After completion of 1 or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back to its starting position, thus enabling a short rack cutter of a practical size to be used.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. Amount of teeth is controlled by the device gearing, and pitch and pressure angle by the rack cutter. This method is utilized for generation of external spur gears, being preferably suited for cutting large, dual helical gears. For creating helical teeth, the cutter slides are inclined at the apparatus tooth helix angle.
The hob is fed into the gear blank to the proper depth and both are rotated together as though in mesh. The teeth of the hob cut into the function piece in successive purchase and each in a slightly different placement. Each hob tooth cuts its profile depending on the form of cutter , but the accumulation of these directly cuts produces a curved kind of the gear teeth, thus the name generating process. One rotation of the work completes the slicing upto certain depth upto which hob can be fed unless the gear includes 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 is not widely used at present.
In gear planing process, the cutter includes true involute rack which reciprocates across the face of the blank and the blank rotates in the correct relationship to the longitudinal motion of the cutter as if both roll together as a rack and gear rack for Machine Tool Industry china pinion. Initially the cutter is usually fed into full tooth depth with cutter reciprocating and blank stationary. Involute shape is produced 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 tool for finishing is impracticable for the bigger pitches which are completed by an individual pointed tool. The number of cuts required is dependent upon how big is the tooth, amount of stock to be removed, and the type of material.