After completion of 1 or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back to its starting position, thus enabling a short rack cutter of a practical size to be used. Cutter is again fed back to depth and routine is repeated. Number of teeth is controlled by the machine gearing, and pitch and pressure position by the rack cutter. This method can be used for generation of exterior spur gears, being ideally fitted to cutting large, double 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 the two 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 own profile depending on the form of cutter , however the accumulation of these directly cuts produces a curved form of the gear teeth, therefore the name generating procedure. One rotation of the work completes the slicing upto certain depth upto which hob is certainly fed unless the apparatus has a wide face.
This methodis specially adopted to cutting large teeth which are difficult to cut by formed cutter, and to cut bevel-gear teeth. It is not widely used at present.
In gear planing procedure, the cutter includes true gear rack for Machine Tool Industry 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 though both roll with each other as a rack and pinion. Initially the cutter can be fed into full tooth depth with cutter reciprocating and blank stationary. Involute shape 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 usage of the formed tool for finishing is certainly impracticable for the bigger pitches which are finished by a single pointed tool. The amount of cuts required depends upon how big is the tooth, quantity of stock to be removed, and the kind of material.