After completion of one or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back again to its starting position, thus allowing a short rack cutter of a practical size to be utilized. Cutter is once again fed back to depth and routine is repeated. Number of teeth is controlled by the device gearing, and pitch and pressure position by the rack cutter. This method is utilized for generation of external spur gears, being preferably suited for cutting large, double helical gears. For making helical tooth, the cutter slides tend at the apparatus tooth helix angle.
The hob is fed in to the gear blank to the correct depth and the two are rotated together as though in mesh. One’s teeth of the hob cut into the function piece in successive order and each in a somewhat different placement. Each hob tooth cuts its profile based on the shape of cutter , however the accumulation of these straight cuts produces a curved form of the gear teeth, hence the name generating procedure. One rotation of the work completes the trimming upto certain depth upto which hob can be fed unless the apparatus includes a wide face.
This methodis specifically adopted to cutting large teeth which are difficult to cut by formed cutter, and to cut gear rack for Machine Tool Industry bevel-gear teeth. It is not widely used at present.
In gear planing process, the cutter consists of 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 though both roll with each other 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 generated as the blank rotates and involute rack cutter feeds longitudinally.
In the other method, both roughening and completing cuts are taken with single pointed tools. The utilization of the formed tool for finishing can be 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, quantity of stock to be eliminated, and the kind of material.