Gear Tooth Generation

Figure 6 shows some teeth of a rack and pinion engaged. It can be seen from this that as the radius of the base circle is extended to infinity, the involute line becomes a straight line at right angles to the line of action.

Figure 6 Rack contact.

The majority of gear generating equipment uses this principle and the involute is therefore generated by a series of flats that approximate the involute profile. The gears are generated by a cutter with a tooth profile of the straight-sided basic rack.

Figure 7 Gear cutting. (Shigley)

There are some grinding machines that generate a true involute, by mounting the gear to be ground on the shaft, which is attached to two steel discs of the same diameter as the base circle, and two steel bands hold the discs so that as the shaft is moved a true involute is generated.