bs 328-2-2-1972

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BRITISH STANDARD BS 328-2:1972

Specification for

Twist drills and

combined drills and

countersinks —

Part 2: Combined drills andcountersinks (centre drills)

UDC 621.951.4

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BS 328-2:1972

This British Standard, having

been approved by the MechanicalEngineering Industry StandardsCommittee, was published underthe authority of the ExecutiveBoard on28 July 1972

© BSI 03-1999

First published, June 1928

First revision, August 1950

Second revision, July 1972

The following BSI referencesrelate to the work on thisstandard:

Committee reference MEE/73Draft for approval 71/37365

ISBN 0580 07015 8

Co-operating organizations

The Mechanical Engineering Industry Standards Committee, under whosesupervision this British Standard was prepared, consists of representativesfrom the following Government departments and scientific and industrial

organizations:

Associated Offices Technical Committee Engineering Equipment Users’ Association

Association of Consulting Engineers Gas Council

Association of Hydraulic Equipment Institution of Civil Engineers

Manufacturers Ltd. Institution of Gas Engineers

Association of Mining, Electrical and Institution of Heating and VentilatingMechanical Engineers Engineers

British Compressed Air Society Institution of Mechanical Engineers

British Electrical and Allied Manufacturers’ Institution of Mechanical Engineers

Association* (Automobile Division)

British Gear Manufacturers’ Association Institution of Plant Engineers

British Internal Combustion Engine Institution of Production Engineers*Manufacturers’ Association Locomotive and Allied Manufacturers’

British Mechanical Engineering Association of Great BritainConfederation London Transport Executive

British Pump Manufacturers’ Association Machine Tool Trades Association*

British Steel Industry Ministry of Defence

Crown Agents for Oversea Governments and Ministry of Defence, Army Department Administrations National Coal Board

Department of Employment and Productivity National Physical Laboratory

(H.M. Factory Inspectorate) (Department of Trade and Industry)

Department of the Environment Process Plant Association

Department of Trade and Industry Royal Institute of British Architects

Department of Trade and Industry — Telecommunications Engineering

National Engineering Laboratory Manufacturing Association

Electricity Council, the Central Electricity Water Tube Boilermakers Association

Generating Board and the Area Boards inEngland and Wales

The scientific and industrial organizations marked with an asterisk in theabove list, together with the following, were directly represented on thecommittee entrusted with the preparation of this British Standard:

Society of Motor Manufacturers and Twist Drill Association

Traders Ltd.

Amendments issued since publication

Amd. No. Date Comments

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Contents

Page

Co-operating organizations Inside front cover

Foreword ii1 Scope 1

2 Manufacturing requirements for combined drillsand countersinks (centre drills) 1

3 Dimensions of combined drills and countersinks (centre drills) 1

4 Designation 1

5 Combined drills and countersinks (centre drills) for centreholes without protecting chamfer. Type A 2

6 Combined drills and countersinks (centre drills) for centreholes with protecting chamfer. Type B 3

7 Combined drills and countersinks (centre drills) for centreholes with radius form. Type R 4

Appendix A Recommended dimensions for centre holes. Type A 6

Appendix B Recommended dimensions for centre holes. Type B 7

Appendix C Recommended dimensions for centre holes. Type R 8

Figure 1 — Single-ended combined drills and countersinks(centre drills). Type A (d < 0.8 mm) 2

Figure 2 — Double-ended combined drills and countersinks(centre drills). Type A (d > 1 mm) 2

Figure 3 — Combined drills and countersinks (centre drills). Type B 3

Figure 4 — Combined drills and countersinks (centre drills). Type R 4

Figure 5 — Type A centre hole 6

Figure 6 — Type B centre hole 7

Figure 7 — Type R centre hole 8Table 1 — Dimensions of combined drills and countersinks

(centre drills). Type A 3

Table 2 — Dimensions of combined drills and countersinks

(centre drills). Type B 4

Table 3 — Dimensions of combined drills and countersinks

(centre drills). Type R 5

Table 4 — Dimensions for centre holes. Type A 6

Table 5 — Dimensions for centre holes. Type B 7

Table 6 — Dimensions for centre holes. Type R 8

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Foreword

In order to keep abreast of progress in the industries concerned, BritishStandards are subject to periodical review. Suggestions for improvements will berecorded and in due course brought to the notice of the committees charged with

the revision of the standards to which they refer.

A complete list of British Standards, numbering over 9,000, fully indexed andwith a note of the contents of each, will be found in the BSI Catalogue which maybe purchased from BSI Sales Department. The Catalogue may be consulted inmany public libraries and similar institutions.

The subject of combined drills and countersinks was first dealt with in BS 985,which was published in 1941 as a war emergency British Standard at the requestof the Ministry of Supply. The contents of BS 985 were incorporated in a revisionof BS 328 in 1950, becoming Part 2 of that standard when BS 985 waswithdrawn.

This latest revision of this Part of this British Standard, prepared under theauthority of the Mechanical Engineering Industry Standards Committee, has

been undertaken in order that this Part may be in agreement with DraftInternational Standards DIS 25401) and DIS 25412) and ISO RecommendationR 8663), which have been formulated by the International Organization forStandardization.

A British Standard does not purport to include all the necessary provisions of acontract. Users of British Standards are responsible for their correct application.

Compliance with a British Standard does not of itself confer immunityfrom legal obligations.

Summary of pages

This document comprises a front cover, an inside front cover, pages i and ii,pages 1 to 8 and a back cover.

This standard has been updated (see copyright date) and may have hadamendments incorporated. This will be indicated in the amendment table onthe inside front cover.

1) Draft International Standard ISO/DIS 2540, “Centre drills for centre holes with protecting

chamfer. Type B”.

2) Draft International Standard ISO/DIS 2541, “Centre drills for centre holes with radius form.Type R”.3) ISO Recommendation R 866, “Centre drills for centre holes without protecting chamfer.

Type A”.

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1 Scope

This Part of this British Standard gives designations and dimensions for the following types of centre drills.

1) Type A, combined drills and countersinks (centre drills) for centre holes without protecting chamfers.

2) Type B, combined drills and countersinks (centre drills) for centre holes with protecting chamfers.

3) Type R, combined drills and countersinks (centre drills) for centre holes with radius form.

Appendix A, Appendix B and Appendix C show the recommended dimensions for centre holes.

2 Manufacturing requirements for combined drills and countersinks (centredrills)

Combined drills and countersinks (centre drills) shall comply with the following requirements.

1) The drills shall be sharpened ready for use and shall be well finished.

2) The flutes shall be so designed that the cutting lips are equal.

3) The pilot drill is to be provided with adequate back taper and relief.4) The countersink shall be ground to provide lip clearance. The included angle shall be 60° maximum,each lip being equally inclined to the axis.

5) The body of the drill shall be truly cylindrical and the body, the drill and the drill point shall be trulyco-axial.

6) The flutes may be straight or spiral at the option of the manufacturer.

7) The drills shall be right-hand cutting unless otherwise specified.

3 Dimensions of combined drills and countersinks (centre drills)

The three standard types of combined drills and countersinks (centre drills) shall be made in accordancewith the dimensions given in Table 1, Table 2 or Table 3, as appropriate.

4 Designation

Combined drills and countersinks (centre drills) shall be designated by the Type, the pilot diameter d andthe body diameter d1.

Examples of designations:A 0.63/3.15

B 1.6/6.3

R 1.6/4

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5 Combined drills and countersinks (centre drills) for centre holes withoutprotecting chamfer. Type A

Type A single-ended and double-ended combined drills and countersinks are illustrated in Figure 1 andFigure 2 and the dimensions of these shall be in accordance with Table 1.

Figure 1 — Single-ended combined drills and countersinks (centre drills).Type A (d < 0.8 mm)

Figure 2 — Double-ended combined drills and countersinks (centre drills).Type A (d > 1 mm)

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Table 1 — Dimensions of combined drills and countersinks (centre drills) Type A

6 Combined drills and countersinks (centre drills) for centre holes with

protecting chamfer. Type BType B combined drills and countersinks are illustrated in Figure 3 and the dimensions shall be inaccordance with Table 2.

All dimensions are in millimetres.

d d1 l L

k12 h9 max. min. max. min.

(0.5)

3.15

1.0 0.8

21 19(0.63) 1.2 0.9

(0.8) 1.5 1.1

1.0 1.9 1.333.5 29.5

(1.25) 2.2 1.6

1.6 4.0 2.8 2.0 37.5 33.5

2.0 5.0 3.3 2.5 42 38

2.5 6.3 4.1 3.1 47 433.15 8.0 4.9 3.9 52 48

4.0 10.0 6.2 5.0 59 53

(5.0) 12.5 7.5 6.3 66 60

6.3 16.0 9.2 8.0 74 68

(8.0) 20.0 11.5 10.1 83 77

10.0 25.0 14.2 12.8 103 97

NOTE Sizes in brackets should be avoided whenever possible.

Figure 3 — Combined drills and countersinks (centre drills). Type B

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Table 2 — Dimensions of combined drills and countersinks (centre drills). Type B

7 Combined drills and countersinks (centre drills) for centre holes with radiusform. Type R

Type R combined drills and countersinks are illustrated in Figure 4 and the dimensions shall be in

accordance with Table 3.


d d1 d2 l L

k12 h9 k12 max. min. max. min.

1.0 4.0 2.12 1.9 1.3 37.5 33.5

(1.25) 5.0 2.65 2.2 1.6 42 38

1.6 6.3 3.35 2.8 2.0 47 43

2.0 8.0 4.25 3.3 2.5 52 48

2.5 10.0 5.30 4.1 3.1 59 53

3.15 11.2 6.70 4.9 3.9 63 57

4.0 14.0 8.50 6.2 5.0 70 64(5.0) 18.0 10.60 7.5 6.3 78 72

6.3 20.0 13.20 9.2 8.0 83 77

(8.0) 25.0 17.00 11.5 10.1 103 97

10.0 31.5 21.20 14.2 12.8 128 122


Figure 4 — Combined drills and countersinks (centre drills). Type R

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Table 3 — Dimensions of combined drills and countersinks (centre drills). Type R


d d1 Radius, r l L

k12 h9 max. min. (approx.) max. min.

1.0 3.15 3.15 2.5 3.0 33.5 29.5

(1.25) 3.15 4.0 3.15 3.3 33.5 29.5

1.6 4.0 5.0 4.0 4.25 37.5 33.5

2.0 5.0 6.3 5.0 5.4 42 38

2.5 6.3 8.0 6.3 6.7 47 43

3.15 8.0 10.0 8.0 8.5 52 48

4.0 10.0 12.5 10.0 10.6 59 53

(5.0) 12.5 16.0 12.5 13.2 66 606.3 16.0 20.0 16.0 17.0 74 68

(8.0) 20.0 25.0 20.0 21.1 83 77

10.0 25.0 31.5 25.0 26.8 103 97


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Appendix A Recommended dimensions for centre holes. Type A

A Type A centre hole is illustrated in Figure 5 and recommended dimensions are shown in Table 4.

Table 4 — Dimensions for centre holes. Type A

Figure 5 — Type A centre hole


d l D

nominal min. nominal

(0.5) 0.8 1.06

(0.63) 0.9 1.32

(0.8) 1.1 1.70

1.0 1.3 2.12

(1.25) 1.6 2.65

1.6 2.0 3.35

2.0 2.5 4.25

2.5 3.1 5.30

3.15 3.9 6.70

4.0 5.0 8.50

(5.0) 6.3 10.60

6.3 8.0 13.20

(8.0) 10.1 17.00

10.0 12.8 21.20


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Appendix B Recommended dimensions for centre holes. Type B

A Type B centre hole is illustrated in Figure 6 and recommended dimensions are shown in Table 5.

Table 5 — Dimensions for centre holes. Type B

Figure 6 — Type B centre hole


d l D

nominal min. nominal

1.0 1.3 3.15

(1.25) 1.6 4.0

1.6 2.0 5.0

2.0 2.5 6.3

2.5 3.1 8.0

3.15 3.9 10.0

4.0 5.0 12.5

(5.0) 6.3 16.0

6.5 8.0 18.0

(8.0) 10.1 22.4

10.0 12.8 28.0


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Appendix C Recommended dimensions for centre holes. Type R

A Type R centre hole is illustrated in Figure 7 and recommended dimensions are shown in Table 6.

Table 6 — Dimensions for centre holes. Type R

Figure 7 — Type R centre hole


d D

nominal nominal

1.0 2.12

(1.25) 2.65

1.6 3.35

2.0 4.25

2.5 5.30

3.15 6.704.0 8.50

(5.0) 10.60

6.3 13.20

(8.0) 17.00

10.0 21.20


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