After completion of 1 or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back to its starting position, thus allowing a short rack cutter of a practical size to be used. Cutter is again fed back to depth and cycle is repeated. Quantity of teeth is managed by the device gearing, and pitch and gear rack for Machine Tool Industry china pressure position by the rack cutter. This technique can be used for generation of external spur gears, being ideally suited for cutting large, dual 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 correct depth and both are rotated together as though in mesh. The teeth of the hob cut into the work piece in successive purchase and each in a somewhat different placement. Each hob tooth cuts its profile based on the shape of cutter , but the accumulation of these straight cuts creates a curved type of the gear teeth, thus the name generating process. One rotation of the task completes the slicing upto particular depth upto which hob is certainly fed unless the gear has a wide face.
This methodis specifically adopted to cutting large teeth which are hard to cut by formed cutter, and to cut bevel-gear teeth. It is not widely used at present.
In gear planing procedure, the cutter contains 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 collectively as a rack and pinion. Initially the cutter is usually 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 technique, both roughening and completing cuts are taken with single pointed tools. The usage of the formed tool for finishing is certainly impracticable for the larger pitches which are completed by a single pointed tool. The number of cuts required is dependent upon the size of the tooth, quantity of stock to be removed, and the type of material.