After completion of one or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back to its starting position, thus enabling a short rack cutter of a practical size to be utilized. Cutter is once again fed back to depth and routine is repeated. Amount of teeth is managed by the machine gearing, and pitch and pressure angle by the rack cutter. This method is used for generation of exterior spur gears, being preferably fitted to cutting large, double helical gears. For producing helical teeth, the cutter slides tend at the gear tooth helix angle.
The hob is fed into the gear blank to the gear rack for Machine Tool Industry proper depth and the two are rotated together as if in mesh. The teeth of the hob cut in to the function piece in successive order and each in a somewhat different placement. Each hob tooth cuts its own profile based on the shape of cutter , however the accumulation of these straight cuts generates a curved form of the gear teeth, thus the name generating process. One rotation of the task completes the cutting upto specific depth upto which hob is usually fed unless the apparatus includes a wide face.
This methodis specifically adopted to cutting large teeth which are difficult to cut by formed cutter, and also to cut bevel-gear teeth. It is not widely used at present.
In gear planing process, the cutter contains true involute rack which reciprocates across the face of the blank and the blank rotates in the correct relationship to the longitudinal motion of the cutter as though both roll with each other as a rack and pinion. Initially the cutter is fed into complete tooth depth with cutter reciprocating and blank stationary. Involute shape is generated as the blank rotates and involute rack cutter feeds longitudinally.
In the other method, both roughening and finishing cuts are taken with single pointed tools. The utilization of the formed device for finishing is usually impracticable for the larger pitches which are finished by an individual pointed tool. The number of cuts required depends upon the size of the tooth, amount of stock to be removed, and the type of material.