After completion of 1 or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back again to its starting position, thus enabling a short rack cutter of a practical length to be used.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 again to depth and routine is repeated. Amount of teeth is managed by the machine gearing, and pitch and gear rack for Machine Tool Industry pressure position by the rack cutter. This method is used for generation of external spur gears, being ideally fitted to cutting large, double helical gears. For creating helical tooth, the cutter slides are inclined at the gear tooth helix angle.
The hob is fed into the gear blank to the proper depth and the two are rotated together as if in mesh. One’s teeth of the hob cut into the work piece in successive order and each in a somewhat different position. Each hob tooth cuts its profile based on the shape of cutter , however the accumulation of these straight cuts creates a curved kind of the gear teeth, therefore the name generating process. One rotation of the work completes the cutting upto particular depth upto which hob is usually fed unless the apparatus has a wide face.
This methodis specially adopted to cutting large teeth which are tough 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 includes accurate 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 together as a rack and pinion. Initially the cutter is definitely fed into complete tooth depth with cutter reciprocating and blank stationary. Involute form is generated 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 utilization of the formed device for finishing is definitely impracticable for the bigger pitches which are finished by a single pointed tool. The number of cuts required is dependent upon the size of the tooth, amount of share to be eliminated, and the type of material.