After completion of one or two teeth, the blank and gear rack for Machine Tool Industry cutter stop feeding and the cutter is withdrawn and indexed back again to its starting position, thus enabling a brief rack cutter of a practical length to be used. Cutter is again fed back 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 technique can be used for generation of external spur gears, being ideally fitted to cutting large, double helical gears. For generating helical tooth, the cutter slides are inclined at the apparatus tooth helix angle.
The hob is fed in to the gear blank to the correct depth and both are rotated together as though in mesh. One’s teeth of the hob cut in to the function piece in successive order and each in a somewhat different placement. Each hob tooth cuts its own profile based on the form of cutter , however the accumulation of these straight cuts creates a curved type of the gear teeth, therefore the name generating procedure. One rotation of the task completes the cutting upto specific depth upto which hob is certainly fed unless the gear has a wide face.
This methodis specifically adopted to cutting large teeth which are difficult to cut by formed cutter, and also to cut bevel-gear teeth. It isn’t widely used at present.
In gear planing process, the cutter includes true 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 if both roll with each other as a rack and pinion. At first the cutter is fed into complete 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 technique, both roughening and finishing cuts are taken with single pointed tools. The utilization of the formed tool for finishing is usually impracticable for the larger pitches which are finished by a single pointed tool. The amount of cuts required depends upon the size of the tooth, amount of share to be eliminated, and the kind of material.