After completion of 1 or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back again to its starting position, thus enabling a short rack cutter of a practical duration to be utilized. Cutter is once again fed back to depth and routine is repeated. Quantity of teeth is controlled by the machine gearing, and pitch and pressure position by the rack cutter. This method can be used for generation of exterior spur gears, being ideally fitted to cutting large, dual helical gears. For creating helical tooth, the cutter slides are inclined at the gear tooth helix angle.
The hob is fed in to the gear blank to the proper depth and the two are rotated together as though in mesh. The teeth of the hob cut in to the work piece in successive purchase and each in a somewhat different placement. Each hob tooth cuts its profile depending on the form of cutter , however the accumulation of these straight cuts creates a curved form of the gear teeth, thus the name generating process. One rotation of the work completes the slicing upto specific depth upto which hob is fed unless the gear 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 is not widely used at the moment.
In gear planing process, the cutter gear rack for Machine Tool Industry consists of true involute rack which reciprocates across 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 is 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 technique, both roughening and finishing cuts are taken with single pointed tools. The use of the formed device for finishing is definitely impracticable for the bigger pitches which are finished by an individual pointed tool. The number of cuts required depends upon how big is the tooth, amount of share to be taken out, and the kind of material.