After completion of one or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back to its starting position, thus enabling a short rack cutter of a practical duration to be utilized. Cutter is again fed back to depth and gear rack for Machine Tool Industry china routine is repeated. Number of teeth is managed by the machine gearing, and pitch and pressure position by the rack cutter. This method is used for generation of external spur gears, being preferably fitted to cutting large, double helical gears. For producing helical tooth, the cutter slides are inclined at the gear tooth helix angle.
The hob is fed in to the gear blank to the correct depth and both are rotated together as if in mesh. The teeth of the hob cut in to the function piece in successive purchase and each in a slightly different placement. Each hob tooth cuts its own profile based on the shape of cutter , but the accumulation of these directly cuts creates a curved kind of the gear teeth, therefore the name generating process. One rotation of the work completes the cutting upto particular depth upto which hob is fed unless the apparatus has a wide face.
This methodis specially adopted to cutting large teeth which are challenging to cut by formed cutter, and to cut bevel-gear teeth. It is not widely used at present.
In gear planing process, the cutter contains 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. Initially the cutter is usually fed into complete tooth depth with cutter reciprocating and blank stationary. Involute shape is generated 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 device for finishing can be impracticable for the larger pitches which are completed by an individual pointed tool. The number of cuts required is dependent upon the size of the tooth, quantity of share to be eliminated, and the type of material.