BS 4582-1:1970

Co-operating organizations
Foreword
Specification
1 General
1.1 Scope
1.2 Terminology and notation
1.3 Standard modules
1.4 Basic rack tooth profile
2 Design details
2.1 Outside diameter and centre distance
2.2 Modification of addendum and centre distance
3 Accuracy of gear blanks and gears
3.1 General
3.2 Dual flank composite testing - test pressures and
     limits of tolerance
3.3 Limits of tolerance on blanks and gear elements
4 Limits and tolerances of assembly
4.1 Centre distance
4.2 Depth of engagement
5 Information to be given on drawings
5.1 Recommendation
Appendices
A Centre distance and addendum modification
B Examples of calculation
C Comparable metric modules and diametral pitches
D Single flank composite testing: limits of tolerance
E Calculation of measuring pin dimensions for
     external and internal spur gears
Tables
1 Standard modules
2 Data for spur pinions of unit module having fewer
     than 17 teeth
3 Centre distances for spur gear pairs of unit module
     for the conditions given in 2.3, para. 1
4 Forces appropriate to the module suitable for brass
     and steel product gears
5 Dual flank composite error tolerances
6 Limits of tolerance on gear blanks
7 Limits of tolerance on tooth profile
8 Limits of tolerance on pitch
9 Limits of tolerance on tooth alignment
10 Limits of tolerance on radial run-out of teeth
11 Limits of tolerance on tooth thickness
12 Tolerance on centre distance of mounting
13 Minimum depth of engagement for spur gear pairs
     with 28 to 33 teeth (z2 + z1)
14 Minimum depth of engagement for spur gear pairs
     with more than 33 teeth (z2 + z1)
Figures
1 Basic rack tooth profile for unit normal module
2 Basic rack tooth profile for unit normal module
     with backlash allowance
3 Limiting values of addendum modification
     coefficient
4 Minimum permissible addendum modification
     coefficient for helical pinions (alpha n = 20 deg)
5 Tolerance zone for profile error
6 Examples of information to be given on drawings
7 Chart for normal backlash when x1 + x2 = y

Covers gears having modules of 1 mm and less including first and second preferences. Two basic racks (one with backlash allowance); modification of addendum and centre distance to suit various conditions. Four grades of accuracy with elemental and dual flank composite test tolerances. Appendices give information on single flank testing, calculation of measuring pin dimensions and examples of calculations for various design conditions. Metric equivalent of BS 978-1.

This British Standard relates to involute spur, helical and crossed helical gears, having modules of one millimetre and finer, 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 involved 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; photo­ graphic instruments.

Class 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 use 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 cycloidal type spur gears, conforming to BS 978, Part 2†.

Examples of calculation are given in Appendix B.