Worm Gear Mfg.

This is how a tap and aluminium blank are set up for the cutting of the worm wheel. The blank (not shown here) is center drilled to 10 mm to fit the toolpost and held down during the cutting.The blank's diameter is calculated to give the required number of teeth. As the tap slowly turns it advances the blank while cutting the teeth. At each revolution the crossfeed is advance a few thousandths of an inch until the desired tooth depth is reached.

This shows a blank in place with a finer pitch tap (1/4-20). The dead center is not used on such small taps.