 17 88Fax +43-1/3 68 42 [email protected]

Singapur/SingaporeLMT Singapore Representative Office1 Clementi Loop #4-04Clementi West District ParkSingapore 12 98 08Fon +65 64 62 42 14Fax +65 64 62 42 [email protected]

Spanien/SpainLMT Boehlerit S.L.C/. Narcis Monturiol, 11 Planta 1a08339 Vilassar De Dalt (Barcelona)Fon +34-93/7 50 79 07Fax +34-93/7 50 79 [email protected]

Tschechien/Czech RepublicLMT FETTE spol. sr.o.Drázni 7627 00 Brno-SlatinaFon +420-5/48 21 87 22Fax +420-5/48 21 87 [email protected]

LMT Fette spol. sr.o.Kancelaf BoehleritVodni 1972. CZ-760 01 ZLINFon +420 57 72 14 989Fax +420 57 72 19 061

Türkei/TurkeyBöhler Sert Maden Takim Sanayive Ticaret A.S.Ankara Asfalti ü zeri No.22 Kartal 81412 IstanbulP.K. 167Fon +90-216/3 06 65 70Fax +90-216/3 06 65 [email protected]

Ungarn/HungaryLMT Boehlerit KFT.Kis-Duma U.6PoBox 2036 Erdliget Pf. 322030 ErdFon +36/23 52 19 10Fax +36/23 52 19 [email protected]

USAKanada/CanadaLMT-FETTE Inc.18013 Cleveland ParkwaySuite 180Cleveland, Ohio 44135Fon +1-2 16/3 77-61 30Fax +1-2 16/3 77-07 87

Pictures were generously provided by the following machinetool manufacturers:

Getriebebau Nord Schlicht & Küchenmeister, BargteheideGleason-Pfauter Maschinenfabrik GmbH, LudwigsburgLiebherr Verzahntechnik GmbH, Kempten

© by FETTE GMBHThis publication may not be reprinted in whole or part withoutour express permission. All rights reserved. No rights may be derived from any errors in content or fromtypographical or typesetting errors.Diagrams, features and dimensions represent the currentstatus on the date of issue of this catalogue. We reserve theright to make technical changes. The visual appearance ofthe products may not necessarily correspond to the actualappearance in all cases or in every detail.

Important information

Page

Important information 4

Services 5

An introduction to FETTE 6

4

Important informationArticle numbersTo speed up order supply and toavoid confusion, orders should al-ways specify the article numberslisted in this catalogue.

PricesThis catalogue does not containprices. Prices can be found in thelatest price list for standard arti-cles. Please consult us for a quotewith regard to semi-standard orspecial items.

Minimum order valueOrders with a total value of lessthan DM 200.00 are subject to aprocessing surcharge of DM50.00. We trust that you will appre-ciate the need for this measure.

Tool groupsOur wide range of hobbing tools isdivided into tool groups, which aremarked in the index at the side ofthe page and are thus easily locat-ed.

Product rangeThe entire FETTE catalogue prod-uct range with some 15,000 stan-dard items, 1,100 in the hobbingarea alone, is subject to continu-ous improvement. As part of thisprocess, we not only introducenew and therefore technologicallysuperior products into our range,but also take care to remove out-dated products from it.

In some cases it could happen thatwe do not carry in stock the itemwhich you have ordered. In thiscase you will in general receiveproducts from us technologicallybetter product, but at least anequivalent alternative. In case ofdoubt, our sales team is availableto determine a design that will pro-duce best possible results for you.

By following this procedure, youcan be sure that you are always besupplied with tools, which aretechnologically to the newest stan-dard. For that reason, we do notfeel not obliged to supply tools,which are still shown in the cata-logue, or which have been clearedfrom the programme already inter-nally.

Catalogue number indexAll catalogue numbers, arranged innumerical order and with the pagenumber, are listed on page 193.

DIN Standard indexAn index on all DIN Standard num-bers covered is listed on page194.

Technical detailsTechnical application details of ageneral nature commence on page125, whereas the specific techni-cal details concerning individualproduct groups are directly as-signed to the section concerned.

Special formsShould you be unable to find a so-lution to your machining tasksamong the 1,100 items which westock, special forms are availableupon request, including formsmanufactured specifically to yourdrawings.

5

Services

PVD-Coating

Grinding Services

6

Application advice and serviceProduction on modern machine tools combined with up-to-date CNC technique

Design and development

FETTE – a brief introduction

Quality assurance

Training

Heat treatment

Ecology and environment protection are part of the companyphilosophy, recognizable on the factory grounds

Hobsfor spur gears, straight- or helical tooth, with involute flanks

Cat.-No. Page

Hobs for the manufacture of straight spur gears, straight or helical tooth, with involute flanks 10

Explanatory notes on the descriptions and size tablesfor hobs for straight spur gears 11

Solid-type hobsrelief ground, DIN 58411 2002 13relief ground, in solid carbide 2008 14relief ground, DIN 8002 A 2022 15relief turned, DIN 8002 B 2031 16relief ground, DIN 8002 B 2032 16relief ground 2033 17relief ground, for spur gears to DP 2042 18for straight spur gears 2026 47

Multiple-gash hobs 19

Solid carbide hobs 26

Roughing hobs 32relief turned, 20 gashes, with drive slot 2051 34relief ground, 20 gashes, with drive slot 2053 34relief turned, 16 gashes, with drive slot 2055 34relief ground, 16 gashes, with drive slot 2057 34relief turned, 20 gashes, with keyway 2061 35relief ground, 20 gashes, with keyway 2063 35relief turned, 16 gashes, with keyway 2065 35relief ground, 16 gashes, with keyway 2067 35

Roughing hobs with indexable carbide inserts 36with 19 blade rows 2163 39

Carbide skiving hobs 40Solid carbide 2028 44with 12 or 15 brazed-on blade rows 2129 45with indexable carbide inserts 2153 46

Ffsfo

Ffsfu

Hobs for producing straight- and helical-tooth spur gears with involute flanks

The fundamental geometrical con-cepts of a spur gear hob for gener-ating gears with involute flanks arelaid down and explained in detailin DIN 8000. According to this, thebasic body of a hob is always aworm. If this worm is now providedwith flutes, cutting teeth result.These become capable of cuttingby being backed off or relieved.

This relieving operation is carriedout on machine tools specially de-veloped for this process; it is verytime consuming and therefore alsoexpensive. For hobs to moderateaccuracy specifications, reliefturning is sufficient; for stricterquality requirements the hob is re-lief ground.

Generally, relief turned hobsachieve quality class B approxi-mately to DIN 3968. Relief groundhobs achieve quality classes A, AAand higher. The highest qualityclass in DIN 3968 is AA. For ex-ceptionally high quality require-ments it is usual to restrict the tol-erances of quality class AA stillfurther. Quality class correspond-ing to AAA to DIN 3868, without

comment, means the restriction to75 % of the AA tolerances for allmeasurable variables.

If special tolerance restrictions ofthe AA tolerance are required, thisis also done with the AAA refer-ence, but the individual measur-able variables and the tolerancerestriction are now given in % ordirectly in µm. E.g. quality classAAA to DIN 3968, item nos. 16 and17 restricted to 50 % of the toler-ance of AA.

The purpose of hob tolerances isto assign the tools to a qualityclass according to their accuracy.On the basis of the hob qualityclasses, the expected gear qualitycan then be forecast.

Not all requirements aimed at a”good gear quality“ in the widersense, e.g. very quiet running or aspecific addendum- and deden-dum relief are achieved solelythrough a high cutter quality. Forsuch needs, hobs with a definedcrowning depth have proved suc-cessful. Depending on the loadand the required gear perfor-

mance, the suitable crowningdepth can be selected from thevarious tables N102S, N102S/3 orN102S/5. It must be noted that thetool depth crowning is not trans-mitted completely to the gear. Thelower the number of teeth of thegear, the less the effective convex-ity portion.

10

Tolerances for hobs with special class tolerance values in 1/1000 millimetres

0,63–1 1–1,6 1,6–2,5 2,5–4 4–6,3 6,3–10 10–16 16–25 25–40

FfSfo 25 28 32 36 40 50 63 80 100FfSfu 12 14 16 18 20 25 32 40 50

N 102 S FfSo 4 4 4 5 6 8 10 12 16FfSu 0 0 0 0 0 0 0 0 0FfSao 16 16 16 20 24 32 40 50 64FfSau 8 8 8 10 12 16 20 25 32FfSfo 12 14 16 18 20 25 32 40 50FfSfu 8 8 8 10 12 16 20 25 32

N 102 S/3 FfSo 4 4 4 5 6 8 10 12 16FfSu 0 0 0 0 0 0 0 0 0FfSao 12 14 16 18 20 25 32 40 50FfSau 8 8 8 10 12 16 20 25 32FfSfo 8 8 8 10 12 16 20 25 32FfSfu 4 4 4 5 6 8 10 12 16

N 102 S/5 FfSo 0 0 0 0 0 0 0 0 0FfSu 0 0 0 0 0 0 0 0 0FfSao 8 8 8 10 12 16 20 25 32FfSau 0 0 0 0 0 0 0 0 0

ModuleTolerance range

involute withtop convexity

FfSfo

FfSfuFfSao

FfSau

Tolerance range

FfSfo

FfSfu

Tool root section Tool tooth tipForm deviation of the cutting edge

Notes to the descriptions and size tablesfor spur gear hobs

Owing to the many different hobversions available, their presenta-tion in a product catalogue mustbe restricted to a range which isintended as a representative se-lection. Standardized referenceprofiles to DIN 3972 or DIN 58412and size series to DIN 8002 or DIN58411 were selected for inclusionin the catalogue.

For cutter designs such as broach-tooth type roughing hobs or skiv-ing hobs, the size tables werebased upon works standardswhich maximize usefulness withinthe constraints of the design crite-ria.

These standard tools can, how-ever, only cover part of therequired hob range, and possiblevariants are therefore brieflylisted below.

DimensionsThe four main dimensions of thehobs are stated in the followingsequence: cutter diameter, cuttingedge length, total length and borediameter; e.g. for module 8, cat.no. 2032; dia. 125 x 130/138 x dia. 40.Diverse measurements may be-come necessary due to the work-piece shape, because of the limi-tation of the cutter dimensions dueto the measurements and perfor-mance of the hobbing machine,through the dimensions of theavailable cutter arbors or toachieve specific cutting par-ameters or machining times.

Cutter materials

The standard material is the high-speed EMo5Co5 (material no.1.3242).

Gear materials whose tensilestrength values exceed 1200N/mm or which are intended forvery high cutting speeds andfeeds are manufactured from pow-der metallurgical high-speed steel.

Carbides are increasingly beingemployed for high-performancehobbing and for skive hobbing.

Coating

A hard coating with a thickness of2 to 3 µm increases the life of thehobs, or permits higher cuttingrates. Further information on thecoatings can be found on Pages151 and 152 in the technical sec-tion of the catalogue.

Basic tooth profilesThe definition and description ofthe various reference tooth profilesare found in the technical part ofthe catalogue on pp. 137 to 148.

Pressure angleThe pressure angle, as also themodule, is determined by the gearcutting data of the workpiece andmust be taken into account whendeciding on the basic hob profile.

Tip edge chamferTo protect the tip edges againstdamage, they are chamfered. Thistip edge chamfer can be producedduring manufacture with a suitablydimensioned hob. To determinethe hob reference or basic profilecorrectly, the complete gearcutting data are needed. The sizeof the tip edge chamfer dependson the number of teeth, i.e. whenusing the same hob for differentnumbers of gear teeth, the cham-fer will decrease with a smallernumber of teeth. For a large toothnumber range, several differentcutters are needed.Information about these relation-ships and recommended chamfersizes can be made available on re-quest.

Profile modificationThe purpose of the profile modifi-cation is to reduce or avoid theinterference when the teeth rollinto mesh while a gear pair is run-ning under load. To decide on thebasic profile of the hob, the com-plete tooth cutting data or the

workpiece drawing are necessary.The size of the profile modificationproduced depends, similarly aswith the tip edge chamfer, on thenumber of teeth.

ProtuberanceThe protuberance creates a clear-ance cut in the root of the tooth, sothat during the next operation thegrinding wheel or the rotary shav-ing cutter does not machine thetooth root. This prevents stresspeaks through grinding- or shav-ing stages.

The protuberance basic profilesare not standardized and are sup-plied on request to your require-ments. If you do not have relevantexperience, we can submit sug-gestions and if necessary prepareprofile plots for your gear cuttingdata.

Multi-start hobs

Multi-start hobs are used to in-crease hobbing output. This ap-plies particularly in the case ofgears with small modules (� mod-ule 2.5) and relatively large num-bers of teeth. In the case of hobswith axially parallel flutes, thenumber of starts should be select-ed so that a lead angle of 7.5° isnot exceeded. The approachingtooth flanks of the hob can other-wise be expected to produce aninferior surface quality on the gearflanks.

Lead directionWith the usual uni-directional hob-bing of helical spur gears, the leaddirection of the hob and the helixdirection of the gear are the same;with contra-directional hobbingthey are opposite. In the case ofstraight spur gears both right-hand- and left-hand cutters can beused. Normally, one uses right-hand cutters.

11

12

Topping cuttersThe outside diameter of the gearis topped by the tooth root of thehob. Changes in the tooth thickn-ess also result in changes of theoutside diameter.

ChamferWhen hobbing helical spur gearswith large diameters, the hobscannot always be chosen longenough to cover the entire workingarea. To prevent excessive wear ofthe hob teeth in the approacharea, the hob is provided with a ta-pered chamfer. For gears withdouble-helical teeth, two hobswith chamfer may be necessary, ifthe distance between the twotooth rows is relatively small.

Depending on whether hobbing isby the climb or conventional meth-od, the chamfer — generally 5 to 6x module long and 5° to 10° angleof inclination — is situated on theentering- or leaving end of thecutter.

Rake

Unless otherwise agreed, hobshave a rake of 0°. This does notapply to broaching tooth typeroughing hobs, which have a rakeof +8°, and indexable insert andskive hobs, which have a rake of-10° to -30°.

GashesA high number of gashes increas-es the cutting capacity of the hobsand the density of the envelopenetwork; they do however also re-duce the useful tooth length,unless the cutter diameter isincreased accordingly. For solidtype hobs the gashes are up to ahelix angle of 6° made axially par-allel and over 6° with helix.

DP and CPIn English-speaking countries, dia-metral pitch and circular pitch areused instead of the module. lt isbest to convert the above valuesinto module and to proceed withthe calculated module in the usualway.

The equations for the conversioninto module are:

m = 25.4 / DPm = 25.4 · CP / 3.1416

13

Solid-type hobs

l1l3

d1 d2

for spur and helical gears to module pitch

20° pressure anglebasic profile N2 to DIN 58412quality grade 7 to DIN 58413single start right-handedwith keyway1)

KHSS-E EMo5Co5

Dimensions in mm Number ofgashes

Ident No.m d1 I3 I1 d2

2002 relief ground ■ DIN 58411Cat.-No.

0,2 25 6 12 8 8 11933100,2 32 12 16 13 10 12020970,25 25 6 12 8 8 12020990,25 32 12 16 13 10 1193347

0,3 25 10 16 8 8 11933560,3 32 12 13 10 12030020,35 25 10 8 8 12030040,35 32 12 13 10 1193383

0,4 25 10 16 8 8 11933920,4 32 12 13 10 11934090,45 25 10 8 8 12030060,45 32 12 13 10 1193427

0,5 25 10 16 8 8 11934360,5 32 12 13 10 11934450,6 25 10 8 8 11934540,6 32 12 13 10 11934630,6 40 20 24 16 12 1193472

0,7 25 14 162) 8 8 11934810,7 32 20 24 13 10 11934900,7 40 16 12 1193506

0,75 25 14 162) 8 8 12030080,75 32 20 24 13 10 11935240,75 40 16 12 1193533

0,8 25 14 162) 8 8 11935420,8 32 20 24 13 10 11935510,8 40 16 12 1193560

0,9 32 20 24 13 10 11935790,9 40 16 12 11935881,0 32 13 10 11935971,0 40 16 12 1193604

1) Standard design: 8 mm bore without keyway2) This size is only supplied with a single indicator hub.

14

Solid-type hobs

l1l3

d1 d2


20° pressure anglebasic profile N2 to DIN 58412quality grade 7 to DIN 58413single start right-handedwith keyway1)

Solid carbide



2008 relief groundCat.-No.

0,2 25 7 10 8 12 11937020,25 1193704

0,3 25 9 12 8 12 11937060,3 32 12 16 13 11937080,35 25 9 12 8 11937100,35 32 12 16 13 1193712

0,4 25 9 12 8 12 11937140,4 32 12 16 13 11937160,45 25 9 12 8 11937180,45 32 12 16 13 1193720

0,5 25 13 16 8 12 11937220,5 32 12 13 11937240,6 25 13 8 11937260,6 32 12 13 11937280,6 40 20 25 16 1193730

0,7 25 15 18 8 12 11937320,7 32 20 25 13 11937340,7 40 25 16 1193736

0,75 25 15 18 8 12 11937380,75 32 20 25 13 11937400,75 40 25 16 1193742

0,8 25 15 18 8 12 11937440,8 32 20 25 13 11937460,8 40 16 1193748

0,9 25 15 18 8 12 11937500,9 32 20 25 13 11937520,9 40 16 1193754

1,0 25 15 18 8 12 11937561,0 32 20 25 13 11937581,0 40 16 1193760

1) Standard design: 8 mm bore without keyway

15

Solid-type hobs

l0l3

d1 d2


20° pressure anglebasic profile II to DIN 3972quality grade A to DIN 3968single start right-handedwith drive slot

KHSS-E EMo5Co5



2022 relief ground ■ DIN 8002 ACat.-No.

1 50 25 44 22 14 12020131,25 12020151,5 56 32 51 12 12020171,75 1202019

2 63 40 60 27 12 12020212,25 70 50 70 12020232,5 12020252,75 1202027

3 80 63 85 32 12 12020293,25 12020313,5 12020333,75 90 70 94 1202035

4 90 70 94 32 12 12020374,5 10 12020395 100 80 104 12020415,5 1202043

6 115 100 126 40 10 12020456,5 12020477 12020498 125 130 156 12020519 1202053

10 140 160 188 40 10 120205511 160 170 200 50 9 120205712 170 185 215 120205913 180 200 230 120206114 190 215 245 1202063

15 200 225 258 60 9 120206516 210 238 271 120206717 220 120206918 230 260 293 120207119 240 1202073

20 250 286 319 60 9 120207521 260 290 320 120207722 270 290 120207923 280 310 340 120208124 1202083

25 290 310 350 60 9 120208526 310 320 360 80 120208727 320 330 370 120208928 120209129 340 340 380 120209330 1202095

16

Solid-type hobs

l1l3

d1 d2


20° pressure anglebasic profile II to DIN 3972single start right-handedwith drive slot

KHSS-E EMo5Co5

Dimensions in mm Ident No.2032

Ident No.2031

Number ofgashesm d1 I3 I1 d2

2031 relief turned ■ Quality grade B/C to DIN 3968 ■ DIN 8002 B

2032 relief ground ■ Quality grade A to DIN 3968 ■ DIN 8002 BCat.-No.

0,5 50 16 22 22 14 1203953 21154250,75 1203955 21067901 25 31 1203951 1205165

1,25 50 25 31 22 14 1203960 12051741,5 56 32 38 12 1203979 12051831,75 1203957 1205192

2 63 40 46 27 12 1203997 12052092,25 70 50 56 1203959 12052182,5 2116023 12052272,75 1204022 1205236

3 80 63 69 32 12 1204031 12052453,25 1204040 12052543,5 1204059 12052633,75 90 70 78 1204068 1205272

4 90 70 78 32 12 1204077 12052814,5 10 1203961 12052905 100 80 88 1204095 12053075,5 1203963 1205316

6 115 100 108 40 10 1203871 12053256,5 2116027 12053347 2116028 12053438 125 130 138 1204148 12053529 1203963 1205361

10 140 160 170 40 10 1203924 120537011 160 170 180 50 9 1203933 120538912 170 185 195 1203942 120539813 180 200 210 2116972 120540514 190 215 225 2251076 1205414

15 200 225 235 60 9 2206629 120542316 210 238 248 2206630 120543217 220 – 226441018 230 260 270 2106631 120545019 240 – 1203986

20 250 286 296 60 9 2106632 120547821 260 290 300 1203967 120398822 270 2106633 210547523 280 310 320 1203969 120399024 1203971 2107384

25 290 320 330 60 9 1203973 211792626 310 80 1203975 225116827 320 330 340 1203977 120399228 1203980 120399429 340 340 350 1203982 120399630 2106635 2117930

17

Hobs

l1l3

d1 d2

For economical production on modern hobbing machines


20° pressure anglebasic profile II to DIN 3972quality grade A to DIN 3968single start right-handedwith keyway

KHSS-E EMo5Co5 – TiN-coated




1 50 44 50 22 15 12057712 63 80 90 27 12057732,5 70 90 100 12057753 80 110 120 32 12057774 90 120 130 12057795 100 140 150 12057816 115 40 12057837 125 12057858 140 180 190 50 12057879 14 1205789

10 160 200 210 1205791

18

Dimensions in mm Number ofgashesd1 I3 I1 d2DP

Solid-type hobs

l1l3

d1 d2

for spur and helical gears to DP (Dia-metral Pitch)

20° pressure anglebasic profile: ha0 = 1.25 · m, öa0 = 0.3 mquality grade A to DIN 3968single start right-handedwith keyway

KHSS-E EMo5Co5


1 290 320 330 60 91,25 250 286 2961,5 220 238 2481,75 200 225 235

2 180 200 210 50 92,5 140 160 170 40 103 125 130 1383,5 115 100 108

4 115 100 108 40 105 100 80 88 326 90 70 787 12

8 80 63 69 32 129

10 70 50 56 2711

12 63 40 46 27 121314 56 32 38 221516171819 50 25 31 22 142021222324

25 50 25 31 22 142627282930

19

Multiple-gash hobs

20

Coated solid-type hobs with a highnumber of gashes are ideally suit-ed to high-performance hobbingof straight spur gears. Solid-typehobs are more stable than anytype of composite hob. The highnumber of gashes permits a highrate of chip removal, and the toollife is increased substantially bythe coating and, where applicable,re-coating.

Compared to conventional hobs,high-performance hobs are re-quired to have:

■ A higher tool life quality;■ Shorter machining times;■ At least equal if not superior

gear quality.

These requirements are interrelat-ed, such that measures which forexample reduce the machiningtime may have a detrimental effectupon the tool life or the gearquality.

Hobs can be optimized only inconsideration of the machining en-vironment. Based upon the ge-ometry and the material and qual-ity characteristics of the gear inquestion, the hob design andcutting parameters must bematched such that the require-ments are broadly fulfilled.

Tip chip thickness

The tip chip thickness is an impor-tant criterion for hob design andoptimization.

The tip chip thickness is the theo-retical maximum chip thicknesswhich can be removed by the hobsteeth.

The following hob characteristicsand cutting parameters are takeninto account during calculation ofthe tip chip thickness:

■ Module■ Number of teeth■ Helix angle■ Profile displacement■ Cutter diameter■ Number of gashes■ Number of starts■ Axial feed■ Cutting depth.

Increased tool life quality

An increase in the number ofgashes is a design measure with adecisive, positive effect upon thetool life quality. The increase in thenumber of gashes results in thevolume to be machined being dis-tributed over a greater number ofcutter teeth, and the tip chip thick-nesses being reduced.

Smaller tip chip thicknesses re-quire smaller cutting forces, whichreduce the stresses placed uponthe cutting edges of the hob andlead to lower wear. Lower tip chipthicknesses enable higher tool lifequalities to be achieved.

Assuming that the hob diameter

remains unchanged, however, anincrease in the number of gashesreduces the number of regrindswhich are possible. If the numberof gashes is selected so that onlyone to three regrinds are possible,the hob is described as an super-fine-tooth cutter.

Hobs with 20 to 30 gashes and auseful tooth length for approxi-mately 10 regrinds are describedas multi-tooth cutters.

Whether multi-tooth or superfinetooth hobs are the ideal tools for aspecific gear hobbing task mustbe determined by means of a costanalysis. The cost structure andcapacity exploitation of the user'sinstallation are also decisive fac-tors.

Developments over recent yearshave shown that in the majority ofcases, the multi-tooth cutter is themost suitable tool.

A cutter with a high number ofgashes also generates a denserenvelope network, i.e. the profileform of the gear is improved. Thisis particularly significant for work-pieces with a small number ofteeth.

fa

δx

d

δx [mm] = facos β0

2 ·

sin αn

4 · da0

δx [mm] = depth of the feed markingfa [mm/WU] = axial feedβ0 = helix angleαn = pressure angleda0 [mm] = tip circle diameter of the hob

Depth of the feed markings

21

In order to achieve a high tool lifequality, high-performance hobsmust be coated. Titanium nitride(TiN) is generally employed as acoating at present. The high de-gree of hardness of the TiN coat-ing and the reduction in frictionbetween the chips and the cuttingfaces and flanks of the cutter teethpermit higher cutting speeds andfeeds together with considerablylonger tool life.

When the hob is sharpened, theTiN coating is removed from thecutting faces. Pitting increases onthe now uncoated cutting faces,and the tool life quality is reduced.In order to exploit the high perfor-mance potential of these hobs tothe full, it follows that hobs forhigh-performance machining mustbe re-coated.

The tool life quality is obviously al-so increased if the cutter length isextended, since the shift distanceis extended by the same quantitywith which the cutter length is in-creased.

The shift strategy has a consider-able influence upon the tool lifequality. The strategy for high-per-formance hobbing is described ascoarse shifting.

The shift increment is calculated inthe familiar way by dividing theavailable shift distance by thenumber of workpieces or work-piece packs which can be ma-chined between two regrinds. Onconventional hobbing machines,the standard procedure was toshift the hob through once by theshift increment calculated in this

way, and then to regrind it. Practi-cal experience has shown how-ever that the tool life quality israised considerably if the hob isshifted through several times withan increasing shift increment. It isimportant that the starting point forthe subsequent shift pass is dis-placed with each shift by a smalldistance in the direction of shifting.

Coarse shifting also enables thewear development to be observedclosely and the specified wearmark width to be adhered to with-out difficulty.

Shift distance

Shift increment withconventional shifting

shift pass

shift pass

shift pass

shift pass

Shift direction

SG

SK

SK =

Shift increment withcoarse shifting

SG =

Starting point offset

Coarse shifting

Conventional shifting

Starting point

th

3rd

2nd

1st

Shift strategy: coarse shifting

22

Shorter machining times

The machining time (productiontime) for the hobbing process isdetermined on the one hand bythe gear width and number ofteeth and on the other by thecutting speed, hob diameter,number of starts, and axial feed.

The gear width and the numberof teeth are fixed geometricvalues. The cutting speed islargely dependent upon the gearmaterial, and its tensile strengthand machineability.

The machining time changes as afunction of the hob diameter,however. With a small hob diam-eter and with the cutting speedunchanged, the hob spindle andtable speeds increase, and themachining time is reduced. At thesame time, a reduction in hob di-ameter results in a reduction inthe machining distance for axialmachining.

When selecting the hob diameter,note that the number of gashes islimited by this dimension, andthat a high number of gashes isrequired for good tool life qual-ities and lower cutting forces.

The cutter diameter should there-fore only be sufficiently small toenable a specified cycle time tobe achieved. An unnecessarilysmall cutter diameter impairs thetool life and gear quality.

High axial feeds and multi-starthobs reduce the machining timeconsiderably. However, they alsolead to higher tip chip thick-nesses, the increase in which isinfluenced more strongly by thenumber of starts than by the in-creased axial feed.

A relatively high feed should beselected, and the number ofstarts kept as low as possible.This combination produces thelowest tip chip thickness. Thetwo variables are of equal import-ance for calculation of the ma-chining time, i.e. the machiningtime is determined by the prod-uct of the feed and the number ofstarts.

The number of starts should al-ways be increased when the feedis limited by the depth of the feedmarkings before the maximum tipchip thickness is reached. The depth of the feed markings is

dependent upon whether the gearis to be finish-hobbed or subse-quently shaved or ground.

δ y [mm]

z0

mnαnz2

i

=

=

===

envelop cutdeviationnumber of startsof the hobnormal moduleprofile anglenumber of teethon the gearnumber of gashesof the hob

δy

d

δ y [mm] =π2 · z0

2 · mn · sinαn

4 · z2 · i2

=

Envelop cut deviations

th =z2

· da0 · π · (E + b + A)

z0 · fa · vc · 1000

thz2

da0

E

b

Az0favc

==

=

=

=

====

machining timenumber of teeth of thegear to be machinedtip circle diameterof the hobapproach lengthof the hobtooth width of the gearto be machinedidle travel distance of the hobnumber of starts of the hobaxial feedcutting speed

[min]

[mm]

[mm]

[mm]

[mm]

[mm/WU][m/min]

Machining time (production time) for hobbing

23

Gear quality

The gear quality is determined pri-marily by the accuracy of the hob-bing machine, the quality of thehob, stable clamping of the work-piece, and zero radial and axialrunout of the workpiece and hob.

The axial feed and the diameter ofthe hob are decisive for the depthof the feed markings. In considera-tion of the gear quality producedduring finish-hobbing or subse-quent processes such as shavingor grinding, the depth of the feedmarkings and therefore the feedmust be limited.

The number of starts and the num-ber of gashes have a bearing uponthe magnitude of the envelopingcut deviations. The hob diameter,number of gashes, number ofstarts, axial feed, and cuttingdepth are included in the calcula-tion of the tip chip thicknesses,

and therefore influence the cuttingforces and thereby also the qualityof the gear.

With regard to the quality aspects,not only must the correct hobquality to be specified to DIN 3968or comparable hob standards foreach hobbing arrangement; the tipchip thickness, feed markings andenveloping cut deviations must al-so be checked to ensure that theylie within the specified limits.

SummaryOptimization of the hobbing pro-cess must entail consideration ofthe entire system, comprising thehobbing machine, workpiece, hob,and cutting parameters.Should one variable in this systemchange, the effects upon the vari-ous targets must be examined,with regard to both economicaland quality aspects.

An ideal high-performance hob isalways geared to the individualgear generating task. The size table shown on Page 25 shouldtherefore only be regarded as aguide by means of which the hugerange of possible hob diameterscan be limited and a contributionconsequently made towards re-duction of the costs.

123468

1012141618202224262830

ModuleCutting Speed Vm/min60

50

40

30

20

10

10 20 30 40 50 60 70Machineability in %

24

Description of the workpiece:

■ Module

■ Pressure angle

■ Helix angle

■ Number of teeth

■ Tip circle diameter

■ Depth of tooth or root circle diameter

■ Profile displacement factor orstandards for setting the tooththickness

■ Width of the gear

■ Material and tensile strength

■ Number of workpieces to bemachined; lot size, if applicable

Description of the hob employed:

■ Hob diameter

■ Cutting edge length

■ Number of gashes

■ Number of starts

■ Cutting material

■ Coated/uncoated

■ Coating with hob in new condi-tion, reground with or withoutre-coating

Description of the process parameters:

■ Cutting speed

■ Feed

■ Shift increment

■ Number of workpieces clamped in the pack

■ Single-cut/multiple-cut process

■ Climb or conventional hobbing

Description of theresults:

■ Tool life quality per regrind

■ Length of the wear mark on thehob

■ Machining time per workpieceor workpiece pack

In the event of quality problems:

■ Quality attained on the workpiece

Formulation of the optimization objectives:

Possible targets may include:

■ Shorter machining times

■ Superior tool life quality

■ Superior gear quality

Note when formulating the objec-tives that measures which are suit-able for attainment of, for exam-ple, the objective "improvement ofthe gear quality" influence the ma-chining time and gear generationcosts.

The objective must therefore al-ways be supplemented by a qual-itative and quantitative specifica-tion of the remaining processresults.

Limit values imposed bythe machine must bespecified, such as:

■ Max. cutter diameter

■ Max. cutter length

■ Max. cutter spindle and tablespeed

■ Max. shift distance

We can also optimize your hobbing process

For this purpose we require a complete description of theworkpiece, the hob previouslyused, the process parameters,and the results. A clear targetmust be specified for optimization.

25

Multiple-gash hobsRecommended structural dimensions


Dimensions in mm Number ofgashesm d1 I3 I1 d2

1 to 4 80 120 130 3290 13, 15, 17, 19

140 150 or 20170 180

1 to 6 100 140 150170 180

110 140 150 40 13, 15, 17, 19200 210 20, 21

120 160 180 321) or 24190 210 40

125 200

l1l3

d1 d2

1) Or bore diameter 40 mm

26

Solid carbide hobs

Modern solid carbide hobs boast the following characteristics:

■ High cutting speeds

■ Short machining times

■ Long tool life

■ High suitability for dry machining

■ Re-coating not required for P carbides

■ Lower gear generation costs (according to the machining task)

Introduction

Carbide hobs permit cuttingspeeds into the high-speed cutting(HSC) range, and significantlyhigher than those possible withhigh-speed steel hobs.

The development of suitably ratedhobbing machines enables the ad-vantages of solid carbide cuttersto be exploited in practical use.

The combination of high-speedcutting (HSC) and dry machiningpresents substantial potential forrationalization.

27

mm onwards is considerably low-er. The substrate reacts more fa-vourably.

By contrast, fine-grain carbideshave as yet only been developedfor the K types. Fine-grain car-bides permit very high hardnessvalues and consequently a high re-sistance to wear, combined withexcellent toughness.

Consequently, fully coated K sub-strates generally permit higher toollife qualities when compared withhobs manufactured from P car-bides, which lose their cutting facecoatings at the first regrind at thelatest. P carbide hobs must there-fore be changed more frequently.

TiN, manufactured by means ofPVD, continues to be the mainsubstance employed for the hardmaterial layer of hobs. TiN pos-sesses excellent chemical resis-tance to the hot steel chips. In ad-dition to its hardness of 2200 HV,

its relatively high toughness makesit particularly attractive for hobs.

The logistics aspect represents adecisive advantage. TiN is thecoating which, owing to its lowpressure characteristics, can bere-coated more easily. This is es-sential following grinding of thecutting face of hobs with a K typesubstrate.

Newly developed coatings such asTiCN and (TiAIN)can attain longer tool life travel fora given application, but have yet tobe accepted by the market, partic-ularly with regard to the re-coatingaspect.

Carbide types andcoatings

The carbide types generally usedare those of the main machininggroups K and P. The types presentadvantages and disadvantagesaccording to their material compo-sition (alloying elements and com-ponents) and their grain size.

Whereas K carbides, owing to thetendency of chips to bond to theuncoated substrate, can only beemployed fully coated, P carbidescan also be employed in uncoatedform. There is therefore no needfor the cutting face to be re-coatedfollowing regrinding. This reducesthe maintenance costs for P car-bide hobs considerably.

In addition, P carbides are lesssensitive to temperature, and thestrong progressive increase inwear which takes effect from aflank wear of approximately 0.2

Advantages: Disadvantages:

Advantages: Disadvantages:

● Re-coating not necessary following regrinding

● Low maintenance costs (regrinding only)

● Shorter maintenance times, consequently:

● Fewer tools in circulation (lower capital investment)

● Lower progressive rise in wear when the coating is penetrated,consequently:

● Lower risk of built-up edges

● Shorter tool life in the reground condition, therefore:

● More frequent tool changes required

● Generally longer tool life, therefore:

● Less frequent tool changing

● Fine-grain grades possible, therefore:

● Greater toughness and greater hardness

● Cannot be employed uncoated, i.e. removal of the coating andre-coating is required, therefore:

● Higher maintenance costs

● Longer maintenance times, therefore:

● More tools in circulation (greater capital investment)

● Strongly progressive increase in wear following penetration ofthe coating, consequently:

● Greater risk of built-up edges

Use of coated solid carbide hobs with P type substrate Maintenance process: regrinding (flank coated, cutting face uncoated)

Use of coated solid carbide hobs with K type substrate Maintenance process: removal of coating - regrinding - re-coating (flank and cutting face coated)

28

Cooling lubricants are not eco-nomically justifiable, because theyincrease the production costs ow-ing to the very high costs of theirsupply and disposal. Up to 16% ofthe total gear production costs canbe saved by dry machining.

Furthermore, cooling lubricantsmay pose disadvantages for tech-nological reasons. The use of cool-ing lubricants in many hobbing op-erations involving carbide cuttingedges, for example, may lead topremature failure of the tool owingto stress cracking (temperatureshock). For this reason, cuttingspeeds are limited to 250 m/minfor wet machining (in comparisonwith 350 to 450 m/min for dry ma-chining). The table shows the ad-vantages and disadvantages ofcooling lubricant with regard tocarbide hobbing.

The main problem with dry ma-chining lies in the increase incutting temperature. Up to 80% ofthe heat which is generated is dis-sipated with the chips, providedattention has been paid to correcttool design and suitable cuttingparameters are employed.

The configuration of the tool is de-pendent upon the data of the gearto be manufactured. A significantinfluencing factor is the tip chipthickness, which is derived fromthe cutter design (number ofstarts, number of gashes, diame-ter), the workpiece geometry(module, number of teeth, cuttingdepth, helix angle) and the select-ed feed. An important considera-tion is that dry machining requiresobservance not only of an upperlimit to the tip chip thickness, butalso of a minimum thickness value.The greater the chip volume, thegreater the quantity of heat whichan individual chip can absorb. Thismust be taken into account in or-der to ensure that during dry ma-chining, the greater part of the ma-chining heat is dissipated by thechips.

Machining with andwithout coolant

The machining of steel materialsgenerates considerable quantitiesof heat at the point of chip re-moval. If the temperatures reachexcessive levels, the cutting edgesof the tool are rapidly destroyed.

In order to cool the tool and at thesame time to lubricate the cuttingedge, cooling lubricants have inthe past been applied to the con-tact point between the cuttingedge and the material to be ma-chined. Cooling lubricants alsohave the function of flushing awaythe chips which are produced.

Cooling lubricants, however, haveconsiderable ecological, econom-ic, and in many cases also techno-logical disadvantages.

Cooling lubricants present an eco-logical hazard since they impactthe environment in the form of oilvapour and oil mist, and canpresent a health hazard to hu-mans.

Advantages Disadvantages

Machine ● Supports chip removal ● Aggregates (filters, pumps, etc.), therefore:

● Lower heating up of the machine ● Greater space requirements

● Additional operating expenditure (maintenance, power, etc.)

Tool ● Cooling of the tool ● Lower tool life owing to the formation of cracksperpendicular to the cutting edge (thermal shock)

● Lubrication of the friction zones

Workpiece ● Lower heating ● Cleaning necessary

● Lower dimensional deviations

● Protection against corrosion

Environment ● Binding of graphite dust ● Health riskduring cast iron machining

Further costs ● Tempering of the workpiece, ● Purchasing coststhus faster measurement

● Inventory costs

● Contaminated chips, therefore:

● Expensive recycling processes and

● Higher disposal costs

Advantages and disadvantages of the use of cooling lubricant during hobbing

29

At the point of chip generation,however, far higher temperaturesoccur which under certain circum-stances may rise to approximately900 °C, as indicated by incandes-cent individual chips. Based uponthese observations, a transversemicrosection from a workpiecesubjected to the dry machiningprocess under optimum machiningconditions for the HSC hobbingprocess was examined for pos-sible changes to the microstruc-ture.

The tooth flanks machined by theHSC process and the referencesamples of a turned blank ana-lysed for the purpose of compari-son revealed no changes to themicrostructure attributable to themachining process.

As already mentioned, HSC ma-chining must be considered inconjunction with dry machining.The first studies were performedon HSC hobbing machines in theearly 1990s. This process nowpermits dry machining of gears ina secure process at cuttingspeeds of up to 350 m/min.

320

300

280

260

240

220

200

180

160

140

120600 700 800 900 1000 1100

Cut

ting

spee

d v

c [m

/min

]

Tensile strength [N/mm2]

Dry machining

Wet machining

Cutting speeds for a range of material tensile strengths, carbide hobbing, dry and wet, module 2

High-speedcutting (HSC)

The advantages of high-speedcutting are:

■ High surface quality and shortmachining times (depending upon the machiningapplication)

■ Low cutting forces, with resulting benefits for the dimensional accuracy of theworkpiece and the tool life

Owing to the low contact timebetween the chip and the cuttingedge, the heat which is generateddoes not have time to flow into thetool or the workpiece. The tool andthe workpiece thus remain rela-tively cold. By contrast, the chipsare heated very strongly and mustbe removed very quickly in orderto prevent the machine from heat-ing up.

In an example application, HSCmachining without cooling lubri-cant led to the workpieces beingheated to approximately 50-60 °C.

Applications andcutting data

The proven applications for solidcarbide tools for gear and pinionmanufacture lie in a module rangefrom m = 0.5 to m = 4. The toolsare generally manufactured asstable monoblocs with bore- orshank-type mounting arrange-ment. The shank type is recom-mended for smaller tools. Thecutting speeds are in the rangefrom 150 to 350 m/min, accordingto the module size and process(dry or wet machining).

The diagram shows the differencein cutting speeds for dry and wethobbing of materials with a rangeof tensile strengths. The values inthe diagram apply to a solid car-bide hob, m = 2.

Substantially higher cutting speedscan be achieved with dry hobbingthan with wet hobbing.

30

Maintenance

When regrinding solid carbidehobs, ensure that the thermalstress on the tooth tip is kept to aminimum. A defined edge treat-ment is also recommended. De-pending upon the hob design (e.g.positive or negative rake angle,width of the tooth lands), approxi-mately 10 to 20 regrinds are pos-sible.

The "de-coating" and "re-coating"processes are required in additionfor hobs manufactured from Ktype carbide.

Further information on the mainte-nance of solid carbide hobs canbe found on Page 168.

Wear behavior

Flank wear is the chief form ofwear occurring on carbide hobs.

Pitting, which occurs on HSShobs, is not normally significant oncarbide hobs. Chipping at thecutting edge following penetrationof the carbide coating may occa-sionally be observed. The chipsmay adhere to the uncoatedcutting edge of K types followingpenetration of the coating. Thepoint of first penetration of thecoating must therefore be delayedas long as possible.

The increase in wear is progressivefrom a wear mark width of approx.0.1 mm upwards, and has a con-siderable influence upon the eco-nomic viability of the process. Wetherefore recommend that a wearmark width of 0.15 mm not be ex-ceeded, and that the cutter be re-coated following each regrind.Chip adhesion to the worn andtherefore uncoated cutting edgesis much less common with the Ptypes. Re-coating is not thereforenecessary with these types.

t3H12

dH5 A

A0,2

b3H11f2

f2

r3

r3

Drive slot dimensions of a carbide hob

Structural dimensions

The size table indicates the hob di-mensions for which FETTE stockscarbide blanks. The blanks do nothave drive slots. A drive slot cantherefore be provided on either theleft-hand or the right-hand indica-tor hub, as desired by the cus-tomer.

FETTE recommends drive slotswith reduced gash depth for car-bide hobs. The gash dimensionscan be found in the table below.

Bore diameter b3 t3 r3 f2Permissible deviation Permissible deviation

8 5,4 2,00 0,6 –0,2 0,4 0,110 6,4 2,25 0,8 0,513 8,4 2,50 1,016 2,80 –0,3 0,6 0,222 10,4 3,15 1,227 12,4 3,50 0,832 14,4 4,00 1,6 –0,440 16,4 4,50 2,0 –0,5 1,0 0,350 18,4 5,0060 20,5 5,6070 22,5 6,25 2,5 1,280 24,5 7,00

100 8,00 3,0 1,6 0,5

t3 = 1/2 depth to DIN 138

31

Size table for solid carbide hobs

l1

d1 d3d2

l3c

Number ofgashes

Dimensions in mm

d1 I3 I1 d2 c d3 h0

56 82 100 22 9 42 3 1963 112 130 27 48 470 160 180 32 10 54 580 790 40 66 8

100 180 200 72 10120 208 230 50 11 80 13

56 52 70 22 9 42 3 1963 72 90 27 48 470 100 120 32 10 54 580 790 40 66 8

100 120 140 40 72 10120 138 160 50 11 80 13

Short version

Long version

d1 = outside diameterl3 = cutting edge lengthl1 = total lengthc = shoulder widthd2 = bore diameterd3 = shoulder diameterh0 = max. profile height

Recommended structural dimensions

Roughing hobsHigh cutting capacities areachieved with the heavy dutyrouching hob when roughing gearsfrom module 6 onwards with hightooth numbers and large gearwidths.

These high cutting capacities aremade possible by a favourablecutting edge geometry and thedistribution of the metal removalcapacity over a relatively largenumber of tool cutting faces.

Because of its even cutting edgeload, this tool is particularly quietin operation, even with maximumfeeds and high chip thickness.

The design of the heavy dutyroughing hob is based on the fol-lowing considerations:

■ The volume of metal to be re-moved when cutting gears in-creases quadratically with themodule, whereas the number ofgashes, because of the greaterprofile height, becomes smallerin the usual cutter sizes. Thisresults in a greater load on theindividual cutter teeth.

■ Approximately 75 % of the me-tal removal work takes place inthe tip area of the cutter teeth.This results, particularly whenroughing, in an extremely un-even load and wear distributionon the cutter teeth. The greatertip corner wear determines theduration of the service life,whereas the cutting edges inthe tooth centre- and root areashow only very little wear.

■ An efficient and economicalhob must therefore have a verylarge number of gashes, with-out making the outside diam-eter of the cutter too large. Thenumber of tip cutting facesshould exceed that of the flankand root cutting edges.

32

33

These requirements are met per-fectly by the FETTE heavy dutyroughing hob with its verticallystaggered teeth. The cutter teethonly have the full profile height inevery second tooth row. The inter-mediate teeth are limited to about1/3 of the profile height.

This design principle makes it pos-sible to acommodate 16 or 20flutes on a still practicable cutterdiameter.

The 8 or 10 complete teeth on thecutter circumference are generallysufficient for producing the profileshape within the required toler-ances. The heavy duty roughinghob can therefore also be used asa finishing cutter.

Depending on the quality required,the heavy duty roughing hob isavailable either relief turned or re-lief ground.

For roughing, the cutter teeth canbe provided with offset chipgrooves, which divide the chipsand reduce cutting forces andwear.

Roughing hobs can be regroundon any standard hob grinder. Onceset, the gash lead can be retained,independent of the gash depth.Roughing hobs are manufacturedwith axially parallel gashes up tolead angle of 6°, which is a condi-tion for sharpening by the deepgrinding method.

The design principle of the rough-ing hob is of course not limited tothe basic profiles for involute toothsystems to module or diametralpitch, but can also be used for allother common profiles and forspecial profiles.

00

B

A

Schnitt A–0 Schnitt B–0

2,25 · m

1,5 · m

0,75 · m

F2 F1 F2

Metal removal areas on the cutter tooth:

tooth tip corresponds to area F 1 ≈ 75 %tooth root corresponds to area F 2 ≈ 25 %

tooth gash volume = 100 %

Face plane of a roughing hob

Section A-0 Section B-0

34

Dimensions in mm

m d1 I3 I0 d2

6 150 108 140 507 126 1588 160 144 1769 162 194

10 170 180 214 60

11 180 198 232 6012 190 216 25013 200 234 26814 210 252 286

15 230 270 310 8016 240 288 33018 260 318 36020 290 360 406 100

22 300 396 442 10024 310 432 47827 330 486 53230 340 540 586

Heavy duty roughing hobs

l0l3

d1 d2

(roughing type hobs)for spur and helical gears to module pitch

20° pressure anglebasic profile III to DIN 3972with positive rake (undercut)optionally with chip breaker groovessingle start right-handedwith drive slot

KHSS-E EMo5Co5

2051 relief turned ■ Quality grade B/C to DIN 3968 ■ with 20 gashes

2053 relief ground ■ Quality grade A to DIN 3968 ■ with 20 gashes



Cat.-No.

35

Ident No.2067

Ident No.2065

Ident No.2063

Ident No.2061

Dimensions in mm

m d1 I3 I0 d2

6 150 108 118 50 1208017 1208053 1209205 12090237 126 136 1208019 1208055 1209214 12090258 160 144 154 1208021 1208057 1209223 12090289 162 172 1208023 1208059 1209232 1209030

10 170 180 190 60 1208025 1208061 1209241 1209032

11 180 198 208 60 1208027 1208063 1209250 120903412 190 216 226 1208029 1208065 1209269 120903713 200 234 244 1208031 1208067 1209278 120903914 210 252 262 1208033 1208069 1209287 1209041

15 230 270 280 80 1208035 1208071 1209296 120904316 240 288 300 1208037 1208073 1209303 120904618 260 318 330 1208039 1208075 1209312 120904820* 287 1208041 1208077 1209321 120905020 290 360 372 100 1208043 1208079 1209011 1209052

22 300 396 408 100 1208045 1208081 1209013 120905524 310 432 444 1208047 1208083 1209015 120905727 330 486 498 1208049 1208085 1209017 120905930 340 540 552 1208051 1208087 1209019 1209061

Heavy duty roughing hobs

l1l3

d1 d2

(roughing type hobs)for spur and helical gears to module pitch

20° pressure anglebasic profile III to DIN 3972with positive rake (undercut)optionally with chip groovessingle start right-handedwith keyway

KHSS-E EMo5Co5





Cat.-No.

* For hobbing machines with max. capacity = 290 mm dia. and for max.cutter lenght = 330 mm.

36

Roughing hobs with indexable carbide inserts

Roughing hob with indexable carbide inserts in operation

37

The rough hobbing of gears formmodule 5 onwards can be carriedout extremely economically withthis modern tool.

The design concept is the combi-nation of the known advantages ofthe hobbing process with the per-formance of carbide and the econ-omy of indexable inserts. Using in-dexable carbide inserts, largevolumes of metal can be removedwithin a given time at high cuttingspeeds.

Regrinding, which is necessarywith conventional hobs, is elimin-ated. This saves the cost of sharp-ening and of tool changes. Thewear marks on the individualcutter teeth vary according to theprocess. In the large-gear sector,these can only be partly equalizedby shifting. Hobs therefore alwayscontain teeth with different wearmark widths. When using index-able inserts, only those insertsneed be turned or replaced whichhave reached the maximum wearmark width.

To change the indexable inserts orthe segments, it is not necessaryto remove the cutter form the ma-chine. This results in short hobbingmachine downtimes.

Changing the indexable inserts al-so makes it possible to match thecarbide grade optimally to the gearmaterial.

To use these carbide tipped toolssuccessfully, it is necessary tohave hobbing machines which of-fer sufficient rigidity as well as therequired speed and drive power.

ConstructionFETTE indexable insert hobs con-sist of a cutter body, onto whichthe tooth segments are screwedand indexable carbide inserts. The latter are held by clampingscrews in the insert seats of thesegments.

A helical groove has been re-cessed into the cylindrical cutterbody. The flanks of the grooveground according to the cutterlead.

The parts of the ground cylindricalshell which remain between thegroove windings act as supportsurfaces for the tooth segments.Two cylindrical pins arranged inthe tooth segments are guided inthe groove and determine the po-sition of the segments. The segments are fixed to thecutter body by inhex screws.

The seats for the indexable car-bide inserts are arranged tangen-tially on the tooth segments. Within a segment, the seats are ar-ranged alternately if possible. The purpose of this arrangement isto keep the axial reaction forces onthe cutter and the tangential

cutting force components on thegear as low as possible.

Cutter body

Tooth segment

38

The indexable carbide insertsmust completely cover the cuttingedges of the cutter tooth. The ne-cessary number of indexable in-serts and their arrangement de-pend on the dimensions of theinserts and on the size of the gear.To render the pre-cutting of thegear optimal for skive hobbing orgrinding, the carbide hobs with in-dexable inserts can be made sothat they produce both a rootclearance cut (protuberance) and achamfer on the gear (see fig. be-low).

In the range from module 5 tomodule 10 each cutter tooth onlyholds one insert, which covers theentire flank length.

From module 11 onwards, eachflank is fitted with an indexable in-sert offset to the opposite flank. Inspecial cases, versions with asingle insert covering each flankare also possible with these mod-ule sizes.

Cutting edge construction module 5–10

Cutting edge construction module 11–20

Profile design with protuberance and chamfer

39

Roughing hobs

l1l3

d1 d2

with indexable carbide insertsfor spur and helical gearsto module pitch

20° pressure anglebasic profile by arrangementsingle start right-handedwith keyway

Carbide - TiN-coated

Dimensions in mm Ident No.Number ofindexable inserts1)

Number ofsegments

Number oftooth rowsm d1 I3 I1 d2

2163Cat.-No.

5 190 95 144 60 19 24 96 –6 114 165 12242067 210 133 185 –8 152 206 12242159 171 227 –

10 190 248 1224224

11 280 209 269 80 19 24 192 –12 229 289 122423313 248 310 –14 267 331 1224242

15 280 286 352 80 19 24 192 –16 300 305 373 122425117 324 394 –18 343 415 122426019 362 436 –

20 300 382 457 80 19 24 192 1224279

Spare parts and indexable inserts: design on request.1) The number of indexable inserts may change according to the basic profile.

40

Carbide skiving hobsDesigns

Depending on the module size andthe accuracy requirements, 3 skiv-ing hob designs can be basicallydistinguished:

■ Solid carbideup to and including module 4FETTE Cat. no. 2028

■ Brazed-on carbide tipsfor modules above 4FETTE Cat. no. 2129

■ Indexable carbide insertsfor modules from 5 upwardsFETTE Cat. no. 2153

Process andrange of applications

Skive hobbing is a machining pro-cess in which skiving hobs areused for cutting rough-milled andhardened gears.

The main area of application is thehobbing of straight and helicalspur gears. In addition, externalsplines, roll profiles and a largenumber of special profiles whichcan be generated by the hobbingmethod can be machined with theskiving hob. There are various rea-sons for using this process:

Finish-hobbing of gearsSkive hobbing eliminates harden-ing distortion and improves thequality of the gear.

The metal removal capacity is con-siderably higher with skive hob-bing than with the usual grindingprocesses. It is therefore economi-cal to replace grinding by skivehobbing in the range of coarse andmedium gear tolerances.

Gear quality grade 6 to DIN 3962can be quoted as an approximatevalue for the attainable accuracy.

Profile- and flank modifications,too, such as depth crowning, toothface setback or width crowning,can be produced by suitable hobprofiles and corresponding ma-chine motions.

Preparation for grindingFor high gear quality requirements,the gears are ground. The gearcutting costs can be markedly re-duced if the hardening distortion isbefore grinding removed by skivehobbing, at the same time remov-ing material down to the necessarygrinding allowance. Grinding timesand costs are reduced while gain-ing additional grinding capacity.

The tool

DesignThe characteristic design featureof skiving hobs is the negative tiprake angle. The tip rake angle isdescribed as negative when thecutting faces of the teeth lie, in thedirection of the cutting motion, infront of the tool reference plane.The tool reference plane is theplane in which lie the tip cuttingedges of the axially parallel cutterand cutter axis.

Due to the negative tip rake angle,the flank cutting edges are inclinedin relation to the effective refer-ence plane (plane perpendicular tothe cutting motion) and in this wayproduce a peeling cut.

The negative rake angle is greaterin the root area of the hob teeththan in the tip area. The tip cuttingedges have no effective back rakeand cannot therefore generate acurling cut. It therefore follows thatthe skiving hobs should only pro-duce flank chips and that protu-berance cutters are used forroughing the gears.

Tool materialLow chip thickness and hardenedgear materials make severe de-mands on the edge strength of thetool material. As the tool materialfor skiving hobs, carbides of ISOapplication groups K 05 to K 15are used.

Fig. 1

– γ

λs

vc

–γ = Kopfspanwinkelλs = Neigungswinkel der Flankenschneidevc = Schnittgeschwindigkeit

Fig. 2

- γ = tip rake angleλs = back rake of the flank cutting edgevc = cutting speed

41

A special position among theabove designs is occupied by theskiving hob with indexable carbideinserts. This cutter type does notrequire regrinding. Only those in-serts which have reached themaximum wear mark width areturned or changed.

It is understandable that a cutterassembled from cutter body, toothsegments and indexable insertscannot offer the same accuracy asa cutter in solid carbide. This iswhy the cutter with indexable in-serts is particularly suitable forpreparing the workpiece for grind-ing.

By far the most common skivinghob is the bore type. Solid carbideskiving hobs have a drive slot onone or both ends, for manufactur-ing reasons. For hobs with a highquality grade, preference shouldwhere possible be given to boreswith drive slot over those with key-way. A precise bore can be manu-factured more easily without akeyway, and the run-out of the hobon the hobbing machine is also re-duced. For extreme accuracy re-quirements, a shank-type tool alsopermits compensation of the run-out between cutter arbor andcutter.

Quality grades

Skiving hobs are generally manu-factured in quality grade AA to DIN3968. If required, the solid carbideand brazed-on carbide tip typescan also be manufactured in qual-ity grade AAA (75% of the toler-ances of AA).

A concave flank shape is usual forthe skiving hob, to achieve a slighttip relief on the workpiece.

Preparation forskive hobbing

The machining allowance dependson the module size and the hard-ening distortion. Experience hasshown that for the module range 2to 10 it lies between 0.15 and 0.30mm/flank.

The tooth root must be pre-machined deeply enough to pre-vent the tooth tip of the skivinghob from cutting into it.

We recommend hobs protuber-ance, e.g. FETTE Cat. no. 2026.

The hardness of the gear must forthe skive hobbing process be lim-ited to HRC 62 +2.

Solid-carbide skiving hob

Skiving hob with indexable carbide inserts

Skiving hob with brazed-on carbide strips

Skiving hob with brazed-on carbide tips

42

For high quality requirements,hobbing must always be done inseveral cuts. For the last cut, a re-moval of 0.1 mm/flank should beaimed at, to affect the structure ofthe gear material as little as pos-sible.

Cooling

Intensive cooling of the tool, work-piece, holding fixture and machinewith the cutting oils usual for hob-bing, the temperature-dependenterror values are reduced and theservice life of the skiving hobs isextended.

Wear and tool lifevalues

Wear mark width

The wear mark width on the skiv-ing hobs should not exceed 0.15mm.

Cutting forces increase with great-er wear mark width and with verythin chips deflection of the hobcutting edges will occur.

This may have the following con-sequences:quality losses, chipping of carbidecutting edges and excessivestructural changes through tem-pering and re-hardening process-es on the gears.

Uniform wear throughshifting

Wear only occurs on the toothflanks of the skiving hobs. Thewear marks are relatively shortand follow the contour of the en-gagement lines.

By shifting the hob in the axial di-rection after hobbing a gear or setof gears, the wear is distributedevenly over the flank cutting edges

and over the entire cutting edgelength of the hob. This process isfurther facilitated if the hobbingmachine is equipped with a syn-chronous shifting arrangement.This arrangement ensures that themachine table makes an additionalturn when the tangential slide ismoved. The relative position of thehob motion then remains as setduring centering.

Tool life between regrinds

The life between regrinds of a hobequals the sum of the lengths of allhobbed workpiece teeth betweentwo regrinds of the hob.

The calculation of the life betweenregrinds, the tool requirement, theproportional tool costs etc. isbased on the life between regrindsper cutter tooth. This depends onthe module value and on the hard-ness of the material being cut. Ex-perience has shown the tool lifebetween regrinds to lie between 2and 4 m per cutter tooth for skivehobbing.

Gear cutting quality

The gear quality when skive hob-bing depends on the interaction ofa large number of components andparameters, such as:

■ skiving hob (cutting material,correctly sharpened, sufficentaccuracy)

■ rigid hobbing machine■ accurate and stable clamping

of hob and workspiece■ hob aligned with an absolute

minimum of runout■ accurate centering■ correct selection of cutting

speed, feed and metal removalper flank

■ adherence to the maximumwear mark width

■ material, preparation and heattreatment of the workpieces

Cutting conditions

Cutting speed

The cutting speed depends on themodule size and on the hardnessof the gear. As an approximate val-ue, a cutting speed of 36 m/mincan be quoted for module 30 andof 110 m/min for module 2.

For the lower modules, higher val-ues between 140 and 160 m/minare also possible. These highcutting speeds do however reducethe service life of the skiving hoband the workpiece structure is in-creasingly affected.

For workpiece hardness valuesfrom HRC 62 upwards, the cuttingspeed should be limited initially to70 m/min and then optimized inconsideration of the cutting resultand the service life of the tool.

Feed

The structure of surfaces ma-chined with hobs is affected by thedepth of the feed markings. Thedepth of the feed mark increasesquadratically with the value of thefeed. It is therefore logical to dis-tinguish between feeds for finish-ing and for roughing.

Approximate value for the feed:

For the finishing cut1.5 to 2 mm/workpiece rotation

for the roughing cutup to 4 mm/workpiece rotation

Climp hobbing method

Climb hobbing for skive hobbing ispreferred since this yields the bestservice life of the skiving hobs.

Removal per flank

To maintain a reasonable servicelife of the hobs, not more than0.15 ÷ 0.20 mm/flank should beremoved in one cut.

43

angle, the grinding wheel must beset off-centre. The measurementfor the setting of the grindingwheel depends on the cutter diam-eter in question and is shown inthe regrinding diagram, which isenclosed with every cutter.Cutting faces must be ground with

low roughness depth in order toprevent flaws and micro-chippingon the cutting edges. The toler-ances of DIN 3968, insofar as theyconcern the gashes, must bemaintained.

= cutting face offset= cutter diameter

uda

u

da

Cut

ter

dia

met

er (m

m)

189

188

187

186

185

184

183

–45,4 –45,8 –46,2 –46,6 –47,0 –47,4

Cutting face offset u (mm)

Cutting face regrinding diagram for carbide skiving hobs

Pitch- and tooth trace deviationsare caused by the hobbing ma-chine.

The profile shape depends basi-cally on the quality of the hobs.The cutting parameters, the hard-ness of the workpieces and thewear condition of the cutters affectmainly the cutting forces, whichreact on tool and machine andthus contribute to the tooth quality.

Under good conditions and withcareful working the gear qualitygrade 6 to DIN 3962 can beachieved with a surface roughnessof 1to2 µm.

Hobbing machine

In principle, conventional hobbingmachines are also suitable forskive hobbing. The decisive factoris the condition of the machine.

It is vital to keep the play in thehob spindle thrust bearing and inthe table- and feed drive as low aspossible.

Obviously, modern hobbing ma-chines with dual-worm table driveor hydraulic table pre-loading, withcirculating ball spindle for the axialfeed and prestressed thrust bear-ing of the hob spindle offer betterpreconditions for good gear qual-ity. Arrangements for automaticcentering and for synchronousshifting are also desirable.

Maintenance of theskiving hob

The skiving hob should be sharp-ened when the wear mark hasreached a width of 0.15 mm. Dia-mond wheels are used for grindingwith the traverse grinding or thedeep grinding process.Because of the negative tip rake

44

Skiving hobs

l1l3

d1 d2

Solid carbide

for finishing hardened (highly tempered)spur and helical gears to module pitch

20° pressure anglebasic profile: ha0 = 1.15 · m, öa0 = 0.1 · mquality grade AA nach DIN 3968single start right-handedwith keyway

Carbide – TiN coated




2 80 100 120 32 15 23528902,5 23528913 90 40 23528923,5 100 120 140 23528934 4021516

45

Skiving hobs

l1l3

d1 d2

with brazed-on carbide insertsfor finishing hardened (highly tempered)spur and helical gears to module pitch

20° pressure anglebasic profile: ha0 = 1.15 · m, öa0 = 0.1 · mquality grade AA nach DIN 3968single start right-handedwith keyway

Carbide

Dimensions in mm Number oftooth rows



4,5 130 130 150 40 12 12231355 1223139

5,5 160 140 160 50 12 12231376 12231467 170 12231558 150 170 12231649 180 1223173

10 190 160 180 50 12 122318211 220 180 200 60 122319112 190 210 122320813 240 200 220 122325314 250 220 240 1223217

15 250 230 250 60 12 122326216 260 240 260 122322617 250 270 80 122327118 270 270 290 122323519 280 300 122329020 280 290 310 1223244

46

Skiving hobs

l1l3

d1 d2

with indexable carbide insertsfor finishing hardened (highly tempered)spur and helical gears to module pitch

20° pressure anglebasic profile: ha0 = 1.15 · m, depth of cut 2.15 · mquality grade AA to DIN 3968single start right-handedwith keyway or drive slot

Carbide

Dimensions in mm Ident No.Number ofindex inserts

Number ofsegments

Number oftooth rowsm d1 I3 I1 I11) d2

2153Cat.-No.

5 160 79 127 147 50 19 19 76 –6 94 145 165 12240007 190 110 163 183 –8 126 180 200 12240199 142 197 217 –

10 158 215 235 1224028

11 220 173 232 256 60 21 21 84 –12 189 250 274 122403713 250 205 267 291 23 23 92 –14 220 285 309 1224046

15 250 236 302 326 60 23 23 92 –16 252 320 344 122405517 280 268 337 365 80 –18 284 355 383 122406419 299 373 401 –

20 280 315 390 418 80 23 23 92 1224073

1) with drive slot

Spare parts and indexable inserts: design details on request.

47

Solid-type hobs

l1l3

d1 d2

for straight spur gears with straight andhelical teeth to module with protuberancefor rough hobbing prior to grinding or skivehobbing

20° pressure anglebasic profile: ha0 = 1.4 x m, öa0 = 0.4 x mallowance per flank: qP0 = 0.09 + 0.0125 x mprotuberance value:prP0 = 0.129 + 0.0290 x m up to module 7prP0 = 0.181 + 0.0235 x m above module 7quality grade A to DIN 3968single-startwith keyway


Dimensions in mm Ident No.left-handed

Ident No.Right-handed

Number ofgashesm d1 I3 I1 d2

2026Cat.-No.

1 70 50 56 27 17 1223334 12233442 90 100 15 1223326 12233463 80 110 120 32 1223338 12233484 90 120 130 14 1223340 12233505 100 140 150 1223343 12233526 140 40 1223345 12233557 150 1223347 12233578 160 160 170 50 1223349 12233599 170 1223351 1223361

10 180 180 190 1223353 122336312 200 200 210 60 12 1223356 1223365

49

Hobsfor internal gears, with straight or helical teeth, involute flanks

Cat.-No. Page

Explanatory notes 50

Solid-type hobs 2082 51

50

Explanatory notesHobs for internal gears are de-signed for a specific gear. Themeasurements for the maximumand the minimum cutter diameterand the maximum cutter widthmust then be taken into account,for which the internal hobbinghead is dimensioned.

ln the case of internal gears withlarge profile displacement, themaximum permissible cutter widthmay be insufficient for cutting thecomplete teeth, if the hob is di-mensioned in the usual way. It isthen necessary to fix the moduleand the pressure angle of the hobdifferently from those of the inter-nal gear.

On the hob, one tooth is definedas a "setting tooth" and markedaccordingly. The cutter must bepositioned on the hobbing ma-chine so that the setting tooth iswhen new placed in the "machinecentre". Although the setting toothwill shift in the axial direction whenthe hob is reground, it is not nec-essary to correct the position ofthe hob determined in the newcondition and fixed by spacers.

The hobs offered for finishinginternal gears are only to a limitedextent suitable for roughing. Bear-ing in mind the tool costs, reliefturned hobs with a lead matchedto the workpiece should be usedfor roughing.

51

Solid-type hobs

l1l3

d1 d2

for internal gears to module pitchstraight or helical teeth

20° pressure anglebasic profile II to DIN 3972quality grade AA to DIN 3968single start right-handedwith keyway

KHSS-E EMo5Co5

Dimensions in mm Number ofgashesm d1 I3 I1 d2


5 360 45 65 100 306 52 728 66 86 24

10 80 90 2212 94 10414 108 11816 122 132 2018 136 146 1820 150 160 16

The structural dimensions listed are approximate values, which can be changed according to thesize of the internal hobbing head and the tooth data of the gear.

For internal hobs greater than module 20, workpiece drawings and dimensions of the internalhobbing head must be submitted, so that the structural dimensions of the hob can be deter-mined accordingly.

Hobsfor compressor rotors and pump spindles

Cat.-No. Page

Hobs for compressor rotors 54

Rotor hobsRoughing cutters, as roughing hobs (broach-tooth type) 2091 55Finishing cutters, as solid-type hobs 2092 56

Hobs for pump spindlesFinishing cutters, as solid-type hobs 2094 57

Hobs for compressor rotorsRotors are the multi-thread feedscrews of a screw compressor,which are arranged in pairs insidea housing. The meshing screwthreads have a symmetrical or anasymmetrical profile.

Quiet running and good efficiencyof the rotors are determined by theaccuracy of the rotor profiles.

The advantages of hobbing pro-duce favourable results in rotormanufacture:

■ High pitch accuracy■ Low distortion owing to even,

constant chip removal in allgaps

■ Trouble-free maintenance ofthe hob, which is reground onlyon the cutting faces.

The use of this technology for rotormanufacture requires the develop-ment of the required analysis pro-grams for rotor and hob profilesand high standards of manufactur-ing in the area of precision hobs.

High demands are placed on therigidity, output, thermal stabilityand feed accuracy of the hobbingmachines.

The successful use of hobs alsodepends on the degree to whichthe tool manufacturer on the onehand and the rotor producer or -designer on the other hand com-municate with each other aboutthe production constraints im-posed on profile shape, amount ofplay and play distribution. Thisprocess then does allow modernand economical production, when

quality and output depend primari-ly on the tool and the machine.

54

Female rotor

Male rotor

Rotors: face plane view

55

Rotor hobs, for roughing

l1l3

d1 d2

for screw compressorsfor male and female rotors as heavy-duty roughing hobswith 16 flutesaxially parallel gashes

single startwith keyway

KHSS-E EMo5Co5

Dimensions in mm

Cutter dimensions

Rotor dia. m Profile height d1 I3 I1 d2

2091 relief turnedCat.-No.

47/44,5 ≈ 5,2 ≈ 10,2 112 90 106 4081,6 ≈ 9,1 ≈ 17,5 140 154 170 50

102 ≈ 11,4 ≈ 22 170 184 200 60127,5 ≈ 14,2 ≈ 27,5 212 234 250163,2 ≈ 18,2 ≈ 35,5 265 299 315 80204 ≈ 22,7 ≈ 44 305 319 335 100204 ≈ 22,7 ≈ 44 335

The structural dimensions are approximate values for rotor measurements L/D = 1.65.

When ordering, workpiece drawings of the rotors and data abaut the profileat the face plane (list of coordinates) must be made available.

Owing to their size, not all rotorscan be generated by hobbing. Fur-thermore, the choice of tools is al-so influenced by the process al-ready in place and the machineswhich are available. FETTE played a leading part in theintroduction of the hobbing pro-cess for the manufacture of rotors.FETTE can therefore call uponconsiderable experience in advis-ing its customers.

The advantages of the hobbing method are undisputed and can be summar-ized as follows:

■ Quick and trouble-free production of rotors with good surfaces and accu-rate profiles and pitch.

■ The sealing strips on the tooth tip and the sealing grooves in the tooth rootof the rotors can be generated in one operation with the flanks.

■ Hobbed rotors can be exchanged at any time, thanks to their uniform ac-curacy.

■ Simple and economical maintenance of the tools, since the hobs are onlyreground on the cutting face.

for male rotors

for female rotors

56

Rotor hobs, for finishing

l1l3

d1 d2

for screw compressorsfor male and female rotors

quality grade AA restricted to DIN 3968 axially parallel flutes

single startwith keyway

KHSS-E EMo5Co5

Dimensions in mm

Cutter dimensions

Rotor dia. m Profile height d1 I3 I1 d2


47/44,5 ≈ 5,2 ≈ 10,2 140 74 90 6081,6 ≈ 9,1 ≈ 17,5 190 124 140 80

102 ≈ 11,4 ≈ 22 236 154 170127,5 ≈ 14,2 ≈ 27,5 265 196 212 100163,2 ≈ 18,2 ≈ 35,5 300 249 265204 ≈ 22,7 ≈ 44 305 299 315204 ≈ 22,7 ≈ 44 335

for male rotors

for female rotors

The structural dimensions are approximate values for rotor measurements L/D = 1.65.

The entire profile, including the sealing strip and slot, is machined one on operation. The out-side diameter of the rotors is ground to finish size.

When ordering, workpiece drawings of the rotors and data about the profile at the faceplane (list of coordinates) must be made available.

57

Hobs

l1l3

d1 d2

for screw pumpsfor drive or trailing spindle

quality grade AA restricted to DIN 3968 single startwith keyway

KHSS-E EMo5Co5

Dimensions in mm

Hob dimensions

d1 I3 I1 d2


18 x 10,8 10,8 x 3,6 100 52 60 32 1620 x 12 12 x 4 55 6330 x 18 18 x 6 112 72 8035 x 21 21 x 7 118 82 9038 x 22,8 22,8 x 7,6 125 87 95 4045 x 27 27 x 9 140 98 106 1852 x 31,2 31,2 x 10,4 150 104 112 5060 x 36 36 x 12 160 110 11870 x 42 42 x 14 180 122 132

Hob for drive spindle

Hob for trailing spindle

Number ofgashes

Drive spindleD x d1)

Trailing spindleD x d1)

1) D = Outside diameter, d = inside diameter

The overall dimensions shown are recommended values and may be adapted to the working space ofthe hobbing machine both in length and in diameter.

When ordering, the following workpiece data must be quoted: measurements about the profile atface plane, outside diameter, inside diameter, lead and direction of lead – normally drive spindleright-hand, trailing spindle left-hand.

Drive and trailing spindles

Hobsfor sprockets, timing belt pulleys and splines

Cat.-No. Page

Hobs for sprocketsrelief turned 2301 60relief turned 2311 61relief turned 2331 62relief ground 2341 63

Hobs for timing belt pulleysrelief ground 2342 64relief ground 2352 65

Hobs for spline shaftsrelief ground 2402 66relief ground 2412 66relief ground 2422 67relief ground 2432 67relief ground 2442 68

Hobs for p.t.o. shaftsrelief ground 2444 69relief ground 2472 70

Hobs for involute spline shaftsrelief ground 2452 71

Hobs for serrated shaftsrelief ground 2462 72

60

Hobs

l1l3

d1 d2

for sprockets to DIN 8196 for roller and barrel chainsto DIN 8187, 8188

basic profile to DIN 8197single start right-handedwith keyway

KHSS-E EMo5Co5


Dimensions in mm

Hob dimensions

d1 I1 d2

Chain

Pitch Roller/barrel dia.

Number ofgashes

Ident No.

5,0 3,2 56 38 22 12 12262046,0 4 12262138,0 5 63 27 12262319,525 6,35 70 46 1226268

12,7 7,92 80 56 327,75 12262867,77

12,7 8,51 122629515,875 10,16 90 69 10 122630219,05 11,91 100 88

12,071226320

25,4 15,88 110 108 40 122633931,75 19,05 125 133 122635738,1 22,23 140 150 1226366

25,4 122637544,45 160 170 50 9 1226384

27,94 122639350,8 28,58 170 190 2111640

29,21 122641963,5 39,37 190 235

39,68 2110189

76,2 47,63 225 290 60 211018848,26 2108994

61

Hobs

l1l3

d1 d2

for sprockets for Gall’s chains (heavy) to DIN 8150

single start right-handedwith keyway

KHSS-E EMo5Co5


3,5 2 50 31 22 12 21101906 3 38 12268298 3,5 56 2110191

10 4 51 122684715 5 63 69 27 122685620 8 80 98 32 122686525 10 90 108 10 122687430 11 100 133 122688335 12 150 211019240 14 110 170 40 211019345 17 125 190 211019450 22 140 210 122690955 24 122691160 26 160 235 50 9 122691370 32 180 290 122691580 36 190 122691790 40 210 325 60 1226919

100 45 220 365 1226921110 50 240 410 1226923120 55 250 1226925

Dimensions in mm

Hob dimensions

d1 I1 d2

Chain

Pitch Roller dia.

Number ofgashes

Ident No.

62

Hobs

l1l3

d1 d2

for sprockets for barrel chainsto DIN 8164

single start right-handedwith keyway

KHSS-E EMo5Co5


15 9 90 69 32 12 122731720 12 100 98 10 122732925 15 110 108 40 122733830 17 125 133 122734735 18 150 122734940 20 140 170 122736545 22 190 122737450 26 160 210 50 9 122737655 30 170 122737860 32 180 235 122738065 36 190 260 122738270 42 210 290 60 122738480 44 220 122738690 50 240 325 1227388

100 56 250 365 1227390

Dimensions in mm

Hobs dimensions

d1 I1 d2

Chain

Pitch Roller dia.

Number ofgashes

Ident No.

63

Hobs

l1l3

d1 d2

for sprockets with involute flankswith tip relief

30° pressure anglequality grade A to DIN 3968single start right-handedwith keyway

KHSS-E EMo5Co5


Ident No.PitchInch d1 I3 I1 d2


5/16 70 63 69 27 16 12275063/8 80 32 12275151/2 90 70 78 12275245/8 80 88 14 12275333/4 100 92 100 1227542

1 110 120 130 12 122755111/2 150 160 170 50 12275602 190 215 225 1227579

64

Hobs

l1l3

d1 d2

for synchroflex timing belt pulleystopping cutter

quality grade A to DIN 3968single start right-handedwith keyway

KHSS-E EMo5Co5

Dimensions in mmPitch

Tooth numberrange

Ident No.Number ofgashesd1 I3 I1 d2


T 2,5 se 12– 20 50 25 31 22 14 1228006T 2,5 21– 45 1228015T 2,5 46– 80 1228024

T 5 se 10– 14 56 32 38 22 14 1228033T 5 se 15– 20 1228042T 5 21– 50 1228051T 5 51–114 1228060

T 10 se 12– 15 70 50 56 27 14 1228079T 10 se 16– 20 1228088T 10 21– 45 1228097T 10 46–114 1228104

T 20 se 15– 20 90 80 88 32 14 1228113T 20 21– 45 1228122T 20 46–119 1228131

The "se" tooth gap form is applied up to 20 teeth incl., over 20 teeth = normal profile

65

Hobs

l1l3

d1 d2

for timing belt pulleyswith involute flanks to DIN/ISO 5294topping cutter


KHSS-E EMo5Co5

Dimensions in mmPitch

Tooth numberrange

Ident No.Number ofgashesd1 I3 I1 d2


0,08 MXL10 up to 23 50 25 31 22 14 1203010from 24 2257398

1/8 XXL from 10 12030121/5 XL from 10 56 32 38 12283003/8 L from 10 70 50 56 27 12283191/2 H 14–19 63 69 12283281/2 H from 20 12283377/8 XH from 18 100 80 88 40 1228346

11/4 XXH from 18 115 100 108 1228355

Hobs for timing belt pulleys with straight flanks to DIN/ISO 5294 on request.Our range also includes hobs for timing belt pulleys with special profiles.

66

Hobs

l1l3

d1 d2

for spline shafts


KHSS-E EMo5Co5

Dimensions in mm Dimensions in mm

Ident No.Number

ofgashes

Number of

splinesFor

shldr.dia.

Spline shaft nominal dimesions Hob dimensions

2402 relief ground


d1 I3 I1 d2

I.d. O.d. Wdth ofg 6 a 11 spl. h 9

1), 2), 3), 4) This hob is absolutely identical with the hob marked with the same index number under Cat.-No. 2442.

23 26 6 6 29 56 30 36 22 12 122946126 30 33 63 34 40 27 122947028 32 7 35 122948932 36 6 8 39 39 45 122949836 40 7 43 122950442 46 8 50 122951346 50 9 54 70 44 50 122952252 58 10 62 50 56 122953156 62 66 122954062 68 12 73 122955972 78 10 83 57 63 122956882 88 93 80 32 122957792 98 14 103 90 65 71 1229586

102 108 16 113 100 1229595112 120 18 126 72 80 1229602

11 14 3 6 16 56 26 32 22 12 123021713 16 3,5 18 123022616 20 4 22 30 36 123023518 22 5 25 34 40 1230244211) 25 28 63 27 1230253232) 28 6 31 39 45 1230262263) 32 35 1230271284) 34 7 37 44 50 123028032 38 6 8 41 123029936 42 7 45 123030642 48 8 52 70 50 56 123031546 54 9 58 123032452 60 10 64 57 63 123033356 65 69 80 32 123034262 72 12 77 65 71 123035172 82 10 87 90 123036082 92 97 72 80 123037992 102 14 107 100 1230388

102 112 16 117 112 40 1230397112 125 18 131 82 90 1230404

2412 For spline shafts to DIN ISO 14 – medium series ■ Cutting to shoulder, with 2 lugs and chamfer

2402 For spline shafts to DIN ISO 14 – light series ■ Cutting to shoulder, with 2 lugs and chamfer

67

Hobs

l1l3

d1 d2

for spline shafts


KHSS-E EMo5Co5


Ident No.Number gashes

Number of

splinesFor

shldr.dia.


2422 relief ground

2432 relief ground Cat.-No.

d1 I3 I1 d2


** Hobs may have 2 lugs for some spline shaft dimensions with 10 splines

16 20 2,5 10 22 56 30 36 22 12 123099418 23 3 25 63 34 40 27 123100121 26 28 123101023 29 4 31 39 45 123102926 32 34 123103828 35 37 70 44 50 123104732 40 5 43 123105636 45 48 80 50 56 32 123106542 52 6 55 123107446 56 7 59 57 63 123108352 60 5 16 63 123109256 65 68 123110962 72 6 75 100 65 71 123111872 82 7 85 123112782 92 6 20 95 72 80 123113692 102 7 105 1231145

102 115 8 119 112 82 90 40 1231154112 125 9 129 1231163

11 15 3 4 17 63 34 40 27 14 123166213 17 4 19 123167116 20 6 23 39 45 123168018 22 25 123169921 25 8 29 70 50 56 123170624 28 32 123171528 32 10 36 123172432 38 42 90 57 63 32 123173336 42 12 47 123174242 48 53 100 65 71 16 123175146 52 14 57 123176052 60 65 125 72 80 40 123177958 65 16 70 123178862 70 75 123179768 78 83 140 82 90 1231804

2432 For spline shafts to DIN 5471 ■ Cutting to shoulder, with 2 lugs and chamfer

2422 For spline shafts to DIN 5464 ■ Cutting to shoulder, with 1** lug and chamfer

68

2442 relief ground

Hobs

l1l3

d1 d2

for spline shafts


KHSS-E EMo5Co5


Ident No.Number

ofgashes

Number of

splinesFor

shldr.dia.


Cat.-No.

d1 I3 I1 d2


1), 2), 3), 4) This hob is absolutely identical with the hob marked with the same index number under Cat.-No. 2412.

211) 25 5 6 28 63 34 40 27 12 1232420232) 28 6 31 39 45 1232439263) 32 35 1232448284) 34 7 37 44 50 123245732 38 8 42 70 50 56 123246636 42 46 123247542 48 10 52 90 57 63 32 14 123248446 52 12 57 123249352 60 14 65 100 65 71 123250958 65 70 123251862 70 16 75 123252768 78 83 112 72 80 40 123253672 82 87 123254578 90 95 140 82 90 16 123255482 95 100 123256388 100 105 123257292 105 20 111 92 100 123258198 110 116 1232590

105 120 126 160 102 110 50 1232607115 130 136 1232616130 145 24 151 1232625

2442 For spline shafts to DIN 5472 ■ Cutting to shoulder, with 2 lugs and chamfer

69

2444 relief ground

Hobs

l1l3

d1 d2

for p.t.o. shafts to DIN 9611


KHSS-E EMo5Co5

Cat.-No.

63 50 56 27 12 1232689

56 32 38 22 14 1232661

63 40 46 27 14 1232670

Form 128.91 ± 0.05 x 34.79 ± 0.06 x 8.69 –0.09

–0.166 splines with 2 lugs and chamfer

Form 2DP 16, EW 30°, da = 34.6721 teeth with chamfer

Form 3DP 12, EW 30°, da = 44.3320 teeth with chamfer

P.t.o. shafts

Dimensions in mm

Hob dimensions

d1 I3 I1 d2

Number ofgashes

Ident No.

70

Hobs

l1l3

d1 d2

for spline shafts with involute flanksto DIN 5480


KHSS-E EMo5Co5




0,6 50 25 31 22 14 12339190,8 12339281,0 12339371,25 12339461,5 56 32 38 12339552,0 63 40 46 27 12339642,5 70 50 56 12339733 12339824 80 63 69 32 12339915 90 70 78 12340086 100 80 88 12340178 115 100 108 40 1234026

10 125 130 138 1234035

71

Hobs

l1l3

d1 d2

for spline shafts with involute flankspreviously DIN 5482


KHSS-E EMo5Co5

Dimensions in mm Ident No.Number ofgashesSpl. shaft nom. size m d1 I3 I1 d2


15 x 12 1,6 56 32 38 22 1217 x 1418 x 1520 x 17

1233018

22 x 1925 x 2228 x 25 1,7530 x 2732 x 28

1233027

35 x 3138 x 34 1,9 63 40 46 2740 x 36 123303642 x 3845 x 41 248 x 4450 x 4552 x 47 123304555 x 5058 x 5360 x 5562 x 57 2,165 x 6068 x 6270 x 6472 x 66

1233054

75 x 6978 x 7280 x 7482 x 76 2,25 70 50 5685 x 7988 x 8290 x 8492 x 86

1233063

95 x 8998 x 92

100 x 94

72

Hobs

l1l3

d1 d2

for serrated shafts to DIN 5481with staight flanks for involute flankform on the component


KHSS-E EMo5Co5

Dimensions in mm Ident No.Number ofgashes*Serr. sh. nom. size Pitch d1 I3 I1 d2


7 x 8 0,842 50 25 31 22 16 12334108 x 10 1,010 1233429

10 x 12 1,152 123343812 x 14 1,317 123344715 x 17 1,517 123345617 x 20 1,761 56 32 38 123346521 x 24 2,033 123347426 x 30 2,513 123348330 x 34 2,792 123349236 x 40 3,226 123350840 x 44 3,472 63 40 46 27 123351745 x 50 3,826 123352650 x 55 4,123 123353555 x 60 4,301 123354460 x 65 4,712 70 50 5665 x 7070 x 7575 x 8080 x 8585 x 9090 x 95 123355395 x 100

100 x 105105 x 110110 x 115115 x 120120 x 125

* Hobs will be supplied with 12 gashes whilst stocks last.

Hobsfor worm gears

Page

Hobs for worm gears 76

76

Hobs for worm gearsFlank forms

The flank form of a worm gear hobis determined by the flank form ofthe driving worm. The various flankforms are standardized in DIN3975, which distinguishes be-tween ZA, ZN, ZI and ZK worms,according to the generating meth-od.

■ The ZA worm has a straight-line flank profile in its axialplane. This flank form is op-tained when a trapezoidal turn-ing tool is applied so that itscutting edges are in the axialplane.

■ The ZN worm has a straight-line flank profile in its normalplane. This flank form isachieved when a trapezoidalturning tool set at axis height isapplied so that its cutting edgeslie in the plane inclined by themean lead angle and the wormprofile is generated in this set-ting.

■ The ZI worm has involuteflanks in its face plane. Thisflank form is produced, for ex-ample, when the worm profile isgenerated by a straight-linedcutting or grinding elementwhose axis is inclined to theworm axis by the mean lead an-gle and to the normal plane onthe worm axis by the pressureangle "α0".

■ The ZK worm has a convexflank form in the axial plane.This worm form is generatedwhen a double taper wheeltrued under the pressure angleα0 is inclined into the mean leadangle, where the line of symme-try of the wheel profile passesthrough the intersection of theaxes and generates the wormprofile in this position.

Apart from the standardized flankforms, there are special forms, ofwhich the follow flank form is themost used.

The above worm profile forms canalso be used in DUPLEX wormdrives. DUPLEX worms have dif-ferent leads on the left- and right-hand flanks. As a result, the tooththicknesses on the worms changecontinuously in the course of thelead, and an axial displacement ofthe worm in relation to the wormgear makes it possible to adjustthe backlash.

The specification factors of wormgear hobs are determined essen-tially by the worm gear data.

In order to prevent edge bearing ofthe driving worm in the worm gear,the hobs used for producing theworm gears must under no cir-cumstances have a pitch cylinderdiameter that is smaller than thecentre circle diameter of the worm.Owing to the relief machining, thediameter of the hob is reduced byregrinding. The pitch cylinder di-ameters of the worm gear hob inthe new condition must thereforebe greater than those of theworms. This dimension is deter-mined as a function of the module,the centre circle diameter, and thenumber of threads.

The outside diameter of a newworm gear hob is thus calculatedas follows:

Centre circle diameterof the worm

+Pitch circle increase

+2 x addendum of the worm

+2 x tip clearance

77

Processes and designs

Worm gear hobs are available in arange of designs. A distinction isdrawn between the followingtypes:

Radial methodCylindrical hobs are employed forthis method. The hob enters theworm radially to full tooth depth,and can be displaced tangentiallyby a small distance in order to im-prove the enveloping cut on theflanks. This hobbing method hasthe shortest machining time and isgenerally employed for worm gearhobs with helix angles up to ap-proximately 8°. The cutting edgelength must be at least as long asthe penetration length for theworm gear to be machined. Long-er hobs can of course also beshifted.

γm

αo

αo

ab

αoαo

do = ∞

dm

γm

αo

do

dm

γm

Bore-type hob with drive slot for radial hobbing

turning tool shaper-type cutter turning tool milling cutter

gene

ratin

glin

e

ZN-WormZA-Worm

ZI-Worm ZK-Worm

grinding wheelgrinding wheel

78

Tangential methodThis method is suitable for single-and multiple-start worm drives; thehobbing machine must howeverbe equipped with a tangential hob-bing head. The hobs have a rela-tively long taper lead section,which must remove the greaterpart of the metal. The cylindricalregion contains one or two finish-ing teeth per hob start. The hob isset to the centre distance prior tothe commencement of machining,and the penetration rangebetween the hob and the wormgear must then be traversed tan-gentially. By selection of suitablefeed values, the enveloping cutswhich determine the tooth formcan be modified as required. Ow-ing to the long tangential runs, thismethod results in substantiallylonger hobbing times than the ra-dial method.

The simplest forms of worm gearhob for tangential hobbing are thesingle- or multi-start fly-cut hobs.Fly-cut hobs are hobs with onlyone cutting tooth per start. Theyare relatively simple and low-costtools, but they also have the low-est metal removal capacity.

Duplex worm gear hob

Worm gear hob for tangential hobbing

Shank-type worm gear hob for radial hobbing

79

Shaving wormsFor high-precision worm gears,shaving worms are also employedfor finish profiling of rough-hobbedworm gears. Shaving worms havelift allowances of only a few tenthsof a millimetre, minimum relief an-gles, and a high number of gash-es. Of all worm gear hobs, their di-mensions most closely resemblethose of the driving worm, andthey therefore also produce thebest bearing contact patterns.

Radial Methodwith constant centre distance

The use of modern CNC hobbingmachines has enabled FETTE todevelop a method which permitsthe use of economical tools. Theworm gear hobs used in the pasthad to be re-adjusted each timethey were reground, i.e. the bear-ing contact pattern had to be relo-cated. This entails high productioncosts.

In the new method, cylindrical ra-dial hobs are employed the flanksof which are axially relief-ma-chined. The usual tangential hob-bing is thus replaced at higher he-lix angles (>8°). The tool settingcan be calculated as for the newcondition. The setting is optimizedwhen the tool is first used, and thetool is then used with the samecentre distance and tool cuttingedge angle over the entire lifespan.

By careful selection of the ar-rangement, a bearing contact pat-tern is produced which can be at-tained reliably by each regrindaccording to the requirements ofthe worm gear.

Since the tools are radial hobs,this hob concept has the advan-tage of shorter hobbing times incomparison with conventional tan-gential hobbing.

Leaving endLeading end

Contact lines on the worm gear flank


Axi

al p

itch

Cen

tre

cut

Engagement area

80

Engagement area andbearing contact pattern

The essential variables which de-termine the tooth form of the wormgear and the engagement area areas follows: module, number ofteeth, profile displacement, andthe associated helix. The complex computation of theengagement conditions in theworm gear can now be performedvery precisely by means of power-ful PCs.

In practice, bearing contact pat-terns with a percentage contactarea of 50-70% are desirable. The FETTE software enables ourspecialist department to produce

the optimum tool design. Worm gear hobs with high num-bers of starts can thus now be de-signed very accurately and reli-ably. It must be pointed outhowever that the engagement areais determined in advance by thegear manufacturer, and can onlybe reduced in size by the toolmanufacturer. The bearing contact pattern duringhobbing must be generated suchthat an contact ratio of >1 is pro-duced. Cases in which the user ispresented with a tool adjustmentproblem can be simulated theoret-ically by FETTE on the computer. A corresponding correction canthus be made. Our applications engineers are al-

so available for on-site assistance.Selected calculations are shown inthe diagrams.


Distance between worm and gear flank

0.005 mm to 0.010 mm 0.010 mm to 0.015 mm� 0.005 mm

Topography of the worm gear flank

81

Instructions for ordering:

Worm gear hobs can be manufac-tured as bore-type hobs with key-way or drive slot, or as shank-typehobs. Generally, preference is giv-en to the less expensive bore-typehobs. However, if the hob diam-eters are very small and the pro-files very high, it may be necessaryto select a shank type. The dia-gram on the right can be used todetermine whether a bore-typehob is suitable or a shank-typehob is required. If the latter is se-lected, please quote the make andtype of the hobbing machine andthe dimensions of the working ar-ea or of the shank-type hob, asshown in the diagram.

The component dimensions can-not be standardized for the rea-sons given above. They must beadapted to the technical data ofthe drive worms and to the hob-bing processes.

The following information is re-quired for manufacture of thesehobs:

■ Axial module ■ Pressure angle■ Pitch circle diameter of the

worm■ Number and direction of

starts■ Flank form to DIN 3975

(A, N, I or K)

The above data can of course alsobe supplied in the form of wormand worm gear drawings.

Unless otherwise specified, thehobs are designed as follows:

■ Addendum = 1.2 x m■ Depth of tooth = 2.4 x m■ Non-topping■ Tooth profile relief ground■ Cylindrical hob for radial milling

up to a lead angle of approx. 8°■ Hob for tangential hobbing,

with lead on the leading end iflead angle > 8°

Shank dimensions

6 7 8 9 10 11 12 13 14 15 16 17 18

13

12

11

10

9

8

7

6

5

4

3

2

1

Bore-/shank-type hob

ZF = dmm

dm = Pitch circle diameter

Bore-type hobpossible

Shank-type hobnecessary

Figure for form (ZF)

Mod

ule

(m)

d5 d1 d2d3

d

L5

Without taper leadradial hobbing

left-handcut

right-handcut

d4

L4

L3*

L*

L2*SW

L1

* State if known to theperson ordering

Taper lead on the lefttangential hobbing

L6*

Taper lead on the righttangential hobbing

L6*

Hobsfor special profiles

Hobs for special profiles 84

Special and single-position hobsThe hobbing process with its well-known advantages is, in additionto the standard operating- and slipgears as well as gears for belt andchain pulleys, also suitable for alarge number of special profiles, ofwhich a few examples are shownhere. Hobs for particularly fre-quently used special profiles havebeen dealt with in detail in the ear-lier sections of this catalogue,such as the special-purpose hobsfor rotors and screw spindles, aswell as for internal gears.

The term "special profiles" applies

to all profile types which are notcovered by a standard.

The most common types are spe-cial-purpose hobs for: ratchetwheels, feed- and conveyorwheels, conveyor rolls, cardboardrolls, multi-edge profiles, slottedplates, orbit gears and cyclogears.

The special form of certain specialprofiles often makes it necessaryto design the cutter as a single-po-sition hob. The profile helix is inthis case not uniformly shaped

over the entire length of the hob,but the cutter teeth or tooth por-tions have varying profile forms.These hobs have to be aligned intheir axial direction with the work-piece and/or centre line of the ma-chine, to make sure that the spe-cially shaped teeth are meshing inthe intended position.

Provided that the profile standardallows this, single-position hobscan be manufactured for severalsetting positions and with a longereffective length, to improve econo-my.

84

Examples of special profiles which can be generated by hobbing

85

.

Example of profiles which can be hobbed with single-position hobs

Multi-start single-position fly-cut hob for ratchets of various pitches

Special hops for pump wheels with orbit gears

Gear milling cuttersfor racks and worms

Cat.-No. Page

Worm thread milling cuttersmilled, straight teeth 2500 88

Rack milling cutters/worm thread cuttersmilled, straight teeth 2512 89

Worm thread roughing cuttersmilled, staggered teeth 2513 90

Rack milling cutters/worm thread cuttersrelief turned, straight teeth 2521 91relief ground, straight teeth 2522 92as gang milling cutters 2560 93as circular milling cutters, ganged-up 2561 94

88

Worm thread milling cutters

d2 d1

b1for module pitch

20° pressure anglebasic profile I to DIN 3972with offset teethand one tooth for checking

HSS

Dimensions in mm Ident No.m d1 b1 d2

2500 straight tooth, milled, with ground landsCat.-No.

1 70 8 22 12344191,5 12344372 12344552,5 12344733 80 10 12344913,5 12345163,75 12 –4,5 13 12345435,5 100 15 27 –6,5 18 –8 22 1234605

10 125 27 32 1234623

This design can also be used as a gear milling cutter for roughing and as a rack tooth cutter.

We also manufacture: worm thread milling cutters of larger dimensions with different basic profiles, also available as trapezoidal thread milling cutters with millimetre pitch.

89

Rack and worm milling cutters

d2 d1

b1module pitch

20° pressure anglebasic profile I to DIN 3972with one tooth for checking

KHSS-E EMo5Co5

Dimensions in mm Ident No.m d1 b1 d2

2512 staggered tooth, milled, with ground landsCat.-No.

1 140 8 40 12352121,5 12352212 10 12352302,5 12352493 12352583,5 12 12352674 12352764,5 14 12352855 12352946 145 16 12353017 19 12353108 22 12353299 150 25 1235338

10 27 1235347

We also manufacture: rack milling cutters with larger dimensions,different basic profiles and with 10° inclined profile.

90

Worm milling cutters for roughing

b1

d1d2

A

20°

for roughing gears, tooth racks and wormsof module pitch

20° pressure angle, straight flanksbasic profile IV to DIN 3972without tooth for checkingstaggered chip breakers form module 10

KHSS-E EMo5Co5

Dimensions in mm

m d1 b1 d2 A

2513 staggered tooth, milled, with ground landsCat.-No.

5 140 13 40 2,565,5 14 2,866 145 15 3,176,5 17 3,487 18 3,797,5 19 4,108 20 4,419 150 23 5,04

10 25 5,6711 28 6,3012 30 6,9313 155 34 7,5614 160 36 8,2015 165 38 8,8316 170 40 9,4717 180 43 50 10,1118 190 46 10,7519 195 48 11,3920 200 50 12,03

These milling cutters are designed for the straight flank roughing of gears, racks and worms. They are manufactured without a tooth for checking, to achieve a high cutting rate. They are sharpened by tracing the profile at the backed-off surfaces. The tooth tip width A given in the table can be used as a checking dimension.

91

Rack milling cutters/worm milling cutters

Form B

10°

d2 d1

b1

Form A

module pitch

20° pressure anglebasic profile I to DIN 3972form A: with straight profileform B: with 10° inclined profile*

KHSS-E EMo5Co5

Dimensions in mm Ident No.Form B

Ident No.Form Am d1 b1 d2

2521 straight tooth, relief turnedCat.-No.

1 140 8 40 1235711 12358551,5 1235720 12358642 1235739 12358732,5 10 1235748 12358823 1235757 12358913,5 1235766 12359084 1235775 12359174,5 11 1235784 12359265 13 1235793 12359356 145 15 1235800 12359447 17 1235819 12359538 20 1235828 12359629 150 22 1235837 1235971

10 25 1235846 1235980

* Only available until stock is depleted

Unless otherwise specified, we supply form A.

We also manufacture: rack milling cutters with larger dimensions and different basic profiles.

92

Rack milling cutters/worm milling cutters

Form B

10°

d2 d1

b1

Form A

module pitch

20° pressure anglebasic profile I to DIN 3972form A: with straight profileform B: with 10° inclined profile*

KHSS-E EMo5Co5

Dimensions in mm Ident No.Form B

Ident No.Form Am d1 b1 d2

2522 straight tooth, relief groundCat.-No.

1 140 8 40 1236319 21258161,5 1236328 22546792 1236337 12364712,5 10 1236346 12364803 1236355 12364993,5 1236364 12365054 1236373 12365144,5 11 1236382 22223485 13 1236391 12365326 145 15 1236408 12365417 17 1236417 12365508 20 1236426 12365699 150 22 2120452 1236578

10 25 1236444 1236587


Unless otherwise specified, we supply form A.

We also manufacture: rack milling cutters with larger dimensions and different basic profiles.

93

Rack tooth gang cutters

b3

tooth row n

d2

d1

pwith several tooth rows for racks to module pitch

20° pressure anglebasic profile I or II to DIN 3972

KHSS-E EMo5Co5

Dimensions in mm

Number of gashes

Z = 14 Z = 18 Z = 22

d1 d2 d1 d2 d1 d2m


1 70 27 100 32 125 401,251,51,752 90 32 125 40 160 502,252,52,753 110 140 1803,253,53,754 125 40 160 50 200 604,254,54,755

Rack tooth gang cutters are used on the conventional horizontal milling machines as well as on the special automatic rackmilling machines. Standardized constructional dimensions therefore do not exist. The above table is intended for guidance andshould facilitate the selection of milling cutter overall dimensions. The cutter width depends on the module (m) and the numberof tooth rows (n).

b3 = m · π · n

For larger cutter widths (over 40 mm) the helical-fluted version is preferable (3-5° RH helix). The tools can also be made in theform of topping cutters. For gear sizes above module 5, rack gang milling cutters are recommended. See cat. no. 2561.

Unless otherwise specified, we supply with basic profile I to DIN 3972.

To process your order correctly, we need in addition to the gear data the required number of tooth rows on the cutter.

m = modulep = pitch = m · πn =number of tooth rowsb3 = cutter width = m · π · nz = number of gashes

94

High-precision rack tooth gang cutters

1 2 3 4d2 d1

b1for tooth racks to module pitch

20° pressure anglebasic profile I to DIN 3972with additional grinding slots, with offset keyways

KHSS-E EMo5Co5

Dimensions in mm Number ofgashesm d1 b1 d2


3 140 9,425 40 203,25 10,2103,5 10,995 183,75 11,7814 150 12,5564,5 14,1375 15,708 165,5 17,2796 18,8496,5 160 20,420 507 21,9918 25,1339 28,274 14

10 31,416

Rack tooth gang cutters for the simultaneous machining of several tooth gaps are made up of severalsingle-profile circular-type milling cutters. Through the continual offsetting of the gashes in relation to thedrive slot the individual cutters are successively coming (helically) to the point of cutting addition. This feature particularly promotes quiet running of the milling machine under heavy chip loads.

To allow regrinding combined in a gang, the individual cutters are provided with an additional closely tolerated keyway (grinding slot), so that an axially parallel position of the cutting faces on the arbor is guaranteed.

Rack tooth gang cutters are profile relief ground with parallelly flat lapping of the contact faces. To improve tool life, these milling cutters are made exclusively of cobalt alloyed super high speed steel.

For extreme precision requirements the tolerances for pitch, flank form, gash spacing, cutting face position as well as cutting edge concentricity lie within quality grade AA to DIN 3968.

consecutively numbered as: cutter no. 1, 2, 3, 4

Gear milling cuttersfor spur gears

Cat.-No. Page

Gear milling cuttersrelief turned, for module pitch 2601 98

Gear milling cutters for large tooth systems 100

End mill type gear cuttersRoughing cutters 2620 102Finishing cutters 2621 103

Stepped roughing cuttersrelief turned, stepped-up style 2630 104

Roughing gear cutterswith indexable carbide inserts, arranged tangentially 2667 105

Circular-type gear profile cutterswith form indexable inserts 2675 106

Gear finishing cutters 107

98

Involute gear cutters

d2 d1

for spur gears to module pitch

20° pressure anglebasic profile I to DIN 3972

HSS* / KHSS-E EMo5Co5

Dimensions in mm

m d1 d2


0,3 35 130,40,5 40 160,60,70,750,80,9 5011,251,5 60 221,7522,252,5 652,75 70 2733,25 753,53,75 8044,25 854,54,75 905 325,5 956 1006,5 10577,5 11088,5 11599,5 120

1011 135 4012 14513 15514 16015 165

* Available only while stocks last.

If required, we also supply involute gearcutters above module 10 in sets of 8 units.

Involute gear cutters are supplied in complete sets as well as singly. When ordering single gear cutters, the cutternumber or the number of teeth to be cutmust be specified.

We also manufacture:Involute gear cutters with other pressure angles or to CP. Involute gear cutters for cutting spur gears with less than 12 teeth.

Specification of Sets

from module 0.3 to module 10 in sets of 8 units

from module 11 to module 20 in sets of 15 units

Cutter No. 1 for 12– 13 teethCutter No. 2 for 14– 16 teethCutter No. 3 for 17– 20 teethCutter No. 4 for 21– 25 teethCutter No. 5 for 26– 34 teethCutter No. 6 for 35– 54 teethCutter No. 7 for 55–134 teethCutter No. 8 for 135– ∞ teeth

Cutter No. 1 for 12 teethCutter No. 11/2 for 13 teethCutter No. 2 for 14 teethCutter No. 21/2 for 15– 16 teethCutter No. 3 for 17– 18 teethCutter No. 31/2 for 19– 20 teethCutter No. 4 for 21– 22 teethCutter No. 41/2 for 23– 25 teethCutter No. 5 for 26– 29 teethCutter No. 51/2 for 30– 34 teethCutter No. 6 for 35– 41 teethCutter No. 61/2 for 42– 54 teethCutter No. 7 for 55– 79 teethCutter No. 71/2 for 80–134 teethCutter No. 8 for 135– ∞ teeth

99

Involute gear cutters

d2 d1

for spur gears to module pitch

20° pressure anglebasic profile I to DIN 3972


Dimensions in mm

m d1 d2


16 170 4017 180 5018 19019 19520 205

* Available only while stocks last.

If required, we also supply involute gearcutters above module 10 in sets of 8 units.

Involute gear cutters are supplied in complete sets as well as singly. When ordering single gear cutters, the cutternumber or the number of teeth to be cutmust be specified.

We also manufacture:Involute gear cutters with other pressure angles or to CP. Involute gear cutters for cutting spur gears with less than 12 teeth.

Specification of Sets

from module 0.3 to module 10 in sets of 8 units

from module 11 to module 20 in sets of 15 units

Cutter No. 1 for 12– 13 teethCutter No. 2 for 14– 16 teethCutter No. 3 for 17– 20 teethCutter No. 4 for 21– 25 teethCutter No. 5 for 26– 34 teethCutter No. 6 for 35– 54 teethCutter No. 7 for 55–134 teethCutter No. 8 for 135– ∞ teeth

Cutter No. 1 for 12 teethCutter No. 11/2 for 13 teethCutter No. 2 for 14 teethCutter No. 21/2 for 15– 16 teethCutter No. 3 for 17– 18 teethCutter No. 31/2 for 19– 20 teethCutter No. 4 for 21– 22 teethCutter No. 41/2 for 23– 25 teethCutter No. 5 for 26– 29 teethCutter No. 51/2 for 30– 34 teethCutter No. 6 for 35– 41 teethCutter No. 61/2 for 42– 54 teethCutter No. 7 for 55– 79 teethCutter No. 71/2 for 80–134 teethCutter No. 8 for 135– ∞ teeth

100

Gear cutters for large-size gearsThe machining methods for gearswith large modules differ consider-ably in practice. Number and sizesof the gears, the efficiency of thegear cutting machine as well asmachinability and gear quality areonly a few of the factors which af-fect the selection of the cuttingtools.

Gear milling cutter for roughing, Cat.-No. 2667, with indexable carbide inserts

Gear finishing cutter, Cat.-No. 2675, with indexable carbide inserts, involute profileGear milling cutter for roughing, stepped-up type, Cat.-No. 2630

End mill type gear cutter(for roughing) Cat.-No. 2620

101

FETTE has considerable experi-ence in the design of these tools.For pre-machining, in particular,high-performance roughing cut-ters have been developed for avery wide range of machine tools.The solid-type designs are intend-ed for use on conventional gearcutting machines (Cat.-No. 2630).We supply end mill type gear cut-ters (Cat.-Nos. 2620 and 2621) forlarge modules, for example formachining gear segments on bor-ing mils. For gear cutting ma-chines with powerful motor millingheads, we manufacture millingcutters with carbide-tipped blades(Cat.-Nos. 2675 and 2667).

FETTE also designs and manufac-tures custom-designed profile cut-ters in a range of designs for theproduction of special forms. In ad-dition, our experience is at ourcustomers' disposal regarding theuse and maintenance of thesetools.

Profile roughing cutter for rotary pistons (Roots blower)2-section, 312 mm dia. x 260 x 120 dia., 92 indexable inserts

Circular-type gear profile cutterm 50, 20° p.a., 11 teeth, without roof radius, 295 mm dia. x 190 x 80 dia., 136 indexable inserts

End mill type gear cutter (roughingcutter) m 48-stub, 20° p.a., 150 dia. x180 mm length, 22 indexable inserts

102

End mill type gear cutter (roughing cutters)

d1d2d3

l3

l2l1

20°

for gears and racks

20° pressure angle, basic profile IV to DIN 3972with straight flanks, spiral fluted, with female thread and centring, for screw-on, 2 spanner flats

KHSS-E EMo5Co5

2620 milled and groundCat.-No.

This cutter version is also supplied as a finishing cutter for racks with basic profile I or II to DIN 3972.

Mounting dimensions for adaptor mandrels

Adaptor tapers optionallyMorse taper DIN 1806Morse taper DIN 2207Metric taper DIN 1806Steep taper DIN 2080


d3 (inches)

20 60 120 4 11/4 36 45 1022 65 1252426 70 13028 75 135 11/2 4230 8032 85 14034 90 14536 95 2 56 50 1238 100 15040 105 15542 11044 11546 120 160 6 21/2 7048 12550 130

m d1 l1 Z

Overall cutter dimensions

d2 l2 l3

Adapter dimensions

Dimensions in mm

d3 (inches)

BSW 11/4 – 7 Gg 36 70 40 9,5BSW 11/2 – 6 Gg 42 90BSW 2 – 41/2 Gg 56 115 45 11,5BSW 21/2 – 4 Gg 70 130

d2 d1 l1 l2

d1 d2 d3

l2

l1

Adaptor taper

103

End mill type gear cutters (finishing cutters)

d1d2d3

l1

l2

l3

template

involute profile

20° pressure angle,basic profile I or II to DIN 3972straight fluted, with female thread and centre bore, for screw-on, 2 spanner flats

KHSS-E EMo5Co5

2621 relief turned ■ with ground profile landsCat.-No.

Dimensions in mm

End mill type gear cutters with involute profiles are generally not designed for a number of teeth range but vor special gear op-erations with a specific numer of teeth.

When ordering, therefore, please provide workpiece drawings or precise gear data.

To achieve high profile accuracy and surface quality, the cutters are ground with a profile land. For maintenance we supply, if required, checking gauges and grinding templates for tool grinding machines: Studer-Oerlikon, Aldridge or Schuette. The referende cylinder for checking the profile is the ground outside diameter of the cutter.

20 70 115 66 115 62 120 60 120 11/4 36 45 1022 76 72 120 66 125 62 12524 84 120 78 74 6826 90 84 78 72 13028 98 90 84 78 135 11/2 4230 104 98 125 90 8232 110 125 104 96 130 88 14534 118 110 102 9436 124 130 116 130 108 135 98 145 2 56 50 1238 130 135 122 135 114 140 104 15040 136 128 140 120 145 110 15542 144 140 134 145 126 150 11644 150 150 140 155 130 155 12046 156 146 136 160 125 160 21/2 7048 164 160 152 142 13050 170 160 160 148 135

Number of teeth range Adaptor dimensions

m d1 I1 d1 I1 d1 I1 d1 I1 d3 (Zoll) d2 l2 I3

12 … 16 17 … 25 26 … 54 55 … ∞

104

Circular type gear roughing cutters

d1d2

Basic profile IV DIN 3972

b1

DIN 138

Radial-rake � 8°

stepped-up type

20° pressure anglealternate cutting with keyway

KHSS-E EMo5Co5

Dimensions in mm Ident Nr.Number ofgashesm d1 b1 d2


12 145 28 40 16 212208514 160 32 212926616 170 37 212503618 180 42 50 212503720 200 46 212500522 210 50 212500624 220 54 212500726 240 58 60 212926828 250 63 212168030 260 68 2129276

12 160 28 50 18 212587414 175 32 212926716 190 37 212170118 210 42 60 212689820 225 46 212288322 240 50 212750024 250 54 212750126 275 58 80 212926928 290 63 212927530 300 68 2129277

Series I cutter

Series II cutter

Stepped-up pre-machining is a process well-tried in practice for gear sizes above 10 module. An advantage of this cutter design is the relatively low power requirement as the chips are at thesteps only formed in the direction of the circumference and hardly any lateral loads are occurring.Another feature is the relatively simple maintenance by tool face grinding.

When enough machine power is available, these cutters can also be used as gang cutters for simultaneous machining of two adjacent tooth gaps.

Two overall dimension series have been established in practice for stepped-up roughing cutters.Special dimensional requirements can however also be taken into account with these cutters.

105

Gear roughing cutters

b1

d1

k

d2

t

20°

m 6-10 m 12-14 m 16-18 m 20-36

with indexable carbide inserts

20° pressure anglebasic profile IV to DIN 3972with keyway to DIN 138optionally with drive slot

2667 staggered toothCat.-No.

* For round tip forms

1 2 3 3.1.

FormCat.-No.

Form Cat.-No. l s d b d1

1 1185-11 12,7 6,35 14,3 0,78 5,32 1185-31 19,05 6,35 14,3 0,78 5,33 1185-33 25,4 5 14,3 5,53.1. 1185-32 25,4 5 14,3 1,1 5,54* 1185-15 15,88 7,94 12,7 5,45* 1185-35 19,03 6,35 14,3 5,8

Indexable inserts precision ground indexable 4 times

m d1 b1 d2 z k t

Overall dimensions Profile

6 160 50 50 12 3,14 17 12220 60 16 16280 80 20 20

8 180 50 12 4,41 23 12220 60 16 16 1150-86280 80 20 20

10 180 60 50 12 5,67 12220 60 16 16280 80 20 20

12 200 50 12 6,93 33 18250 60 16 24320 80 20 30

14 200 50 12 8,20 18250 60 16 24320 80 20 30

16 200 70 50 12 9,47 49 24250 60 16 32320 80 20 40

18 200 50 12 10,75 24250 60 16 32320 80 20 40

20 220 80 60 12 12,03 6 18280 80 16 8 24360 100 20 10 30

22 250 60 12 13,32 65 6 24300 80 16 8 32360 100 20 10 40 1150-80

24 250 60 12 14,61 6 24300 80 16 8 32360 100 20 10 40

26 320 100 80 16 15,89 8 32400 100 20 10 40

28 320 80 16 17,18 8 32400 100 20 10 40

30 320 80 16 18,46 80 8 40400 100 20 10 50

32 340 80 16 19,76 8 40420 100 20 10 50

34 340 80 16 21,05 95 56420 100 20 70

36 340 80 16 22,35 56420 100 20 70

d

l

s

b

d1

Dimensions in mm Number of indexable inserts Clamping screws

106

Circular-type gear profile cutters with form indexable inserts, Cat.-No. 2675These gear milling cutters arehigh-performance tools for finish-milling. A double negative cuttergeometry combined with a highnumber of blades produces goodcutting behaviour (peeling cut). In-dexable inserts with high accuracyand surface finish quality produceclean gear flanks. In addition, longservice life is ensured by additionalhard material coatings.

Example: external gear

Module 16α0 = 20°z = 89

Cutter diameter: 300Bore diameter: 80Form indexable inserts: 24

For rough-hobbing we recommend gear roughing cuttersFETTE Cat.-No. 2667.

Example: internal gear

Module 10α0 = 20°z = 94

Cutter diameter: 380Bore diameter: 80Form indexable inserts: 30Indexable inserts for chamfer: 10

107

Gear finishing cutter■ With carbide form indexable

inserts■ Involute profile■ For external or internal gears■ Alternate cutting■ With keyway or drive slot to DIN■ Pressure angle 20°■ z = number of blades

The range shows guide values forhigh numbers of gear teeth. Thecutter diameters are determined bythe number of cutting edges. Alter-native structural dimensions are pos-sible.

Carbide form indexable inserts

■ Involute profile■ For external or internal gears■ Ground on all faces■ 2 cutting edges■ Supplied in sets

1 set = z off

These form indexable inserts havetwo cutting edges in the new condi-tion. They can be employed on boththe right-hand and left-hand sides.

The indexable inserts can be re-ground. Regrinding entails surfacegrinding of the cutting faces, but onone side only.

When regrinding sets, note the dif-ference between right-hand and left-hand indexable inserts.

d1d2

b1

l

s

R

When regrinding

L

b

Regrind

b2

Module z = 24 z = 28 z = 32

810 d1 300 350 42012 b1 70 80 10014 d2 80 80 100161820222426

Module l b s

8 25,40 5,0010 31,75 6,3512 31,75 6,3514 38,10 7,1416 44,45 14,30 7,9418 50,80 7,9420 57,15 8,7322 66,68 9,5324 66,68 9,53

Gear milling cuttersfor multi-start worm gears and conveyor screws (rotors)

Cat.-No. Page

Profile milling cutters for multi-start worm gears and conveyor screws with special profiles 110

Rotor roughing cutters, with indexable carbide inserts 2695 111

Rotor profile cutters, with inserted blades 2690 112

110

Profile milling cutters for coarse-pitch worms and conveyor screwswith special profiles

In addition to the usual worm mill-ing cutters with straight flanks(Cat.-Nos. 2500, 2512, 2521,2522), we manufacture specialcutters for producing any desiredscrew type gears by the single in-dexing method.Such workpieces are, for example,screw pumps for liquids and gas-es, extruder worms, multi-start in-volute worms for drives etc.

Fig. 1: Workpiece: conveyor screwpair, 2-start, for a screw pump;tool: profile finishing cutter,straight teeth, relief ground.

Fig. 2: Workpiece: drive- and trail-ing spindle of a liquid feed pump;tool: profile finishing cutter, stag-gered teeth, relief ground.

Fig. 3: Workpiece: female rotor ofa screw compressor; tool: profileroughing cutter with insertedblades, staggered teeth, see alsoCat.-No. 2690.

We have at our disposal universalcomputer programs to determinethe cutter profiles for any desiredform of thread.

If the cutter profiles are not yetknown, we require data in accor-dance with fig. 4 about the screwsto be cut, i.e.:

1. the lead of the screw H2. the coordinates in the face

planer r, ö, αs or axial plane co-ordinates r, a, αA

Coordinates in the axial plane arefound with the equation a = arc ö · H/2π

tan αA = tan αs · H/2rπ

Fig. 1

Fig. 2

a

r

αA

P

ö

P

αS

r

Cross-section in face plane Cross-section in axial plane

Fig. 4Fig. 3

111

2695Cat.-No.

Number ofinserts

Roughing cutters for rotorswith indexable carbide insertsfor screw compressors

HL = male rotorNL = female rotorindexable inserts arranged tangentiallywith keyway to DIN 138

b1

d1d2

b1

HL NL for male rotors for female rotors

Dimensions in mmForm Designation Clamping screw

12,70 6,35 14,29 1185-117,94 15,88 1185-15

A15,88 M4-2176419,05 6,35 14,29 1185-3112,70 M4-20859 1150-80

B7,94 15,88 M4-19730-2

C 19,05 6,35 14,29 M4-21056

D25,40 M4-2092419,05 1185-35

L S d

A B C D

d

L

S

Indexable insert forms

These tools are, because of theirhigh cutting rates and trouble-freemaintenance, particularly econom-ical.The profile is formed polygonallyform straight sections and con-tains a minimum allowance for fin-ish milling.

To achieve finishing allowanceswhich are as parallel as possible,modified forms are used in addi-tion to the standard indexable in-serts. These are provided withchamfers or rounded edges.For rotors in stainless chromiumalloys or for machines with low

drive power, the tools can be fittedoptionally with KHSS indexable in-serts with ridges.

Dimensions in mm

100 22 HL 220 60 6025– 36NL

127,5 27,5 HL 250 70 8032– 45NL

163,2 35,5 HL 8040– 56NL

204 44 HL 300 100 10050– 70NL

255 55 HL 320 12563– 85NL 100

318 70 HL 350 16070–100NL 125

Outside diameter Profile height Type d1 b1 d2

Rotor measurements Cutter measurements (variable)

112

Rotor profile cutters

Male rotor Female rotor

for screw compressors for male rotors or female rotors with inserted bladesblades radially and axially resettableblade clamping by chucking wedge and screwwith keyway

ARoughing cutter with profile undersize staggered chip breakers positive rake angle + 10° radial, + 10° axial

BFinishing cutterrake angle 0° radial, 0° axial

KVHSS-E EV4Co

2690 staggered teeth ■ with profile ground landsCat.-No.

Cutter for male rotor

Cutter for female rotor

Dimensions in mmNumber of

blades

127,5 27,5 210 70 50 60 16163,2 35,5 220 85 65204,0 44,0 235 105 80255,0 55,0 290 125 100 80

340 100 20318,0 70,0 360 160 125400,0 86,0 380 200 160

Outside diameter Profile height d1 b1 male rot. b1 female rot. d2

Rotor dimensions Cutter dimensions

Circular type cutters for rotorsmust be kept in close limits as regards their outside diameter, since changes in diameter will affect the generated screw profile.This is why these tools are groundby the land grinding method.The blades are radially adjusted bymeans of set screws, the width adjustment is made possible by

the staggered serrations in stepsof 0.25 mm.The cutting profiles top the rotoro.d. and generate the entire gapprofile including tip radii and sealing strips.To deal with enquiries, we needworkpiece drawings with profiledata. We carry out the computa-tion of the cutter profiles.

Replacement blades are pre-machined with grinding allowanceon the profile and are ground onthe cutting faces.

b1

d1d2

b1

HL NL

Gear milling cuttersfor sprockets, timing belt pulleys and slip-on gears

Cat.-No. Page

Form milling cutters for sprocketsto match chains to DIN 8187, 8188 2701 116

Form milling cutters for timing belt profilesfor timing belt pulleys 2742 117

Form milling cutters for spline shaft profilesto DIN / ISO 14, DIN 5464, 5471, 5472as well as for p.t.o. shafts to DIN 9611 2730 118

Form milling cutters for spline shafts and serrated shaftsas separate circular milling cutters matched up 2731 120

Gear chamfering cutterswith straight flanks 2801 122with curved flanks 2802 122as end mill type cutters 2803 122as V-shaped/bell-shaped cutters 2804 121

Rolling racks 122

116

Cutter no. 1 for 8– 9 teethCutter no. 2 for 10–13 teethCutter no. 3 for 14–20 teethCutter no 4 for 21–34 teethCutter no. 5 for 35– ∞ teeth

Form milling cutters

d2 d1

for sprocketsfor roller- and barrel chains to DIN 8187, 8188



6 15/64 4 5/32 63 226,35 1/4 3,38 5/16 5 3/16

9,525 3/8 706 15/64

6,35 1/4

12,7 1/2 7,75 5/16

7,938,51

15,875 5/8 10,16 90 2719,05 3/4 11,9 15/32

12,07 1/2

25,4 1 15,88 5/8 10030 11/4 105 3231,75 19,05 3/4 11038,1 11/2 22,22 7/8 125

25,4 144,45 13/4 140 40

27,9450,8 2 28,57 11/8

29,2157,15 21/4 35,71 113/32 15063,5 21/2 39,37 170 50

39,68 19/16

76,2 3 47,62 17/8 19048,26

Specification of setsin sets of 5 units


Form milling cutters for sprockets aresupplied both in complete sets and sin-gly.When ordering single cutters, pleasespecify the cutter number or the numberof teeth to be cut.

We also manufacture:Form milling cutters for sprockets with oth-er or larger dimensions or with insertedblades, for sprockets to match Gall’s chainsto DIN 8150 and 8151, barrel chains to DIN8164, SAE chains, Renold chains and forsprockets of other systems.

mm inches approx. mm inches approx. mm mm

Pitch Roller/barrel diameter d1 d2

117

Cutter no. 1 for 10–13 teethCutter no. 2 for 14–20 teethCutter no. 3 for 21–34 teethCutter no. 4 for 35–71 teethCutter no. 5 for 72– ∞ teeth


d1

rK

d2

b1

r1h h1

b

r2

αd1

rK

d2

b1

r1h h1

b

r2

α

for timing belt pulleyssemi-toppingpositive rake angle

KHSS-E EMo5Co5


When cutting timing belt pulleys using the single indexing method, the tooth tip radius r1 is semi-topped. The profile height h1

on the cutter therefore depends on the number of teeth to be cut. This number must also be quoted to facilitate order processing.

For gears with different belt pitches or with special profiles we require dimensional data as shown in the figure above.

Dimensions in mmSpecifications of sets

for metric pitchesto DIN 7721

T 2,5 SE to 20 63 5 22T 2,5 N over 20T 5 SE to 20 6T 5 N over 20T 10 SE to 20 9T 10 N over 20T 20 SE to 20 70 18 27T 20 N over 20

Cutter no. 1 for 10–13 teethCutter no. 2 for 14–20 teethCutter no. 3 for 21–34 teethCutter no. 4 for 35–71 teethCutter no. 5 for 72– ∞ teeth

d1 b1 d2

Cutter dimensions

T

Specifications of setsfor inch pitchesto DIN ISO 5294

5,08 = 1/5" XL 63 5 229,525 = 3/8" L 8

12,70 = 1/2" H 1022,225 = 7/8" XH 80 18 3231,75 = 11/4" XXH 90 26

z

Dimensions in mm

d1 b1 d2

Cutter dimensions

T Symbol

rk = ext. radiusb = gap widthα = gap angleh = depth of cuth1 = height of tooth on cutterr1 = tooth tip radiusr2 = tooth root radius

118


d1d2

b1

d1d2

b1for spline shaft profiles

KHSS-E EMo5Co5

2730 relief turned or relief groundCat.-No.

*Nominal dimension: inside dea. x outside dea. x spline width Unless otherwise specified, we supply form D in the relief turned version.

Dimensions in mm

23 x 26 x 6 6 63 10 2226 x 30 x 6 1228 x 32 x 6 1332 x 36 x 6 8 1136 x 40 x 7 1242 x 46 x 8 1346 x 50 x 9 70 14 2752 x 58 x 10 1656 x 62 x 10 1862 x 68 x 1272 x 78 x 12 10 1682 x 88 x 12 80 19 3292 x 98 x 14 20

102 x 108 x 16 21112 x 120 x 18 23

DIN ISO 14 - light seriesNominal dimension* Number of splines d1 b1 d2

Spline shaft dimensions Cutter dimensions

DIN ISO 14 - medium seriesNominal dimension* Number of splines d1 b1 d2

DIN 5464 Nom. dimens.* Number of splines d1 b1 d2

11 x 14 x 3 6 56 6 2213 x 16 x 3,516 x 20 x 4 818 x 22 x 521 x 25 x 5 63 923 x 28 x 6 1026 x 32 x 6 1228 x 43 x 7 1332 x 38 x 6 8 1136 x 42 x 7 1242 x 48 x 8 1346 x 54 x 9 70 14 2752 x 60 x 10 1656 x 65 x 10 1862 x 72 x 1272 x 82 x 12 10 1682 x 92 x 12 80 19 3292 x 102 x 14 20

102 x 112 x 16 21112 x 125 x 18 23

16 x 20 x 2,5 10 56 5 2218 x 23 x 321 x 26 x 3 723 x 29 x 4 6326 x 32 x 4 828 x 35 x 432 x 40 x 5 70 10 2736 x 45 x 5 1242 x 52 x 6 1346 x 56 x 752 x 60 x 5 16 80 9 3256 x 65 x 5 1062 x 72 x 6 1172 x 82 x 782 x 92 x 6 20 9092 x 102 x 7 12

102 x 115 x 8 13112 x 125 x 9



119

Dimensions in mm

2730 relief turned or relief groundCat.-No.

DIN 5471 – 4 splinesNominal dimension* d1 b1 d2

Spline shaft dim. Cutter dimensions

11 x 15 x 3 56 11 2213 x 17 x 4 1216 x 20 x 618 x 22 x 6 63 1421 x 25 x 824 x 28 x 8 1628 x 32 x 10 1732 x 38 x 10 70 22 2736 x 42 x 10 2342 x 48 x 12 2746 x 52 x 14 2852 x 60 x 14 80 34 3258 x 65 x 16 3862 x 70 x 16 4068 x 78 x 16 45

DIN 5472 – 6 splinesNominal dimension* d1 b1 d2

Spline shaft dim. Cutter dimensions

DIN 9611 – 6 splines d1 b1 d2

P.t.o. shaft 1** Cutter dimensions

21 x 25 x 5 63 9 2223 x 28 x 6 1026 x 32 x 6 1228 x 34 x 7 1332 x 38 x 8 70 14 2736 x 42 x 8 1642 x 48 x 10 1746 x 52 x 12 80 18 3252 x 60 x 14 2058 x 65 x 14 2262 x 70 x 16 2368 x 78 x 16 90 2772 x 82 x 16 2978 x 90 x 16 3382 x 95 x 16 3688 x 100 x 1692 x 105 x 20 3898 x 110 x 20 40

105 x 120 x 20 100 45115 x 130 x 20 45130 x 145 x 24 54

28,91 x 34,79 x 8,69 70 11 27

Form Awithout clearance lugswithout chamfer

Form Bwithout clearance lugswith chamfer

Form Cwith clearance lugswithout chamfer

Form milling cutters for splineshaft profiles are supplied reliefturned or for increased accuracyalso relief ground. Gang cuttersfor the simultaneous machining ofseveral workpieces on automaticspline shaft milling machines arealso available. The cutters are de-signed as roughing- or finishingcutters, depending on the type ofapplication.

Standardized spline shafts com-prise, among others:

DIN ISO 14 – light seriesDIN ISO 14 – medium seriesDIN 5464 – heavy series

DIN 5471 – 4 splines, internallycentredDIN 5472 – 6 splines, internallycentredDIN 9611 – p.t.o. shafts

Form milling cutter designs provid-ed with clearance lugs (forms Cand D) guarantee in the case ofinternally centred spline shaftsperfect bearing down to the splineshaft root. Chamfering (forms Band C) is used to achieve the re-quired clearance in the flute cor-ners of the hubs. Flank-centredspline shafts which have a clear-ance for the inside and outside di-ameters in the spline hub, can be

produced with cutter type A. Thecutters of form E – for clearance atthe root and the spline flanks – areintended as roughing cutters forgrinding allowance. The cutterswith extended flanks are suitablefor through-cutting of a shoulder.This type can be combined with allforms from A to E.Form cutters for involute gearshafts to DIN 5480 and DIN 5481as well as for serrated shafts toDIN 5481 are also manufacturedon request.

Unless otherwise specified, we supply form D in the relief turned version.

* Nominal dimension: inside dia. x outside dia. x spline width** P.t.o. shafts 2 and 3 on request

Form D (standard)with clearance lugswith chamfer

Form Egrinding size cutter

Forms A-Efor through-cuttinga shoulder

120


d1d2

b1for straight sided and involute splineshafts designed as gang cutters6° positive rake anglestaggered keyways1 set (gang) equals 2 unitscutter no. 2 with 2 keyways

KHSS-E-PM

Dimensions in mm

d1 b1 d2


75 to 85 10 401214161820

This cutter design is mainly used for the batch production of slip gears on automatic spline shaft milling machines (e.g. Hurth type). Within the set, the cutters are precision ground for exact width, profile symmetry and equal outside diameters to close tolerances. Cutter no. 2 of a set is given a second keyway, which is offset by 1/2 tooth pitch.

The main fields of application are spline shafts with parallel flanks as well as shafts with involute flanks.

When ordering, please quote dimensional and tolerance data or provide drawings of the workpiece profiles to be machined.

121

FETTE gear chamfering cuttersIt is imperative in gear production tomachine flanks and tip face edges ofgears after they have been hobbedor produced by the single indexingmethod. Partly, this means deburringthe tooth edges, but very often func-tion-governed forms must be provid-ed on the flanks and the tip faceedges. This form is generally deter-mined by the task which the gearhas to perform. The best knownforms are simple chamfers, semi-cir-cular roundings, crowned roundingsand crowned V-profiles, which mustbe present both on the external andon the internal gears.

For machining gear face edges, ma-chines have been developed whichallow the economical milling of theedge forms. A distinction must here

be made between two machiningprocesses, the correct process be-ing determined by the type of theedge form.

Semi-circular or V-shaped roundingsare produced with end-mill type cut-ters which are designed with outsideprofiled cutting edges (fig.1). Theprofile of the cutting edges is de-signed in accordance with the gearto be machined. The rotary and theaxial motion of the gear are con-trolled by the machine, leaving thetooth edge roundings to be done bythe copying or tracer process.

V-shaped meshing facilitations, de-burring of gears as well as thecutting of special edge forms aregenerally performed with bell-typecutters (fig. 2), using the shaping

method. With this process, a left-hand and a right-hand tooth flankare machined at the same time. Thecutting edges of a bell type cutterare internally profiled and the cuttercuts mainly with the inner contours.

The cutting diameters of the geartooth rounding-, V-type and debur-ring cutters depend on the gear sizeto be machined – i.e. on the moduleand the number of teeth of the gear.In addition, different tooth edgeforms are decisive for the construc-tion of the gear chamfering cutters.These factors result in a multitude ofdesign possibilities, so that gearchamfering cutters must be regard-ed as purely special cutters whichhave to be adapted to each type ofgear form.

For any number of teeth of one module size and for pressure angles of 15° or 20° only one cutter is required.

Gear chamfering cuttersfor chamfering tooth edges

HSS

Dimensions in mm

m d2 l11 13 80 1259311 1259918 – –1,25 1259320 1259927 – –1,5 1259339 1259936 – –1,75 1259348 1259945 – –2 1259357 1259954 – –2,25 1259366 1259963 – –2,5 1259375 1259971 – –2,75 1259384 1259981 – –3 1259393 1259990 – –3,25 1259400 1260005 – –3,5 1259419 1260014 – –3,75 1259428 1260023 – –4 1259437 1260032 – –4,5 1259446 1260041 – –5 18 1259455 1260050 – –5,5 1259464 1260069 – –6 1259473 1260078 – –6,5 1259482 1260087 – –7 25 110 1259491 1260096 – –8 1259507 1260103 – –

2801 relief ground ■ with straight flanks

2802 relief ground ■ with curved flanks

2803 2804

Cat.-No.

d2

l1

40° d2

l1R

d2

l

40°d2

l1R

Fig. 1

2801 2802

2803 2804

Fig. 2

2801 2802 2803 2804Ident no. Ident no. Ident no. Ident no.

122

Rolling racksFETTE manufacture rolling bars forthe production of gears on all popular rolling machines. Extremeaccuracy and maximum servicelife are the quality characteristichere, too. FETTE provide an exceptionally comprehensive ser-vice in this sector. The tools can bemade for spline shaft joints to DIN5480 (up to module 1.25), for spline shaft joints to ANSI B92.1-1970 (up to DP 20/40) or forknurled work to DIN 82 RAA.

When enquiring, please statethe machine on which the tool isto be used.

Rolling racks for teeth

Rolling racks for helical teeth

Technical notes and tables

Page

Comparison of module pitch 126

Tolerances for single-start hobs 127

Tolerances for multiple-start hobs 128

Hob inspection documents 130

Effect of cutter deviations and cutter clamping errors on the gear 132

Effect of the quality grade of the hob on gear quality 134

Tool holding of hobs in the hobbing machine 135

Basic tool profile and gear profile in hobbing 137

Basic profiles for spur gears with involute teeth 138

Standardized basic profiles for straight spur gears with involute teeth 139

Basic hob profiles 140

Profiles of common gears and equivalent basic hob profiles 144

Cutting materials for hobs 149

Hard material coatings for gear cutting tools 151

Cutting conditions in hobbing 155

Tool cutting edge angles, profile generating length, shift distance, axial distance 162

Maintenance of hobs 168

Protuberance hobs 179

Wear phenomena in hobbing 182

Gear milling cutters with indexable inserts 192

Catalogue number index 193

DIN-number-index 194

126

Comparison: module pitch - diametral pitch - circular pitch

Pitch

Pitch Module DP CP Pitch Module DP CP Pitch Module DP CPmm mm mm

0,31416 0,1 2,84987 28 22,22500 7/8

0,34558 0,11 2,98451 0,95 22,79899 3 1/2

0,37699 0,12 3,06909 26 23,81250 1 5/16

0,39898 200 3,14159 1 25,13274 80,43982 0,14 3,17500 1/8 25,40000 10,44331 180 3,32485 24 26,59892 30,45598 175 3,62711 22 26,98750 1 1/16

0,49873 160 3,92699 1,25 28,27433 90,50265 0,16 3,98982 20 28,57500 1 1/8

0,53198 150 4,43314 18 29,01689 2 3/4

0,56549 0,18 4,71239 1,5 30,16250 1 3/16

0,62831 0,20 4,76250 3/16 31,41593 100,62832 127 4,98728 16 31,75000 1 1/4

0,66497 120 5,49779 1,75 31,91858 2 1/2

0,69115 0,22 5,69975 14 33,33750 1 5/16

0,75997 105 6,28319 2 34,55752 110,78540 0,25 6,35000 1/4 34,92500 1 3/8

0,79796 100 6,64970 12 35,46509 2 1/4

0,83121 96 7,06858 2,25 36,51250 1 7/16

0,87965 0,28 7,85398 2,5 37,69911 120,90678 88 7,93750 5/16 38,10000 1 1/2

0,94248 0,30 7,97965 10 39,89823 20,99746 80 8,63938 2,75 41,27500 1 5/8

1,09557 0,35 8,86627 9 43,98230 141,10828 72 9,42478 3 44,45000 1 3/4

1,24682 64 9,52500 3/8 45,59797 1 3/4

1,25664 0,40 9,97456 8 47,62500 1 7/8

1,32994 60 10,21018 3,25 50,26548 161,41372 0,45 10,99557 3,5 50,80000 21,57080 0,50 11,11250 7/16 53,19764 1 1/2

1,58750 1/16 11,39949 7 56,54867 181,59593 50 11,78097 3,75 62,83185 201,66243 48 12,56637 4 63,83716 1 1/4

1,72788 0,55 12,70000 1/2 69,11504 221,73471 46 13,29941 6 75,39822 241,81356 44 14,13717 4,5 78,53982 251,88496 0,60 14,28750 9/16 79,79645 11,89992 42 14,50845 5 1/2 81,68141 261,99491 40 15,70796 5 87,96459 282,04204 0,65 15,87500 5/8 91,19595 7/8

2,09991 38 15,95930 5 94,24778 302,19911 0,70 17,27876 5,5 100,53096 322,21657 36 17,46250 11/16 106,39527 3/4

2,34695 34 17,73255 4 1/2 109,95574 352,35619 0,75 18,84956 6 113,09734 362,49364 32 19,05000 3/4 125,66371 402,51327 0,80 19,94911 4 127,67432 5/8

2,65988 30 20,42035 6,5 141,37167 452,67035 0,85 20,63750 13/16 157,07963 502,82743 0,90 21,99115 7 159,59290 1/2

m = 25,4 m = 8,08507111 x CPDP

Module

DP = 3,14159265 DP = 25,4CP m

Diametral Pitch

CP = 3,14159265 CP = mDP 8,08507111

Circular Pitch

127

Tolerances for single-start hobsfor spur gears with involute teeth to DIN 3968 in µµm.

Itemno.* Measurement Symbol Quality

grade

For module range

above above above above above above above above above0,63–1 1–1,6 1,6–2,5 2,5–4 4–6,3 6,3–10 10–16 16–25 25–40

Diameterof the bore

frp

fps

frk

FfN

ftN

FtN

fHN

FfS

fs

fHF

FHF

fe+–

Fe

1

4

5

6

7

8

10

11

12

13

14

15

16

17

Radial runout atthe indicator hubs

Axial runout atthe clamping face

Radial runout atthe tooth tips

Form- and position deviationof the cutting face

Individual pitchof the gashes

Cumulative pitchof the gashes

Gash lead over100 mm hoblength

Form deviation ofthe cutting edge

Tooth thicknesson the referencecylinder

Hob lead fromcutting edge tocutting edge in thedirection of spiral

Hob lead in the direction of spiralbetween any cutting edges of a turn

Base pitch sectionfrom cutting edgeto cutting edge

Base pitch withinan engagementarea

* Item no. of the measurement points to DIN 3968** In accordance with the works standard, FETTE Hobs of quality grade B are made with bore tolerance H 5.

AA H 5A H 5B H 6**C H 6D H 7

AA 5 5 5 5 5 5 6 6 8A 5 5 5 6 8 10 12 16 20B 6 6 6 8 10 12 16 20 25C 10 10 10 12 16 20 25 32 40

AA 3 3 3 3 3 4 5 5 6A 3 3 3 5 5 8 8 10 10B 4 4 4 6 6 10 10 12 12C 6 6 6 10 10 16 16 20 20D 10 10 10 16 16 25 25 32 32

AA 10 10 12 16 20 25 32 40 50A 12 16 20 25 32 40 50 63 80B 25 32 40 50 63 80 100 125 160C 50 63 80 100 125 160 200 250 315D 100 125 160 200 250 315 400 500 630

AA 10 10 12 16 20 25 32 40 50A 12 16 20 25 32 40 50 63 80B 25 32 40 50 63 80 100 125 160C 50 63 80 100 125 160 200 250 315D 100 125 160 200 250 315 400 500 630

AA 10 10 12 16 20 25 32 40 50A 12 16 20 25 32 40 50 63 80B 25 32 40 50 63 80 100 125 160C 50 63 80 100 125 160 200 250 315D 100 125 160 200 250 315 400 500 630

AA 20 20 25 32 40 50 63 80 100A 25 32 40 50 63 80 100 125 160B 50 63 80 100 125 160 200 250 315C 100 125 160 200 250 315 400 500 630D 200 250 315 400 500 630 800 1000 1250

AA 50A 70B 100C 140D 200

AA 6 6 6 8 10 12 14 18 22A 10 11 12 14 16 20 25 32 40B 20 22 25 28 32 40 50 63 80C 40 45 50 56 63 80 100 125 160

AA 16 16 16 20 25 32 40 50 63A 25 28 32 36 40 50 63 80 100B 50 56 63 71 80 100 125 160 200C 100 112 125 140 160 200 250 320 400D 100 112 125 140 160 200 250 320 400

AA 4 4 4 5 6 8 10 12 16A 6 7 8 9 10 12 16 20 25B 12 14 16 18 20 25 32 40 50C 25 28 32 36 40 50 63 80 100D 50 56 63 71 80 100 125 160 200

AA 6 6 6 8 10 12 14 18 22A 10 11 12 14 16 20 25 32 40B 20 22 25 28 32 40 50 63 80C 40 45 50 56 63 80 100 125 160D 80 90 100 112 125 160 200 250 320

AA 4 4 4 5 6 8 10 12 16A 6 7 8 9 10 12 16 20 25B 12 14 16 18 20 25 32 40 50C 25 28 32 36 40 50 63 80 100

AA 8 8 8 10 12 16 20 25 32A 12 14 16 18 20 25 32 40 50B 25 28 32 36 40 50 63 80 100C 50 56 63 71 80 100 125 160 200

No. 7

No. 8

No. 10

No. 11

No. 12

No. 14

No. 15

No. 16, 17

cutting depthaxial plane

spec. line

u

42

1

4 2

1

3

12

11

10

100 mm

fHN

FfS

HN · Hi (HN ± H)

HN · Hi (HN ± H)

n · HN · Hi (HN ± H)

engagement area

tei

+–

+–

+–

–

128

Tolerances for multiple start hobs

Itemno.

Measurement Symbol Qualitygrade

For module range


2–4start

5–7start

AA H 5

A H 5

B H 6

AA 5 5 5 5 5 5 6 6 8

A 5 5 5 6 8 10 12 16 20

B 6 6 6 8 10 12 16 20 25

AA 3 3 3 3 3 4 5 5 6

A 3 3 3 5 5 8 8 10 10

B 4 4 4 6 6 10 10 12 12

AA 10 12 16 20 25 32 40 50 63

A 16 20 25 32 40 50 63 80 100

B 32 40 50 63 80 100 125 160 200

AA 12 16 20 25 32 40 50 63 80

A 20 25 32 40 50 63 80 100 125

B 40 50 63 80 100 125 160 200 250

AA 10 10 12 16 20 25 32 40 50

A 12 16 20 25 32 40 50 63 80

B 25 32 40 50 63 80 100 125 160

AA 10 10 12 16 20 25 32 40 50

A 12 16 20 25 32 40 50 63 80

B 25 32 40 50 63 80 100 125 160

AA 20 20 25 32 40 50 63 80 100

A 25 32 40 50 63 80 100 125 160

B 50 63 80 100 125 160 200 250 315

AA 50

A 70

B 100

AA 6 6 8 10 12 14 18 22 28

A 11 12 14 16 20 25 32 40 50

B 22 25 28 32 40 50 63 80 100

AA 6 8 10 12 14 18 22 28 36

A 12 14 16 20 25 32 40 50 63

B 25 28 32 40 50 63 80 100 125

AA 8 10 12 14 18 22 28 36 45

A 14 16 20 25 32 40 50 63 80

B 28 32 40 50 63 80 100 125 160

1

4

5

6

7

8

10

11

12

Diameter of the bore

Radial runout at the indicator hubs

Axial runout at the clamping faces

Radial runout at thetooth tips

Form- and position deviation of the cuttingface

Individual pitch of thegashes

Cumulative pitch of thegashes

Gash lead over 100 mmhob length

Form deviation of the cutting edge

frp

fps

frk

FfN

+ftN –

FtN

+fHN –

FfS

2start

3–4start

5–6start

Tolerances in µm

129

For module range

Itemno.

Measurement Symbol Qualitygrade


2start

3–4start

5–6start

2start

3–4start

5–6start

2–3start

4–6start

AA –25 –28 –32 –36 –40 –50 –63 –80 –100

A –25 –28 –32 –36 –40 –50 –63 –80 –100

B –50 –56 –63 –71 –80 –100 –125 –160 –200

AA 4 4 5 6 8 10 12 16 20

A 7 8 9 10 12 16 20 25 32

B 14 16 18 20 25 32 40 50 63

AA 4 5 6 8 10 12 16 20 25

A 8 9 10 12 16 20 25 32 40

B 16 18 20 25 32 40 50 63 80

AA 5 6 8 10 12 16 20 25 32

A 9 10 12 16 20 25 32 40 50

B 18 20 25 32 40 50 63 80 100

AA 6 6 8 10 12 14 18 22 28

A 11 12 14 16 20 25 32 40 50

B 22 25 28 32 40 50 63 80 100

AA 6 8 10 12 14 18 22 28 36

A 12 14 16 20 25 32 40 50 63

B 25 28 32 40 50 63 80 100 125

AA 8 10 12 14 18 22 28 36 45

A 14 16 20 25 32 40 50 63 80

B 28 32 40 50 63 80 100 125 160

AA 5 5 6 7 8 11 13 16 20

A 7 8 9 10 12 16 20 25 32

B 14 16 18 20 25 32 40 50 63

AA 6 7 8 11 13 16 20 25 32

A 9 10 12 16 20 25 32 40 50

B 18 20 25 32 40 50 63 80 100

AA 8 8 8 11 14 17 20 25 31

A 14 15 17 20 22 28 35 45 56

B 28 31 35 39 45 56 70 88 112

AA 10 10 10 13 16 19 22 29 35

A 16 18 19 22 26 32 40 51 64

B 32 35 40 45 51 64 80 101 128

13

14

15

18

19

Tooth thickness on thereference cylinder

Hob leadfrom cutting edge tocutting edge in the direction of spiral

Hob leadin the direction of spiralbetween any cutting edges in oneaxial pitch

Pitch deviationbetween adjacent threads of a tooth segment

Pitch deviation between any two spirals of a tooth land within the hob lead

fs –

+fHF –

FHF

+fpx –

Fpx

2–3start

4–6start

Tolerances in µm

130

Hob inspection recordsThe tolerances of single-start hobsfor spur gears with involute teethare laid down in DIN 3968 and thetolerances for the hobs used inprecision engineering in DIN58413.The tolerances for multi-start hobsand for hobs with special profiles

are defined in works standards orby agreement between manufac-turer and customer.The hobs are classified into gradesA, B, C, D and the special gradeAA. For extreme requirements it isusual to agree further restrictionsof the tolerances of quality grade

AA, which is then referred to asquality grade AAA.The deviations of the measuredvalues can be written or markeddown by hand, they can be me-chanically recorded or stored in acomputer.In the case of quality grades AA or

Ident No.: 2352101 Tip circle diameter: 58.979 Lead angle: 02° 43'33"Hob No.: E1305 Cutting edge width: 150 Lead: 7.8314Module: 2.49 Bore diameter: – Basic profile: –Pressure angle: 20° 00'00" Handing/nbr. of starts: R1 Profile modification: –Tooth addendum: 3.82 Number of gashes: 14 Cutting depth: –Axial tooth thickness: 3.9154 Cutting face offset: 0 Material: –Tooth height: 6.6 Gash lead: 1.E + 100 Hardness: HRc –

Intended value Actual valuefrp 5 AA 2 AAA

Intended value Actual valuefrk 12 AA 7 AAA

Intended value Actual valueFfn 12 AA 5 AAA

Intended value Actual valueFtN 25 AA 11 AAAftN 12 AA 8 AAA

Intended value Actual valuefHN 50 AA 5 AAA

Intended value Actual valuefps 3 AA 2 AAA

Intended value Actual valuefps 3 AA 2 AAA

Intended value Actual valuefrp 5 AA 2 AAA

Intended value Actual valueFHF 6 AA 3 AAAfHF 4 AA 1 AAA

Intended valueFpx 4fpx 2

Tolerances to:DIN 3968 AAA

Date: 15 Jan 1998

Checked: Mumsen

Drwg. no.: 61574

Measur. file: E1305 05M

HOB MEASUREMENT

20 my

RWF

Intended value Actual valueFHF 6 AA 2 AAAfHF 4 AA 1 AAA

Intended value Actual valueFe 8 AA 4 AAAfe 4 AA 2 AAA

Intended value Actual valueFe 8 AA 3 AAAfe 4 AA 2 AAA

Intended valueFpx 2fpx 1

(4) Right-hand radial runout: (5) Right-hand axial runout: (5) Left-hand axial runout: (4) Left-hand radial runout:

(6) Radial runout at the tooth tip (7) Form and location of the cutting face

(8,10) Pitch of the gashes (11) Gash lead

(14, 15) Right-hand lead (14, 15) Left-hand lead (16, 17) Right-hand base pitch (16, 17) Left-hand base pitch

Right-hand axial pitch Left-hand axial pitch

NL R mm

. 5 6.6

1 3 5K F

N1 14 mm

0 100

L R

NL R

NL R

NL R

NL R

NF K

NF K

131

AAA it is usual to record the devia-tions of the measured values in aninspection report. The inspectionreport is used for monitoring thehob throughout its entire servicelife.The inspection report becomesparticularly clear and informative

when the base pitch or the formdeviation of the cutting edge andthe deviation of the hob lead arerepresented in the form of dia-grams.These diagrams can then be di-rectly compared with the profiletraces of the machined gears and

interpreted.The test report is shown here in areduced size; the original size isDIN A3.

(LF) Intended value Actual valueFfS 6 AA 3 AAARemarks:

(13) Tooth thickness fs Intended value Actual value–16 AA –3 AAA

(RF) Intended value Actual valueFfS 6 AA 2 AAA

Date: 15 Jan 1998

Checked: Mumsen

Drwg. no.: 61574

Measur. file: E1305 05M

HOB MEASUREMENT

20 my

RWF

Tip

Root

0

6.6

3.82

(12) Form deviation of the cutting edge

132

The effect of cutter deviations and cutter clamping errors on the gear (for single-start hobs with 20° pressure angle and relief rake angle of approx. 10°)

The quality of a hobbed gear is theproduct of the interaction of vari-ous components and productionconditions.The deviations from the intendedgeometry of the hob and theclamping errors of the cutter onthe hobbing machine play an im-

portant part in this.In hobbing, a distinction is madebetween the deviations on the en-veloping helix of the cutter and thedeviations on the cutting faces ofthe cutter.The deviations of single-start hobsaffect the quality of the gear main-

ly in the form of profile deviations.It is here important to know inwhich order of magnitude the devi-ations on the hob and clamping er-rors of the cutter affect gear qual-ity.

Nature of the deviation

Deviations on the enveloping helixof the hob

Deviationson the cutting faces of the hob

Clamping errors of the hob on thehobbing machine

Item no. & symbol of the deviation acc. to DIN 3968 (-Sept. 1960)

Representation of the deviationDesignation and symbols of the deviation acc. to VDI 2606

Hobs

Path of contact

Tip Root

Profile formation zone

pz

1 cutter turn

fs

Active profile height

Tip Root

active profile height

Tip Root

1Hob revolution

100

Profile zone generating

1 Hob revolution

1 Hob revolution

Total base pitch deviation Fpe within anengagement area

No. 17Fe

No. 15FHF

No. 6frk

No. 13fs

No. 12FfS

No. 7FfN

No. 10FtN

No. 11fHN

No. 4frP

No. 5fps

Cutter lead height deviation in the direction of start FHF between any cutting edges in one convolution

Radial runout fra on the tooth tip

Tooth thickness deviation fs on the basic reference cylinder

Form deviation FfS of the cutting edge

Form- and position-deviation FfNof the cutting faces

Cumulative pitch deviation FpNof the gashes (cutting faces)

Gash lead deviation fHN over 100 mmcutter length

Radial runout frP on the two indicatorhubs

Axial runout frx on the clamping faces

133

These relationships are shown inthe table. It must be rememberedthat the working accuracy of thehob can be considerably affectedby faulty regrinding. A check of thedeviations on the cutting faces ofthe hob should therefore be madeobligatory after each regrind.

The correct inspection procedurefor hobs, the necessary equipmentand the evaluation of the measure-ment results are described in detailin VDI/VDE Recommendation2606.

Typical course of the deviation Remarks

Effect of the deviation Order of magnitude of the effect

Gear

Profile deviation ≈ 100 %

≈ 100 %

≈ 20 %

(≈ 100 %)

> 100 %

≈ 100 %

≈ 10 %

≈ 10 %

≈ 10 %

≈ 30 %

≈ 100 %

Profile deviation(only the deviation of the profile formation zone in question is effective)

Form deviation in the bottom of the toothspace(only the deviation of the tip cutting edgesforming the root cylinder is effective)

(Tooth thickness deviation)

Diameter deviations

Profile deviation

Profile deviation

Profile deviation

Profile deviation

Profile deviation

Profile deviation(only the deviation of the profile forming zone is effective)

KopfFuß

KopfFuß

KopfFuß

KopfFuß

KopfFuß

KopfFuß

rechte Flanke

linke Flanke

KopfFuß

KopfFuß

The tooth thickness deviation of the cutter is generally compensated by a correction of thecentre distance of the hobbing machine and istherefore not effective as a tooth thickness deviation on the gear. From this correction,changes result on the following diameters of the gear:

root circle and effective root circle, tip circle inthe case of topping cutters, effective tip circle inthe case of cutters with semi-topping.

Root Tip

Root Tip

Root Tip

Root Tip

Root Tip

Root Tip

Root Tip

Root Tip

Left-handed flank

Right-handed flank

134

Effect of the quality grades of the hob on gear quality For spur gears, the tolerances oftheir specification factors are givenin DIN 3962 to DIN 3967. The toothquality is subdivided into twelvequality stages, which are identifiedby the numbers 1 to12. Gear qual-ity 1 is the most accurate.

The permissible deviations for sin-gle start hobs are laid down in DIN3968. Depending on the accuracy,a distinction is made between fivequality grades, namely the qualitygrades A, B, C, D and the specialgrade AA.

The base pitch on the hob providessome guidance about the total pro-file deviation on the gear. It there-fore makes sense to compare thebase pitch deviation Fe within anengagement area of the hob withthe total profile deviation Ff of thegear.

It must be considered howeverthat the total profile deviation maybe caused not only by deviationson the hob itself, but also by thehobbing machine, errors in hoband workpiece clamping, and the

cutting forces.The table of "Attainable gear qual-ities" is based upon the assump-tion that 2/3 of the total profile de-viation on the tooth is caused bythe hob, and the remainder by theinfluencing factors stated above.

Notes concerningDIN 3968 tolerances,page 127

The permissible deviations for sin-gle-start hobs are laid down in DIN3968.

There are 16 individual deviations,which are partly interdependent,and one cumulative deviation.

The contact ratio deviation Fe

within an engagement area, as acollective deviation, is the most informative value when assessinghob quality. It also allows, within limits, to forecast the flank form ofthe gear.

To maintain hob quality, it is nec-essary to check the permissibledeviations after each sharpeningoperation for form and position,pitch and direction of the cuttingfaces (item nos. 7 to 11).

Attainable gear qualities to DIN 3962 part 1 – 8.78 (F1)

Quality gradeto DIN 3968

for single-starthobs

Fe

from from from from from from from from from from from1 1,6 2 2,5 3,55 4 6 6,3 10 16 25to to to to to to to to to to to1,6 2 2,5 3,55 4 6 6,3 10 16 25 40

Module ranges

AA 7 7 7 8 7 7 7 8 8 7 7

A 9 10 9 9 9 9 8 9 9 9 9

B 11 11 11 11 10 11 10 11 11 10 10

C 12 * 12 12 12 12 12 12 12 12 12

* Inferior to gear quality 12

135

Tool holding of hobs in the hobbing machineTool holding has two essentialfunctions: firstly to transmit thetorque, and secondly to locate thetool in the machine. The same ap-plies of course to the interfacebetween the hobbing machine andthe hob/cutter arbor. The geomet-rical arrangement of this connec-tion is largely determined by thehobbing machine manufacturer.

The following two chief arrange-ments are employed at the inter-face between the hob and thehobbing machine/cutter arbor: thebore-type and the shank-typehob.

The bore-type hob has the follow-ing sub-categories:

■ Bore with keyway for positivetorque transmission

■ Bore with drive slot on one orboth ends for positive torquetransmission

■ Bore with frictional torquetransmission on the hob face

The shank-type hob has the fol-lowing sub-categories:

■ Short cylindrical shanks ateach end with positive torquetransmission

■ Tapered shank at each endwith positive torque transmis-sion.

■ Different types, cylindrical andtapered, on the drive and sup-port ends.

■ Hollow shank taper type

■ Steep-angle taper on the driveend and cylindrical or tapertype on the support end.

One of the variants describedabove, adapted to the functionand the task in question, is gener-ally recommended by the machinemanufacturer upon purchase of ahobbing machine. Note that thereare differences in cutter head de-sign and therefore in tool holdingarrangement from one hobbingmachine manufacturer to the next.The use of adapters for holdingequivalent tools should be regard-ed only as a last resort, as in themajority of cases it results in a lossin quality on the machined work-piece. For this reason, the com-patibility of the interface must beclarified prior to purchase of ahobbing machine. A large numberof hobs is required if hobbing ma-chines are employed with differenttool holding arrangements.

The most widely used hob type isthe bore-type hob with keyway.The reasons for this are partly his-torical. Shank-type hobs are em-ployed only where necessitated bygeometric constraints or higherquality requirements. Bore-typehobs are a good choice for smallproduction runs and where re-quirements on the workpiece ac-curacy are not particularly strin-gent. Hobs are generally manu-factured from high-speed steel,with a keyway to DIN 138. Geo-metric requirements permit de-signs with a drive slot on one orboth ends to DIN 138 (and also inshortened versions). Carbide hobsare always manufactured withdrive slots on one or both ends,and almost always in the short-ened design (1/2 drive slot depthaccording to DIN 138). Bore-typehobs may also be manufacturedwithout keyway or drive slot.

Hobs with short cylindrical shanksat both ends are increasingly beingused, particularly for large produc-tion runs. The advantages are fasttool changing and very low runoutof the hob in the machine. Pre-alignment on the cutter arbor isnot required. There is no interfaceelement (cutter arbor). When hob-bing machines are purchased, at-tention must be given to the com-patibility of hobs on hobbingmachines from different manufac-turers.

The other hob types describedabove represent further possiblesolutions which should howeverbe regarded as special cases forthe fulfilment of specific customerrequirements.

Where necessary, worm gear hobsare manufactured with an interfacegeometry adapted to the hobbingmachine (refer to the worm gearhob chapter).

136

� Runout indicator surface� Mounting surface� Clamping force






Taper 1:10


Taper 7:24

Hob clampingFrictional torque transmission

Hob clampingDrive slots at both ends

Hob clampingHSK hollow taper shank

Hob clampingCylindrical shank

Hob clampingKeyway

Hob clampingTapered shank

Hob clampingDrive slot at one end

137

Basic tool profile and gear profile in hobbing

0070 A

Hob

Gear

h FaP

0

Protuberanceinvolute

h aP

0h F

fP0h f

P0

h P0

h prP

0

α tK

αt

αtpr

Chamferinvolute

Effective involute

Profile reference linePP

sta

staK

d Fa d a

d FaV

h Kd bp

r

d

qt

x Em

n

C0

FStVd f

E

d b

ψb

prtP0

d bK

dFf

V

dFf

α tKα

t α tpr

pt2

Rack pitch lineof engagement

Pre-formed helical spur gear face profile with chamfer and root clearance cut, with corresponding basic profile of the pre-forming tool.

138

Basic profiles for spur gears with involute teethThe flank profiles of spur gearswith involute teeth are in the facesection (plane of section perpen-dicular to the gear axis) circular in-volutes.

The form of the involute dependsamong others on the number ofteeth on the gears. With an in-creasing number of teeth the cur-vature of the involute becomesprogressively weaker. At an infinitenumber of teeth the spur gear be-comes a tooth rack with straightflanks. The tooth rack can there-fore take the place of a spur gearand ensures an even and trouble-free transmission of motion whenmeshing with a companion gear.

Since the form of a rack is easierto describe than that of a spurgear, it suggested itself to applythe tooth values of spur gears tothe 'reference (basic) tooth rack'and to refer to the latter as the ba-sic profile.

The definition of the basic profile isas follows:

The basic profile of a spur gearis the normal section throughthe teeth of the basic toothrack, which is created from theexternal gear teeth by increas-ing the number of teeth up toinfinity and thus arriving at aninfinite diameter. The flanks of the basic profile ofan involute tooth system arestraight lines. Values of the ref-erence profile are identified bythe additional index P.

The basis for the measurementson the basic profile is the modulem. The module is a length meas-urement in mm. It is obtained asthe quotient from the pitch p andthe number π. It is usual to definethe measurements of the basicprofile in proportion to the module.

The profile reference line intersectsthe basic profile so that the tooth thickness and the tooth spacewidth correspond to half the pitch.

The addendum is generally 1 · m.

Since the tooth tips of a compan-ion gear must not touch the bot-tom of the space between theteeth of the gear, the dedendumhfP, of the basic profile is largerthan its addendum by the amountof the tip clearance cP.

The profile angle αP, on the basicprofile is equal to the normal pres-sure angle of the correspondinggear.

Details of standardized basic pro-file for spur gears are found in:

DIN 867 DIN 58400 ISO 53

p = p · m

hfP

hP

root line

profile reference line

tooth centre line

tooth root space

fillet radius

tip line

mating profile

haP

CPöfP

CP

aP

hwP

sP =p2 eP =

p2

Basic profile of a spur gear

p = m · π = Pitch

eP = Tooth space width on the profile reference line

sP = Tooth thickness on the profile reference line

hP = Profile height

haP = Addendum

hfP = Dedendum

αP = Profile angle

öfP = Root fillet radius

hwP = Common tooth heigt of basic profile and mating profile

cP = Tip clearance between basicprofile and mating profile

The basic profiles of spur gears aredenoted by the index p.

Basic profile for spur gears

139

Standardized basic profiles for spur gears with involute flanksBasic profiles for involute teeth

Symbols:

p = Pitch

eP = Tooth space width on the profile reference line

sP = Tooth thickness on the profile reference line

hP = Profile height

haP = Addendum

hfP = Dedendum

αP = Profile angle

öfP = Root fillet radius

hwP = Common tooth heigt of basic profile and mating profile

c = Tip clearance between basicprofile and mating profile

m = Module

Ca = Addendum tip relief

hCa = Height of the addendum tip relief

DIN 867 – Basic profile for spur gears (cylindrical gears with involute teeth)haP = mhfP = m + ccP = 0,1 · m bis 0,3 · m

= 0,4 · m in special caseshwP = 2 · m öfPmax. = 0,25 · m at cP = 0,17 · m

= 0,38 · m at cP = 0,25 · m= 0,45 · m at cP = 0,3 · m

ISO 53 – Basic profile for spur gears with involute flanksp = m · π

sP =p2

haP = mhfP = 1,25 · mhP = 2,25 · mαP = 20°öfP = 0,38 · mCaP = 0,02 · mhCaP = 0,6 · m

hfP

hP

haP

cPöfP

cP

aP = 20°

hwP

p = p · m

sP =p2 eP =

p2

hfP

hP

haP

öfPaP

hCaP

p

p2

p2 CaP

Fig. 1.00

Fig. 1.01

140

Basic hob profilesDefination of the basichob profiles

The definition of the basic hobprofile is generally derived fromthe basic profile of the spur gearteeth. This procedure applies tospur gear teeth only within limitsand cannot be used for specialtooth systems, since no basic pro-files exist for these.

The basic hob profile can generallybe defined as follows:

The basic hob profile is the normalsectional profile of an imaginarytooth rack, which meshes with theworkpiece teeth under the follo-wing conditions:

1. The basic profile line of the rackrolls on a defined pitch circle di-ameter of the workpiece.

2. The pitch of the rack is equal tothe pitch on the pitch circle di-ameter.

3. Meshing with the workpiece takes place:a) according to the basic law of

the tooth system, the com-mon perpendicular passingthrough the contact point of

pitch circle and reference line(rolling point) in the contactpoint of gear flank and toothrack flank, or

b) through relative paths of partsof the tooth rack profile on theworkpiece.

The computing and design effortfor determining the basic profiledepends on the nature of theworkpiece teeth. The simplest isthe determination of the basic hobprofile for spur gears with involuteflanks.

Basic hob profile for spurgears with involute flanks

The hob or tool profile is the mat-ing profile of the spur gear teeth.The profile reference lines of thebasic hob- and spur gear profilecoincide, i. e. the tooth thicknessSpo equals half the pitch. The ad-dendum haP0 corresponds to thededendum hfP, on the basic spurgear profile and the addendum ra-dius öaP0 is equal to the dedendumradius öfP on the basic spur gearprofile.

The same hob can be used forproducing spur- and helical gears

with any number of teeth, helix an-gles and profile displacements, ifthe basic hob profile does not con-tain any profile modifications suchas chamfer, tooth profile correc-tions, protuberance etc.

Standardized basic hob profilesare shown in: DIN 3972 DIN 58412

Basic hob profile and hob profile

The basic hob profile must not beconfused with the hob profile. Although the basic profile formsthe basis for the calculation of thehob profile, the diameter and thenumber of starts of the hob alsoaffect the hob profile. The detailsconcern the hob manufacturer. Hehas to ensure that hobs with thesame basic profile produce identi-cal teeth within the scope of thepermissible hob tolerances.

hNfP0

hP0

hNaP0

Werkzeug-Profilbezugslinie

hfP0

haP0

sP0 =p2

öfP0

aP0

öaP0

Basic hob profile

p = m · π = Pitch

sP0 = Tooth thickness

hP0 = Profile height

haP0 = Addendum

hfP0 = Dedendum

dP0 = Flank angle(pressure angle)

öaP0 = tip radius

öfP0 = root fillet radius

hNaP0 = effective addendumheight

hNfP0 = effective dedendumheight

Values of the basic toolprofile are identified bythe addition of PO indexes.

Basic cutter profile

Tool profile reference line

141

Basic hob profiles to DIN 3972Symbols:

haP0 = addendum of the basic profile

hP = profile height ofthe gear = cutting depth

hP0 = profile height of the basic profile

sP0 = tooth thickness

öaP0 = tip radius


DIN 3972 – basic profile I –20° pressure anglehaP0 = 1,167 · mhP = 2,167 · mhP0 = 2,367 · möaP0 ≈ 0,2 · möfP0 ≈ 0,2 · m

sP0 =π

· m2

for finishing

DIN 3972 – basic profile II –20° pressure anglehaP0 = 1,250 · mhP = 2,250 · mhP0 = 2,450 · möaP0 ≈ 0,2 · möfP0 ≈ 0,2 · m

sP0 =π

· m2

for finishing

DIN 3972 – basic profile III –20° pressure anglehaP0 = 1,25 · m + 0,25

3

mhP = 2,250 · mhP0 = 2,450 · möaP0 ≈ 0,2 · möfP0 ≈ 0,2 · m

sP0 =π

· m2

q = 0,253

m · sin 20°

for machining prior to grinding or shaving

DIN 3972 – basic profile IV –20° pressure anglehaP0 = 1,25 · m + 0,60

3

mhP = 2,250 · mhP0 = 2,450 · möaP0 ≈ 0,2 · möfP0 ≈ 0,2 · m

sP0 =π

· m2

q = 0,6 3

m · sin 20°

for machining prior to finishing

öfP020°

sP0

hP0hP

haP0

öaP0

öfP020°

sP0

hP0hP

haP0

öaP0

öfP020°

sP0

hP0hP

haP0

öaP0

q

öfP020°

sP0

hP0hP

haP0

öaP0

q

Fig. 2.00

Fig. 2.01

Fig. 2.02

Fig. 2.03

142

Basic hob profiles to DIN 58412Symbols:

hfP0 = dedendum of the basic profile

hPw = distance beween the tooth rootand the end of the straight flankof the basic profile



sP0 = π · m = tooth thickness2

öaP0 = tip radius


U1 For gears with basicN1 cutter profile

V1 to DIN 58400

U2 For gears with basicN2 cutter profile

V2 to DIN 867

DIN 58412 – basic profile U I –topping – 20° pressure anglehfP0 = 1,1 · mhPw = 2,2 · mhPw = 2,2 · mhP = hP0 = 2,6 · m from module 0,1 ÷ 0,6hP = hP0 = 2,45 · m over module 0,6 ÷ 1öaP0 ≈ 0,2 · möfP0 ≈ 0,2 · m max. sizefor finishing

DIN 58412 – basic profile N 1 –non-topping – 20° pressure anglehfP0 = 1,3 · mhPw = 2,4 · mhP = 2,6 · m from module 0,1 ÷ 0,6hP = 2,45 · m over module 0,6 ÷ 1hP0 = 2,8 · m from module 0,1 ÷ 0,6hP0 = 2,65 · m over module 0,6 ÷ 1öaP0 ≈ 0,2 · möfP0 ≈ 0,2 · m max. sizefor finishing

DIN 58412 – basic profile U 2 –topping – 20° pressure anglehfP0 = 1 · mhPw = 2 · mhP = hP0 = 2,25 · möaP0 = 0,2 · möfP0 = 0,2 · m max. sizefor finishing

DIN 58412 – basic profile N 2 –non-topping – 20° pressure anglehfP0 = 1,2 · mhPw = 2,2 · mhP = 2,25 · mhP0 = 2,45 · möaP0 = 0,2 · möfP0 = 0,2 · m max. sizefor finishing

DIN 58412 – basic profile V 1 –non-topping – 20° pressure anglehfP0 = 1,3 · mhP = 2,6 · m from module 0,3 ÷ 0,6hP = 2,45 · m over module 0,6 ÷ 1hP0 = 2,8 · m from module 0,3 ÷ 0,6hP0 = 2,65 · m over module 0,6 ÷ 1

sP0 = π · m – 2q2 cos α

öaP0 = 0,1 · möfP0 = 0,2 · m max. sizeq = 0,05 · m + 0,03

for pre-machining

DIN 58412 – basic profile V 2 –non-topping – 20° pressure anglehfP0 = 1,2 · mhP = 2,25 · mhP0 = 2,45 · m

sP0 = π · m – 2q2 cos α

öaP0 = 0,1 · möfP0 = 0,2 · m max. sizeq = 0,05 · m + 0,03for pre-machining

öfP0 20°

sP0

hP0hPw

hfP0

öaP0 15°

öfP0 20°

sP0

hP0hPw

hfP0

öaP0 15°

hP

öfP0 20°

sP0

hP0hPw

hfP0

öaP0 15°

öfP0 20°

sP0

hP0hPw

hfP0

öaP0 15°

hP

öfP0 20°

sP0

hP0hP

hfP0

öaP0

q

öfP020°

sP0

hP0hP

hfP0

öaP0

q

Fig. 3.00

Fig. 3.01

Fig. 3.02

Fig. 3.03

Fig. 3.04

Fig. 3.05

}

}

143

Basic hob profiles for diametral pitch teethSymbols:

hfP0 = addendum of the basic profile



sP0 = tooth thickness

hCP0 = height of the correction

CP0 = width of the correction

RCP0 = radius of the correction

öaP0 = tip radius

öfP0 = root fillet radiusöfP0

20°

sP0

hP0

haP0

öaP0

hP

RCP0

hCP0

CP0

öfP0

14° 30'

sP0

hP0

haP0

öaP0

hP

öfP0

20°

sP0

hP0

haP0

öaP0

hP

öfP0

20°

sP0

hP0

haP0

öaP0

hP

For teeth to BS 2062, Part 1, 1959, for DP 1 ÷ DP 20 20° pressure angle

haP0 = 1,25 25,4DP

hP = 2,25 25,4DP

hP0 = 2,45 25,4DP

sP0 = 1,5708 25,4DP

hCP0 = 0,63 25,4DP

CP0 = 0,019 25,4DP

RCP0 = 12,9 25,4DP

öaP0 = 0,39 25,4DP

öfP0 = 0,2 25,4DP

For teeth to AGMA 201.02 - 1968 for DP 1 ÷ DP 19.99 14°30' pressure angle

haP0 = 1,157 25,4DP

hP = 2,157 25,4DP

hP0 = 2,357 25,4DP

sP0 = 1,5708 25,4DP

öaP0 = 0,209 25,4DP

öfP0 = 0,2 25,4DP

For teeth to AGMA 201.02 - 1968 for DP 1 ÷ DP 19.99 20° pressure angle

haP0 = 1,25 25,4DP

hP = 2,25 25,4DP

hP0 = 2,45 25,4DP

sP0 = 1,5708 25,4DP

öaP0 = 0,3 25,4DP

öfP0 = 0,2 25,4DP

For teeth to AGMA 201.02 - 1968 for DP 1 ÷ DP 19.99 20° pressure anglestub-tooth

haP0 = 1 25,4DP

hP = 1,8 25,4DP

hP0 = 2 25,4DP

sP0 = 1,5708 25,4DP

öaP0 = öfP0 = 0,2 25,4DP

Fig. 4.00

Fig. 4.01

Fig. 4.02

Fig. 4.03

144

h

ha

hf

öfP0

h

öaP0α

p

hP0

haP0

sP0

h

ha

hf

CaP

hCaP

öfP0

öaP0

p

hP0h

haP0

sP0

RCP0hCP0

öaP0

pP0

hP0h

haP0

öfP0sP0

hFfP0

aKP0

h

ha

hf

aK

hK

Involute teeth for spur- and helical gears,basic cutter profile e. g. DIN 3972 I-IV.

When ordering please quote:Module, pressure angle, basic profile ofthe teeth (fig.1.00) or basic hob profile(fig. 2.02).

Involute teeth for spur- and helical gearswith addendum tip relief. This profileshape is used to avoid interference whenthe gears roll into mesh.

When ordering please quote:Module, pressure angle, number of teeth,helix angle, profile displacement and tipcircle dia. of the gear, basic profile of theteeth, height and width of the tip relief orbasic hob profile.

Gears of high-speed transmissions arecorrected in the tooth tips to reducenoise. In this correction the elastic toothdeflection has been taken into account.The cutter correction is then matched tothe number of teeth to be cut on the gear.

Involute teeth for spur- and helical gearswith tip chamfer.

When ordering please quote:Module, pressure angle, number of teeth,helix angle, profile displacement and tipcircle diameter of the gear, basic profile ofthe teeth, radial amount and angle of thechamfer or basic hob profile.

The tip chamfer can be regarded as aprotective chamfer, which protects thetooth tip edge against damage and bur-ring. For long production runs it is advis-able to chamfer the gear tip edge simul-taneously with the hob. The number ofteeth range which can be cut with onehob is in that case limited, since the sizeof the chamfer would be reduced withfewer teeth/gear and greater with moreteeth/gear.

Workpiece Basic cutter profileh = profile height = cutting depth hP0 = profile heightha = addendum haP0 = addendumhf = dedendum α = pressure angle

p= m = moduleπ

Workpiece Basic cutter profilehCaP = height of the tip relief hCP0 = height of the correction over

CaP = tip relief the reference lineRCP0 = radius of the correction

Workpiece Basic cutter profilehK = radial amount of the tip chamfer hFfP0 = effective dedendum αK = angle of the chamfer of the basic cutter profile

αKP0 = profile angle of thechamfer flank

Fig. 5.02

Fig. 5.01

Fig. 5.00

Profiles of current tooth systems and corresponding basic hob profiles

145

Involute tooth system, for spur- and heli-cal gears with root (protuberance) clear-ance. This profile formation is chosen forgears which are pre-machined for shav-ing, grinding or skiving.

When ordering please quote:Module, pressure angle, basic profile ofthe tooth system, machining allowanceand root clerance or basic hob profile.

Gears which are cut with shaving- orgrinding allowance are best made with aprotuberance cutter. The tooth root clear-ance obtained with this increases the ser-vice life of the shaving tool and improvesthe quality of the shaved or ground gear.

Involute tooth system for spur- and heli-cal gears with root (protuberance) clear-ance and tip chamfer.

This profile is used for gears which arepre-machined for shaving or grinding andwhich are to exhibit a tip chamfer in thefinished condition.

When ordering please quote:Module, pressure angle, number of teeth,helix angle, profile displacement and tipcircle diameter of the gear, basic profile ofthe tooth system, radial amount and an-gle of the chamfer or basic hob profile.

Involute teeth for spur- and helical gearsfor the simultaneous topping of the out-side diameter (topping cutter). This profiletype can also be used for all the previousprofiles under 5.00 to 5.04.

When ordering please quote:'Topping cutter' and the details accordingto the pofiles 5.00 to 5.04.

Topping cutters are mainly used for rela-tively small gears, to achieve good con-centricity of the tooth system in relationto the bore. In particular, topping cuttersare used when the bore is only finish ma-chined after the teeth have been cut.When the parts are clamped over thetooth tips, accurate concentricity of thebore in relation to the teeth is guaranted.

h

ha

hf

q h

öaP0

p

hP0

haP0

öfP0sP0

PrP0

h

ha

hf

hK

aK

q

öfP0

öaP0

p

hP0h

haP0

sP0

PrP0

aKP0

hFfP0

h

ha

hf

öfP0

öaP0

p

hP0

haP0

sP0

Workpiece Basic cutter profileq = Machining allowance PrP0 = amount of protuberance

Workpiece Basic cutter profilehP0 = h

Workpiece Basic cutter profile

Fig. 5.03

Fig. 5.04

Fig. 5.05

146

Sprocket tooth system for roller- andsleevetype chains to DIN 8187 and 8188,tooth system of the sprockets to DIN8196, basic hob profile to DIN 8197.

When ordering please quote:Chain pitch, roller diameter, DIN standardof the chain.

Sprocket tooth system for Gall's chains(heavy) to DIN 8150.


The basic cutter profile for heavy Gall'schains to DIN 8150 is not standardizedand is made by us with a pressure angleof 20°.

Sprocket tooth system for barrel chainsto DIN 8164.


The basic cutter profile for barrel chainsto DIN 8164 is not standardized and ismade by us with a pressure angle of 20°.

Spline shaft tooth system; basic cutterprofile without clearance lug, withoutchamfer (flank centred).

When ordering please quote:Inside diameter di, outside diameter da,spline width b, number of splines, toler-ances for da, di, b. Possibly also DINstandard of the splines shaft. Designa-tion: ‘Without clearance lug, withoutchamfer’.

Flank centred spline shafts which findsufficient clearance for the internal andthe external diameter in the splineway,are produced with hobs without lug andwithout chamfer. It must be noted that fortechnical reasons inherent in hobbing nosharp-edged transition can occur fromthe spline flank to the inside diameter ofthe spline shaft. The size of the roundingcurve depends on the spline shaft dimen-sions. It must be ensured that no overlap-ping occurs between the rounding curveand the splineway. It may be necessary tofall back on a tool with clearance lug.

öaP0

pP0

hP0

haP0

sP0

24°

dadf

d

dadf

d

p

hP0

haP0

öaP0

sP0

20°

40°

dadf

d

p

hP0

haP0

öaP0 sP0

20°

40°

dFf

di

da

b

Workpiece Basic cutter profilep = chain pitch pP0 = 1,005 · p = pitch of the d1 = roller diameter basic profiled = pitch circle diameter haP0 = 0,5 · d1df = d–d1 = root circle diameterda = tip circle diameter

Workpiece Basic cutter profiledf = d – d1 öaP0 = 0,54 · d1

haP0 = 0,5 · d1hP0 = d1 + 2 to d1 = 5hP0 = d1 + 2,5 for d1 > 5

Workpiece Basic cutter profiledf = d – d1 öaP0 = 0,54 · d1

haP0 = 0,5 · d1haP0 = d1 + 1,5

Workpiece Basic cutter profiledi = inside diameterda = outside diameterb = spline widthdFf = form circle diameter

Above dFf the spline flanks are straight, below dFf the rounding curve starts

Fig. 5.06

Fig. 5.07

Fig. 5.08

Fig. 5.09

147

Spline shaft tooth system; basic cutterprofile with clearance lug and chamfer.

When ordering please quote: Inside diameter di, outside diameter da,spline width b, number of splines size ofthe chamfer g, tolerances for da, di, b.Possibly also DIN designation of thespline shaft. Designation: ‘with lug andchamfer’.

In order to achieve with internally centredspline shafts a correct bearing down onto the spline shaft base, the hob is gener-ally made with lug. The necessary clear-ance in the slot corners of the splinewayis achieved by the chamfer.

Spline shaft tooth system; basic cutterprofile with lug without chamfer (bottomfitting).

When ordering please quote:Inside diameter di, outside diameter daspline width b, number of splines, toler-ances for da, di, b. Possibly also DINstandard of the spline shaft. Designation:‘With lug without chamfer’.

The details under fig. 5.10 apply to thelug. A chamfer is not necessary if suffi-cient clearance exists between the splineshaft outside diameter and the corre-sponding splineway outside diameter.

Spline shaft tooth system; basic cutterprofile without lug with chamfer (bottomfitting).

When ordering please quote:Inside diameter di, outside diameter da,spline width b, number of splines, toler-ances for da, di, b. Size of the tip chamferg. Possibly also DIN standard of thespline shaft. Designation: ‘Without lugwith chamfer’.

If internally centred spline shafts are cutwith hobs without lug, chamfering on theteeth of the splineway must ensure thatinterferance with the rounding curve ofthe shaft are impossible.

Spline shaft tooth system; basic cutterprofile with one lug with chamfer (Side ormajor diameter fitting). This profile occurse. g. in the case of SAE spline shafts.

When ordering please quote:Inside diameter di, outside diameter da,spline width b, number of splines, toler-ances for da, di, b. Size of the tip relief g.Possibly also DIN- or SAE standard of thespline shaft. Designation: ‘With one lugand chamfer’.

Flank-centred multi-splined shafts have avery deep spline profile and are generallyproduced with hobs which only have oneraised tooth tip. The tooth tips of the ba-sic cutter profile are so narrow that thereis only sufficient space for one lug (equiv-alent to raised tooth tip).

dg

da

b di

g x 45°

dg

da

b di

da

b

g x 45°

didFf

da

b

g x 45°

dgdi

Workpiece Basic cutter profiledi = inside diameterda = outside diameterdg = base diameterb = spline widthg = width of the tip relief

Workpiece Basic cutter profiledi = inside diameterda = outside diameterdg = base diameterb = spline width

Workpiece Basic cutter profiledi = inside diameterda = outside diameterb = spline widthg = width of the tip chamferdFf = form diameter

Workpiece Basic cutter profiledi = inside diameterda = outside diameterdg = base diameterb = spline widthg = width of the tip chamfer

Fig. 5.10

Fig. 5.11

Fig. 5.12

Fig. 5.13

148

Spline shaft tooth system; basic cutterprofile with raised tooth for through-cutting a shoulder.

When ordering please quote:Collar dia. dB and also the details as under profiles 5.09 to 5.13.

If in the case of spline shafts the spline-way is to be pushed against a shoulder ofthe spline shaft, the hob cuts into thisshoulder. Since, however, the outside di-ameter of the shoulder must not be ma-chined off, the teeth on the basic cutterprofile must be made correspondinglyhigher.

Serrations to DIN 5481; nominal diameter7 x 8 up to 55 x 60. Basic cutter profilewith convex flanks for straight workpieceflanks. Cutters with straight flanks can al-so be used for the nominal diameterrange stated above, if this has been ar-ranged with the customer in advance.

When ordering please quote:DIN standard of the serration and toler-ances. Unless otherwise arranged, wesupply the hobs with straight flanks forconvex workpiece flanks, as under fig.5.16.Serrations are used for making form-fitplug-on connections.

Serrations to DIN 5481; nominal diameter7 x 8 to 55 x 60 and 60 x 65 to 120 x 125.Basic cutter profile with straight flanks forconvex workpiece flanks. For the nom.diameter range 7 x 8 to 55 x 60 basiccutter profiles as under 5.15 can also beused.

When ordering please quote:DIN standard of the serrations and toler-ances.

External spline profiles with involuteflanks to DIN 5480 and special standards.

When ordering please quote:Module, pressure angle, tip circle diame-ter, root circle diameter, diametral two-rollmeasurement, DIN standard of the exter-nal spline.

dg

da

bdi

g x 45°

dB

hP0

pP0

sP0

haP0

öf da

df

d

60°

p2

dad

di

2aP0öfP0

p

sP0

haP0

aP0

öaP0

hP0

daddf

öfP0

p

haP0

30°

60°

öaP0

hP0

pP0 2

Workpiece Basic cutter profilehaP0 = 0,60 · m hP0 = 1,25 · möaP0 = 0,16 · möfP0 = 0,10 · m

Workpiece Basic cutter profiledi = inside diameterda = outside diameterdg = base diameterb = spline widthdB = shoulder diameterg = width of the tip chamfer

Workpiece Basic cutter profiledf = root circle diameterd = pitch circle diameterda = tip circle diameter

Workpiece Basic cutter profile

Fig. 5.14

Fig. 5.15

Fig. 5.16

Fig. 5.17

149

Cutting materials for hobsHobs in particular are subject toclear technological limits with re-gard to the selection of an idealcutting material. Owing to the highmanufacturing precision requiredin gear manufacture, solid toolsare preferred, for example. Not allmaterials are suitable for the man-ufacture of solid hobs, however.Certain high-speed steels (HSS)are therefore a popular choice;

Together with carbon (C), the alloy-ing elements tungsten (W), molyb-denum (Mo), vanadium (V) andchromium (Cr) form carbides,which are very hard and resistantto abrasion. High contents ofthese elements therefore improvethe resistance to wear, but alsotend to reduce the toughness tosome degree. Powder metallurgi-cal high-speed steels represent asolution to this problem, as theycan be provided with highertoughness reserves than conven-tional HSS grades for a givenhardness.

carbides have also been gaining inpopularity recently.

HSS is a generic term for a groupof high-alloy steels whose alloycomposition enables them to besubjected to extremely high pre-cipitation heat treatment. Cobaltalloyed high speed steels are nowemployed for the manufacture ofall but a very few high speed steel

gear cutting tools. Cobalt (chemi-cal symbol: Co) increases the redhardness and the heat resistance,thus permitting higher cuttingspeeds in tool use.

C Co W Mo V CrMaterial no. Abbreviation Trade designation

Chemical breakdown in % weight

1.3202 S 12-1-4-5 (EV4Co) – 1,37 4,8 12 0,8 3,8 4,31.3207 S 10-4-3-10 (EW9Co10) – 1,27 10 9,5 3,5 3,21.3243 S 6-5-2-5 (EMo5Co5) – 0,92 4,8 6,4 5 1,9

1.3344 S 6-5-3 ASP 2023 1,28 – 6,4 5 3,1 4,1S 6-5-3-9 ASP 2030 8,5 4,2S 10-2-5-8 ASP 2052 1,60 8 10,5 2 5 4,8

1.3241 S 6-7-6-10 ASP 2060 2,30 10,5 6,5 7 6,5 4,2S 10-2-5-8 S390 PM 1,60 8 10,8 2 5 4,75S 12-0-5-5 CPM REX T15 1,55 5 12,25 – 4S 10-5-3-9 CPM REX 76 1,50 9 10 5,25 3,1 3,75

Conventionally melted steels

Powder metallurgical high-speed steels (PM/HSS)

Chemical analysis of common HSS grades

0

1000

2000

3000

4000

5000

6000

Ulti

mat

e be

ndin

g st

reng

th (

N/m

m2)

63 64 65 66 67 68 69

Rockwell Hardness HRC

Conventional HSS

PM/HSS

Stress perpendicular tothe direction of rolling

Stress parallel to thedirection of rolling

Carbide HSS

Application temperatures1250

1000

750

500

250

0

Tem

pera

ture

/°�C

Coated

HSS

Toughness

Res

ista

nce

to a

bras

ion

Coated

Carbide

150

"Carbide" is a generic term forpowder metallurgical high-speedsteels, which consist essentially ofthe hard materials tungsten car-bide (WC), titanium carbide (TiC)and tantalum carbide (TaC), andthe auxiliary metal cobalt (Co). Acomparison of the technologicalcharacteristics of high-speedsteels and carbides can be foundin the table on the right.

A classification system for thechemical composition similar tothe HSS material numbers doesnot exist for carbides. Carbidesare classified into "Main groups ofchip removal" and "Groups of ap-plication" by the ISO 513 standardaccording to their applications.

The most suitable carbide is there-fore selected according first to thematerial to be machined, and sec-ond to the anticipated stress uponthe tool, which is also reflected inthe grades table.

A comparison shows that HSS issignificantly tougher, whilst car-bide has the greater resistance toabrasion. For this reason, HSS isoften easier to use in practice. Itceases to be practically viable as atool material, however, when the

cutting speed is increased drasti-cally in order to achieve substan-tially higher metal removal capac-ities. The application temperaturelimit of HSS is approximately 500°C, that of carbides approximately1000 °C. This characteristic makescarbide predestined for machiningat increased cutting speeds andfor dry machining, provided thetools are used on suitable ma-chines.

Hardness HV10 800–900 1200–1900Ultimate bending strength N/mm2 5000 1000–2500Density g/cm3 8–8,3 11–15Modulus of elasticity 103 N/mm2 217 480–660Coefficient of thermal expansion µm/(m °C) 10–13 5–7Thermal conductivity (up to 20°C) W/(m °C) 19 30–100

Characteristic Unit HSS Carbide

M WC Stainless austenitic M 10 FinishingTiC, (Ta, Nb) C steels and elevated M 20 General tasks

Co temperature metals M 30 RoughingM 40 Heavy roughing

K WC Short chipping K05 FinishingCo cast iron and K10 General tasks

non-ferrous metals K20 Light roughingK30 Medium roughingK40 Heavy roughing

P WC Long chipping steels and P10 FinishingTiC, (Ta, Nb) C cast steel materials P20 General tasks

Co P30 Light roughingP40 Medium roughingP50 Heavy roughing

Main groups of Constituents For machining Group of Operatingchip removal application conditions

Classification of carbides according to ISO 513

Machining from the solid in Skive Re-coatingGrade ISO 513 Coating Steel Cast iron hobbing following regrinding

� Recommended application � Also suitable

FETTE carbide grades for hobs

FC222N HC-P25 Tin (PVD) � Not required

FC232N HC-P30 TiN (PVD) � � Required

FC612N HC-K15F TiN (PVD) � � Required

FW606 HW-K10 – � –

151

Hard material coatings for gear cutting toolsThe ion plating process, whichpermitted the decisive break-through in the manufacture of tita-nium nitride coatings (TiN) for car-bides in the early nineteen-eighties,opened up considerable perfor-mance reserves in machine toolapplications. 15 years on, coatedtools now represent around 80%of the market, and considerablymore when considered in terms ofmachined workpiece volume.

Ion plating is a physical vapourdisposition process. Followingmeticulous cleaning and degreas-ing, the tools are placed in an an-nular arrangement on rotatingmounts in a vessel, the recipient,which is evacuated to a high vacu-um. Titanium is vaporized from acrucible located in the centre ofthe vessel. Nitrogen in gaseousform and the neutral gas argon areinjected into the recipient througha number of valves. A carbon car-rier gas is required in addition forthe manufacture of titanium car-bonitride (TiCN). Finally, an electri-cal glow discharge is ignited at adefined pressure of a few mil-lionths of a bar. The gas is ionized,and a plasma is created whichsupplies the energy required forthe chemical reaction

2 Ti + N2 → 2 TiN

Gold titanium nitride is depositedupon the tool surface. During thecoating process, the high-energyions in the plasma continuallybombard the layer as it forms. Likelittle steam hammers they com-pact the TiN, which consequentlybecomes particularly firm andhard.

The temperature of the tools ismaintained at 450 °C during theprocess. This low process temper-ature also enables high speedsteels to be coated without risk ofdistortion or thermal damage to

the microstructure. Carbides canalso be coated. The integrity of thecutting edge is of great importancefor hobs. Here too, the low pro-cess temperature of the ion platingprocess ensures that the embrit-tlement of the cutting edge, whichpresents such problems with car-bides, is avoided. The coatings,which are only a few µm in thick-ness, enable very sharp cuttingedges to be attained on the hobs.

HMHSS

4000

3000

2000

1000

0

Vic

kers

Har

dnes

s H

V1

TiN TiCN

Tool holder

Neutral Gas(argon)

Vakuum chamber

Evaporationcruicible

Vakuum pump

(10–5 mbar)

Reaction gas 2(hydrocarbon)

Reaction gas 1(nitrogen)

Evaporated titanium

Plasma

Schematic diagram of a PVD process

152

The enormous increases in tool lifeover that of uncoated tools can beattributed to the physical frictionand the chemical characteristics,in addition to the high hardness.The low chemical affinity of the TiNto the hot steel chip leads to lowerfriction and in turn to less frictionalheat, thereby reducing the wear.

The coating acts as a barrier whichprotects the underlying substrateagainst wear.

The higher cutting and feedspeeds possible with coated toolsare particularly advantageous forthe user. A chief factor is not onlythe longer tool life, but also the re-duction in production times. Coat-ed hobs thus recoup their coatingcosts within a very short space oftime.

The tool life of an HSS hob usedfor the manufacture of a sun wheelwas increased five-fold from 100to 502 finished wheels by the ap-plication of a TiN coating. Follow-ing regrinding, the tool was not re-coated, and was therefore coatedonly on the flank, and not on thecutting face. It nevertheless at-tained an average tool life of 251finished wheels in this condition.Over a total of 22 regrinding cy-cles, a total of 2300 wheels weremanufactured with the uncoatedhob and 6024 with the coated hob,i.e. 2.6 times the number. The rela-tively low additional cost of the TiNcoating was therefore recoupedwith ease.

Re-coating following regrinding (ofthe cutting face) of a worn HSStool is also economically viable.Use of the ion plating process forTiN coating presents no problems.The tool can be re-coated severaltimes; alternatively, the coatingcan also be removed chemically ina bath.

The combination of TiN on carbideis somewhat more complicated,although repeated coating is stillpossible. Removal of the coatingfrom carbide in the bath is howev-er difficult, owing to the chemicalaffinity of the carbides and the TiNcoating.

Re-coating of the grey-violet TiCNpresents greater problems, since

TiCN has a multi-layer structure.Structures of this kind cannot sim-ply be "stacked" one upon theother without difficulty. Removal ofthe coating from HSS by immer-sion in a bath is possible, but stillmore complex than with TiN. Oncarbide, the problems describedabove are also encountered.

The gold TiCN Plus is an interest-ing coating type. Essentially, this isa TiCN multi-layer coating withhigh resistance to abrasion. A pureTiN surface coat is however de-posited at the end of the coatingprocess. As a result, the frictionbehaviour of the chip on the tool isinfluenced chiefly by the TiN- sur-face layer, the abrasion resistanceby the underlying TiCN. TiCN Plus

is more conducive to re-coatingthan TiCN.

Workpiece:Material:Tool:Dimensions:Module:Number of starts:Number of gashes:Quality grade:

Sun wheel17CrNiMo6HSS hobd 90 x 80 mm3 mm112AA

10

8

6

4

2

0

Toll

life

trav

el p

er c

utte

r to

oth

(m)

TiN TiN / reground Uncoated

Cutting data

Cutting depth:Cutting speed:Axial feed:Tip chip thickness:Shift length:

6,808 mm65 m / min3 mm / WU0,224 mm54,3 mm

Chip

Coating

Wedge

Workpiece

Coating

++=

Higher hardnessLower frictionReduced diffusionLower wear

153

Development of wear

The cutting edge in use is subjectto a range of external influenceswhich combine to produce toolwear. The process temperature isparticularly significant. The chiefsources of process heat and theirapproximate contribution to theoverall temperature are:

■ Plastic deformation in the toolimmediately ahead of thecutting edge: 60%

■ Friction phenomena betweenthe chip and the tool cuttingsurface: 20%

■ Friction phenomena betweenthe workpiece and the toolflank: 20%

Part of this heat (approximately5-10%) flows into the tool andleads to softening of the cuttingmaterial. The higher the workingtemperature, the softer the cuttingmaterial becomes, and the lowerthe resistance which it can presentto the abrasive wear. Approxi-mately 75-80% of the heat is dissi-pated through the chip.

The wear mechanisms of scaling(oxidation) and diffusion increaseparticularly strongly with risingtemperature. Their dramatic in-crease with rising temperature de-fines a critical application temper-ature limit above which the tool lifeis reduced drastically, and ulti-mately beyond the limit of eco-nomic viability.

Each cutting material therefore hasa range of optimum cutting speedsfor each specific task. The materialto be machined, the requisite man-ufacturing tolerances, the speci-fied machining conditions such asthe system rigidity and the efficacyof cooling, and the thermal stabil-ity of the cutting material have amajor influence upon the cuttingspeed.

Mechanicaloverloading Pressure

welding

Built-up edge

Oxidation

Abrasion

Diffusion

Workpiece

Chip

Wedge

Causes of wear on the cutting edge

Carbide

HSS

0 100 200 300 400 500 600 700 800 900 1000

1500

1000

500

0

Vic

kers

Har

dne

ss H

V10

Temperature/°C

Red hardness of HSS and carbide

154

Hobbing has the additional phe-nomenon of strong local variationsin stress upon the cutter teeth.This is a consequence of the toothprofile to be manufactured on theworkpiece arising only with suc-cessive cuts of a number of cutterteeth engaging in turn. The metalremoval capacity is provided prin-cipally by the tooth tips, whichgenerate relatively large-volumechips capable of sinking a corre-sponding quantity of heat. By con-trast, much thinner chips are gen-erated in the region of the toothflanks of the hob; the particular en-

gagement conditions mean thatthe effective relief angle is also rel-atively small there, and the cut ischaracterized by a comparativelyhigh frictional component whichgenerates heat. At the same time,relatively thin, low-volume chipswith a low heat-sinking capacityare generated. Consequently, acorrespondingly high quantity ofenergy flows into the tool.

The resulting locally exaggeratedwear is compensated for by shift-ing. Shifting produces a more eventool stress distribution, with regard

both to the hob as a whole, and tothe individual cutter tooth. Boththe abrasive and the thermallygenerated wear mechanisms aredistributed more evenly over thetool.

During coarse shifting, in particu-lar, cutter regions temporarily unin-volved in the machining processhave sufficient opportunity to cooldown.

The cutting conditions applicableto hobbing are principally thecutting speeds and the feeds.

Cutting speed/temperature

a – Initial edge wearb – mechanical abrasionc – built-up edged – oxidatione – diffusion

Wea

r

e

d

b

a

Total

c

Causes of wear against temperature (according to Vieregge)

155

Cutting conditions in hobbingThe cutting conditions applicableto hobbing are principally thecutting speeds and the feeds.

The cutting speeds and feedsquoted in these “cutting condi-tions in hobbing” must be regard-ed as recommendations. The userwill in normal cases be able to cuthis gears properly with these rec-ommended values. An optimiza-tion of the cutting values is onlypossible on the site, taking into ac-count all the peripheral aspects.

The objectives of optimization maydiffer. Examples:

■ Short machining times;

■ High tool life quality;

■ Low tool or gear costs;

■ Improvement of the gear quali-ty.

A correct choice of cutting condi-tions is only possible if the interre-lation of the workpiece, the hoband the hobbing machine is takeninto account.

The cutting conditions in hobbingare mainly affected by:

■ Gear material: chemical analy-sis, heat treatment, tensilestrength, microstructure, ma-chineability;

■ Cutting material of the cutter:HSS, carbide, chemical analy-sis, working hardness, redhardness, coating type;

■ Condition of the hobbing ma-chine: stability, accuracy;

■ Workpiece clamping: radialrunout, axial runout, avoidanceof deformation and vibration;

■ Clamping of the hob: radialrunout, axial runout, smallestpossible hob spindle bearingclearance;

■ Gear size: module, cuttingdepth;

■ Tool life and tool life quality;

■ Requisite gear quality.

Important for determining thecutting conditions are not least thevarying demands made on theroughing and finishing operations.

For roughing, the highest possiblefeeds are selected in order for ahigh rate of metal removal to be at-tained. The surface quality of theflank which can be attained is ofsecondary importance.

The cutting conditions during fin-ishing must be chosen so that therequired gear quality and surfacefinish are achieved.

Attention must of course be paidto economic aspects during selec-tion of the cutting conditions. Itmay be necessary to calculate thetool and machine costs and themachining times in order to ascer-tain the most favourable combina-tion of cutting parameters.

156

Cutting materialsfor hobs

(See also Page 149)KHSS (cobalt alloyed super highspeed steels), and increasingly al-so carbides, are the chief materialsfrom which hobs are manufac-tured.

The maximum economic cuttingspeed for (coated) KHSS hobs is120 m/min for the machining ofgears with small modules frommetals which are easily machined.The KHSS most frequently em-ployed is EMo5Co5 (S 6-5-2-5,material no. 1.3243)

Higher-alloyed KHSS must be em-ployed for gear materials with atensile strength above 1200N/mm2. Powder metallurgical high-speed steels are a good choice forthis application. They can be sub-jected to higher precipitation heattreatment but still have a highertoughness than comparable steelsmelted conventionally.

Powder metallurgical high-speedsteels are of course also suitablefor gear materials with a tensilestrength below 1200 N/mm2 ifhigher cutting parameters or high-er tool life qualities must beachieved than those attained byEMo5Co5.

Hobs manufactured from KHSSare generally coated with TiN.Hobs manufactured from carbidefor machining of gears up to ap-proximately module 3 from the sol-id can be employed at cuttingspeeds which are higher by a fac-tor of three than those which canbe achieved by KHSS hobs. Thesehobs are always coated, generallywith TiCN Plus.

Machineability

The machineability of a gear mate-rial can be referenced to a range ofcharacteristics. Whether a material

can be machined easily or not isdetermined by whether it can bemachined at high or low cuttingspeeds, and with an acceptabletool life quality and wear markwidths.

The machineability can howeveralso be assessed according to therequisite cutting forces, or theease or difficulty with which a fa-vourable surface quality can be at-tained.

For the selection of the cuttingspeed for hobbing, it must first beassumed that a certain wear markwidth must not be exceeded (seealso "Maintenance of hobs, Page168). High wear leads to geometricdeviations in the cutting edges ofthe cutter teeth, and to highcutting forces. The result is a re-duction in gear quality. Since thewear increases superproportion-ately beyond a certain magnitude,the wear mark width must also bereduced for economic reasons. Atthe same time, however, an eco-

4 Chrome/nickel/molybdenum steels5 Nickel/molybdenum steels6 Chrome/molybdenum steels

7 Chromium steels andchrome/vanadium steels

8 Silicon/manganese steels

Brinell hardness N/mm2

Mac

hine

abili

ty in

%

Tensile strength N/mm2

400 500 600 700 800 900 1000 1100 1200 1300 1400 1500

75

70

65

60

55

50

45

40

35

30

25

20

15

10

100 150 200 250 300 350 450400

1

2

7

6

3

5

8

4

1 Plain carbon steels2 Nickel steels and chrome/nickel steels

(low alloy)3 Chrome/nickel steels

Diagram 1: Machineability of the gear materials

157

nomic tool life between successivecutter regrinds must be ensured.Excessively short tool life leads tolong down times of the hobbingmachine for the purpose of cutterchanges, and to high regrindingcosts. In this case, the machine-ability of the gear material is there-fore assessed in relation to thecutting speed at an appropriatetool life quality and wear markwidth. The machineability of thegear material as a function of itschemical composition and the ten-sile strength Rm in N/mm2 or theBrinell Hardness HB can be takenfrom Diagram 1 (original diagramas [1], with minor modifications).The machineability of B1112 steelto AISI (American Iron and SteelInstitute) was specified as 100% ata cutting speed of 55 m/min forthis purpose; all other steel gradeswere categorized relative to thesevalues. The machineability is indi-cated in percent.

Note however that the machine-ability is influenced not only by thetensile strength, but also by thedifferent microstructures. The rela-tive machineability probably alsovaries for other cutting speedranges, as gears with small mod-ules are machined at cuttingspeeds which are around twice ashigh as those for which the curvesshown were produced. It can how-ever be safely assumed that themachineability must be assesseddifferently for coated and uncoat-ed hobs, as the chip formation dif-fers markedly.

Cutting speed vc [m/min]

Diagram 2 shows the cuttingspeed as a function of the moduleand the machineability. This cutting speed relates to thecutting material S-6-5-2-5 (1.3243,EMo5Co5), and applies to theroughing cut (machining from thesolid).

For the finishing (second) cut, thecutting speed can be increased bya factor of 1.2.

The cutting speed can be multi-plied by a factor of 1.25 for coatedKHSS hobs.

Cut

ting

spee

d v

c [m

/min

]

80

70

60

50

40

30

20

10

0

Machineability in %

1

2

3

4

5

6

8

10

14

18

25

32

20 7030 40 50 60

Module

Diagram 2: Cutting speed when hobbing

158

A further a table of recom-mended values have been com-piled, based upon practical experi-ence, for the cutting speed for ma-chining with hobs on which thecutting material is KHSS S-6-5-2-5(1.3243, EMo5Co5). The commongear materials are assigned to thecategories "good", "medium" and"difficult" on the basis of their ma-chineability. The cutting speedsare shown for each module for theroughing cut and for the finishingcut. Table 1 is sub-divided intohobs with TiN coating and uncoat-ed hobs.

Carbide hobs for machining ofgears up to approximately module3 from the solid can be used withor without cooling lubricant as fol-lows:

Gear material: case hardening andheat-treatable steels, tensilestrength up to 800 N/mm2

Cutting speed:220 to 250 m/minwith cooling lubricant;280 to 350 m/minwithout cooling lubricant.

These hobs are all coated, gener-ally with TiCN Plus.

MachineabilityGood Medium Difficult

Tensile strength Tensile strength Tensile strengthup to 700 N/mm2 up to 900 N/mm2 up to 1.200 N/mm2

Roughing Finishing Roughing Finishing Roughing FinishingModule

m/min m/min m/min

16 Mn Cr 5, C 15, C 35, Ck 45, C 60, 18 Cr Ni 8, 34 Cr Ni Mo 6 V,20 Mn Cr 5, 15 Cr Ni 6 42 Cr Mo 4, 37 Mn Si 5, 30 Cr Mo V9 V,

18 Cr Ni 8, 17 Cr Ni Mo 6 40 Ni Cr Mo 7

< 2 100 130 75 98 55 772 92 120 69 90 50 703 84 110 63 82 40 564 76 99 57 74 30 425 68 88 51 66 26 366 60 84 45 63 25 357 56 78 42 59 24 348 52 73 39 55 23 329 48 67 36 50 22 31

10 44 62 33 46 21 2912 38 53 29 41 20 2814 35 49 26 36 19 2716 33 46 25 35 18 2618 30 42 23 32 17 24

< 2 75 90 56 67 34 412 69 83 52 62 31 373 63 75 47 56 29 354 57 68 43 52 26 315 51 61 38 46 23 286 45 56 34 41 22 267 42 55 32 38 21 258 40 52 30 36 20 249 38 49 29 35 19 25

10 37 48 28 34 18 2312 34 44 26 32 17 2214 32 42 24 29 16 2116 30 39 23 28 15 2018 27 35 20 24 14 1820 25 31 19 25 13 1722 23 29 18 23 13 1725 22 28 17 22 12 1628 20 25 15 20 11 1432 18 23 14 18 10 13

Table 1: Recommended cutting speed values for the machining of solid-type KHSS hobs

Without TiN coating

With TiN coating

159

Axial feed fa[mm/workpiece rotation]

The axial feed is specified in mmper workpiece rotation.

Owing to the large number of pa-rameters which influence the ma-chining process during hobbing,experience has shown that the ax-ial feed is best specified as a func-tion of the tip chip thickness.

The tip chip thickness is the theo-retical maximum chip thickness re-moved by the tips of the hob teeth.

The tip chip thickness is regardedas a criterion for the hob stress;high tip chip thicknesses meanhigh cutting forces and short toollife.

The tip chip thicknesses are in-creased when the module, axialfeed, cutting depth and number ofstarts are increased. The tip chipthicknesses are reduced when thenumber of gear teeth, hob diame-ter and number of gashes are in-creased.

Hoffmeister [2] has devised a for-mula for the maximum tip chipthickness.

If this formula is transposed, theaxial feed can be calculated as afunction of the other gear parame-ters. Experience has shown a tipchip thickness of 0.2 to 0.25 mmto be a realistic value.

For economic reasons, as high anaxial feed as possible is aimed for,as the machining time is reducedproportional to the increase infeed.

Note however that the depth of thefeed markings increases quadrati-cally with the axial feed, and thatdifferent maximum feed markingdepths are permissible accordingto the machining step such as fin-ish-milling, rough-hobbing prior toshaving, or rough-hobbing prior togrinding, depending upon the gearquality or the allowance.

If carbide hobs are employed formachining from the solid, the max-imum tip chip thickness must bebetween 0.12 and 0.20 mm. Forcarbide hobbing without cooling

lubricant, in particular, 80% of theheat generated by the cutting pro-cess must be dissipated by thechips. Adequate chip cross-sec-tions are therefore required. Forthis reason, the tip chip thicknessshould not be less than 0.12 mm.

Cutting depth

ra0

h1 max

Workpiece

Centre of hob

mZ2ß0xPra0i

faae

ModuleNumber of teethHelix angle (radian)Profile displacement factorHalf hob diameterNumber of gashes/numberof startsAxial feedCutting depth2,718282

Example:

faa

==

49

ra0i

==

5512/2

ß0xP

==

160,2

mZ2

==

446

h1 = 0,3659 Dissertation by Bernd Hoffmeister 1970

ra0m

h1 max = 4.9 · m · Z2(9.25 · 10–3 · β0 – 0.542) · e–0.015 · β0 ·

· e–0.015 · xp ·

· · [mm]0.511

(–8.25 · 10–3 · β0 – 0.225)· i–0.877 ·

fam

0.319am

======

===

Maximum tip chip thickness

th [min]Z2

da0 [mm]

E [mm]

b [mm]

A [mm]

Z0

fa [mm/WU]Vc [m/min]

Machining timeNumber of teeth ofthe gear to be cutTip circle diameterof the hobLead lengthof the hobTooth width of thegear to be cutIdle travel distanceof the hobNumber of startsof the hobAxial feedCutting speed

==

=

=

=

=

=

==

th = [min]Z2 · da0 · π · (E + b + A)

Z0 · fa · Vc · 1000

Machining time (production time) for hobbing

fa

δx

dδx [mm] = fa

cos β0

2 ·

sin αn

4 · da0

δx [mm] = Depth of the feed marking

fa [mm/wr] = Axial feedβ0 = Helix angleαn = Profile angleda0 [mm] = Tip circle diameter

of the hob

Depth on the feed markings

160

Number of starts of the hob

With the exception of worm gearhobs, multiple start hobs have thefunction of increasing hobbingperformance.

It is known that the axial feed mustbe reduced for a given tip chipthickness when the number ofstarts is increased (formula for themaximum tip chip thickness ac-cording to Hoffmeister).

It is also known that the depth ofthe feed markings is dependentupon the axial feed (formula for thedepth of the axial feed markings).

There is therefore a relationshipbetween the number of starts, thetip chip thickness and the axialfeed, and between the axial feedand the depth of the feed mark-ings.

In the formula for the machiningtime, the number of starts and theaxial feed form part of the denomi-nator, i.e. the greater the productof the number of starts and the ax-ial feed, the shorter the machiningtime.

The objective is therefore to selecta product of the number of startsand the axial feed which is as highas possible without the tip chipthickness and the depth of thefeed markings becoming toogreat.

Specification of the number ofstarts on the basis of the tip chipthickness and the depth of thefeed markings

Table 2 shows the optimization ofthe number of starts and the axialfeed by way of an example gear.

The number of starts 1 to 5 and aconstant tip chip thickness of 0.2mm were entered in columns 2 to 6.

Line 11 contains the maximumfeeds permissible at a tip chipthickness of 0.2 mm.

Line 12 shows the product of thenumber of starts and the axialfeed.

The relative machining time in col-umn 2 is made equal to 1 and themachining times in the followingcolumns calculated in relation tocolumn 2.

Line 13 shows clearly that for agiven tip chip thickness, the short-est machining time can beachieved with the single-start hob.Line 14 also shows however thatthe depth of the feed markings be-comes excessive, at 0.206 mm.

With the two-start hob, the feedmust be reduced to approximately30% of that of the single-start hob.This is however compensated forto some degree by the number ofstarts, as the table speed is dou-bled for the same cutting speed.Since the depth of the feed mark-ings is only 0.019 mm, however,the axial feed of 4.78 mm is accep-table, either for rough-hobbingprior to shaving or grinding.

If it is therefore assumed that thegear is being rough-hobbed priorto shaving or grinding, the two-start hob, with a product of feedand number of starts of 9.56, rep-resents the most economic solu-tion.

The single-start hob is not an op-tion, as it permits a maximum feedof only 4.78 mm even with the sin-gle-start hob owing to the depth ofthe feed markings, and the prod-uct of the number of starts and theaxial feed would only be 4.78.

The three-start hob is also unsuit-able in this case, as the product ofthe number of starts and the axialfeed is only 7.14, owing to themaximum tip chip thickness.

Specification of the number ofstarts should therefore first entailcalculation of the maximum axialfeed for the permissible depth ofthe feed markings. A hob shouldthen be selected with the numberof starts which produces thegreatest product of number ofstarts and axial feed without themaximum axial feed being ex-ceeded owing to the depth of thefeed markings or the maximum tipchip thickness (line 11).

Line/column 1 2 3 4 5 6

Table 2: Feeds and depth of the feed markings for multiple start hobs

1 Module 2,52 Pressure angle [°] 203 Number of teeth 294 Helix angle [°] 155 Profile displacement factor 0,26 Cutting depth 5,637 Cutter diameter 1108 Number of gashes 249 Number of starts z0 1 2 3 4 5

10 Tip chip thickness 0,2 0,2 0,2 0,2 0,211 Axial feed fa 15,71 4,78 2,38 1,46 0,9912 z0 x fa 15,71 9,56 7,14 5,84 4,9513 Relative machining time 1 1,64 2,2 2,69 3,1714 Depth of the feed markings 0,206 0,019 0,005 0,002 0,001

161

Enveloping cut deviations

Despite the economic advantagesoffered by multiple start hobs, theaccuracy of the gear must not beignored. Whether multiple starthobs selected as described abovecan in fact be used must thereforebe considered on a case-by-casebasis.

The number of cutter teeth whichprofile a tooth flank depends uponthe number of teeth and the pres-sure angle of the gear, and thenumber of gashes, pitch and num-ber of starts of the hob.

Provided the number of gashes re-mains unchanged, the number ofcutter teeth forming the profile forexample on two- or three-starthobs is reduced to half or one-third. The envelope network whichis generated is less dense, and theenveloping cut deviations arise inthe form of deviations in the profileform. Calculation and examinationof the enveloping cut deviations isparticularly important when thenumber of gear teeth is low, as

particularly large enveloping cutdeviations arise in this case owingto the strong curvature of the pro-file and the relatively large torsion-al angle of the workpiece percutter tooth.

The enveloping cut deviations canbe reduced considerably by in-creasing the number of gashes.

Influence of the numberof cutter starts upon theflank form and pitch of the gear

For generation of the gear flanksas an envelope network, as is typi-cal for hobbing, it must also beconsidered that each cutter toothflank only generates one envelop-ing cut, and also that the relativelocation of the enveloping cuts toeach other is dependent upon theaccuracy of the cutter lead and theindexing precision of the hobbingmachine.

Single-start hobs have no influ-ence upon the indexing precisionof the gear, since the same cutterteeth always machine all teeth ofthe workpiece. Deviations in leadon single-start hobs only influencethe flank form of the machinedgear.

By contrast, multiple start hobs al-so have an effect upon the index-ing precision of the gear if thenumber of gear teeth is divisible bythe number of starts of the cutter.In this case, the profile of a toothgap is machined only by the teethof one cutter start. Under thesecircumstances, the deviations inpitch of the cutter leads produceperiodic deviations in pitch on theworkpiece. Since the deviations inpitch can only be eliminated in partfor example by shaving, multiplestart roughing hobs with a shavingallowance should preferably beselected for which the quotient ofthe number of gear teeth and thenumber of cutter leads is not an in-teger.

Surface structure

However, it should also be ensuredthat the quotient of the number ofgashes and the number of leadsduring finishing is not an integer.The enveloping cuts will otherwisebe generated at different heightsfrom lead to lead, and the toothflanks will acquire a honeycombedsurface structure.

Limitation of the numberof leads on the hobs withaxially parallel gashes

On hobs with axially parallel gash-es, ensure that the increase in thenumber of leads does not result ina helix angle of 7.5° being exceed-ed. The surface quality on the cor-responding gear flank will other-wise be impaired owing to theexcessive wedge angle on theleaving cutter flank.

Referances[1] Schmidthammer: Cutting conditions for

hobbing: FETTE Cat.-No. 1137: Gear cutting tools

[2] B. Hoffmeister: Dissertation, Aachen 1979

δ y [mm]

z0

mnαnz2

i

=

=

===

Magnitude of theenveloping cutdeviationNumber ofcutter startsNormal moduleProfile angleNumber ofgear teethNumber ofgashes of thecutter

δy

d

δ y [mm] =π2 · z0

2 · mn · sinαn

4 · z2 · i2

=

Enveloping cut deviations

162

Tool cutting edge lengthA distinction must be drawn inhobbing between the pre-cuttingzone and the profile generatingzone. The greater part of the vol-ume to be machined is removed inthe pre-cutting zone. The pre-cutting zone is at the end of thehob which first enters the body ofthe gear during axial machining.The hob must be positioned until itcompletely covers the pre-cuttingzone. This cutter length, the mini-mum required, is termed the toolcutting edge length.

The penetration curve (fig. 1) of thetip cylinder of the gear and thecutter must be known for calcula-tion of the tool cutting edge length.For the considerations below, it isassumed that the gear is helicaland that the cutting axis is inclinedto the horizontal by the pivotingangle (β - γ0). A further assumptionis that where a helix angle ispresent, it is always greater thanthe lead angle. The direction ofview of the penetration curve isfrom the main machine columnin the direction of the cutter andthe gear. The two tip cylinderspenetrate each other at a depthequivalent to the cutting depth.The intersecting line between thetwo bodies is a 3-dimensionalcurve which follows both on thegear and the cutter cylinder. Wherereference is made below to thepenetration curve, the projectionof the intersecting line into a planeaxially parallel to the cutter axis isunderstood.

The form and dimension of thepenetration curve are dependentupon:

■ The tip circle diameter of thegear;

■ The cutter diameter;

■ The pivoting angle(helix angle β of the gear, leadangle γ0 of the cutter);

■ The cutting depth.

The formulae for calculation of thepenetration curve can be found inthe Chapter "Wear phenomena inhobbing", Page 188, fig. 13).

All cutter teeth which do not passthrough the penetration curve (fig.2) during rotation of the cutter donot make contact with the gearbody. They are not therefore in-volved in chip formation. With re-spect to the horizontal whichpasses through the intersection"S" of the gear axis and the cutteraxis, Point 1 is the highest andPoint 1' the lowest point of thepenetration curve.

Gear

Cutter

Fig. 1: Gear/cutter penetration

l 4

Left-handed gear Left-handed cutter

Direction of feed ofthe cutter head

Climb hobbing

Conventionalhobbing

Cutter axis

Gear axis

Gear

l 1

l 4'

l 1'

4'

1'

3'

3

1

4

1A

s

fa [mm/wr

Samedirectionß > γ0

ß - γ0

l = Tool cuttingedge length

View of the cutter and gear from the main machine column

Fig. 2: Ascertainment of the tool cutting edge length from the penetration curve

163

Helical teeth

Climb hobbing, same lead directionWhen the cutter moves from up-wards to the lower face of the gearduring climb hobbing, the cuttertooth whose path passes throughPoint 1 is the first to intersect thetip cylinder of the gear. This cuttertooth is then located in a plane atright-angles to the cutter axis, inwhich Points 1 and 1A are located.The distance to the point "S",measured parallel to the cutter ax-is, is equal to the path of which "S"and 1A are the end points. It isequivalent to the cutter length forthe Point 1 in relation to the sec-tion through the axis "S".

Following one rotation of the gear,the cutter has moved upwards bythe axial feed. A parallel at a dis-tance "fa" to the horizontal throughPoint 1 intersects the penetrationcurve at Points 3 and 4. Thehatched band between the par-allels through Points 1 and 4 corre-sponds to the band of materialwhich is pushed continuously intothe working area of the cutter dur-ing the machining process. Point 4is the point on the penetrationcurve which is still involved in ma-terial removal and is located fur-thest from the axis intersection"S". All cutter teeth whose pathsrun through the penetration curve

but which are located further awayfrom the Point "S" are not involvedin the material removal process.The cutter length corresponding toPoint 4 is marked "I4" in fig. 2. Thisis the tool cutting edge length ofthe cutter during climb hobbing ofa helical-tooth gear with a cutterwhich has the same direction oflead as the gear.

Since the cutter is generally shift-ed towards the cutter enteringside, the entering side is posi-tioned at the start of the machiningprocess according to the toolcutting edge length calculated asdescribed above. If a shorter toolcutting edge length were to be se-lected for the cutter teeth wouldbe absent in the entering zone,and the following teeth would haveto assume part of the missingteeth's function of material remov-al. This could lead to overloadingof the first teeth in the enteringzone. Were an excessively longtool cutting edge length to be se-lected, the cutter would not be ec-onomically viable, as the teethahead of the tool cutting edgelength would not be used.

Climb hobbing, opposite lead directionIf a right-hand (opposite lead di-rection) cutter is employed in place

of the left-handed cutter, the toolcutting edge angle (β + γ0) changesand the gear runs from left to rightinto the working area of the cutter(penetration curve). The outmostpoint involved in material removalis Point 1.

The cutter length corresponding toPoint 1 is then the tool cuttingedge length. The tool cutting edgelength is shorter in climb hobbingwith a cutter with opposite lead di-rection than with a cutter with thesame lead direction. It is not af-fected by the magnitude of thefeed.

Conventional hobbing, samelead directionIf the cutter moves downwards on-to the upper face of the gear, thecutter tooth whose path passesthrough the point 1' is the first tointersect the tip cylinder of thegear, and the tool cutting edgelength is equal to the length l1’.

Since the two halves of the pene-tration curve to the left and right ofthe normals on the cutter axisthrough the point "S" are congru-ent and are inverted around thenormal by "S" and around thecutter axis, l1’ = l1 und l4’ = l4.

Tool cutting edge length (continued)

164

Tool cutting edge length (continued)

Further combinations of hob-bing method and direction oflead of gear and hob

Table 1 shows the leading end,pivoting angle and tool cuttingedge length for different combina-tions of hobbing method and di-rection of lead of gear and hob."Leading end left" means that thegear runs from left to right into thepenetration curve. "Leading endleft l4 up" means that the toolcutting edge length is equal to thedimension l4 in the penetrationcurve. It is located on the left-handside in relation to the gear axis.The cutter side on which the toolcutting edge length is located isfacing upwards.

Again the assumptions are:Direction of view from the mainmachine column towards thecutter and the gear. On a helicalgear, the helix angle is greaterthan the lead angle of the cutter. View of the cutter and the gear from the main machine column

Cutter: right-hand start Cutter: left-hand start

Gear Right-hand lead Left-hand lead Straight teeth Right-hand lead Left-hand lead Straight teeth

Climb hobbing

Conventionalhobbing

Left Left Left Right Right Right

β – γ0 β + γ0 γ0 β + γ0 β – γ0 γ0

l4 Left, up l1 Right, up l1 Right, up l1 Left, up l4 Right, up l1 Left, up

Left Left Left Right Right Right

β – γ0 β + γ0 γ0 β + γ0 β – γ0 γ0

l1 Right, down l4 Left, down l4 Left, down l4 Right, down l1 Left, down l4 Right, down

Leading end

Pivoting angle

Tool cutting edge length

Leading end

Pivoting angle

Tool cutting edge length

Table 1

165

Profile generating lengthfor hobbing

Profiling of the gear takes placeexclusively in the profile generat-ing zone, which is arranged sym-metrical to the pitch point. Theprofile generating zone is calculat-ed in the face plane of the gearand is represented there by lPa andlPf.Profile generation takes place dur-ing hobbing on the engagementlines (fig. 3). The area in whichgeneration takes place is limitedby the intersections of the engage-ment lines with the tip circle diam-eter of the gear and by a line con-necting the transition points fromthe tip radii to the flank of the basichob profile (tip form height).The greater interval between theend points of the engagementlines, either in the tip region (lPa) orthe root region (lPf) of the hob pro-file, is regarded as the definitivelength. Whether the end points ofthe engagement lines in the tip re-gion or in the root region of the ba-sic hob profile are decisive is de-pendent upon the profile dis-placement of the gear. Refer hereto figs. 4 and 5: fig. 4 represents agear with positive and fig. 5 a gearwith negative profile displacement.The greater of the two values - lPaor lPf - is then converted from theface plane to the axial plane of thehob and termed the "profile gener-ating length IP0".

lP0

lP0

2

lP0

2

C

Fig. 3

da

hFaP0

lPf

öaP0

Fig. 4

da

hFaP0

lPa

öaP0

Fig. 5

tan αt = tan α / cos βlPa = 2 · (ha0 – x · mn – ρa0 ·

(1 – sin α)) / tan αt

db = z · mn · cos αat / cos βcos αat = db / da

d = z · mn / cos βlPf = 2 · (da / 2 · cos (αat – αt) – d/2) /

tan αt

IflPa > lPf, then lP0 = lPa · cos γ0 / cos βIflPf > lPa, then lP0 = lPf · cos γ0 / cos βha0 = addendum on the hobx · mn = profile displacementρa0 = tooth tip radius on the hobα = pressure angleβ = helix anglez = number of teethmn = normal moduleda = tip circle diameter of the gear γ0 = lead angle of the hob

Profile generating length

166

Shift distanceThe chip cross-sections within theworking area of a hob are knownto be very different. In conse-quence, the individual cutter teethare subject to different loads, andtherefore exhibit non-uniform wearpatterns. It is therefore logical forthe hob to be moved tangentiallyin stages once one or more work-pieces have been machined in oneposition. This tangential move-ment is termed "shifting".

Shifting continuously brings newteeth into the working area of thehob. The worn teeth leave theworking area and the wear is dis-tributed uniformly over the usefulcutter length. The number of work-pieces upon which a gear profilecan be generated between suc-cessive regrinds is determined bythe length of the hob and thereforealso by the length of the shift dis-tance.

In view of economic considera-tions - high tool life quality, lowproportional tool costs, low ma-chine downtimes for cutter chang-es - shift distances are selected

lP0

lP0

2

lP0

2

C

Shift direction

l3

lsle

lP0

2≈ 1 · mn ≈ 2 · mn

l3lelslP0

====

Useful length of cutterTool cutting edge lengthShift distanceLength of the profile generating zone

Fig. 6: Ascertainment of the shift distance

which are as long as possible. Themaximum length of the shift dis-tance is determined by the designof the hobbing machine and there-fore represents an absolute limit.The relationship between the use-ful cutter length, the tool cuttingedge length, the length of the pro-file generating zone and the shiftdistance is shown in fig. 6.

ls = l3 – le – lP0 / 2 – 3 x mn

The quantity 3 x mn makes allow-ance for the incomplete teeth atthe ends of the hob.

167

Axial distance in hobbing

The axial distance of a hob duringaxial machining is generally com-posed of the approach distance,the width of the gear and the idletravel distance. Fig. 7 represents aschematic diagram of the axialdistance of a hob during climbhobbing.

The approach distance is the dis-tance which the hob must travelparallel to the gear axis, from thefirst point of contact to the point atwhich the intersection of the cutterand the gear axis has reached thelower face plane of the gear body.

The approach distance is equal tothe height of the highest point onthe penetration curve above thehorizontal plane through the inter-section of the cutter and gear ax-es. The formulae for calculation ofthe penetration curve can befound in the Chapter "Wear phe-nomena in hobbing", Page 188, fig. 13.

The approach distance can alsobe calculated with sufficient accu-racy by means of the following for-mula:

For straight teeth:

E = h · (da0 – h)

For helical teeth:

E = tan η · h · da0 + da – hsin2 η

E = approach distanceh = cutting depthda0 = cutter diameterη = pivoting angleda = tip circle diameter of the gear

No idle distance, except for asafety allowance, is required forstraight teeth.

The idle distance for helical teeth isdetermined by the profile-generat-ing zone in the face plane (fig. 8).

The dimensions for IPa and IPf aredetermined by the formulae in theChapter "Profile generating lengthfor hobbing" and are calculated asfollows:

If lPa > lPf, then U = lPa x tan βIf lPf > lPa, then U = lPf x tan βU = idle distanceAxial distance = E + b + U

da

hFaP0

lPf

öaP0

lPa

U

UFor conventionalhobbing

For climbhobbing

Normal cutter/gear plane

U = Idle distance

Fig. 8

U

b

E

EbU

===

Approach distanceGear widthIdle distance

Fig. 7

( )

Axial distance

168

IntroductionIn the field of the machining pro-cesses for the manufacture of gears, hobbing occupies a promi-nent position which, also in the future, can only be maintainedthrough constant improvements inquality and economy. From this point of view, hobbingmust be regarded as a systemconsisting of machine, tool andcutting parameters, which must al-ways be optimized afresh as re-gards an extremely wide range ofgear cutting tasks. Through developing high-perfor-mance hobbing machines andhobs the machine cycle times andthe auxiliary process times wereconsiderably shortened. This didof course increase the importancein the analysis of the gear cuttingcosts for a specific workpiece thetool costs, the costs of the toolchange and the maintenancecosts of the hob. It was therefore essential to ad-vance also the technology of theregrinding of hobs by means ofhigh-performance grinding me-thods, such as the deep grindingprocess, and by means of suitableabrasives adapted to the varioushob cutting materials. Therefore,grinding wheels made from cry-stalline cubic boron nitride (CBN)and diamond should be used inaddition to the conventional grind-ing materials such as silicon car-bide (SiC) and corundum (Al2O3).Although the initial purpose whenregrinding a hob is to remove thewear marks from the cutter teeth,a range or other requirementsmust be met which are formulatedbelow as a task description.

Task descriptionAs with every metal removing ma-chining process with a definedcutting edge, wear marks occur onthe cutting edges of the cutterwhich affect chip formation, pro-duce higher cutting forces andwhich could therefore reduce gearquality. This is why the wear has tobe removed when it has reached acertain value. The maximum widthof a still permissible wear mark willbe discussed below. All relief turned or relief groundhobs are sharpened by grinding on

the cutting face. This processmust with such high-quality preci-sion tools be carried out expertlyand with the necessary care. Regardless of the design, the dimensions, the cutting edge geo-metry and the material of the hobs,the following requirements mustabsolutely be met when regrind-ing:

■ The cutting face geometry mustbe produced in accordance withthe quality grade of the hob,

■ heat stress on the cutter materi-al by the grinding process mustbe restricted to a minimum,

■ the roughness of the cutting fac-es and therefore the ragged-ness of the cutting edges mustbe kept as low as possible,

■ grinding methods and aids mustbe chosen so that maintenanceand inspection costs are keptwithin economical limits.

AII preparations, the executionand the supervision of the regrind-ing process must have as their aimthe total observation of the re-quirements listed above.

In addition, the following pointsmust be observed during main-tenance operations on carbidehobs:

Carbide hobs assigned to the "ISO K" group:1. Remove coat2. Sharpen the cutting face3. Re-coat

Carbide hobs assigned to the "ISO P" group:

Regrind cutting faceRe-coating is not required.

Wear phenomena on the hobWhere reference is made to thewear mark width in the context ofhobbing, this generally refers tothe length of the flank wear on thetip corners of the cutter teeth. Infig. 1, this is described as flankwear. This particularly markedform of flank wear also determinesthe end of the service life of thehob.

In the upper curve of fig. 2 thecharacteristic course is represent-ed for the formation of the wear

1.6

1.2

0.8

0.4

0

Wea

r p

er p

iece

µm

/Stc

k.

Number of gears

0.25

0.20

0.15

0.10

0.05

0

Wea

r m

ark

wid

th B

0 80 160 240 Pieces 320

mm

Fig. 2: Flank wear as a functionof the number of workpieces cut

Cutting edgerounding

Chipping

Crater

Flank wear(hollow cone)

Flankwear

Fig. 1: Forms of wear on the hobtooth

Maintenance of hobsmark width. This does not developproportionately to the number ofworkpieces cut.The lower curve in fig. 2 has amarked minimum for the propor-tionate wear of a tool at the transi-tion to the progressive part of theupper curve.

For the gear under consideration,the maximum wear should nottherefore exceed 0.25 mm on TiN-coated HSS hobs or 0.15 mm oncarbide hobs if the lowest possibleunit tool costs are an objective.

169

Since the wear curves cannot bedetermined in all cases in the formmentioned, some guide values areincluded in fig. 3.At the same time it also becomesclear, however, that there are arange of other criteria, such ascutting material, module size, pro-duction sequence or requiredtooth quality, according to whichthe wear mark width must be eval-uated. The "Roughing" column in fig. 3shows relatively large wear markwidths for roughing of gears with ahigh module.These certainly already fall withinthe range in which wear increasesprogressively. This can, however,often not be avoided in these cases, because the volume to beremoved increases quadraticallywith the module, whereas thenumber of cutter teeth involved inthe metal removal process remainsthe same or even decreases. Theresults are higher stress on individ-ual cutter teeth and thereforegreater wear.

For finishing, the wear mark widthsmust be markedly lower, becausewear-related cutting edge devia-tions and higher cutting forces re-duce gear cutting accuracy. Experience with titanium nitridecoated (TiN) hobs shows that withwear mark widths from 0.2 mm nolonger the hard coating but the base material determines wear de-velopment. When milling hardened gears withcarbide skiving hobs, a criticalwear mark width is reached at 0.15 mm. The increased cuttingforces and cutting temperaturesresulting from the blunting of thecutting edge not only stress theworkpiece and reduce its quality,but also lead to sporadic chippingand splintering of the tool.On solid carbide hobs for dry ma-chining, the wear should not ex-ceed 0.15 mm. A further increasein wear leads to destruction of thetool. It is therefore important to de-termine the tool life quality per re-grind. The first sign of increasedwear during dry machining is theincrease in workpiece temperatureand in sparking. Should sparkingbecome severe, the machining

process must be stopped immedi-ately.For economical operation, weardistribution is of decisive impor-tance, in addition to the wear markwidth. If the wear of each individual cuttertooth is examined, the distributionis found to be that shown in thehatched curve in fig. 4, if the cutterhas been used in one position on-ly. Conversely, if the cutter is dis-placed axially (shifted) followingeach machining cycle, new teethare continuously brought into theworking area. The wear is distrib-uted evenly over a greater numberof cutter teeth, and the productiv-ity between successive regrinds isincreased several times.

0,6

0,5

0,4

0,3

0,2

0,1

0

Wea

r m

ark

wid

th

3 6 10 20Module

Roughing of KHSS-E + TiN Finishing of KHSS-E + TiN

Carbide skiving hobs Solid carbide hob

Fig. 3: Wear mark width for different hob materials

Number of cutter teeth

0,6

0,5

0,4

0,3

0,2

0,1

0

Wea

r m

ark

wid

th B

0 80 160 240

mm

140120100 180 200 220604020

1600 gears with shiftingShift increment: 0.64 mm per clamping

40 gears without shiftingScatter

Fig. 4: Wear mark width when hobbing with and without shifting

The experienced craftsman in thetool grinding shop knows by look-ing at the wear mark width and thewear distribution whether a hobhas been used correctly from thepoints of view of quality assuranceand economy. If the recommendedvalues are substantially over- orundershot, this should always bereported to the production sector.

170

Requirements placed uponthe cutting surface grinder

Machine data:Table speed 250-600 mm/min withHSS tools, 80-150 mm/min withcarbide tools, according to moduleand qualityFeed 0.10-0.20 mm

General remarks:Radial/axial runout of the grindingdisk < 0.01 mm. A grinding diskform which is as rigid as possibleshould be selected. If possible, se-lect small contact surfaces. Emul-sions should be preferred to oil forthe grinding of carbide.

Vibrations between workpiece andtool impair the surface quality. Allstructural and clamping elementsin the torque transmission system

between the workpiece and thegrinding disk must be kept as rigidas possible in order to avoid vibra-tions.

Incorrect grinding conditions maycause the grinding disk facing todisintegrate. The facing is cleaned,i.e. the reside adhering to the fac-ing removed, by hand by means ofa no. 2 stone (e.g. from Winter).

Dressers for diamond grinding disksDressing facility with centrifugalbrakeSilicon carbide grinding disk e.g.3" x 1" x 1/2" / 37C60-N5VCBN diamond powder and dress-ing stone

Important:Carbide hobs are very sensitive toimpact. Protect the tooth tips dur-ing transport and storage.

Grindingstroke

Hob

Diameter 150 bis 200 mmRadial and axialrunout < 0,010 mm

Grinding disk

Pitch

Cutter arborDo not use a pressing mandrel.Avoid subjecting the hob toimpact and/or tension.

Feed motionup to0.20 mm

Return stroke

Fig. 5: Requirements placed upon the cutting face grinder

Grinding disks data:

HSS-hobs Carbide hobsGeometry: 1K222-150-2-3,3-50,8 K222-150-2-3,3-50,8Grain size: CBN151 D126Concentration: C125 C100 = 4,4 carat/cm3

Bond: 66 K-plus 888 RYA (synthe resin)Cutting speed: v = approx. 35 m/s v = 23–25 m/sCoolant: Oil, e.g. Shell Garia TC Emulsion e.g. Castrol S DC 83 Cooling oil pressure: (oil, e.g. Shell Garia TC)8–10 barCooling oil delivery:Approx. 100 l/min

171

Hob tolerancesThe flank cutting edges of the hobare formed by the intersection ofthe cutting faces with the reliefturned or relief ground helical sur-faces of the tooth flanks. Since during the hobbing process thetooth profile is formed by envelop-ing cuts and each individual envel-oping cut is generated by anothercutting edge of the tool, both theexact form of the cutting edgesand the relative position of thecutting edges to each other mustbe correct.

Regrinding on the cutting face al-ways creates new cutting edges.The working accuracy of a hobcan therefore be considerably im-paired by regrinding. The cuttingedges produced by regrinding onlyachieve their correct form and po-sition when the newly createdcutting faces correspond to theoriginal ones in form, position, or-ientation and pitch. Only if regrinding is faultless, willtool accuracy be kept identicalwith the new condition. The toler-ances of single-start hobs for purgears with involute teeth are quot-ed in DIN 3968. Depending on theaccuracy, a distinction is madebetween five quality grades,namely AA, A, B, C and D.

The standard contains the permis-sible deviations for 17 values to bemeasured. Five of these aloneconcern the cutting faces.

Regrinding must therefore be car-ried out so that the permissible deviations for the following meas-urement values are maintained:

■ form and positional deviation ofthe cutting faces,

■ individual and cumulative pitchof the gashes and

■ lead of the gashes.

For high-precision hobs it there-fore also goes without saying thatthe tolerances are checked onsuitable inspection instruments af-ter each regrind.

Radial runouts on the indicatorhubs and axial runouts on theclamping surfaces (item nos. 4 & 5 DIN 3968)

A prerequisite for all repair and in-spection operations on the hob isthat the grinding and measuringarbors are running true and thatthe indicator hubs of the hob runtrue to each other and to the arbor(figs. 6 & 7).

The aim is to superimpose the axisof the cutter screw with the instan-

taneous rotary axis and to checkthis by measuring the radial run-outs.

Fig. 6: Measurement of the radial runout on arbor and indicator hubs and ofthe axial runout on the clamping surfaces

Value to be measured

Radial runout at the two indicator hubs based on the axis of the bore

Axial runout at the clamping surfaces based on the axis of the bore

Qualityclass

Symbolof thedevia-tion

Tolerances in µm (1 µm = 0,001 mm) at module

over over over over over over over over over0,63 1 1,6 2,5 4 6,3 10 16 25to to to to to to to to bis1 1,6 2,5 4 6,3 10 16 25 40

frp

fps

Fig. 7: Permissible radial and axial runouts to DIN 3868

5 5 5 5 5 5 6 6 8

5 5 5 6 8 10 12 16 20

6 6 6 8 10 12 16 20 25

10 10 10 12 16 20 25 32 40

3 3 3 3 3 4 5 5 6

3 3 3 5 5 8 8 10 10

4 4 4 6 6 10 10 12 12

6 6 6 10 10 16 16 20 20

10 10 10 16 16 25 25 32 32

The highest points measured at the two indicator hubs must not be offset by more than 90°.

AA

A

B

C

D

AA

A

B

C

D

not determinded

172

If the high or low points of the twoindicator hubs lie in one axial planeof the cutter, the axis of the cutterscrew and the rotary axis are offset– the cutter does not run true.

If the high or low points of the twoindicator hubs are rotationally dis-played in relation to each other, therotary axis and the axis of thecutter screw are askew, i.e. thehob wobbles, and axial runout willalso be found.

When working with or on the hob,the user must know that he will on-ly achieve a sound tooth systemwhen cutting, faultless geometrywhen regrinding and an informa-tive and reproducible result whenchecking the hob if the radial andaxial runouts are kept as small aspossible.

It is therefore understandable thatthe permissible deviations for theradial and axial runouts are veryrestricted and that it is essential tomeasure them not only during theacceptance test of the hob, but al-so during the inspection after eachregrind.

Form- and positional deviationof the cutting faces(item no. 7 DIN 3968) The cutting faces are generated bythe straight lines which normallypass through the cutter axis of thehob (fig. 8a). In the cases wherethese straight lines pass in front ofor behind the cutter axis, they formnegative or positive rake angleswith the radials (fig. 8b, c). Accord-ing to the rake angle, the grindingwheel and the dressing diamondmust be set in front of or behindthe cutter axis by the cutting facedistance “u”. The same does ofcourse also apply to the heightsetting of the gauge stylus whenchecking the form- and positionaldeviation (fig. 9).

For roughing cutters with a posi-tive rake angle it is enough tomaintain the u-measurementspecified in the cutter markingwhen regrinding. In the case of fin-ishing cutters with positive or neg-ative rake angle, e.g. carbide skiv-ing hobs, the u-measurementmust be read off a regrinding dia-gram as a function of the cutter di-ameter.

This regrinding diagram applies tothe cutter diameter, the rake angleand the relief grinding operationand is supplied with the cutter (fig. 9).

Deviations from the specified valueof the cutting face distance resultin flank form and base pitch devia-

tions on the hobbed workpieces.

b)

–u

a)

+u

Fig. 9: Setting the gauge stylus for a) positive rake angle b) negative rake angle

a) b) –u c)+u

Fig. 8: Rake angle on the hob

173

A bigger rake angle (fig. 11) elon-gates the cutter tooth and reducesthe profile angle.

A smaller rake angle (fig. 12) re-sults in a shorter cutter tooth and agreater profile angle.

The cutting face form deviationscan be divided into three mainforms: crowned, concave and un-dulating.

The crowned cutting face form isfound when hobs which have agash lead are ground with straightdressed grinding wheels. Thiscrowning increases with shortergash lead, greater tooth heightand large grinding wheel diame-ters.

Hobs with crowned cutting faces(fig. 13) produce workpiece teethon which too much material remains in the tip and root area.These gears exhibit an unevenrunning behaviour and reduced load bearing capacity and aretherefore not accepted.

By choosing a grinding wheel witha smaller diameter the crownedform on the cutting face can be re-duced. A correspondingly crow-ned grinding wheel, manufacturedin or dressed to this shape, gener-ates a straight or even concavecutting face (fig. 15).

Cutting face offset distance u (mm)

189

188

187

186

185

184

183

–45,4 –45,8 –46,2 –46,6 –47,0 –47,4

Cut

ter

dia

met

er (m

m)

Drawing no.: 1-46276-01 relief groundDiameter = 189.52

u = –47,5Cutter no.:Module:

P25010

Fig. 10: Cutting face regrinding diagram for carbide skiving hobs

Fig. 11:Positional deviation of the cutting face a) Faulty, positive cutting face

position b) Elongated cutter tooth c) The workpiece tooth becomes

thicker at the head, tip contactThe broken-line contours indicatethe theoretically correct profile ofthe cutter- or workpiece tooth.

Fig. 12:Positional deviation of the cutting face a) Faulty, negative cutting face

position b) Shortened cutter tooth c) The workpiece tooth becomes

thinner towards the top

Fig. 13:Form deviation of the cutting facea) Faulty, crowned cutting face b) Crowned cutter tooth c) Concave flank form on the

workpiece tooth, tip and rootcontact

174

Hobs with a slightly concavecutting face produce workpieceteeth with tip- and root relief. Thisform of the deviation from the idealinvolute form is permissible and isin many cases even specified.

Undulating form deviations on thecutting face are generally causedby badly dressed grinding wheelsor worn or badly guided dressingdiamonds (fig. 16).

Pitch deveation of the gashesPitch deviations occur when thedistances of the cutting faces fromeach other are not uniform. Inpractice, individual cutting faceslie in front of or behind the as-sumed radial pitches, which pre-determine the exact specifiedpitch.

If the cutting face of a tooth is fur-ther back than the specified posi-tion, the tooth will generate a flankform which projects beyond thespecified form. A tooth with a pro-jecting cutting face will cut awaytoo much metal at the tooth flank.

Impermissible deviations from theindividual or cumulative pitch ofthe gashes may cause irregularlyor periodically occurring flank formand base pitch deviations on theworkpieces.

To this must be added that theflank form on the workpiecechanges when the cutter is shifted.The reason for this is that it is im-portant where the hob tooth afflict-ed by a pitch deviation, is situatedrelative to the profile forming zonein question and that the corre-sponding tooth changes its posi-tion when shifting.

Individual pitch of the gashes(item no. 8 DIN 3968)If the individual pitch deviations areto be determined by means of du-algauge measurement, the valuesread off must be converted as fol-lows: The measured values for acomplete cutter rotation are added,noting the + or – signs. The diffe-rences correspond to the indivi-dual pitch deviations.

The difference between two adje-cent individual pitch deviations isreferred to as a tooth to tooth pitcherror.

Fig. 15:Cutting face form error on a hobwith gash lead. Ground withstraight-dressed grinding wheel.

Fig. 14:Cutting face on a hob with gashlead. Ground with convex-groundgrinding wheel.


Form- and positional deviation of the cutting faces

Distance µ of the specifiedline from the axial plane(at rake angle 0° = zero)

Inspection diagram

Qualityclass




FfN

AA

A

B

C

D

cutting depth

specif. linie

toot

hro

ot

toot

htip

F fN

cuttingdepth

axial plane

specif. line

u

Fig. 16: Form- and positional deviation of the cutting faces to DIN 3968

10 10 12 16 20 25 32 40 50

12 16 20 25 32 40 50 63 80

25 32 40 50 63 80 100 125 160

50 63 80 100 125 160 200 250 315

100 125 160 200 250 315 400 500 630

175

The measurement can also be car-ried out by comparison with an in-dexing plate or with the indexingarrangement of a measuring ma-chine. The values read off repre-sent in comparison to the zero po-sition of the first gash the cumula-tive pitch of the measured gashes.The individual pitch deviationequals the difference of two adja-cent cumulative pitch deviations(fig. 17).

A summary of the computationprocesses is shown in fig. 18.

Cumulative pitch of the gashes(item no. 10 DIN 3968) The cumulative pitch deviation in-dicates the difference between ac-tual and required gash positions,one cutting face being used forreference.

The cumulative pitch deviationscan be read off directly, if the mea-surement is carried out with theaid of an indexing plate or with acorrespondingly accurate indexingarrangement.

The cumulative pitch deviationscan however also be calculatedfrom the two-dial measurement, ifindividual pitch deviations are ad-ded continuously.

The tolerances in DIN 3968 itemno. 10 relate to the total pitch devi-ation. The total pitch deviation ishere the distance between thebiggest positive and the biggestnegative cumulative pitch devia-tion (fig. 18).

1

2

3

Fig. 17:Pitch deviation of the gashesCutting face 1: theoretically correctly placed. Cutting face 2: pitch too short,tooth profile projects relative tothe profile on the cutting face. Cutting face 3: pitch too great,tooth profile set back relative tothe profile on cutting face 1.

Fig. 18: Computation diagram for individual pitch deviation, tooth to tooth pitch error and cumulative deviation from themeasured value readings of the two-dial measurement

Individual pitch deviation ftN is the difference between thereading of the 2-dial measurement and the correction value. The correction value is determined from the algebraic sumof all read values, divided by the number of pitches

1. Calculation of the correction value0 + 8 – 2 – 4 + 10 + 4 +2 – 2 = + 16

16/8 = + 2 correction value

2. Calculation of the individual pitch deviationindicated value – correction value = individual pitch deviation0 – (+2) = –2+8 – (+2) = +6–2 – (+2) = –4–4 – (+2) = –6+10 – (+2) = +8+4 – (+2) = +2+2 – (+2) = 0–2 – (+2) = –4

Tooth to tooth pitch error fuN is calculated by subtractingthe previous individual pitch deviation from the individualpitch deviation.

Cumulative pitch deviation FtN results from the additionof the individual pitch deviations.

Individual pitch deviation ftN, tooth to tooth pitch error fuN, cumulative pitch deviation FtN

Measured valuereadingCumulative pitchdeviation FtN

+2

+4

-2 0

+4 -2

+8

-4+10

+4

-2

+4

0

0

-6

+2

3

4

56

7

81

2

fuN

ftN+10

-100

0

-2

+4

0

-6

+2

+4

+4

= -2

= +4

= 0

= -6

= +2

= +4

= +4

+ (-2)

+ (+6)

+ (-4)

+ (-6)

+ (+8)

+ (+2)

+ ( 0)

+ (-4) = 0

+10

-100 ftN

ftN+10

-100

Measured Individual Tooth to tooth CumulativeCutting- value pitch pitch error pitchface reading deviation deviation deviation

ftN fuN FtN

1/2 0 –2 +8 –22/3 +8 +6

–10+4

3/4 –2 –4–2

04/5 –4 –6

+14–6

5/6 +10 +8–6

–26/7 +4 +2

–2+4

7/8 +2 0–4

+48/1 –2 –4

+20

(1/2) (0) (–2) (–2)16 : 8 = +2 –16 +16 –24 +24

176

Gash lead (item no. 11 DIN 3968) The tolerances for the deviationsin the gash lead are based on anaxially parallel measuring distanceof 100 mm and they apply equallyto hobs with a helix and to hobswith axially parallel gashes.

Directional deviations of the gash-es result in flank form-, base pitchand pressure angle deviations andin the case of diagonal hobbing al-so in tooth thickness and toothlead deviations.

The tolerances for the deviationsof the gash lead are relatively wide,since they only fractionally affectthe tooth geometry. It should betaken into account, however, thatthe effect on the directional devia-tions on tooth accuracy is greaterwith high than with low modules,since the length of the profile for-mation zone increases with themodule size (fig. 19).


Individual pitch of the gashes measured at halftooth height

Qualityclass




ftN

FtN

fHN

AA

A

B

C

D

42

1

ftN

ftN

1 2 3 4 5 6 7 8 910

1112

zero

Inspection diagram

Cumulative pitch of thegashes measured at halftooth height

4 2

1

3

12

11

10

Inspection diagram

FtN

1 2 3 4 5 6 7 8 910

1112

Gash lead over 100 mmcutter lengthbased on the reference cylinder

100 mm

fHN

AA

A

B

C

D

AA

A

B

C

D

± 10 ± 10 ± 12 ± 16 ± 20 ± 25 ± 32 ± 40 ± 50

± 12 ± 16 ± 20 ± 25 ± 32 ± 40 ± 50 ± 63 ± 80

± 25 ± 32 ± 40 ± 50 ± 63 ± 80 ±100 ±125 ±160

± 50 ± 63 ± 80 ±100 ±125 ±160 ±200 ±250 ±315

±100 ±125 ±160 ±200 ±250 ±315 ±400 ±500 ±630

20 20 25 32 40 50 63 80 100

25 32 40 50 63 80 100 125 160

50 63 80 100 125 160 200 250 315

100 125 160 200 250 315 400 500 630

200 250 315 400 500 630 800 1000 1250

± 50

± 70

±100

±140

±200

Fig. 19: Permissible deviations for individual pitch and cumulative pitch of the gashes as well as the gash lead.

177

Regrinding of roughinghobs

FETTE roughing hobs can be re-ground on any hob regrinding ma-chine.

The hobs are manufactured with apositive rake angle. The cuttingface is therefore off-centre. Thedeviation from the centre is indi-cated by the dimension "u", whichis engraved on each hob.

Prior to beginning regrinding work,offset the grinding disk from thecentre by the dimension "u".

On FETTE roughing hobs with a fi-nite gash lead, ensure that thegrinding disk is crowned, in orderto ensure straight cutting faces.

All FETTE roughing hobs have 8(10) teeth groups, each of whichhas 2 gashes, i.e. 16 (20) gashes intotal.

The gash pitch, the form and loca-tion of the gash, and the tip runoutmust be checked following eachregrind operation, for example ona universal pitch tester. The toler-ances should be within qualitygrade A to DIN 3968.

The hob is then ground withthe 8 (10) pitch disk.In this operation, the grinding diskis plunged to the depth of the largetooth gap.

This grinding operation must be performeduntil a smooth transition to the reground tooth tip portionof the 16 (20)-pitch is achieved.

Metal removal in the secondgrinding operation

In order to obtain a perfect gash pitch,the hob is first ground with the 16 (20)pitch disk. The grinding disk is plungedas far as the small tooth gap.

A gash pitch within quality grade A toDIN 3968 should be attained by thisgrinding operation.

Regrinding of roughing hobs

178

When regrinding, ensure that thecorrect grinding disks are select-ed. Particular care must be takenwhen grinding the 8 (10) pitch ow-ing to the greater gash depth. Thefeed rate should not therefore beselected too high, as local heat in-creases otherwise give rise tostresses. Grinding cracks may oth-erwise develop on the cutting face,or complete teeth may be chippedout.

On the basis of our experience, wetherefore recommend the follow-ing grinding parameters for the re-grinding of FETTE heavy-dutyroughing hobs:

FETTE heavy-duty roughing hobswith infinite gash lead (table 1) areground with CBN "B151 C125"grinding disks, with oil or emul-sion.

The circumferential speed of thegrinding disk should be approx. 35m/sec.

FETTE heavy-duty roughing hobswith finite gash lead (table 2) areground dry with ceramic bondedcorundum grinding disks.

For hobs up to approximately 200mm diameter: grain 36, hardnessG-H

For hobs over approximately 200mm diameter: grain 36, hardness F

The circumferential speed of thegrinding disk should be approxi-mately 30 to 35 m/sec.

After each final feed motion, grind-ing should be continued until thegrinding disk ceases to spark, i.e.is no longer engaged, in order toensure a well-ground cutting face.

In order to ensure an optimumlifespan for each hob, we rec-ommend that the hob be re-ground as soon as a wear landof 0.3 and at the most 0.5 mm isreached.

Feed (table speed): When roughing When finishing

Up to module 16 approx. 400 mm/min. 400 mm/min.

Up to module 16 approx. 350 mm/min. 350 mm/min.

over module 20 250 mm/min. 250 mm/min.

Up to module 16 approx. 0,20 mm 0,01 mm


over module 20 0,10 mm 0,01 mm

Feed motion in one pass:

Table 1: Roughing hob with infinite gash lead

Feed (table speed): When roughing When finishing

Up to module 12 approx. 6 m/min. 5 m/min.

over module 12 5 m/min. 4 m/min.


over module 12 0,02 mm 0,01 mm

Feed motion in one pass:

Table 2: Roughing hob with finite gash lead

179

Protuberance hobsGeneral principlesHobs with protuberance areroughing cutters whose profile dif-fers from the standard type to DIN3972 in that protuberances arepresent on the tooth tips whichproject beyond the straight flanksof the basic profile.

The purpose of the protuberanceis to create a clearance cut on thetooth roots of spur gears. This isnecessary when the teeth are tobe finish machined by shaving,grinding or by hobbing with a car-bide skiving hob.

The clearance cut on the gearflank is necessary to avoid a weak-ening of the tooth root through theformation of steps (fig. 1.2). It is al-so intended to make it impossiblefor the grinding wheel or the shav-ing wheel to strike the tooth root ofthe gear, since this would have ad-verse effects – through the deflec-tion of the grinding or shavingwheel – on the quality of the flankform. An additional load on thetooth root through grinding stress-es could then not be excluded. Aclearance cut shape as in fig. 1.3should be aimed at, which resultsafter removing the machining al-lowance in a smooth transition ofthe root rounding into the toothflank. This shape can however notbe achieved in practice, because,for example, a faultless positioningof the grinding wheel relative to theworkpiece would be very expen-sive and compensation of permis-sible dimensional deviations andpossibly occuring heat distortion isnot possible.

Fig. 1.4 shows a generally usedform of the clearance cut. Theclearance size – and therefore alsothe amount of protuberance – ex-

ceeds the machining allowance. Aresidual clearance remains on thefinished gear. Increasing the protu-berance does however also in-crease the root form circle diame-ter (dFf).

On straight spur gears, a distinc-tion must be drawn between theform circle and the effective circle.Tip and root form circles are cir-cles up to which the involute pro-file extends. If, for example, a spurgear has a tip chamfer, the tip formcircle diameter is the diameter atwhich the chamfer begins. The tipform circle diameter is thereforesmaller than the tip circle diameterof the gear by twice the radialheight of the chamfer. The rootform circle diameter is located at

the point at which the root round-ing or the undercut begin. It doesnot follow however that the flanksbetween the tip and root form cir-cle diameter actually engage withthe mating gear, i.e. are actuallyused; this depends upon the tipcircle diameters of the gear pair,the centre distance, and the pres-sure angle which result from theeffective tip and root circle diame-ter. The effective circles may havethe same dimensions as the corre-sponding form circles. The effec-tive tip circle diameter cannothowever exceed the tip form circlediameter, and the effective root cir-cle diameter cannot be smallerthan the root form circle diameter.When specifying the protuberanceit must be ensured that the root

Fig. 1.1

q

FS

Fig. 1.2 Fig. 1.3 Fig. 1.4

dFf

Fig. 1.5

machiningstep

allowance

pro-tuberance

180

form circle diameter is less thanthe effective root circle diameter;only then can it be ensured thatthe effective root circle diametercalculated for the requisite contactratio is actually present.

In some cases one dispenses dur-ing roughing prior to shaving com-pletely with the clearance cut, butmakes sure that the tooth root iscut out sufficiently for the shavingcutter no longer to touch the rootradius of the gear. The minimumand maximum sizes of the clear-ance cut are therefore limited bythe finishing method – shaving orgrinding, form and position of therelative tooth-crest track of theshaving cutter or the grindingwheel, permissible tooth thicknessdeviations etc. – and by theamount of hardening distortion onthe one hand and by the size of theroot form circle diameter on theother hand.

In accordance with the importanceof the root form circle diameter, thedetails given below will only dealwith the effects of the various tooland workpiece parameters on thesize of the root form circle diame-ter.

Generally, all the teeth/gear num-bers of a module can be cut withone protuberance profile.

The addendum of the tools shouldbe greater than 1.25 x m.

The amount of protuberance ismade up of the machining allow-ance and the residual undercut re-maining on the finished gear.These two values depend on thesubsequent machining process,on the size of the workpieces (pin-ion or ring) and on the distortionduring heat treatment. It is there-fore entirely possible that differenttool profiles are needed here. Aspecial design of the tool profilemay also become necessary atsmaller teeth/gear numbers (lessthan 15) and with large negativeprofile displacements.

The parameters for the root formcircle diameter are on the work-piece: module, pressure angle,number of teeth, helix angle andprofile displacementon the hob: addendum, tip circleradius, amount of protuberanceand protuberance angle.

To ensure that no misunderstand-ings will occur in the text belowabout the meaning of the termsused, these terms will be definedwith the aid of the illustration.

Terms used on the basic hob profileFig. 2.1 shows the basic hob pro-file. This is complemented by thedefinition of the terms used in con-junction with the basic profile.

An example showing the differentdimensions of a basic hob profileis given below. This protuberanceprofile has been particularly suc-cessful in many cases.

öaP0 = 0,40 · möfP0 = 0,2 · mαP0 = 20°αprP0 = 10°qP0 = 0,09 + 0,0125 · mprP0 = 0,129 + 0,0290 · m

� module 7(u = 0,039 + 0,0165 · m)

prP0 = 0,181 + 0,0235 · m � module 7(u = 0,091 + 0,011 · m)

haP0 = 1,4 · mhP0 = 2,6 · msP0 = m · π

–2 · qP0

2 cos αP0

öaP0 = tooth tip radiusöfP0 = root fillet radiusαP0 = profile �αprP0 = protuberance angleqP0 = machining allowanceprP0 = amount of protuberancehprP0 = height of protuberancehaP0 = addendumhP0 = profile heightsP0 = tooth thicknessu = root clearance cut on the

finished gearu = prP0 – qP0

hP0

haP0

hprP0

αprP0

öaP0

prP0

qP0

sP0

αP0

öfP0

Fig. 2.1: Basic hob profile in the normal section

protuberanceflank

181

Calculation of the rootform circle diameter

The root form circle diameter canbe calculated using the softwaredeveloped by FETTE.

In theory, the root curve comprisesthe region generated by the toothtip radius and that profiled by theprotuberance flank. The secondregion is an involute profile, inwhich the involute intersects theroot curve of the main involute.The intersection is determined bythe root form circle diameter. In themajority of cases examined, the in-volute region of the undercut curveis not present, however, and theroot rounding generated by thetooth tip radius forms the intersec-tion with the main involute.

It has proved practical to plot thecomputed root curve and to ana-lyse the result of the plot. Theintersection of the root curve withthe main involute following ma-chining is of decisive importancefor evaluation of the root form cir-cle diameter. On gears which havebeen hardened and ground, itmust be considered that hardeningdistortion and incorrect centring ofthe grinding disk result in differentvolumes being ground off theroughed tooth flank. This may re-sult in the root form circle diameterbeing displaced from the theoreti-cal dimension arrived at by calcu-lation. In such cases, it must beensured that an adequate reserveremains between the calculatedroot form circle diameter and therequisite root form circle diameter.

Practical experience has shownthat gears with a small number ofteeth and only a small positive pro-file displacement may lead toproblems if the root form circle di-ameter is too large. The result canbe improved by a smaller protu-berance quantity, a larger adden-dum, or a smaller tooth tip radiuson the basic hob profile.

(1) dNf1 = (2 · a · sin αwt – d2Na2 – d2

b2)2+ d2

b1

(2) dNf2 = (2 · a · sin αwt – d2Na1 – d2

b1)2+ d2

b2

(3) cos αwt =(z1 + z2) · mt

· cos αt2 · a

(4) mt =mn

cos β

(5) tan αt =tan αn

cos β

(6) db = z · mn · cos αt

cos β

Tooth gap profile in the face plane

If the root form circle diameter or the effective root circle diameter are notspecified in the workpiece drawing, the effective root circle diametermust be calculated from the gear pair data according to the following for-mulae:

Calculation of the effective root circle diameter

In formulae (1) and (2), either thetip circle diameter, or if a chamferis present, the tip form circle diam-eter of the corresponding matinggears, are employed as the effec-tive tip circle diameter.

Where:dNf1, dNf2 = effective root circle diameterdNa1, dNa2 = effective tip circle diametera = centre distanceαwt = operating pressure

angledb = base diameterz1, z2 = number of teethmt = real moduleαt = real pressure angleβ = helix angle

machiningallowance

root form circle onthe gear followingmachining

root form circle onthe finished gear

182

Wear phenomena on the hobThe cutting forces

The hobbing process has beenknown for over a century. For al-most as long, people in the tradehave grappled with the problem ofhob wear.Whereas in turning and milling themetal cutting process can be char-acterized by 3 values, namely thecutting speed “v”, the feed “fa”and the infeed “a”, two specialpoints must be taken into accountin hobbing. In contrast to turning and milling,considerably more parameters acton the cutting process. These parameters result from themanufacturing process and be-yond that from the geometry of thetool and the workpiece.

The effects arising from the cuttingprocess cannot easily be ex-plained by the interrelationship ofthese parameters.Thämer (1) found already duringhis studies of the cutting forcesduring hobbing that the cuttingforces occurring on each toolcutting edge can be calculatedfrom the cross-sectional area ofcut involved. Calculating the cross-sectional ar-eas of cut is therefore very impor-tant in this connection. In addition to this, knowing thecrosssectional areas of cut occur-ring in hobbing also makes it pos-sible to forecast the tool wear andto assess the suitability of specificcutting materials.

The chip thicknesses on smallmodules and the chip lengths canbe influenced only slightly by thecutting speed and the feed rate,and are determined principally bythe geometric dimensions of thehob and the workpiece.

Fig. 1. shows the cutting forcesoccurring on the individual cuttingedges for three different axialfeeds, as they arise when conven-tional hobbing a spur gear. At the entering cutter side one cansee that the cutting forces initiallyrise steeply, after which they grad-ually decrease up to the end of theengagement length. Apart from the first working cuttingedges it is found that almost equalcutting forces are present on virtu-ally all other cutting edges despite

different axial feeds. The reasonfor this phenomenon is that thechip shapes at these cutting edgesare determined almost exclusivelyby the cutter- and workpiece size. It can also be seen that the num-ber of cutting edges taking part inthe metal removal increases withfaster axial feed. Whereas in our example only 13cutting edges work on the entryside of the cutter at an axial feed of2 mm per work rotation, this be-comes 17 cutting edges already at4 mm feed per work rotation and

finally 20 cutting edges at 6 mmfeed per work rotation, i.e. about50 % more than at a feed of 2mm.

acc. to Thämer, Aachen Polytechnic

Workpiece

leavinggear flank

enteringgear flank

infeedingcutter flank

outfeedingcutter flank

Cutter

500

400

300

200

kp

+20 +15 +10 +5 ±0 – 5

Cutting edge no.

100

0

fa = 2 mm/WUfa = 4 mm/WUfa = 6 mm/WU

workpiecemzßo

===

5 mm400°

hobdki

γo

===

100 mm102°30'

conventionalhobbing

Fig. 1: Effect of the feed on the cutting force in hobbing

Mai

n cu

ttin

g fo

rce

PH

183

These cutting force diagrams alsoreveal that in hobbing the individu-al cutting edges carry differentloads, which naturally results in anon-uniform wear pattern. The ef-fect of the axial feed on the maxi-mum main cutting force is shownin fig. 2. The cutting force increas-es in the present example degres-sively up to a feed of 3 mm perwork rotation. Over 3mm feed a slightly progressive in-

crease in cutting force is found,which changes at 6 mm into aslightly degressive course. At 10mm feed the cutting force is ap-proximately double that at 4 mmfeed.

The chip thickness which have tobe parted off from the individualcutting edges during hobbing areshown in fig. 3. One can see thatthe chip thickness increase linearyfrom the point of contact towardsthe entering cutter side. They arealmost the same for all axial feedsand only exhibit certain deviationsat the first working cutting edges.At a feed of 10 mm per work rota-tion the maximum chip thicknessis over 0.5 mm. At a feed of 6 mmper work rotation a maximum chipthickness of about 0.45 mm oc-curs in the present case, whereasat a feed of 4 mm per work rotationthe maximum chip thickness be-comes 0.35 mm and at a feed of2 mm per work rotation it becomesabout 0.28 mm.

acc. to Thämer, Aachen polytechnic

conventional hobbing

workpiece mzßo

===

5 mm400°

cutter dki

γo

===

100 mm102°30'

s = 10 mm/Work rot.

fa = 6 mm work rot.0,5

0,4

0,3

0,2

mm

25 20 15 10 5 0

Max

imum

chi

p t

hick

ness

hm

ax

Tool cutting edge no.

0,1

0

fa = 4 mm workrot.

fa = 2 mm workrot.

Fig. 3: Effect of the axial feed on the chip thicknesses

800

600

400

200

kp

0 2 4 6 8 10

Main cutting force PH

Axial feed fa [mm/work rot.]

calculated valuesmeasured values

acc. to Thämer, Aachen polytechnic


workpiece mzßoCk

===

5 mm400°

cutter dkgi

γo

====

100 mm1102°30'

45

Fig. 2: Effect of the axial feed on the maximum main cutting force

184

Ziegler (2) demonstrated that thecutting speed has no appreciableeffect on the main cutting forces (fig. 4). With all materials, the maincutting forces remain almost con-stant at cutting speeds above 50m/min., whereas they rise whenthe cutting speeds decrease. Therise is somewhat steeper duringconventional hobbing than withclimb hobbing. The decreasingtrend is found up to about 50m/min., independently of the mill-ing process and the gear data.

At higher cutting speeds thecutting forces can not be reducedany further. This was confirmedparticularly by the use of a module1.5 carbide hob. For the feed, avalue was chosen with all cutterswhich corresponds numerically toabout 2/3 of the module.The maincutting forces depend apart fromthe machining conditions on theworkpiece dimensions, in particu-lar the number of teeth and profiledisplacement. They are also af-fected, however, by the number ofsegments of the cutter and partic-ularly by the latter's true running.

Ziegler (3) studied, among otheraspects, also the effect of the leaddirections of cutter and workpieceon the circumferential force andthe coordination of this circumfe-rential force with the direction ofrotation of the table. If the lead di-rections of cutter and workpiececorrespond, the component fromthe main cutting force opposes the workpiece rotation. This means that the circumferen-tial force presses the machine ta-ble and therefore the indexingworm wheel more strongly againstthe drive worm. No additional ta-ble motions can then take place. Ifon the other hand the lead direc-tions are opposite, the componentfrom the main cutting force acts inthe direction of rotation of the ta-ble.

If the circumferential force actsagainst the table rotation, it hasvirtually no influence on the latter.If it acts in the same direction,however, the table on conventionalhobbing machines is subjected tomovements at the segment en-gagement frequency, the magni-tude of which corresponds to theplay between the worm and theworm gear, and which may lead toa rough, rippling machining pat-

tern along the tooth flank to bemachined.

acc. to Ziegler, Aachen polytechnic

400

300

200

kp

20

Mai

n cu

ttin

g fo

rce

PH

100

040 60 80 100 120 140 160 180 m/min 220

Cutting speed V

m = 5 mm

m = 3 mm

m = 1,5 mm

Material Ck 45infeed 2 x m

spur teethprofile displacement x = 0

z = 31,

z = 53,

z = 26,

z = 26,

fa = 3 mm/U,

fa = 2 mm/U,

fa = 1 mm/U,

fa = 1 mm/U,

conventionalhobbing,conventionalhobbing,climbhobbing,climbhobbing,

HSS-hob,

SS-hob,

SS-hob,

carbide-hob,

dK =

dK =

dK =

dK =

100 mm,

80 mm,

63 mm,

40 mm,

m =

m =

m =

m =

5 mm

3 mm,

1,5 mm,

1,5 mm,

Gear data Hob datai =

i =

i =

i =

10

10

12

15

Fig. 4: Effect of the cutting speed on the main cutting forces

QFA

14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 –1 –2 –3 –4 –5 –6 –7

QFiQK

QK

QFAQFi

cent

re li

ne

Roughing zone Area of the involute formation

0,25

mm

2


500

kp

14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 –1 –2 –3 –4 –5 –6 –715Entering zone Leaving zone

mziAtv

Ckfam

======

=

4 mm34910240 m/min

1

45

Fig. 5: Cross-sectional areas of cut and cutting forces in the case of a work-piece with only one tooth space

185

The cross-sectional areasof cutTo study the wear behaviour ofhobs it is necessary to know thecross-sectional areas of cut for theindividual cutter teeth. Already thestudy by Ziegler (4) of the cuttingforces presupposed a knowledgeof the cross-sectional areas of cut.

The main cutting force and thecross-sectional area of cut are inhobbing different for each individ-ual tooth of the cutter. This makeshobbing quite different from othermachining processes, where an in-crease in feed immediately pro-duces a change in chip thickness.In fig. 5, the measured cuttingforces below and the calculatedmaximum cross-sectional areas ofcut above are plotted one abovethe other for a particular gear. Thecross-sections are sub-divided ac-cording to the cutting edges onthe tip and on the two flanks of thecutter teeth. It can be clearly seenthat in the roughing zone thecross-sections on the cutter tip faroutweigh those of the flanks. Toobtain the values for this figure,gears with only one tooth spacewere cut, so that the cross-sec-tional area of cut could be coordi-nated with the correspondingcutting force. After the connectionbetween cutting force and cross-sectional area of cut has been es-tablished, the task was to definethe wear forms and their causeson the cutter tooth.

Wear criteriaOn the hob tooth a distinction ismade between flank wear, cuttingedge rounding, chipping and pit-ting (fig. 6). To be able to study thewear behaviour of hobs realistical-ly, the tests were carried out incooperation with the industryunder mass production conditions.In fig. 7 the wear mark width "B"refers to the flank wear. The uppercurve of the figure shows the wellknown characteristic with an in-itially degressive rise, which is fol-lowed by an almost linear section.As the number of units increases,the rise becomes progressive. Inthe lower curve the wear is basedon the number of units cut. A mini-mum is then found and conse-quently a specific value for thewear mark at which the propor-

tional tool costs become minimal.If one looks at the wear of each in-dividual cutter tooth, a representa-tion as shown in fig. 8 results.Here, 40 gears were cut in a quitespecific cutter position.

The roughing work is in the casealways carried out by the samecutting edges, so that maximumwear occurs on a few cutter teethwhich have to be reground al-though other teeth show little or nowear. With axial cutter displace-ment (hob shift) on the other hand,other cutting edges move into themaximum stress area during eachwork cycle, so that a large numberof cutter teeth have a virtuallyidentical wear mark width.

cutting edgerounding

chipping

pitting

flank wear (fillet)

back wear

Fig. 6: Types of wear on the hob tooth

Wea

r p

er p

iece

Wea

r m

ark

wid

th B

0,008

0,006

0,004

0,002

0

Number of gears

1,0

0,8

0,6

0,4

0,2

0

0 80 160 240 320

mm

Stck.

mm/piece

40 120 200


Fig. 7: Flank wear (back wear) as a function of the number of units

186

The effect of the cutting conditionson tool wear is of particular inter-est. The dependence of the wearmark width "B" on the feed isshown in fig. 9. With small feedsthe chip thicknesses and thecutting forces are small, whereasthe number of starting cuts is high.With greater feed the cross-sec-tional areas of cut increase, andwith them the cutting edge stressand temperature, whereas thenumber of starting cuts decreases.

If one looks in fig. 10 at the meanwear as a function of the feed, onecan see that the increase in wearat greater feed is so little, that thereduction in cutting time achievedby increasing the feed is muchmore important than the onlyslightly worse tool wear. It can bededuced from this that in the areastudied an increase in feed is notlimited by the wear, but by the at-tainable gear quality, particularlyas regards the feed markings. Incontrast to the feed, the cuttingspeed affects tool wear far more.We shall come back to this fact lat-er.

Hoffmeister (5) classified the ef-fects on hob wear according tocutter, machining and gear criteria.According to his findings, the wearis influenced by the diameter ofthe tool, the number of starts ofthe tool, and the number of seg-ments. Further influencing factorsare the tip radius, the relief angle ofthe cutter profile, the rake angle ofthe cutting edges, and finally fac-tors such as the tool design andmaterial.

The wear is influenced strongly bythe following machining condi-tions:

The feed "fa", the shift "SH", the in-feed depth "a", the cutting speed"v". Other factors affecting wearare the hobbing process, the con-dition of the hobbing machine, themounting and clamping of tool andworkpiece and finally the coolant.


0,6

0,5

0,4

0,3

0,2

0,1

0

Wea

r m

ark

wid

th B

0 40 80

mm

706050 90 100 110302010

160 gears with shifting(Shift distance: 0,64 mm/clamping)

acc. to Ziegler, Aachen

40 gears without shiftingscatter range

polytechnic

Fig 8: Wear mark width when hobbing with and without shifting


0,6

0,5

0,4

0,3

0,2

0,1

0

Wea

r m

ark

wid

th B

40 80

mm

60 10020


fa = 5 mm / w.p.rev.fa = 4 mm / w.p.rev.fa = 3,2 mm / w.p.rev.

Fig. 9: Wear mark width as a function of the feed

4 6mm w.p. rev.2 3

0,5

0,4

0,3

0,2

0,1

0

Wea

r m

ark

wid

th B

mm

acc. to Ziegler, Aachen polytechnic Feed fa

Fig. 10: Wear mark width as a function of the feed

187

The gear affects hob wear throughits diameter, the module size, thehelix angle of its teeth, the profiledisplacement x � m and throughthe gear width. The effect of thegear material on tool wear mustnot be forgotten either. This largenumber of factors affecting wearcan be divided into two groups.

1. Values which from the geometryof the teeth and the cutter deter-mine the length of the cutting arcand the chip thickness.

2. Technological effects, such ascutting speed, cutting material/tool pairing, cutting edge geome-try, use of cutting oil etc.

Engagement conditions

Hoffmeister (6) distinguishes be-tween the cutter entering and leav-ing sides, which are separated bythe central tooth, and between aprofile generating zone and a pre-cutting zone. The central tooth isthe cutter tooth which is situatedin the axial hob/gear crossingpoint. The central tooth lies in thecentre of the profile generatingzone. The pre-cutting zone de-pends on the external shape of thehob. This will be greater with cylin-drical tools than with tools whichhave a tapered or round leadingend.

To be able to calculate the lengthof the cutting arc and the chipthickness, it was necessary to de-fine the tool/workpiece penetrationcurve accurately.

In the tool/workpiece penetration(7) the penetration curve forms acutting ellipse on the cylindricalgenerated surface of the gear. Theposition of this ellipse depends onthe crossing angle of the two axes.In addition, the shape of the ellipseis determined by the sizes of thehob and the gear.

The essential point for assessingthe correct setting of the tool onthe hobbing machine is the projec-tion of this cutting ellipse in aplane which is parallel to the hob-bing machine. If the designations

given in fig.12 are used, the formu-lae presented in fig. 13 can be de-veloped. With the help of theseformulae a graphic drawing can beproduced which makes it possibleto assess the tool setting (fig. 14).

In the penetration ellipse we obtaina maximum value for the Y-axis.The projection of this value ontothe cutter axis shows the enteringzone for conventional hobbing. Ifthe curve is traced beyond Ymax.up

to a value Y = Ymax. feed per work-piece rotation, we obtain a pointon the curve from which the enter-ing zone for climb hobbing can bedetermined.

The projection of this curve loca-tion onto the cutter axis corre-sponds to the cutter length for theentering zone on helical gearswhen the tool and the gear havethe same direction of lead. If a toolwith a tapered lead is brought intothe consideration, knowledge of

Gear

Hob

Fig. 11: Principle of the penetration curve

A

h

aR

x b

c ß

g

f

L

e

d y

RF

Fig. 12: Proportions of the penetration curve

188

the penetration line is importantparticularly with large gears.

Fig. 15 shows how the approachlengths become decidedly shorterin the tool with tapered lead ascompared with the cylindrical tool.It should here be pointed out thatthe angle and shape of the leadshould also be carefully matchedto the conditions, to prevent over-loading the entering teeth, be-cause this would again lead to pre-mature wear. Backed by theknowledge of the hob positioningon the hobbing machine the wearstudies could now be systemati-cally carried out (fig.16).

In the wear measurements onemakes a distinction between thetip wear, here identified by "BK",the wear of the outgoing cutterflank called "BA", and the wear ofthe approaching flank called "BZ".The outgoing cutter flank is theflank whose relative motion is thesame as that of the leaving gearflank. The approaching tool flank isthe cutter flank towards which thegear flank moves during the gener-ating motion. When comparing the

fa = 6

starting length for


starting lenght for climb hobbing

hob axis

3,7 m

gear centre line

conventional hobbing:Ø 210 x 175 / 229 x Ø 100lead length 40 mmstarting length 138 mm

Climb hobbing:dia 210 x 225 / 279 x dia 100lead length 90 mmstarting length 188 mmfeed fa = 6 mm

Roghing hobwith taper lead angle 8°31'57''

f = c · tan β

RFhRββ0

γ0

WerkzeugradiusZahnhöhe = FrästiefeWerkstückaußenradiusβ0 – γ0Schrägungswinkel derVerzahnungSteigungswinkel desWälzfräsers

=====

=

A = RF – h + R

b = A – a

e = x · tan β

y = d + e

L = f + g

a = R2 – x22

c = RF2 – b2

2

d = ccos β

g = xcos β

Fig. 15: Penetration curve for a hob with lead.Gear: module 10, 405 teeth, helix angle 29°

feed per work rotation

cutting zone for conventional hobbing

cutting zone for climb hobbing

x

y

hob axis

gear

axi

s

Fig. 14: Tool/gear penetration

Fig. 13: Calculation of the penetration curve

189

results of the wear measurementson the hob which had been usedfor climb hobbing with the wearmeasurements on the hob whichhad been used for conventionalhobbing, the direction of rotationof the gear blank and the directionof rotation of the cutter were keptthe same.This means that when the wearcurve is drawn, the central tooth(called 0) lies in the wear diagramfor climb hobbing on the right-hand diagram side, whereas thecentral tooth for conventional hob-bing is situated on the left-hand di-agram side. It can be seen fromthe diagram that in climb hobbingmore teeth participate in the en-tering cut than is the case withconventional hobbing. The stresson the tip cutting edges is withconventional hobbing only slightlygreater than with climb milling.This is explained by the fact thatfewer hob teeth are engaged inconventional hobbing than inclimb hobbing. The stress andtherefore the wear of the ap-proaching cutter flank is highestwith climb milling. This is particu-larly the case in the entering cutterportion with the greater cutting arclength.

The main stress in conventionalhobbing is borne by the teeth ofthe leaving cutter flank. Here, rela-tively severe wear takes placeeven in the profile forming zone.This is explained by the fact that inconventional hobbing the greatercutting arc length still prevailseven in the profile forming zone. Inclimb hobbing the working rangeis therefore situated on the cutterentering side, in conventional hob-bing on the leaving side.

The wear diagrams can also beinterpreted as follows: In climbhobbing the effective relief angle issmaller on the outer cutter toothflank than on the inner one, whichis why the maximum wear on theouter cutter tooth flank can becaused by the effect of the smallerrelief angle. This explanation is notvalid for conventional hobbing. Al-though flank wear also occurs onthe outer cutter tooth flank, the lat-ter has the greater effective reliefangle. For this reason the effect ofthe relief angle cannot be the onlycause of the flank wear. To find a

credible explanation for the originof the flank wear, further studieswere necessary.

Chip geometryin hobbing

Sulzer (8) drew up a computationprocess which accurately deter-mines the geometry of the individ-ual chip. For this purpose he stud-ied the chip formation in a numberof cutting planes during the pas-sage of a cutter tooth. The com-puter now supplies for eachcutting plane numerical valueswhich correspond to the chipthickness formed. These values –shown diagramatically – producehorizontal lines for the cuttingplanes with the designations 1 to 6(fig.18). To gain an overall impres-sion of the size relationships, thescale of the chip forming cross-sections is given on the left-handside of the diagram. The designa-tions for the cutting zones are situ-ated underneath the base line. Thesection AB corresponds to the en-tering cutter flank. Section BC cor-responds to the tooth tip width.Section CD corresponds to theleaving cutter flank. When the val-ues supplied by the computer forthe chip forming cross-sections

are represented by the plotter, weobtain a picture of the chip cross-sections on the cutting planes.This plotter image provides a rep-resentation of the chip cross-sec-tions and the chip outline.

If this calculation of the chip cross-section is carried out with a repre-sentation for all meshing hobteeth, one obtains an overview ofthe chip forming cross-sectionsand the chip forms in hobbing(fig. 19). Furthermore one can rec-ognize the stresses on the individ-ual hob teeth and the varying loadwithin the tooth under observation.

When simulating the individualhobbing processes such as con-ventional hobbing and climb hob-bing and hobbing in the same or inthe opposite direction, the com-puter supplies different chip form-ing cross-sections and forms.Hobbing in the same directionmeans that the direction of startof the hob and the tooth lead ofthe gear are unidirectional, i.e. acutter with right-hand start ma-chines a gear with right-handedteeth and a cutter with left-handstart machines a gear with left-handed theeth.

In the case of hobbing in the oppo-site direction a cutter with right-hand start machines a gear withleft-handed teeth and a cutter with

+25 +20 +15 +10 +5 0 –5 +5 0 –5 –10 –15 –20

1,0

0,8

0,6

0,4

0,2

0

mm

Climb hobbing conventional hobbing

BKBABZ

= tip wear= wear on the leaving flanks= wear on the entering flanks

BA

BZ

BK

BA

BZ

BK

acc. to Hoffmeister, Aachen polytechnic

Fig. 16: Wear distribution on the hob

190

left-hand start machines a gear with right-handed teeth. This com-putational consideration of chipforming geometry confirmed whatThämer (1) had already found inhis studies. Flank wear takes placeprecisely at those transitions fromtool tooth tip to tool flank whichare no longer actively participatingin the metal cutting process. Hestates: "In this case the toolcutting edge which just at this cor-ner no longer removes a chip ex-hibits particularly large wear markwidths, which in turn makes itclear that no direct connection ex-ists between chip thickness andtool wear."

The plotter images produced bySulzer's method (9 and 10) confirmthis assumption. Sulzer's studiescovered mainly the wear behaviourof carbide hobs. Instead of flankwear, he found micro-chipping inthis area. Using the scanning elec-tron microscope, he studied theleaving flanks for chip traces andfound pressure welded depositson the flanks. He states: (11 and12) "The different dircection of thecutting traces and of the streaksindicates that these streaks arecaused by the chips being re-moved. They occur at those pointson the tooth flank which do notcome into engagement with thecutter tooth concerned, i.e. thereis generally a gap between thecutting edge and this flank area."

cutting planes

acc. to Sulzer, Aachen polytechnic

1

2

6

3

4

5

entering flank leaving flanktipA B C D

0,2

mm

1 mm

1 m

m

Fig. 18: Determination of the chip forming cross-sections

workpiece

hob

cutting planes


531 2

46

Fig. 17: Determination of the chip forming cross-sections

the other workpiece flank, where itis welded on. As a result of thecutting motion of the cutter tooththe pressure welds are separated,but are formed afresh by the flow-ing chip. In addition, a workpiecerotation takes place during thecutting motion. This means thatthe workpiece flank moves awayfrom the leaving tool flank. It is thisrelative speed at which the chip ispushed from the cutting face overthe cutting edge. This producestensile forces on the cutting edge

The collision between chip andworkpiece flank can be explainedby the chip form and the chip flow.The cutting process commences atthe leaving flank near the cuttertooth tip. At this stage it can stillcurl freely. After that the tip area ofthe cutter tooth moves into en-gagement. Because of the compli-cated shape and the tight spaceconditions in the tooth gap the chipcan no longer curl freely. It is atthe end pushed by the enteringflank beyond the cutting face to

191

throughout the gear train. It is fea-sible that flank wear could be re-duced by alternate cutting of thetip flanks. Long-term tests in thisfield have not yet been completed,so that no definite statement canas yet be made about the successof this measure.

1 2 3

4 5 6

7 8 9

13 14 15

10 11 12

which can in the case of carbidelead to chipping. When machiningwith high-speed steel, squeezingforces occur at this point whichproduce the greater free flankabrasion. This phenomenon alsooccurs with hobbing in the oppo-site direction, but not to such anextent.

It is therefore easy to regard hob-bing in the opposite direction as a

cure-all for flank wear. With hob-bing in the opposite direction thecircumferential force acts in the di-rection of rotation of the table.Since this circumferential force fa-vours the flank clearance betweenthe worm and the indexing wormwheel, it creates a disturbance inthe indexing gear unit with thesegment engagement frequency.This results in chatter markings onthe gear flanks and vibration

Fig. 19: Different chip forming cross-sections on the meshing hob teeth

References1) Thämer, Investigation of the cutting

force in hobbing. Research report,Aachen polytechnic, 1964

2) Ziegler, Determination of optimumcutting force conditions for hobbing. Re-search report, Aachen polytechnic, 1965

3) Ziegler, Cutting forces when hobbingstraight- and helical tooth spur gears,Research report, Aachen polytechnic,1966

4) Ziegler, Study of the main cutting forcewhen hobbing spur gears. Thesis, 1967, at the Aachen polytechnic

edge- and cutting action geometry. Re-search report, Aachen polytechnic, 1971

10) Sulzer, The prevention of chipping oncarbide hobs. Research report,Aachen polytechnic, 1972

11) Sulzer, Causes and prevention ofchipping when hobbing with carbidetools. Research report,Aachen polytechnic, 1973

12) Sulzer, Performance enhancement incylindrical gear manufacture through aprecise understanding of metal removalkinematics.Thesis, 1973, at the Aachen polytechnic

5) Hoffmeister, Wear life studies andhobbing with carbide. Research report,Aachen polytechnic, 1968

6) Hoffmeister, General wear studies inhobbing. Research report,Aachen polytechnic, 1969

7) Hoffmeister, About wear on hobs.Thesis, 1970, at the Aachen polytechnic

8) Sulzer, Optimum design of hobs and useof carbide in hobbing. Research report,Aachen polytechnic, 1970

9) Sulzer, State and development of car-bide hobbing, study of the cutting


192

Recommended values for the powerrequirement for involute roughing:

Where:

Rm = tensile strength (N/mm2)Vc = cutting speed (m/min)hm1 = mean tip chip thickness

(mm) Value ≈ 0.1 mmz = number of gashes / 2fz = tooth feed (mm)a = radial feed (mm)

(cutting depth)D = tool diametervf = feed (mm/min)Qspez. = power factor

(cm3 min · kW)(Value taken from table)

Formula applicable for full profiledepth:

P(kW) = 3,19 · Mod.2 · vf

1000 · Qspez.

vf = fz · n · z

fz = hm1

Involute gear cutter with indexable insertsInvolute gear cutter

With carbide indexable insertsFor roughing and finish-milling ofinternal and external straight spurgears, and for worm thread andrack cutting

Involute roughing hob

With tangentially arranged carbideindexable inserts, pressure angle20°, basic profile IV to DIN 3972.

These tools permit an economicalproduction process for the rough-ing of large gears.

Under certain conditions, they of-fer considerable advantages forthe roughing of high-strength gearmaterials (Rm > 1000 N/mm2).

The tooth gaps are roughed trape-zoidally with straight-sided flanks.The basic tool profile correspondsto BP IV according to DIN 3972.Other profiles can be supplied asnon-standard versions upon re-quest.

RequirementsThe user of carbide cutting materi-als enables considerable increasesin performance to be achieved. Apowerful and sufficiently rigid ma-chine is however essential. Millingusing the plunge process must al-so be possible. Preference shouldbe given to climb milling.

Involute finishing hob

This method can be employedwhere medium quality require-ments are placed upon the gearquality; quality grade 9 to DIN3962/68 can be attained.

This process is often employed forthe manufacture of ball bearingslewing rims (control gear for jibcranes), and for the profiling of ex-ternal and internal gears.

Design featuresContinuous indexable insertcutting edges enable the entireprofile height to be finish-milled.Problematic transitions are thusprevented from leading to band-ing.

The indexable inserts can be in-dexed twice. A further regrind ispossible on one side. The cuttingedge form is determined by thetooth gap profile specified by thecustomer. It is dependent to alarge degree upon the number ofgear teeth and the profile displace-ment factor.

aD

180500

600

700

800

900

1000

1100

1200

1300

1400

1500

170 160 150 140 130 120 110 100 90 80 70Vc (m/min)

Rm

(N

/mm

2 ) M = 6M = 10M = 14M = 18M = 20M = 22

Recommended value (vc - m/min)

Material Rm/UTS Power factor (N/mm2) Qspez. cm3/min x kW

Unalloyed structural steel – 700 22 – 24

Free cutting steel – 700 22

Structural steel 500 – 900 18 – 20

Heat-treatable steel, medium strength 500 – 950 18 – 20

Cast steel – 950 18 – 20

Case hardening steel – 950 18 – 20

Stainless steel, ferritic, martensitic 500 – 950 16 – 18

Heat-treatable steel, high-strength 950 – 1400 13 – 18

Nitriding steel, heat-treated 950 – 1400 13 – 18

Tool steel 950 – 1400 13 – 18

Stainless steel, austenitic 500 – 950 18 – 20

Grey cast iron 100 – 400 (120–600 HB) 28 – 35

Alloyed grey cast iron 150 – 250 (160–230 HB) 22

Nodular cast iron 400 – 800 (120–310 HB) 24

Malleable cast iron 350 – 700 (150–280 HB) 24

193

Catalogue number indexCat.-No. Page

2412 66

2422 67

2432 67

2442 68

2444 69

2472 70

2452 71

2462 72

2500 88

2512 89

2513 90

2521 91

2522 92

2560 93

2561 94

2601 98

2620 102

2621 103

2630 104

2667 105

2690 112

2695 111

2701 116

2742 117

2730 118

2731 120

2801 122

2802 122

2803 122

2804 122

Cat.-No. Page

2002 13

2008 14

2022 15

2026 47

2028 44

2031 16

2032 16

2033 17

2042 18

2051 34

2053 34

2055 34

2057 34

2061 35

2063 35

2065 35

2067 35

2082 51

2091 55

2092 56

2094 57

2129 45

2153 46

2163 39

2301 60

2311 61

2331 62

2341 63

2342 64

2352 65

2402 66

194

DIN number indexDIN Page

138 30, 46, 111, 112

1806 102

2080 102

2207 102

3968 15–17, 24, 25, 34, 35, 44, 45, 47, 51, 56, 57, 63–72,127, 134, 144, 171, 174, 177

3972 15, 16, 34, 35, 51, 88–94, 98, 102–105, 141, 179, 192

3975 81

5294 117

5464 67,118

5471 67, 119

5472 68, 119

5480 70, 148

5481 72,148

5482 71

58411 13

58412 13, 14, 142

58413 13, 14

7721 17

8002A 15

8002B 16

8150 61, 116, 146

8151 116

8164 62, 116, 146

8187 60, 116, 146

8188 60, 116, 146

8196 60

8197 146

9611 69, 119

58411 13

58412 13, 14

58413 13, 14

Bezeichnung Cat.-No. Ident No. MengeDesignation Quantitiy

Firma n Company

Kd.-Nr. n Customer No.

Name n Name

Abteilung n Department

Telefon n Telephone Fax

Straße n Street

PLZ n Post Code Ort n City

Postfach n P. O. Box

PLZ n Post Code Ort n City

E-Mail

Unterschrift n Signature

WILHELM FETTE GMBHPräzisionswerkzeuge und MaschinenPrecision Cutting Tools and Machines

Grabauer Str. 24 · D-21493 SchwarzenbekPostfach n P.O. Box 11 80 · D-21484 Schwarzenbek

Datum n Date:

Bitte kopieren und faxen an:Please copy and send to:

FAX-BESTELLSCHEIN FAX-ORDER FORM

BESTELLUNG n ORDER

Absender n Sender

++49 (0) 41 51 / 12 688

Pictures were generously provided by the following machinetool manufacturers:

Getriebebau Nord Schlicht & Küchenmeister, BargteheideGleason-Pfauter Maschinenfabrik GmbH, LudwigsburgLiebherr Verzahntechnik GmbH, Kempten

© by FETTE GMBHThis publication may not be reprinted in whole or part withoutour express permission. All rights reserved. No rights may be derived from any errors in content or fromtypographical or typesetting errors.Diagrams, features and dimensions represent the currentstatus on the date of issue of this catalogue. We reserve theright to make technical changes. The visual appearance ofthe products may not necessarily correspond to the actualappearance in all cases or in every detail.

Leitz Metalworking Technology Group

Prin

ted

in G

erm

any,

No.

162

4 (0

405

1 D

TP/G

K)

Gear Cutting Tools• Hobbing• Gear Milling

Gea

r C

utt

ing

To

ols

Belgien/BelgiumSA LMT Fette NVIndustrieweg 15 B21850 GrimbergenFon +32-2/2 51 12 36Fax +32-2/2 51 74 89

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Kieninger GmbHAn den Stegmatten 7 D-77933 Lahr, DeutschlandTel. +49 (0) 7821 943-0Fax +49 (0) 7821 943-213E-mail: [email protected]: www.kieninger.de

Onsrud Cutter LP800 Liberty Drive Libertyville, Illinois 60048, USATel. +1 (847) 362-1560Fax +1 (847) 362-5028E-mail: [email protected]: www.onsrud.com

Indien/IndiaLMT Fette India Pvt. Ltd. 29, II Main RoadGandhinagar, AdyarChennai 600 020Fon +91-44/24 405 136 / 137Fax +91-44/24 405 [email protected]

Mexiko/MexicoLMT Boehlerit S.A. de C.V.Matias Romero No. 1359Col. Letran Valle03650 Mexico D.F.Fon +52 (55) 56 05 82 77Fax +52 (55) 56 05 85 [email protected]

Österreich/AustriaFETTE PräzisionswerkzeugeHandelsgesellschaft mbHRodlergasse 51190 WienFon +43-1/3 68 17 88Fax +43-1/3 68 42 [email protected]

Singapur/SingaporeLMT Singapore Representative Office1 Clementi Loop #4-04Clementi West District ParkSingapore 12 98 08Fon +65 64 62 42 14Fax +65 64 62 42 [email protected]

Spanien/SpainLMT Boehlerit S.L.C/. Narcis Monturiol, 11 Planta 1a08339 Vilassar De Dalt (Barcelona)Fon +34-93/7 50 79 07Fax +34-93/7 50 79 [email protected]

Tschechien/Czech RepublicLMT FETTE spol. sr.o.Drázni 7627 00 Brno-SlatinaFon +420-5/48 21 87 22Fax +420-5/48 21 87 [email protected]

LMT Fette spol. sr.o.Kancelaf BoehleritVodni 1972. CZ-760 01 ZLINFon +420 57 72 14 989Fax +420 57 72 19 061

Türkei/TurkeyBöhler Sert Maden Takim Sanayive Ticaret A.S.Ankara Asfalti ü zeri No.22 Kartal 81412 IstanbulP.K. 167Fon +90-216/3 06 65 70Fax +90-216/3 06 65 [email protected]

Ungarn/HungaryLMT Boehlerit KFT.Kis-Duma U.6PoBox 2036 Erdliget Pf. 322030 ErdFon +36/23 52 19 10Fax +36/23 52 19 [email protected]

USAKanada/CanadaLMT-FETTE Inc.18013 Cleveland ParkwaySuite 180Cleveland, Ohio 44135Fon +1-2 16/3 77-61 30Fax +1-2 16/3 77-07 87

gear cutting_tools ( hobbing, seration , milling etc )

Business