BS 721-1:1963
Current
The latest, up-to-date edition.
Specification for worm gearing Imperial units
Hardcopy , PDF
English
25-04-1963
Co-operating organizations
Foreword
Specification
1 Scope
2 General information on worm gear elements
a Module
b Axial pitch and normal pitch designations
c Diameter factor q
d Worm gear designations
3 Notation
4 Form of threads and teeth
a Standard worm thread surfaces
b Basic rack
c Undercutting of worm threads
d Thread thickness
e Wormwheel teeth and entry gaps
f Wormwheel tooth fillet
g Face width of wormwheel
5 Formulae for calculation of dimensions
a Limiting values of centre distance for given values
of t, T, q and m
b Limiting values of m for given values of C, t, T
and q
c Formulae for detail dimensions of worm and wheel
d Rim section
6 The general system of worm gear design
a Obtaining suitable values of t, T, q and m
b Standard axial modules
c Standard diameter factors (q)
d Determinations of t and T
e Guidance for determination of q
f Procedure for selecting standard worms
7 Tables and dimensions of standard worms and wheels
a Tables of worm gear designations
(i) Standard centre distances for industrial worm
gears
(ii) Standard centre distances for axle
transmission gears
b Examples of worm gear designations
c Detail dimensions of worms and wheels
8 Tolerances
a Worms:
(i) runout of tip diameter
(ii) pitch tolerances
(iii) profile tolerances
(iv) thread thickness tolerances
b Wormwheels: pitch tolerances
9 Normal backlash
10 Working temperatures
11 Efficiency and lubrication
12 Irreversibility
13 Information to be given on drawings by the purchaser
Tables
1 Examples of designations t/T/q/m for industrial worm
gears for all worm speeds
2 Examples of designations t/T/q/m for industrial worm
gears for speeds up to 300 rev/min
3 Recommended numbers of worm threads t and wheel
teeth T for axle transmission worm gears
4 Dimensions of standard worms of unit axial module
5 Worm gear zone factors
6 Stress factors for worm gears
7 Duty factor
Appendices
A Load capacity
A1 Determination of load capacity
A2 Determination of equivalent running time for loading
conditions other than a steady load
A3 Momentary overload capacity
A4 Axle transmission gears
B Examples of calculations
C Design procedure based on axial pitch of worm
D Procedure for the design of worms to suit standard
diametral pitch cutting tools corresponding to the
normal pitch of the worm
Charts
1 Maximum positive value of addendum modification
coefficient for 1 module (kW1)
2 Maximum negative value of addendum modification
coefficient for 1 module (kW2)
3 Determination of q for worm speeds up to 300 rev/min
4 Determination of q for maximum efficiency for any
worm speed
5 Coefficient of friction of worm gears
6 Speed factors for worm gears (for wear) (Xc)
7 Speed factors for worm gears (for strength) (Xb)
8 Expected life factors for strength and wear
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