After completion of 1 or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back to its starting position, thus allowing a short rack cutter of a practical duration to be used. Cutter is again fed back again to depth and routine is repeated. Amount 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 preferably suited for cutting large, dual helical gears. For producing helical the teeth, the cutter slides are inclined at the gear tooth helix angle.
The hob is fed into the gear blank to the proper depth and both are rotated together as if in mesh. One’s teeth of the hob cut into the work piece in successive order 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 straight cuts produces a curved kind of the gear teeth, therefore the name generating procedure. One rotation of the work completes the trimming upto specific depth upto which hob is usually fed unless the gear has a wide face.
This methodis specially adopted to cutting large teeth which are hard to cut by formed cutter, and to cut bevel-gear teeth. It isn’t widely used at present.
In gear planing process, the cutter contains true gear rack for Machine Tool Industry china involute rack which reciprocates over the face of the blank and the blank rotates in the correct relationship to the longitudinal movement of the cutter as though both roll jointly as a rack and pinion. At first the cutter is certainly fed into full tooth depth with cutter reciprocating and blank stationary. Involute form is produced 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 larger 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 removed, and the type of material.