After completion of 1 or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back to its starting position, thus enabling a short rack cutter of a practical duration to be utilized. Cutter is once again fed back to depth and routine is repeated. Amount of teeth is managed by the machine gearing, and pitch and pressure position by the rack cutter. This technique is utilized for generation of external spur gears, being preferably suited for cutting large, double helical gears. For making helical tooth, the cutter slides tend at the gear tooth helix angle.
The hob is fed in to the gear blank to the proper depth and both are rotated together as though in mesh. One’s teeth of the hob cut into the function piece in successive order and each in a somewhat different position. Each hob tooth cuts its own profile depending on the shape of cutter , however the accumulation of these directly cuts produces a curved form of the gear teeth, thus the name generating procedure. One rotation of the task gear rack for Machine Tool Industry completes the cutting upto certain depth upto which hob is certainly fed unless the gear has a wide face.
This methodis specially 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 the moment.
In gear planing procedure, the cutter consists of true involute rack which reciprocates over the face of the blank and the blank rotates in the correct relationship to the longitudinal movement of the cutter as though both roll collectively as a rack and pinion. Initially the cutter is definitely 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 finishing cuts are taken with single pointed tools. The usage of the formed device for finishing is usually impracticable for the larger pitches which are completed by a single pointed tool. The number of cuts required depends upon how big is the tooth, amount of stock to be removed, and the kind of material.