After completion of one or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back again to its starting position, thus allowing a brief rack cutter of a practical length to be used. Cutter is once again fed back again to depth and cycle is repeated. Number of teeth is controlled by the machine gearing, and pitch and pressure position by the rack cutter. This gear rack for Machine Tool Industry china method is utilized for generation of external spur gears, being ideally fitted to cutting large, dual helical gears. For generating helical tooth, the cutter slides tend at the gear 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 into the work piece in successive order and each in a somewhat different placement. Each hob tooth cuts its profile based on the form of cutter , however the accumulation of these straight cuts produces a curved form of the gear teeth, thus the name generating procedure. One rotation of the task completes the slicing upto particular depth upto which hob is fed unless the gear has a wide face.
This methodis specially adopted to cutting large teeth which are challenging 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 consists of accurate 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 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 produced 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 usage of the formed tool for finishing is usually impracticable for the bigger pitches which are finished by an individual pointed tool. The amount of cuts required is dependent upon how big is the tooth, amount of stock to be eliminated, and the type of material.