After completion of one or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back again to its starting position, thus enabling a short rack cutter of a practical size to be utilized.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 device gearing, and pitch and pressure angle by the rack cutter. This method is used for generation of exterior 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 shape 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 difficult to cut by formed cutter, and also to cut bevel-gear teeth. It is not gear rack for Machine Tool Industry widely used at present.
In gear planing procedure, the cutter contains true involute rack which reciprocates across the face of the blank and the blank rotates in the correct relationship to the longitudinal motion of the cutter as if both roll jointly as a rack and pinion. At first 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 method, both roughening and finishing cuts are taken with single pointed tools. The use of the formed tool for finishing can be 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, quantity of stock to be taken out, and the kind of material.