After completion of 1 or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back to its starting position, thus enabling a brief rack cutter of a practical size to be used. Cutter is once again fed back to depth and cycle is repeated. Amount of teeth is managed by the machine gearing, and pitch and pressure position by the rack cutter. This method is used for generation of exterior spur gears, being preferably suited for cutting large, dual helical gears. For making helical tooth, the cutter slides are inclined at the gear tooth helix angle.
The hob is fed in to the gear blank to the proper depth and both are rotated together as if in mesh. One’s teeth of the hob cut into the function piece in successive purchase and each in a somewhat different placement. Each hob tooth cuts its profile depending on the shape 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 task completes the reducing upto particular depth upto which hob can be fed unless the gear has a wide face.
This methodis specifically adopted to cutting large teeth which are hard to cut by formed cutter, and 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 right relationship to the longitudinal gear rack for Machine Tool Industry movement of the cutter as if both roll together as a rack and pinion. Initially the cutter can be 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 technique, both roughening and completing cuts are taken with single pointed tools. The use of the formed tool for finishing is certainly 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 share to be eliminated, and the kind of material.