After completion of one or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back again to its starting position, thus enabling a short rack cutter of a practical size to be utilized. Cutter is again fed back again to depth and cycle is repeated. Quantity of teeth is managed by the gear rack for Machine Tool Industry china device gearing, and pitch and pressure angle by the rack cutter. This method is used for generation of external spur gears, being preferably fitted to cutting large, dual helical gears. For producing helical tooth, the cutter slides are inclined at the gear tooth helix angle.
The hob is fed into the gear blank to the correct depth and both are rotated together as if in mesh. One’s teeth of the hob cut in to the function piece in successive order and each in a slightly different position. Each hob tooth cuts its own profile based on the form of cutter , however the accumulation of these directly cuts produces a curved form of the gear teeth, therefore the name generating process. One rotation of the work completes the slicing upto particular depth upto which hob is fed unless the gear includes a wide face.
This methodis specially adopted to cutting large teeth which are tough to cut by formed cutter, and also to cut bevel-gear teeth. It is not widely used at present.
In gear planing process, the cutter contains 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 collectively as a rack and pinion. Initially the cutter is usually 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 method, both roughening and finishing cuts are taken with single pointed tools. The use of the formed device for finishing is certainly impracticable for the bigger pitches which are finished by a single pointed tool. The amount of cuts required is dependent upon how big is the tooth, amount of stock to be removed, and the kind of material.