After completion of 1 or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back to its starting gear rack for Machine Tool Industry position, thus allowing a brief rack cutter of a practical duration to be utilized. Cutter is again fed back 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 can be used for generation of external spur gears, being preferably suited for cutting large, double helical gears. For generating helical teeth, the cutter slides tend at the gear tooth helix angle.
The hob is fed in to the gear blank to the correct depth and the two are rotated together as if in mesh. One’s teeth of the hob cut into the work piece in successive purchase and each in a somewhat different position. Each hob tooth cuts its own profile depending on the form of cutter , but the accumulation of these directly cuts creates a curved type of the gear teeth, thus the name generating process. One rotation of the work completes the cutting 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 tough to cut by formed cutter, and also to cut bevel-gear teeth. It isn’t widely used at the moment.
In gear planing process, the cutter contains accurate involute rack which reciprocates over the face of the blank and the blank rotates in the right relationship to the longitudinal motion of the cutter as though both roll together as a rack and pinion. Initially the cutter is definitely 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 use of the formed tool for finishing is certainly impracticable for the bigger pitches which are completed by an individual pointed tool. The number of cuts required is dependent upon the size of the tooth, amount of share to be taken out, and the kind of material.