After completion of one or two teeth, the blank and cutter stop feeding and the cutter is withdrawn and indexed back to its starting position, thus enabling a short rack cutter of a practical duration to be used. Cutter is again fed back to depth and routine is repeated. Quantity of teeth is controlled by the machine gearing, and pitch and pressure position by the rack cutter. This method is utilized for generation of external spur gears, being ideally fitted to cutting large, dual helical gears. For making helical the teeth, the cutter slides tend at the apparatus tooth helix angle.
The hob is fed in to the gear blank to the correct 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 somewhat different position. Each hob tooth cuts its profile depending on the shape of cutter , however the accumulation of these directly cuts produces a curved kind of the gear teeth, hence the name generating process. One rotation of the work completes the slicing upto specific depth upto which hob can be fed unless the gear includes a wide face.
This methodis specially adopted to cutting large teeth which are difficult 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 consists of accurate involute rack which reciprocates across the face of the blank and the blank rotates in the right relationship to the gear rack for Machine Tool Industry longitudinal motion of the cutter as if both roll together as a rack and pinion. At first the cutter is fed into full 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 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 share to be taken out, and the kind of material.