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1、BRITISH STANDARD CONFIRMED AUGUST 1990 BS 978-3:1952 Incorporating Amendment No. 1 Gears for instruments and clockwork mechanisms Part 3: Bevel gears UDC 621.833:681-2 Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 01:54:27 GMT+00:00 2006, Uncontrolled Copy, (c
2、) BSI BS 978-3:1952 This British Standard, having been approved by the Mechanical Engineering Industry Standards Committee and endorsed by the Chairman of the Engineering Divisional Council, was published under the authority of the General Council on 24 January 1952 BSI 12-1999 First published Octob
3、er 1941 First revision January 1952 ISBN 0 580 34085 6 Co-operating organizations The Mechanical Engineering Industry Standards Committee under whose supervision this British Standard was prepared consists of representatives from the following Government departments and scientific and industrial org
4、anizations: Admiralty*Institute of Petroleum Air MinistryInstitution of Civil Engineers Associated Offices Technical CommitteeInstitution of Gas Engineers Association of Consulting EngineersInstitution of Heating and Ventilating (Incorporated)*Engineers British Chemical Plant Manufacturers Instituti
5、on of Mechanical Engineers* AssociationInstitution of Mechanical Engineers British Compressed Air Society(Automobile Division) British Electrical and Allied Manufacturers Institution of Production Engineers* Association*Locomotive Manufacturers Association British Engineers Association*Machine Tool
6、Trades Association* British Internal Combustion EngineMinistry of Fuel and Power Manufacturers AssociationMinistry of Labour and National Service British Iron and Steel Federation(Factory Department) British Railways, The Railway Executive*Ministry of Supply* Crown Agents for the ColoniesMinistry of
7、 Transport Department of Scientific and IndustrialMinistry of Works ResearchOffice of the High Commissioner for India Engineering Equipment Users AssociationWar Office Institute of Marine Engineers The Government departments and the industrial organizations marked with an asterisk in the above list,
8、 together with the following, were directly represented on the committee entrusted with the preparation of this standard: Association of Mining Electrical andNational Association of Drop Forgers Mechanical Engineersand Stampers British Clock and Watch ManufacturersNational Association of Lift Makers
9、 AssociationNational Federation of Engineers Tool British Gear Manufacturers AssociationManufacturers British Horological InstituteNational Physical Laboratory Institution of Engineering InspectionNorth East Coast Institution of Engineers Manufacturers of Instrument Gearsand Shipbuilders Milling Cut
10、ter and Reamer Trade AssociationSociety of Motor Manufacturers and Traders Amendments issued since publication Amd. No.DateComments 2408March 1956Indicated by a sideline in the margin Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 01:54:27 GMT+00:00 2006, Uncon
11、trolled Copy, (c) BSI BS 978-3:1952 BSI 12-1999i Contents Page Co-operating organizationsInside front cover Forewordii Section 1. General 1Scope1 2Terminology and notation1 Section 2. Form of gear tooth 3Form of gear tooth2 4Tooth spiral3 5Addendum and dedendum3 6Caliper settings3 Section 3. Permiss
12、ible errors and tolerances 7Pitch errors4 8Tooth thickness tolerance4 Appendix Notation5 Chart 1 Interference factor (Q) for bevel gears6 Figure 1 Straight bevel gear1 Figure 2 Right-hand bevel gear1 Figure 3 Left-hand spiral bevel gear1 Figure 4 Left-hand spiral bevel gear2 Figure 5 Basic rack toot
13、h shape (for unit normal pitch)2 Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 01:54:27 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 978-3:1952 ii BSI 12-1999 Foreword This standard makes reference to the following British Standards: BS 545, Bevel gears (mach
14、ine cut). BS 721, Machine cut gears. C. Worm gearing. BS 2519, Glossary of terms and notation used with gearing. This British Standard supersedes BS 978, “Gears for clockwork mechanisms,” which was published in 1941 as a war emergency measure to assist in the reduction of types and sizes of both gea
15、rs and cutters. As a result of experience gained in its use it became evident that a revision was necessary. It has been considered desirable to divide the standard into four separate parts. These are: Part 1: Involute spur, helical and crossed helical gears; Part 2: Cycloidal type spur gears; Part
16、3: Bevel gears; Part 4 Worm gears. The preparation of Part 4 will be undertaken when the revision of BS 721, “Machine cut gears. C. Worm gearing” has been completed. Suitable hobs and cutters will be dealt with in a later British Standard. It should be noted that this standard is similar to BS 545,
17、“Bevel gears (machine cut)”, that standard having been used as the basis for the preparation of this one. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Sta
18、ndard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 6 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be in
19、dicated in the amendment table on the inside front cover. Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 01:54:27 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 978-3:1952 BSI 12-19991 Section 1. General 1 Scope This part applies to machine cut conical gears, of
20、 the classes described below, connecting intersecting shafts and having pitches from 20 to 80 DP. The teeth shall have a normal pressure angle of 20 at the pitch cone and they may be straight or curved (see Figure 1 to Figure 4). The standard provides for Class A gears for use where a high degree of
21、 accuracy is required, and Class B gears for other applications. For integrating electricity meters the particular form of gear herein specified is not necessary and it is recognised that other existing forms of gear will continue to be used. 2 Terminology and notation The terms and notation shall b
22、e as defined in BS 2519 “Glossary of terms and notation used with gearing.” For the convenience of users an abbreviated list of symbols is given in the Appendix. Figure 1 Straight bevel gear Figure 2 Right-hand spiral bevel gear Figure 3 Left-hand spiral bevel gear Licensed Copy: London South Bank U
23、niversity, London South Bank University, Fri Dec 08 01:54:27 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 978-3:1952 2 BSI 12-1999 Section 2. Form of gear tooth 3 Form of gear tooth The normal section of the British Standard basic rack tooth for bevel gears shall be as shown in Figure 5, and corres
24、ponds to the developed section of the outer ends of the teeth of the crown gear. The tooth flank is straight, with 20 pressure angle, except that a slight easing of the tip is permissible. The amount of this easing shall not exceed that shown in Figure 5. A cutting tool of form counterpart to a sing
25、le flank and root fillet of the basic rack may be used to generate single flanks and root fillets of bevel gear teeth of British Standard form. In general, neither the amount of the tip easing, nor the fillet radius on the bevel gear tooth will be a constant multiple of the pitch at all distances fr
26、om the apex. The root of the tooth shall normally lie on a cone which has its apex coincident with the pitch cone apex, but to suit methods of manufacture, it may be made to lie on another cone which is co-axial with the gear but whose apex is not coincident with the pitch cone apex. The tip cone an
27、gle shall be made so that the tip of the tooth lies parallel to the root of the mating gear, thus producing a constant bottom clearance along the tooth. Figure 4 Left-hand spiral bevel gear Figure 5 Basic rack tooth shape (for unit normal pitch) Licensed Copy: London South Bank University, London So
28、uth Bank University, Fri Dec 08 01:54:27 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 978-3:1952 BSI 12-19993 It is recommended that the face width should not normally exceed either one-third of the cone distance or three times the pitch. 4 Tooth spiral The form of tooth spiral is not standardized
29、as it is dependent on the type of cutter and the method of cutting employed. For this reason the spiral angle at different positions along the face is not specified. 5 Addendum and dedendum The addendum shall be determined by: where kp, the addendum coefficient for the pinion is equal to: orwhicheve
30、r is the greater and kw= kp The value of Q is obtained from Chart 1 attached. NOTE 1If the shafts are at right angles: The dedendum of the tooth shall be equal to the difference between the addendum as determined above and the whole depth of tooth. Normally kw= kp. Where the number of teeth in the t
31、wo gears is small, i.e., when t sec p+ T sec w is less than Q, interference or undercutting will be present and the use of such gears should be avoided. If t is less than the addendum and dedendum shall each be reduced by 0.4 0.0344t sec22 sec p (for unit normal pitch) unless this quantity exceeds 0
32、.065, in which case the gears are outside the scope of this standard. Example. To find the addendum of a pair of spiral bevel gears connecting perpendicular shafts and having the following particulars: T = 45; t = 10; n= 20; 2= 30; Pn= 50 tan p=and so p= 1232 kp is equal to the greater of the values
33、: i.e., k = 0.38. Addendum of pinion =(1 + 0.38) = 0.0276 in. Addendum of wheel =(1 0.38) = 0.0124 in. 6 Caliper settings Caliper settings may be obtained as follows: Then: Caliper thickness setting for wheel, G Caliper thickness setting for pinion, g Caliper height setting for wheel, H Caliper heig
34、ht setting for pinion, h 10 45 - 1 50 - 1 50 - Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 01:54:27 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 978-3:1952 4 BSI 12-1999 Section 3. Permissible errors and tolerances 7 Pitch errors The pitch errors shall not
35、exceed values in accordance with the formula given below, expressed in thousandths of an inch. La = Length in inches of arc of pitch circle over which the error is measured; this shall not exceed half the circumference. NOTEThe results of the measurements are expressed with reference to the working
36、axis of rotation and the permissible errors given include the effects of eccentricity. 8 Tooth thickness tolerance The thickness of the gear teeth shall, in general, be less than the nominal thickness (G for the wheel or g for the pinion). The tolerances shall be in accordance with the formula given
37、 below, expressed in thousandths of an inch. Class of gearMaximum permissible pitch error A B Class of gearTolerance A B Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 01:54:27 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 978-3:1952 BSI 12-19995 Appendix Notat
38、ion AWheel addendum. aPinion addendum. CCone distance. DWheel pitch diameter. dPinion pitch diameter. FFace width. GCaliper thickness setting for wheel. gCaliper thickness setting for pinion. HCaliper height setting for wheel. hCaliper height setting for pinion. kAddendum coefficient PDiametral pitc
39、h. PnNormal diametral pitch. PtTransverse pitch or circular pitch. PnNormal pitch. QInterference factor. TNumber of teeth in wheel. tNumber of teeth in pinion. (gamma)Pitch angle. 2 (sigma)Spiral angle at pitch circle. n (psi)Normal pressure angle. Licensed Copy: London South Bank University, London
40、 South Bank University, Fri Dec 08 01:54:27 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 978-3:1952 6 BSI 12-1999 Chart 1 Interference factor (Q) for bevel gears Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 01:54:27 GMT+00:00 2006, Uncontrolled Copy, (c) BSI
41、 7blank Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 01:54:27 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 978-3:1952 BSI 389 Chiswick High Road London W4 4AL BSI British Standards Institution BSI is the independent national body responsible for preparing Br
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