After completion of one or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back again to its starting position, thus enabling a short rack cutter of a practical length to be used. Cutter is again fed back to depth and cycle is repeated. Quantity of teeth is managed by the machine gearing, and pitch and pressure angle by the rack cutter. This technique is used for generation of external 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 in to the gear blank to the proper depth and the two 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 profile depending on the form of cutter , however the accumulation of these directly cuts produces a curved type of the gear teeth, therefore the name generating process. One rotation of the work completes the cutting upto particular depth upto which hob is definitely fed unless the apparatus includes a wide face.
This methodis specifically 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 process, the cutter includes true involute rack which reciprocates across the face of the blank and the blank rotates in the correct relationship to the longitudinal movement of the cutter as though both roll with each other as a rack and pinion. At first the cutter is usually fed into full 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 gear rack for Machine Tool Industry pointed tools. The usage of the formed device for finishing can be impracticable for the bigger pitches which are completed by a single pointed tool. The amount of cuts required depends upon the size of the tooth, amount of share to be taken out, and the type of material.