After completion of one or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back to its starting position, thus enabling a brief rack cutter of a practical length to be utilized. Cutter is once again fed back to depth and cycle is repeated. Quantity of teeth is controlled by the machine gearing, and pitch and pressure angle by the rack cutter. This technique is used for generation of external spur gears, being ideally suited for cutting large, dual helical gears. For creating helical the teeth, the cutter slides tend at the apparatus tooth helix angle.
The hob is fed into the gear blank to the correct depth and the two 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 placement. Each hob tooth cuts its profile based on the form of cutter , however the accumulation of these straight cuts generates a curved type of the gear teeth, hence the name generating procedure. One rotation of the task 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 tough to cut by formed cutter, and to cut bevel-gear teeth. It isn’t widely used at present.
In gear gear rack for Machine Tool Industry planing procedure, the cutter includes true involute rack which reciprocates across the face of the blank and the blank rotates in the right relationship to the longitudinal movement of the cutter as if both roll jointly as a rack and pinion. Initially the cutter is usually fed into complete 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 method, both roughening and completing cuts are taken with single pointed tools. The utilization of the formed device for finishing is definitely impracticable for the larger 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 taken out, and the kind of material.