After completion of one or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back again to its starting position, thus enabling a brief rack cutter of a practical duration to be utilized. Cutter is again fed back again to depth and cycle is repeated. Number 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 exterior spur gears, being ideally suited for cutting large, dual helical gears. For making helical tooth, the cutter slides are inclined at the gear tooth helix angle.
The hob is fed into the gear blank to the proper depth and both are rotated together as though in mesh. One’s teeth of the hob cut into the work piece in successive order and each in a slightly different position. Each hob tooth cuts its profile based on the form of cutter , but the accumulation of these directly cuts creates 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 is definitely fed unless the gear has a wide face.
This methodis specifically 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 the moment.
In gear planing procedure, the cutter contains true involute rack which reciprocates across the face of the blank and the blank rotates in the gear rack for Machine Tool Industry china correct relationship to the longitudinal motion of the cutter as if both roll with each other as a rack and pinion. Initially the cutter can be fed into complete tooth depth with cutter reciprocating and blank stationary. Involute form is generated 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 usage of the formed tool for finishing is impracticable for the larger pitches which are finished by an individual pointed tool. The number of cuts required is dependent upon how big is the tooth, amount of share to be removed, and the kind of material.