After completion of one or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back to its starting position, thus enabling a short rack cutter of a practical duration to be used. Cutter is once again fed back again to depth and routine is repeated. Amount of teeth is controlled by the gear rack for Machine Tool Industry machine gearing, and pitch and pressure position by the rack cutter. This technique can be used for generation of external spur gears, being ideally fitted to cutting large, dual helical gears. For producing helical tooth, the cutter slides tend at the apparatus tooth helix angle.
The hob is fed in to the gear blank to the proper depth and the two are rotated together as if in mesh. The teeth of the hob cut in to 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 , but the accumulation of these directly cuts generates a curved kind of the gear teeth, thus the name generating procedure. One rotation of the task completes the trimming upto particular depth upto which hob can be fed unless the gear has a wide face.
This methodis specially adopted to cutting large teeth which are difficult to cut by formed cutter, and also to cut bevel-gear teeth. It is not widely used at present.
In gear planing procedure, the cutter consists of accurate involute rack which reciprocates over the face of the blank and the blank rotates in the right relationship to the longitudinal motion of the cutter as if both roll with each other as a rack and pinion. At first the cutter is definitely 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 method, both roughening and completing cuts are taken with single pointed tools. The utilization of the formed device for finishing can be impracticable for the bigger pitches which are completed by an individual pointed tool. The number of cuts required depends upon how big is the tooth, quantity of share to be removed, and the type of material.