BS 6168:1987

Foreword
Committees responsible
Specification
1 Scope
2 Definitions and symbols
3 Basic rack tooth profile
4 Normal modules and normal diametral pitches
5 Fabrication
6 Accuracy
7 Measurement
8 Gear errors and tolerances
9 Hub and rim proportions
10 Allowances for thermal and hygroscopic expansion
11 Information to be given on drawings
Appendices
A Materials
B Lubrication of plastics gears
C Tables of tolerance values
D Addendum modification
E Example calculations of maximum centre distance
       and total gear and housing expansion
F Recommended method for calculation of gear
       stresses
Tables
1 Normal modules
2 Normal diametral pitches
3 Gear errors and tolerances
4 Tolerance on cumulative tooth pitch error over a
       sector of k pitches (Fpk) or arc length L
5 Adjacent pitch error (transverse) tolerance fpt
6 Radial run-out tolerance Fr
7 Radial tooth-to-tooth composite error tolerance
       fi"
8 Radial composite error tolerance Fi"
9 Radial indicator reading tolerance Fl
10 Tooth profile error tolerance ff
11 Tooth alignment error tolerance on face width b,
       F beta
12 Centre distance error tolerance fa
13 Gear blanks tolerances
14(a) Cumulative tooth pitch error tolerance Fpk
       (metric units)
14(b) Cumulative tooth pitch error tolerance Fpk
       (imperial units)
15(a) Adjacent pitch error (transverse) tolerance fpt
       (metric units)
15(b) Adjacent pitch error (transverse) tolerance fpt
       (imperial units)
16(a) Radial run-out tolerance Fr (metric units)
16(b) Radial run-out tolerance Fr (imperial units)
17(a) Radial tooth-to-tooth composite error tolerance
       fi" (metric units)
17(b) Radial tooth-to-tooth composite error tolerance
       fi" (imperial units)
18(a) Radial composite error tolerance Fi" (metric
       units)
18(b) Radial composite error tolerance Fi" (imperial
       units)
19(a) Radial indicator reading tolerance Fl (metric
       units)
19(b) Radial indicator reading tolerance Fl (imperial
       units)
20(a) Tooth profile error tolerance ff (metric units)
20(b) Tooth profile error tolerance ff (imperial units)
21(a) Tooth alignment error tolerance F beta (metric
       units)
21(b) Tooth alignment error tolerance F beta (imperial
       units)
22(a) Tolerances on radial and axial run-out of
       reference surfaces of wheel blanks (metric units)
22(b) Tolerances on radial and axial run-out of
       reference surfaces of wheel blanks (imperial
       units)
23(a) Values of IT (metric units)
23(b) Values of IT (imperial units)
24 Coefficient of friction mu
25 Dimensionless experimental factor Ka
26 Correction coefficient Kb
27 Gear material constant KM
28 Maximum bulk temperature for non-metallic
       materials for continuous operation
29 Application factor KA for speed reducing gears
30 Poisson's ratio
Figures
1 Basic rack tooth profile for normal modules
2 Limits of tip relief of modified basic rack tooth
       profile for normal modules
3 Test loads
4 Tolerance on cumulative tooth pitch error over k
       pitches Fpk
5 Tolerance factor phi p
6 Adjacent pitch error (transverse) tolerance fpt
7 Radial run-out tolerance Fr
8 Radial tooth-to-tooth composite error tolerance
       fi"
9 Radial composite error tolerance Fi"
10 Radial indiator reading tolerance Fl
11 Tolerance factor phi f
12 Tooth profile error tolerance ff
13 Tooth alignment tolerance on face width b, F beta
14 Plastics moulding on metal hub
15 Plastics moulding without hub
16 Plastics moulding with hub
17 Example of a typical drawing
18 Thermal expansion rates
19 Hygroscopic expansion rates
20 Pinion with 10 teeth
21 Tooth form factor YF as a function of number of
       teeth z for different values of addendum
       modification coefficient x
22 Endurance limit for bending stress versus gear
       life (unlubricated PA 66)
23 Endurance limit for bending stress versus gear
       life (unlubricated POM)
24 Size factor YX as a function of gear module
25 Young's modulus versus temperature
26 Endurance limit for contact stress versus gear
       life (unlubricated PA 66)
27 Endurance limit for contact stress versus gear
       life (unlubricated POM)

Dimensional accuracy and material requirements for spur gears in the pitch sizes of 0.5 module to 50 module (48 to 0.5 dp)

This British Standard specifies dimensional, accuracy and material requirements for spur gears made from non-metallic materials in pitch sizes of 0.50 module to 50 module (48 to 0.50 diametral pitch) and also gives guidance on lubrication and lists information to be given on drawings. The ranges of modules and diametral pitches employed include those specified in BS 436-1 and BS 436-2. The basic tooth form and the accuracy grades specified are selected from those specified in BS 436-1 and BS 436-2. Helical gears are not within the scope of this standard.

Surface finish requirements for thermoplastics gears are not specified in this standard as insufficient authoritative data on the subject exists at present.

NOTE 1 Information on the selection of materials and the lubrication of plastics gears is given in Appendix A and Appendix B, respectively. Tables of tolerance values are given in Appendix C. Recommendations for addendum modification and a recommended method of gear stressing are given in Appendix D and Appendix F. Example calculations are given in Appendix E and Appendix F.

NOTE 2 The titles of the publications referred to in this standard are listed on the inside back cover.