After completion of one or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back to its starting position, thus enabling a short rack cutter of a practical size to be used. Cutter is once again fed back to depth and cycle is repeated. Number of teeth is controlled by the machine gearing, and pitch and pressure angle by the rack cutter. This method is utilized for generation of external spur gears, being ideally fitted to cutting large, dual helical gears. For producing helical tooth, the cutter slides tend at the gear tooth helix angle.
The hob is fed in to the gear blank to the proper depth and both are rotated together as though in mesh. The teeth of the hob cut into the work piece in successive order and each in a slightly different position. Each hob tooth cuts its profile depending on the form of cutter , however the accumulation of these directly cuts creates a curved form of the gear teeth, thus the name generating procedure. One rotation of the task completes the reducing upto certain depth upto which hob is fed unless the apparatus includes a wide face.
This gear rack for Machine Tool Industry china methodis specifically adopted to cutting large teeth which are tough to cut by formed cutter, and also to cut bevel-gear teeth. It is not widely used at the moment.
In gear planing process, the cutter contains accurate involute rack which reciprocates across the face of the blank and the blank rotates in the right relationship to the longitudinal motion of the cutter as if both roll jointly as a rack and pinion. Initially the cutter is usually 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 method, both roughening and finishing cuts are taken with single pointed tools. The use of the formed device for finishing is certainly impracticable for the bigger pitches which are finished by a single pointed tool. The number of cuts required is dependent upon the size of the tooth, amount of stock to be eliminated, and the kind of material.