After completion of one or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back again to its starting position, thus allowing a brief rack cutter of a practical size to be used. Cutter is again fed back again to depth and cycle is gear rack for Machine Tool Industry repeated. Number of teeth is managed by the machine gearing, and pitch and pressure angle by the rack cutter. This method can be used for generation of exterior spur gears, being ideally fitted to cutting large, dual helical gears. For generating helical the teeth, the cutter slides are inclined at the apparatus tooth helix angle.
The hob is fed into the gear blank to the correct depth and the two are rotated together as if in mesh. The teeth of the hob cut in to the work piece in successive purchase and each in a slightly different placement. Each hob tooth cuts its profile based on the form of cutter , but the accumulation of these straight cuts generates a curved kind of the gear teeth, hence the name generating process. One rotation of the work completes the reducing upto specific depth upto which hob is definitely fed unless the apparatus includes a wide face.
This methodis specially adopted to cutting large teeth which are difficult to cut by formed cutter, and to cut bevel-gear teeth. It is not widely used at the moment.
In gear planing procedure, the cutter consists of true involute rack which reciprocates across the face of the blank and the blank rotates in the correct relationship to the longitudinal movement of the cutter as if both roll collectively as a rack and pinion. Initially the cutter is usually fed into complete tooth depth with cutter reciprocating and blank stationary. Involute form is generated as the blank rotates and involute rack cutter feeds longitudinally.
In the other method, both roughening and completing cuts are taken with single pointed tools. The utilization of the formed tool for finishing is certainly impracticable for the bigger pitches which are finished by an individual pointed tool. The amount of cuts required depends upon the size of the tooth, quantity of share to be taken out, and the kind of material.