After completion of 1 or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back to its starting position, thus enabling a short rack cutter of a practical size to be utilized. Cutter is again fed back 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 exterior spur gears, being ideally suited for cutting large, double helical gears. For making helical teeth, the cutter slides are inclined at the apparatus tooth helix angle.
The hob is fed into the gear blank to the proper depth and both are rotated together as though in mesh. One’s teeth of the hob cut in to the function piece in successive purchase and each in a slightly different position. Each hob tooth cuts its own profile depending on the shape of cutter , but the accumulation of these directly cuts creates a curved kind of the gear teeth, therefore the name generating process. One rotation of the work completes the cutting upto gear rack for Machine Tool Industry specific depth upto which hob is definitely fed unless the apparatus has a wide face.
This methodis specifically adopted to cutting large teeth which are difficult to cut by formed cutter, and to cut bevel-gear teeth. It isn’t widely used at the moment.
In gear planing procedure, the cutter contains 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 if both roll with each other as a rack and pinion. At first the cutter is certainly fed into full 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 technique, both roughening and completing cuts are taken with single pointed tools. The usage of the formed tool for finishing can be impracticable for the larger pitches which are completed by a single pointed tool. The number of cuts required depends upon the size of the tooth, quantity of share to be removed, and the kind of material.