After completion of 1 or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back to its starting position, thus allowing a brief rack cutter of a practical length to be utilized. Cutter is again fed back to depth and cycle is repeated. Number of teeth is controlled by the device gearing, and pitch and pressure angle by the rack cutter. This method is used for generation of external spur gears, being ideally fitted to cutting large, double helical gears. For creating helical the teeth, the cutter slides are inclined at the gear tooth helix angle.
The hob is fed into the gear blank to the correct depth and both are rotated together as though in mesh. One’s teeth of the hob cut in to the function piece in successive order and each in a somewhat different position. Each hob tooth cuts its own profile depending on the form of cutter , however the accumulation of these directly cuts creates a curved form of the gear teeth, therefore the name generating process. One rotation of the work completes the slicing upto specific depth upto which hob is fed unless the apparatus includes a wide face.
This methodis specially gear rack for Machine Tool Industry china adopted to cutting large teeth which are challenging to cut by formed cutter, and to cut bevel-gear teeth. It isn’t widely used at the moment.
In gear planing process, the cutter includes true involute rack which reciprocates over the face of the blank and the blank rotates in the right relationship to the longitudinal movement of the cutter as if both roll collectively as a rack and pinion. Initially the cutter is certainly fed into full 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 technique, both roughening and finishing cuts are taken with single pointed tools. The usage of the formed tool for finishing is certainly impracticable for the larger pitches which are finished by a single pointed tool. The number of cuts required is dependent upon the size of the tooth, amount of stock to be eliminated, and the type of material.