To cut wheel teeth under CNC control, a fourth axis is required, at right angles to the main spindle, and a stepper motor driven indexing head of some sort. I had a home made rotary table and a 90 deg angle fixture. But my DM2400 mill had no electronic control equipment for the fourth axis. So I built a stepper motor drive to the worm on the rotary table via a toothed belt. This can be seen in the first picture. The blue band is the "anti backlash" device! I also built an electronic driver board for the stepper, which connects to the parallel port on the PC, and wrote the program to intersperse mill commands with rotary table commands.

The overall resolution of this set up is - rotary table worm 60:1, toothed belt drive 3.6:1, stepper increments 200 per rev. This gives a resolution of 43,200 : 1. For a 90 tooth wheel, the stepper does exactly 480 steps, but for, say, a 84 tooth wheel, the theoretical steps is 514.29. So for this the program works out a repeating pattern 514, 515, 514, 514, 514, 514, 515 ... so that there is no accumulated error.

Since the teeth are cut after crossing out, substantial aluminium supporting washers are used to maintain rigid support for the wheel.

For reference to the stepper motor driver board visit www.oatleyelectronics.com  Kit number K179