A Comparison of ISO4156/ANSI B92.2M,-,1980

With OlderImperial Standards

J'ohn FinneySpline Gauges Limited

,(Division ,of IM&IM Pr,ec,ision Systems, Dayto,n. OHI)IPicca,dliUy KilngsburyWarwickshire

England

The purpose of this article is to discuss ISO4156/ANSI B92.2M-.1980 and to compare itwith other, older tandards till in use .. In ourexperience designing and manufacturing splinegauges and other spline measuring or holdingdevices for spHned component manufacturerthroughout the wcrid, we are constantly sur-prised that so many standards have been pro-ducedcovering whai is quite a small ubject.Many of the standards aeemternational tan-dards; others are company standards, which areusually based on international standards ..Almost all have simileritiesi jhat is, they all.deal with splines that have involute flanks of30°,37..50 or 45° pressure angle and are for themost part flank-fitting or occasionally major-diameter-fining.

Space Widthof InternalSpline

ToothThicknessof ExternalSpline

22 GEAR TECHNOLOGY

Although ISO 41.56 was published in 1.981and is widely used in Europe, we find that it isnot u ed as frequentlya . it hould be in theUnited States and United Kingd.om for a num-ber of reasons. Onei that many engineers donot seem. to be aware of it; another is thatbecause it is a metric module standard, the cir-cular pitch is different from that of imperial-standard-based diametral pitch splines. Thisfact. can necessitate buying new cutters; how-ever, this should not present any problemwhere new project are involved, as a modulecutter is no more expensive than a DP (dia-metral pitch) cutter. Also, DP cutters have tobe periedically replaced, SO' why not change tometric plines? Furthermore, spline gaugedesigned to a module standard are no more'expensive than DP gauges. These arguments.of course, cannot apply [0 componentsthathave been made for many years, andthereforehave to be interchangeable.

In our opinion, the main reason that ISO4156 is not used more :inthe e countries is lackof awareness. We hope the following i infor-mative 10 those who have not heard of it anden COli rages tho e who are aware of it to u e .it.We feel Ibis isnecessary because quality con-trol the e days is of the utmost importance.This standard (unlike the previous imperialstandard ) has many cia es of fits that willguarantee sliding, clearance or interference.Also, in genera], components manufactured tothis standard are of a higher quality. astighter

tolerances have to be maintained to achievethese better fits. Section 8.1 of the standard isof paramount importance to component manu-facturers. This paragraph has wide-reachingimplications, as :it means that closer toleranceshave to be maintained to obtain the desired fits,meaning that qualitycontrol during manufac-ture and gauging win have to be increa ed, butthat is inevitable anyway in today's competi-tive global markets ..

ISO 4156/ANSI 892.2M-1980-Its Origins

During the ] 970s it was realized in theUnited Kingdom that with metrication in mind,a new standard for involute splines wasrequired, Up to this time and indeed still today,the most widely 11 ed standards were BS 3550-1963 and ANSI B92.] -1970. Both of thesestandards are. of course, imperial standardsbased on OF. The DF is the number of teethper inch of pitch-circle diameter and as suchprovides a standard series of tooth sizes on var-ious pitch-circle diameters ..The proposed stan-dard, of course, would have to be, likeEuropean standards, metric-mod ule-based,Similar to DP. the module is the ratio of thepitch circle in millimeters to the number ofteeth and provides a standard series of toothsizes. It was not atisfactory simply to convertDF to module because the pitch-circle diame-ters and tooth proportions would still be imper-ial-based and would therefore give no degreeof interchangeability with metric components.

AFNOR (the French national standardsauthority) and DIN were consulted to see ifthere were any standards in existence on whichthe new standard could be based. The existingFrench standard E22-141 was considered to beout of date, as it made no reference to' variationallowance (di cus ed later). The German. stan-dard DIN 5480 seemed to be the only otherpossibility, since it did take into account varia-tion allowance. The result of this consultationwas the realization that more than a new metricstandard was required. What was needed wasan international standard that could be usedthroughout the world ..

To achieve this. working groups were estab-lished at the various standards organizations;the working groups consisted of representa-tives from the United Kingdom, France,Germany, Scandinavia. the United States and

Japan, among others ..At a meeting of all mem-bers in Paris, two draft proposals were put for-ward for consideration: One proposal wasbased on DIN 5480, and the other was a com-pletely new draft proposal by AFNOR andBriti h Standards ..The basis of the tolerancesforthis draft was taken from ISO 286; i.e., tol-erances for plain parts with an additional toler-ance for variation allowance.

After discussion, the new draft was adoptedand contributions from alii member organiza-tions were invited ..The result of the collabora-tion i ISO 4[56. 111is standard also has beenpublished in the United Kingdom as BS 6186.in France as E22-144/E22-] 45, and in theUnited States as ANSI B92.1-1980. It is usedextensively in Europe and is gradually becom-ing more and more popular throughout theUnited States, where transition from imperialto metric is taking place.

Explanation of Variation Allowance& Effective Size

To enable ISO 4156 to be compared withthe older standards. it is nece sary to under-stand the concept of effective fit. The effectivetooth thickness of the space width of a compo-nent is the most important element because it isthis size that determines whether the fit is goodor bad. It is not only the actual tooth. thicknessor space width that determines the resultant fitbetween an external and internal spline. This isbecause, unlike plain pans. splines have multi-ple engaging surfaces. Each of these surfaces issubject to an error of either profile.spacing/index or parallelism, which must beallowed for jf the parts areto fit. This variationallowance is determined by allocating to eachof the elements a permissible tolerance. Thesum of these tolerances is then referred to as anerror allowance e or variation allowance A.

It is generally accepted in most standardsthai. because it is unlikely that. these errors winoccur simultaneously and in their maximumamounts on the same spline, a variationallowance consisting of a percentage of thesum of the positive profHeer:mr. the indexerror and the parallelism error for the length 'ofengagement is allowed.

To achieve at suitable fit. the nominal tooththickness of the external spline and the nomi-nal space width of the internal spline usuallyare equal to one half of the circular pitch at the

,John Fi,nnevis design manager withSpline Gauges Limited,a subsidary of M & MPrecision Systems.Dayton, OH. He hasmore than rwo decadesof experience in 1Mdesign of splint! gauges,master gears and splin»measuring instrumenu.HI! is a member of theShafts for Machiner»Committee of th« BritishStandards Institution.

SEPTEMBER/OCTOBER 1994 23,

pitch-circle diameter. The internal spline isallocateda space width greater than nominal.A machining tolerance m.i determined to.arrive ata maximum and minimum actualspace width, and the variation allowance Ai. isthen subtracted from each value to. arriveat amaximum and minimum effective space width.

Similarly, the external spline is allocated atooth thickness that is less than nominal. Amachining tolerance is used to arrive at a maxi-mum and minimum actual tooth thickness, andthe vaeiarionallowancei added to each valuetoarrive at a maximum and minimum effectivetooth thickness. Table 1 shows a typical fitcondtrion between an external spline and aninternal one.

ANSI B92.1-1970This standard is probably the most widely

used standardtoday. As can be seen fromTable 2, it shows four classes of fit. The maxi-mum effective tooth thickness of the externalsplineand the minimum effective space widthof the internal spline are equal to nominal. Themachining tolerance and effective clearanceare different for each class of fit, resulting inClass 4 being the closest fit and Class 7 beingthe loosest

According to this standard, theallowableerrors for a Class 5 spline (the most widelyused) are

For 30 teeih, 24/48 Df, 300 PATotal Index Variation e 0.038Profile Variaticne +0.005/·0.010Lead Variation = 0.0]0 (for a splinelength of 25)

A described previously, i1 is not acceptedthat aU elements will occur in the same posi-

T.able 1: • eomparingl'oor

SpaceWidth orInternalSpline

Nominal1.661

I .TOOlhThicknessof ExtemalSpline

24 GE AR He H NOL.OGY

values of total index, twice the positive profileand lead variation are used to calculate thevariation allowance; i.e., 0.6 (0.038+ 0.010+0.0]0) = 0.035 (Due to. rounding of variouselemental errors the value is stated as .0.0.38 in.the ANSI tandard.)

For Classes 4, 6 and 7. the machining toler-ances and allowable errors for a Clas .5 plineare multiplied by the following factors:

Class 4= x 0.71Class 6= x ] ..4Class 7= x 2.00.

Because the minimum effective space widthof the internal and the maximum effectivetooth thickness of the external spline are equal,a fit is always guaranteed .. To ensure this, theGO plug gauges and the GO ring gauge have atooth thickness/space widthequal to nominal.(with a tolerance and wear allowed), whichmeans that one single Go. plug gauge and oneGO ring gauge can be used for checking allfnur classes of fit. The NooO gauges have tobe unique to each class of fit.

The only disadvantage of this system is that.while a fit is guaranteed (provided the spline isaccepted by the gauges), the type of fit is not.For example, if you were designing compo-nents requirmgan extremely loose fit, Class 7tolerances would he used, However, :inthe caseof a poorly made component with spline onmaximum metal condition and with excessiveprofile, index and lead error, it is possible forthe gauges to accept the spline, providing, ofcourse, nominal. size .is not exceeded, The fitobtained from this condition would bea tightfit rather than the desired loose fit.

BS 35501..1960In this standard, the tooth proportions are

similar to those in ANSI B92, 1-1970. Theallowable elemental error (profile, spacingand lead errors) are identical to those of aClass 5 spline in ANSI. The only pressureangle referred to. is 30°. There are just twoclasses of fit.. The internal spline have onlyone tolerance band (identical to a CIa s 5ANSI spline). For Clas 2, both extemalandinternal splines have the same tooth thicknesand space width dimensions as an ANS[ Class5 spline. For Class 1 splines, the machiningtolerance and variation allowance are identicalto. Class 2. However, a clearance or deviationallowance Cv is introduced, thus ensuring 111

degree of looseness between the male andfemale splines. The clearance is shown inTable 1. As shown. the tooth thickness dimen-sions of the external splines are displaced oradjusted by the clearance Cv. It also can beconcluded that. while as 3S50 has fewer fits, aClass 1 spline does ensure clearance.

DJN5480DfN 5480 has been in existence for many

years and is predominantly used in Germany,but also is used in many other countries ..It is ametric module standard and was therefore con-sidered a basis for ISO 4156. Its popularity isdue to its 1) being a metric standard, and 2)offering a vast diversity of fits that ANSIB92 ..1-1970 and BS 3550 do not. In the past, ifyou wanted to produce a metric spline, anditwas necessary to achieve a certain fit. DINS480 was the only metric standard available toenable you to achieve this (the only other met-ric standards that were available were olderstandards that did not lake into account varia-tion allowance and therefore were unsuitable),

In this standard, the outside diameter isconsideredlas a basis rather than the pitch-circle diameter; i.e., DIN considers that theoutside diameter of a spline should conformtoa preferential series of whole numbers. Toensure this and to enable common cuttingtools to be used in manufacture, it is neces-sary to correct the tooth profile; i..e., it is notpossible for the nominal tooth thickness (0..5x circular pitch) to occur always on the pitch-circle diameter, but sometimes on a correctedpitch circle, either larger 'or smaller. This cor-rection does not cause any problem to thespline designer, as all corrected sizes arespecified in the standard.

To calculate the variarjonallowance, 60,%of the tooth thickness machining tolerance isused. This means that profile, spacing and leaderrors are not specified .. This can be a disad-vantage if a splined component manufacturerwishes to check these errors on conventional orcomputerized universal gear checkingmachines. In the writer's opinion, DIN 5480, isan excellent standard, but the vast choice offits must cause confusion 10 the inexperienced,In addition, the machining tolerances for someof the closer fits are extremely tight and thevariation allowances consequently minuscule,which must make manufacturing on a produc-

Table 3 - Comparing Two Classes of Fit in 88.3550.1963 30T, 24/48 DP, 30· PA

Class I Class 2

SpaceWidth ofInternalSpline

1.732

::JNominal1.661

1.623_

::JIToothThicknessof ExternalSpline

III =0.033 A=0.037 m = 0.033 A. = 0.037

* Min. possible effective clearance = 0.038 • Actual 1 Effective

Table 4· Comparing HIli Fits in DIN 5480 30T, 1.0 Mod.. 30·PA

Class II H/h Clas 9 H/h Class 7' H/Il Class 6 H/Il

SpaceWidth ofInternalSpline

ominal2.090*

2.045 I.--'1 ".01udI-ToothThicknessof ExternalSpline

I

I

m=O.080 A= 0.045 m =0.040'-=0.023 .=0.020 A= 0.012 m =0.014 A=0.00

I

Effective : • CorrectedI.Actual

tion basis difficult; Having said this, these dayswith modern computerized machinery andmeasuring machines. which have eliminated agreat deal of human error, it is now possible tomanufacture components that are accurate andconsistent, so perhaps there is nothing wrongin setting limits that were at one time consid-ered impossible. Table 4 shows a small selec-tion of fits from this tandard.

ISO 4156/ANSI B92.2M-l980This new standard also allows engineers to

select various types of fits; i.e., sliding, closesliding, clearance and interference. Becausethe splines are not outside-diameter-based, thetooth profiles are not corrected, and the resul-tant outside diameters are not whole numbersand, consequently, do not conform to a pre-ferred series. This, however, does not presentany problem, because a suitable tooth numbercan be selected for a particular application,

The nominal tooth thickness/space width iscalculated in tile same way as ANSI H92.1-1970

SEPTEMBERIOCTOBER 199' 25,

Table 5 . Compariag Four Clru;.ws or fl. Hlhin I. 041561 NS! B92.lM - 1980.30T. 1!0 rvrod., 300PA

I Class 7 :H1b Class 6 HJh Class '5 H~h Clas 4 HJh

SpaceWidlhoflnternalSpline

ominal1.571

ToolhThicknessof ExternalSpline m .. 0.090" .. 0.051 m =0.054 ./..= 0.034 m =0.033)..=0.024 m = 0.019'Ji.= 0.016

Effective

HIe [-IJd

E basic" 0.5 1tIn'""I--'I ......--1~S, basic

Zero

Withoutminimumeffective

With effectiveinterference

Witb effectivelooseness

and BS 3550; i.e .. 0.5 x circular pitch. Thereare four basic classes of fit, referred to as 4H/h,SHih, 6H/h and 7H/h .. The suffix. H refer tothe internal. spline and h to theexternal (asdescribed in ISO 286 limits and fits for plainparts).

Table 5 shows the four HIb fits and can becompared wi,tll the four ANSI fits in Table 2.As can be seen, the fits obtained for Cia ses 4,5 and 6 in ISO 4156 are significantly closerthan those from the older A_NS]standard (par-ticularly Classes 4 and 5). The machining tol-erances for both standards are approximatelyequal.consequently, the closer fits obtained inISO 4156 are due to a reduction in. the varia-lion allowance A.

As slated earlier, Section 8. ~ of the tandardhas wide-ranging implications for the spline

26 GEAR TECHNOlOGV

manufacturer. It rates that the variationallowance A should becalculated using the fol-lowing expression:

The expression is different bam that u ed inANSI B92.]-]970 and BS 3550-]960, whichstates that variation allowance .is calculated asfollows:;l,. = 0.6 [lndex Variation + 2 (Posiuve Profile Variution] +

Lead Variat ion]

The resul! of the expres ion specified in thenewer standard is a value thai is lessthan thatof the old standard, as can be seen fromthefollowing example. A. 30-looth. 1.0 module,30° PA Class 5 spline is used.

Total Index Variarion e FpFp in mierorneters e 3.55 ..[l + '9Fp in mierometers = 3.55 ~47.124 + 9Fp in micmmeters e 33.370Fpin millimeters :::0.033

."

where the length of arc L :: 0.5 x Pilch Circleircumference.

Total Profile Variation = FIFlin micrometers = 2.5 Ij>f + 1.6F/in micrometers '" 2.5(1.375) + 16Ff in micrometers = 19.4375Ffin millimeters = 0.0]9

where Tolerance Factor Ij>f= m + 0.0125 mZ.

Total Lead Varianon « FFin Micrometers e Iff + 5F in Micrometers = I{E + 5F :inMicrometerse 10F i.n Millimeters = 0.0.0

where g isthe spline length in millimeters.Sub titutingthe above values into the new

expression in ISO 4156:

l = 0.6 J (0.033)2 + (0.019)2 +(0.0 I0)2 = 0.024.

Referring to Table 2. we ee thai the allowableerrors of index, profile and lead for an ANSIB92.1-1970 spline are reasonably comparable tothe above (it must. of course, be appreciated thatthe above value for FI i total and should there-

fore be interpreted as ± 0.0095).The variation allowance. however, for an

ISO 4156 spline is less tilan that for an ANSIB92. I -1970 spline; consequently, whenmachining splines to the later standard, greatercare and more rigorous quality control have tobe applied,

The above demonstrates that by using ISO4156, it is possible to maintain closer fits thanthose obtained from the older imperial standards.

Furtb.er Fit VariationsBy using ISO 4156. it is possible to achieve

fits other than those shown in Table 5; i.e., theHih fits. This is made possible by introducingfurther fit classes to the external spline whilemaintaining the H fits on the internal spline (itis beneficial to adjust external splines. as theseare usually machined, while many internalplinesare produced by broaching).

These additional fits are designated f, e, d,js and k, and are obtained by applying a devia-tion allowance (Cv) to the shaft-tooth thick-ness. The deviation allowances to guaranteeclearance for a 30-tooth, 1.0' module spline areas below:

f = --"0.020e = -0.040d = --"0.065

The clearance becomes progressively largerfrom f to. d and ensures loosene s. If interfer-enee is required, it is possible to employ fits kor js- Fit k guarantees interference, and with jsit is most probable that interference will exist.Spline tooth thickness values for the two fitscan be determined by referring to Table 6,which also. shows the clearance fits.

It should be remembered that when usingfits /. e or d, the shaft major diameter andminor diameter also should be adjusted by avalue equal to the deviation allowance dividedby the tangent of the pressure angle.

ISO 4156 specifies only side-fitting splines.The older imperial standards also containedmajor-diameter-fitting splines which could bean advantage in maintaining concentricity; inthis instance, the spline flanks were used asdrivers only,

The fact that ISO 4156 does not containmajor-fitting splines should be offset by thegreater accuracies achievable by using thedose tooth thickness tolerances recommendedin this standard. This, however, may be debar-

NOOOP\u~

• Gauge Tolerance

able by spline manufacturers, who find themajor diameter easier to control than the tooththickness.

Comparison of Gauging PrneedureAll. the standards that have been used for

comparison have a section that clearly definesthe method of tolerancing for gauging. Notethe following points upon which all standardsare in agreement:

An internal spline should at the very [eastbe checked with

L a full-form GO plug gauge designed [Q

check "min. effective" space width,2. a sector-type NOGO plug gauge designed

to check "max. actual." space width,3. an additional composite NOGO plug

gauge to check "max. effective" space w:idth(this is very occasionally required if it is neces-sary to restrict the effective size).

Anexternal spline should at the very leastbe checked with

1. a full-form GO ring gauge designed to.check "max. effective" tooth thickness,

2. a sector-type NOOO ring gauge design-ed to check "min. actual" tooth thickness,

3 .. an additional composite NOGO ringgauge designed to check "min. effective" tooththickness where it is necessary to restrict theeffective size.

The posiuon of the gauge tolerance andwear allowances is the place where the variousstandards do. net agree. As can be seen fromTable 7. ANSI B92.1-1970 places the gaugetolerance within the part tolerance, BS 3550puts the gauge tolerance outside the pan toler-ance, and in mN 5480 and ISO 4156, thegauge tolerances are bilateral .• !

SEPT~MBER/OCToeER '994 27'