Worm and Worm Wheel: a Steel Screw and a Hobbed Bronze Wheel

A worm is a screw that drives a toothed wheel at right angles; with a single-start worm each turn moves the wheel one tooth, so a 30-tooth wheel gives 30:1. Cut the worm on a screw-cutting lathe, make a hob that is a copy of it with cutting edges, gash the bronze wheel on the dividing head, then run the hob through it to finish the teeth. The picture: a worm shaft with its bearings and a hobbed bronze worm wheel from a gearbox.