After completion of one or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back again to its starting position, thus enabling a brief rack cutter of a practical length to be utilized.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 position by the rack cutter. This method is used for generation of external spur gears, being ideally fitted to gear rack for Machine Tool Industry cutting large, dual helical gears. For generating helical tooth, the cutter slides are inclined at the gear tooth helix angle.
The hob is fed in to the gear blank to the correct depth and both are rotated together as if in mesh. The teeth of the hob cut into the work piece in successive order 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 straight cuts produces a curved form of the gear teeth, hence the name generating process. One rotation of the task completes the slicing 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 challenging 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 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 if both roll together 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 technique, both roughening and completing cuts are taken with single pointed tools. The utilization of the formed device for finishing can be impracticable for the larger pitches which are completed by a single pointed tool. The number of cuts required depends upon the size of the tooth, amount of share to be removed, and the kind of material.