After completion of 1 or two teeth, the blank and cutter stop gear rack for Machine Tool Industry feeding and the cutter is withdrawn and indexed back again to its starting position, thus enabling a short rack cutter of a practical size to be utilized. Cutter is once again fed back again to depth and routine is repeated. Number of teeth is managed by the machine gearing, and pitch and pressure angle by the rack cutter. This technique can be used for generation of external spur gears, being preferably fitted to cutting large, double helical gears. For generating helical tooth, the cutter slides tend at the apparatus tooth helix angle.
The hob is fed into the gear blank to the correct depth and the two are rotated together as if in mesh. One’s teeth of the hob cut in to the function piece in successive purchase and each in a somewhat different position. Each hob tooth cuts its profile based on the form of cutter , but the accumulation of these straight cuts generates a curved kind of the gear teeth, therefore the name generating process. One rotation of the work completes the trimming upto specific depth upto which hob is fed unless the gear has a wide face.
This methodis specially 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 the moment.
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 movement of the cutter as though both roll with each other as a rack and pinion. Initially the cutter can be fed into complete 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 finishing cuts are taken with single pointed tools. The usage of the formed device for finishing is impracticable for the bigger pitches which are finished by an individual pointed tool. The number of cuts required is dependent upon how big is the tooth, amount of stock to be taken out, and the kind of material.