After completion of 1 or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back again to its starting position, thus enabling a brief rack cutter of a practical length to be utilized. Cutter is again fed back to depth and cycle is repeated. Number 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 gear rack for Machine Tool Industry suited for cutting large, double helical gears. For making helical the teeth, 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 though in mesh. One’s 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 profile based on the form of cutter , however the accumulation of these directly cuts creates a curved form of the gear teeth, hence the name generating process. One rotation of the work completes the reducing upto specific depth upto which hob is fed unless the apparatus includes a wide face.
This methodis specifically adopted to cutting large teeth which are challenging 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 true involute rack which reciprocates across the face of the blank and the blank rotates in the correct relationship to the longitudinal movement of the cutter as though both roll collectively as a rack and pinion. Initially the cutter is 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 certainly impracticable for the larger pitches which are completed by a single pointed tool. The amount of cuts required is dependent upon the size of the tooth, amount of stock to be taken out, and the type of material.