《BS-978-1-1968.pdf》由会员分享,可在线阅读,更多相关《BS-978-1-1968.pdf(36页珍藏版)》请在三一文库上搜索。
1、BRITISH STANDARD CONFIRMED AUGUST 1990 BS 978-1:1968 Incorporating Amendment No. 1 Specification for Fine pitch gears Part 1: Involute Spur and Helical Gears UDC 621.833.1 BS 978-1:1968 This British Standard, having been approved by the Mechanical Engineering Industry Standards Committee and endorse
2、d by the Chairman of the Engineering Divisional Council, was published under the authority of the General Council on 31 January 1968 BSI 10-1999 First published October 1941 First revision January 1952 Second revision November 1962 Third revision January 1968 The following BSI references relate to t
3、he work on this standard: Committee reference MEE/17, MEE/17/4 Draft for comment 66/14936 ISBN 580 00028 1 Co-operating organizations The Mechanical Engineering Industry Standards Committee, under whose supervision this British Standard was prepared, consists of representatives from the following Go
4、vernment departments and scientific and industrial organizations: The Government department and scientific and industrial organizations marked with an asterisk in the above list, together with the following, were directly represented on the committee entrusted with the preparation of this standard:
5、Associated Offices Technical CommitteeInstitution of Civil Engineers Association of Consulting Engineers*Institution of Gas Engineers Association of Mining Electrical andInstitution of Heating and Ventilating Mechanical Engineers*Engineers Board of TradeInstitution of Mechanical Engineers British Ch
6、emical Plant ManufacturersInstitution of Mechanical Engineers Association(Automobile Division) British Compressed Air SocietyInstitution of Production Engineers* British Electrical and Allied ManufacturersLocomotive and Allied Manufacturers Association*Association of Great Britain British Gear Manuf
7、acturers Association*London Transport Board British Internal Combustion EngineMachine Tool Trades Association* Manufacturers AssociationMinistry of Defence British Iron and Steel FederationMinistry of Labour (H.M. Factory Inspectorate) British Mechanical Engineering FederationMinistry of Power Briti
8、sh Pump Manufacturers AssociationMinistry of Public Building and Works Crown Agents for Oversea Governments andMinistry of Technology National AdministrationsEngineering Laboratory* Electricity Council, the Central ElectricityMinistry of Transport Generating Board and the Area BoardsNational Coal Bo
9、ard in England and WalesNational Physical Laboratory (Ministry of Engineering Equipment Users AssociationTechnology) Gas CouncilRadio Industry Council Institute of Marine Engineers* Royal Institute of British Architects British Horological InstituteMinistry of Technology Electronic Engineering Assoc
10、iationNavy and Vickers Gearing Research Institute of British FoundrymenAssociation Institution of Engineering InspectionNorth-East Coast Institution of Engineers Institution of Engineers and Shipbuilders inand Shipbuilders ScotlandSociety of Motor Manufacturers and Traders Milling Cutter and Reamer
11、AssociationLtd. Ministry of Defence, Army DepartmentUniversity of Sheffield Ministry of Defence, Navy DepartmentManufacturers of fine pitch gears Amendments issued since publication Amd. No.Date of issueComments 3305May 1980Indicated by a sideline in the margin BS 978-1:1968 BSI 10-1999i Contents Pa
12、ge Co-operating organizationsInside front cover Forewordiii 1General 1.1Scope1 1.2Terminology and notation1 1.3Preferred range of normal diametral pitches2 1.4Basic rack tooth profile2 2Design details 2.1Outside diameter and centre distance3 2.2Modification of addendum and centre distance3 3Accuracy
13、 of gear blanks and gears 3.1General13 3.2Dual flank composite testing14 3.3Limits of tolerance on blanks and gear elements15 4Limits and tolerances of assembly 4.1Centre distance17 4.2Depth of engagement18 5Information to be given on drawings Appendix A Centre distance and addendum modification21 A
14、ppendix B Examples of calculations23 Appendix C Comparable diametral pitches and metric modules29 Appendix D Single flank composite testing: Limits of tolerance29 Appendix E Calculation of measuring pin dimensions for external and internal spur gears29 Figure 1 Basic rack tooth profile for unit norm
15、al diametral pitch2 Figure 2 Basic rack tooth profile for unit normal diametral pitch with backlash allowance2 Figure 3 Limiting values of addendum modification coefficient5 Figure 4 Minimum permissible addendum modification coefficient for helical pinions (!n = 20)6 Figure 5 Tolerance zone for prof
16、ile error15 Figure 6 Example of information to be given on drawings20 Figure 7 Chart for normal backlash when x1 + x2 = y28 Table 1 Normal diametral pitch Pn (inch units)2 Table 2 Data for spur pinions of unit diametral pitch having fewer than 17 teeth4 Table 3 Centre distances for spur gear pairs o
17、f unit diametral pitch for the conditions given in clause 2.2.47 Table 4 Forces appropriate to the pitch suitable for brass and steel product gears14 Table 5 Limits of tolerance14 Table 6 Limits of tolerance on gear blanks15 Table 7 Limits of tolerance on tooth profile16 Table 8 Limits of tolerance
18、on pitch16 Table 9 Limits of tolerance on tooth alignment16 BS 978-1:1968 ii BSI 10-1999 Page Table 10 Limits of tolerance on radial run-out of teeth17 Table 11 Limits of tolerance on tooth thickness17 Table 12 Limits of tolerance on centre distance of mounting17 Table 13 Minimum depth of engagement
19、 for spur gear pairs with 28 to 33 teeth (z2 + z1)18 Table 14 Minimum depth of engagement for spur gear pairs with more than 33 teeth (z2 + z1)18 BS 978-1:1968 BSI 10-1999iii Foreword This standard makes reference to the following British Standards: BS 978, Fine pitch gears. BS 978-2, Cycloidal type
20、 gears. BS 978-PD 3376, Addendum No. 1 to BS 978-2, Double circular arc type gears. BS 978-3, Bevel gears. BS 978-5, Hobs and cutters. First published in 1952 and revised in 1962, this British Standard has been further revised under the authority of the Mechanical Engineering Industry Standards Comm
21、ittee. In the 1962 edition, dual flank composite testing was introduced in the form of an appendix to the specification. As this method of test became more widespread, users of the standard were becoming confused between the application of the composite tolerances and application of the individual e
22、lemental tolerances. The prime reason for revision, therefore, has been to give dual flank testing the importance it now deserves by placing it in the mandatory part of the standard as the main accuracy testing procedure. Also care has been taken to ensure that the user is not misled by attempting t
23、o reconcile composite errors with elemental errors. It is necessary to retain the elemental tolerances because these will continue to be used in some fields as acceptance criteria and because they are essential as the basis for manufacturing gears and cutting tools1). Recognizing also that single fl
24、ank testing is used reference to this is made in an appendix. Opportunity has been taken to effect improvements in presentation and in the examples of calculations, and the terminology and notation is in accordance with that agreed within the International Organization for Standardization (ISO). Thi
25、s standard is a companion work to BS 978, “Fine pitch gears”, Part 2, “Cycloidal type gears” (including addendum PD 3376, “Double circular arc type gears”), Part 3, “Bevel gears”, and Part 5, “Hobs and cutters”. A British Standard does not purport to include all the necessary provisions of a contrac
26、t. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i to iv, pages 1 to 29 and a back cover. Thi
27、s standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. 1) BS 978, “Fine pitch gears”, Part 5, “Hobs and cutters”. iv blank BS 978-1:1968 BSI 10-19991 1 General 1.1 Scope This British Standard
28、 relates to involute spur, helical and crossed helical gears, having diametral pitches finer than 20, in four accuracy grades. Examples of application are: Class A. Astronomical apparatus and scientific instruments; colour printing machinery; control systems (when multiple trains of gears are involv
29、ed this grade would generally be used for low speed components where the effect of positional accuracy is important). Class B. Navigational instruments; high speed components of control systems where quietness and smooth running are essential; machine tool speed control; photographic instruments. Cl
30、ass C. General purpose instruments; accounting and calculating machinery; counters; clockwork mechanisms. Class D. Textile machinery; switch operating gear; clockwork mechanisms where accuracy is not the primary consideration. It is recommended that all spur, helical and crossed helical gears for us
31、e in horology should be produced to this British Standard with the possible exception of gears for weight or spring-driven mechanisms in which the pinion is the driven member and has 12 or fewer teeth. In such cases it may be preferable to use gears conforming to BS 978-22). 1.2 Terminology and nota
32、tion As the first step towards achieving international understanding of gears terminology, the terms and definitions of Draft ISO Recommendation No. 8883), “International vocabulary of gears”, have been applied, together with corresponding notation derived from Draft ISO Recommendation No. 889, “Int
33、ernational gear notation, symbols for geometrical data”3). The notation used is as follows: 2) BS 978, “Fine pitch gears”, Part 2, “Cycloidal type spur gears”. 3) To be incorporated in BS 2519, “Glossary of terms for toothed gearing”. aCentre distance avVirtual centre distance dReference circle diam
34、eter d1Reference circle diameter: pinion d2Reference circle diameter: wheel daTip diameter da1Tip diameter: pinion da2Tip diameter: wheel dRMeasuring pin diameter dbBase circle diameter jnNormal backlash jaCoefficient for calculation of backlash lLength of arc PnNormal diametral pitch sArc tooth thi
35、ckness s1Arc tooth thickness: pinion s2Arc tooth thickness: wheel xAddendum modification coefficient x1Addendum modification coefficient: pinion x2Addendum modification coefficient: wheel %x1Secondary addendum modification coefficient: pinion %x2Secondary addendum modification coefficient: wheel yCe
36、ntre distance modification coefficient BS 978-1:1968 2 BSI 10-1999 1.3 Preferred range of normal diametral pitches The pitch shall be selected from the following preferred range. Table 1 Normal diametral pitch Pn (inch units) 1.4 Basic rack tooth profile The shape and proportions of the basic rack t
37、ooth for spur helical and crossed helical gears shall be as shown either in Figure 1 or Figure 2. In the case of helical and crossed helical gears, the shape and proportions of the tooth are on a section at right angles to the pitch cylinder helix. Figure 1 shows the basic rack usually employed wher
38、e it is desired to have minimum backlash, as in servomechanisms. zNumber of teeth z1Number of teeth: pinion z2Number of teeth: wheel zvVirtual number of teeth !nNormal pressure angle !nwNormal pressure angle, operating !tTransverse pressure angle !twTransverse pressure angle, operating “Helix angle
39、at reference cylinder “bHelix angle at base cylinder a BS 978, “Fine pitch gears”, Part 5, “Hobs and cutters”. 3248100160 243664120180 284080140200 Figure 1 Basic rack tooth profile for unit normal diametral pitch Figure 2 Basic rack tooth profile for unit normal diametral pitch with backlash allowa
40、nce BS 978-1:1968 BSI 10-19993 Figure 2 is used where it is desired to have backlash to avoid any risk of jamming and where the load is usually uni-directional, for example, in clockwork mechanisms. When non-topping hobs are used it is permissible to use a hob conforming to Figure 1 basic rack and t
41、o cut at greater depth than normal to obtain the required tooth thickness. For internal gears (Figure 1 and Figure 2 basic racks) the addendum shall normally be 0.850 instead of 1.000. In cases when the tips of the teeth have a radius of 0.25 or greater (up to 0.3 max. as shown) the 1.000 addendum m
42、ay be applied. 2 Design details 2.1 Outside diameter and centre distance For the normal case when both z1 sec3“ and z2 sec3“ are greater than 17 the dimensions are as follows: 2.2 Modification of addendum and centre distance 2.2.1 For an explanation of the principles followed in connection with adde
43、ndum modification see Appendix A. 2.2.2 Where no limitations are imposed, the value of x for any gear whose virtual number of teeth zv is less than 17 is given by the formulae: This gives values in accordance with the lower limiting line XX in Figure 3 and a small and normally negligible amount of u
44、ndercutting is thereby permitted. The addendum modification coefficient for helical pinions from 6 to 16 teeth and helix angles up to 45 is shown in Figure 4. 2.2.3 When the pinion is modified as above and there are no other limitations, the wheel is unmodified and its dimensions are obtained from t
45、he formulae in 2.1; but the dimensions of the pinion and centre distance are as follows: Parallel axis external gear pairs designed as above have backlash at this centre distance. (See Appendix A.) (1)(2) (3)(4) (5) (For spur gears, sec“ = 1) (See Table 2 and Figure 3 and Figure 4) (6) where zv = z
46、sec“ sec2“b . z sec3“(7) (8) (Figure 1 type gears)(9) (Figure 2 type gears)(10) (11) x1 zv sin2 2 - -n= BS 978-1:1968 4 BSI 10-1999 Table 2 Data for spur pinions of unit diametral pitch having fewer than 17 teeth 2.2.4 Enlarged spur pinions with minimum backlash. Spur pinions enlarged according to T
47、able 2 may be engaged with wheels in which x2 is zero, at centre distance derived from Table 3. Gears derived from Figure 1 basic rack will have no backlash at this centre distance. A small and negligible reduction of tip-to-root clearance is obtained at this centre distance. Table 2 is not applicab
48、le to helical gears, for which the formulae in Appendix A are required. Alternatively, spur pinions enlarged according to Table 2 or helical pinions enlarged according to Figure 4 may be engaged with wheels in which x2 = x1, in which case the centre distance is as obtained in 2.1, and Such gears der
49、ived from Figure 1 basic rack will have zero backlash at nominal dimensions. No. of teeth z1 Addendum modification coefficient x1 Tip diameter da1 Increase in circular tooth thickness at standard pitch dia. Recommended minimum number of teeth in mating wheel z2 8a 9a 10 0.5321 0.4736 0.4151 11.0642 11.9472 12.8302 0.3874 0.3448 0.3022 26 25 24 11 12 13 0.3566 0.2982 0.2397 13.7132 14.5963 15.4793 0.2596 0.2170 0.1744 23 22 21 14 15 16 0.1812 0.1227 0.0642 16.3623 17.2453 18.1284 0.1319 0
链接地址:https://www.31doc.com/p-3737353.html