After completion of one or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back again to its starting position, thus allowing a short rack cutter of a practical length to be utilized. Cutter is again fed back to depth and routine is repeated. Quantity 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, dual gear rack for Machine Tool Industry china helical gears. For making helical the teeth, the cutter slides are inclined at the gear tooth helix angle.
The hob is fed into the gear blank to the proper depth and both are rotated together as though in mesh. One’s teeth of the hob cut into the work piece in successive order and each in a slightly different placement. Each hob tooth cuts its own profile depending on the shape of cutter , however the accumulation of these straight cuts creates a curved kind of the gear teeth, thus the name generating process. One rotation of the task completes the cutting upto particular depth upto which hob is fed unless the apparatus includes a wide face.
This methodis specially adopted to cutting large teeth which are hard to cut by formed cutter, and to cut bevel-gear teeth. It isn’t 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 movement of the cutter as if both roll jointly as a rack and pinion. At first the cutter is certainly fed into full 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 completing cuts are taken with single pointed tools. The use of the formed device for finishing is impracticable for the larger pitches which are completed by an individual pointed tool. The amount of cuts required depends upon the size of the tooth, amount of stock to be removed, and the type of material.