After completion of one or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back again to its starting position, thus allowing a brief rack cutter of a practical size to be utilized.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 controlled by the machine gearing, and pitch and pressure angle by the rack cutter. This method is utilized for generation of exterior spur gears, being preferably fitted to cutting large, dual helical gears. For making helical the teeth, the cutter slides are inclined at the gear tooth helix angle.
The hob is fed in to the gear blank to the correct depth and both are rotated together as if in mesh. The teeth of the hob cut in to the function piece in successive purchase and each in a somewhat different position. Each hob tooth cuts its own profile based on the form of cutter , but the accumulation of these directly cuts generates a curved type of the gear teeth, thus the name generating process. One rotation of the work completes the reducing upto particular depth upto which hob is fed unless the gear has 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 isn’t widely used at present.
In gear planing process, the cutter gear rack for Machine Tool Industry contains true involute rack which reciprocates over the face of the blank and the blank rotates in the correct relationship to the longitudinal motion of the cutter as if both roll with each other as a rack and pinion. Initially the cutter is definitely fed into full 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 use of the formed device for finishing is usually impracticable for the bigger pitches which are finished by a single pointed tool. The amount of cuts required depends upon how big is the tooth, quantity of share to be taken out, and the kind of material.