After completion of one or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back to its starting position, thus enabling a brief rack cutter of a practical duration to be used. Cutter is again fed back to depth and routine is repeated. Number of teeth is controlled by the device gearing, and pitch and pressure angle by the rack cutter. This method can be used for generation of external spur gears, being preferably fitted to gear rack for Machine Tool Industry cutting large, dual helical gears. For creating helical tooth, the cutter slides are inclined at the gear tooth helix angle.
The hob is fed in to the gear blank to the proper depth and the two are rotated together as though in mesh. One’s teeth of the hob cut in to the function piece in successive purchase and each in a slightly different position. Each hob tooth cuts its profile depending on the form of cutter , however the accumulation of these straight cuts generates a curved kind of the gear teeth, thus the name generating process. One rotation of the task completes the trimming upto certain depth upto which hob can be 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 to cut bevel-gear teeth. It isn’t widely used at present.
In gear planing procedure, the cutter consists of accurate involute rack which reciprocates across the face of the blank and the blank rotates in the correct relationship to the longitudinal movement of the cutter as though both roll together as a rack and pinion. Initially the cutter is usually 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 technique, both roughening and completing cuts are taken with single pointed tools. The use of the formed tool for finishing is usually impracticable for the bigger pitches which are completed by a single pointed tool. The number of cuts required is dependent upon how big is the tooth, amount of stock to be removed, and the type of material.