After completion of one or two teeth, the blank and gear rack for Machine Tool Industry china cutter stop feeding and the cutter is withdrawn and indexed back to its starting position, thus allowing a short rack cutter of a practical length to be used. Cutter is again fed back to depth and cycle is repeated. Quantity of teeth is controlled by the device gearing, and pitch and pressure position by the rack cutter. This method is used for generation of external spur gears, being ideally suited for cutting large, double helical gears. For creating helical teeth, the cutter slides are inclined at the apparatus tooth helix angle.
The hob is fed in to the gear blank to the proper depth and both are rotated together as though in mesh. The teeth of the hob cut in to the work piece in successive purchase and each in a slightly different position. Each hob tooth cuts its own profile depending on the shape of cutter , but the accumulation of these straight cuts creates a curved type of the gear teeth, hence the name generating procedure. One rotation of the task completes the reducing upto certain depth upto which hob is usually fed unless the apparatus includes a wide face.
This methodis specially 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 motion of the cutter as if both roll jointly as a rack and pinion. At first the cutter is definitely 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 method, both roughening and completing cuts are taken with single pointed tools. The use of the formed tool for finishing is definitely impracticable for the bigger pitches which are completed by a single pointed tool. The amount of cuts required depends upon the size of the tooth, quantity of stock to be eliminated, and the type of material.