After completion of one or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back again to its starting position, thus enabling a brief rack cutter of a practical length to be utilized. Cutter is again fed back to depth and cycle is repeated. Quantity of teeth is controlled by the device gearing, and pitch and pressure angle by the rack cutter. This technique is utilized for generation of exterior spur gears, being preferably suited for cutting large, double helical gears. For creating 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 both are rotated together as if in mesh. The teeth of the hob cut in to the function piece in successive purchase and each in a slightly different position. Each hob tooth cuts its own profile depending on the shape of cutter , but the accumulation of these gear rack for Machine Tool Industry china straight cuts generates a curved kind of the gear teeth, thus the name generating process. One rotation of the work completes the trimming upto particular depth upto which hob is fed unless the apparatus 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 the moment.
In gear planing process, the cutter includes true involute rack which reciprocates across 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 definitely 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 technique, both roughening and completing cuts are taken with single pointed tools. The usage 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 how big is the tooth, amount of share to be eliminated, and the type of material.