BS 721-1:1963

This British Standard applies to worm gearing and comprises cylindrical involute helicoid worms and worm wheels conjugate thereto, the dimensions of which are expressed in inches, Four classes of gears are provided which are related to function and precision. The range of modules is given in convenient steps from 0.052 to 1.

This standard does not refer to pairs of cylindrical gears connecting non-parallel axes known as crossed helical gears.

Cylindrical involute helicoid worms with a normal pressure angle of 20° in a range of axial modules from 0.052 in to 1 in. Design, formulae for calculating worm and wormwheel dimensions; four gear classes, with tolerances for pitch, profile and worm thread thickness, and five grades of backlash for assembly. Drawings show information to be given when ordering. Appendices: determination of load capacity, design calculations for typical gears, design procedure based on axial pitch of the worm, design of worms to suit standard diametral pitch cutting tools corresponding to the normal pitch of the worm.