Gear Hobbing Cycle

Gear Hobbing Cycle

Gear Hobbing Cycle -

(i)Let both the hob and gear blank rotate about their axis.

(ii) Move the gear blank toward the rotating hob (but clear of the hob) until the proper depth of cut is reached. The hob is either to the full height of the teeth (i.e., depth of cut) in hobbing a gear in a single pass, or, in cutting gears of a module over 8 mm in two passes, to a depth of 0.6 of the tooth height for the first pass and 0.4 of the height in the second pass.

(iii) Then, feed the rotating hob, H, along the axis of the gear blank, B, enabling the teeth to be gradually cut over the full face of the gear blank. The feed rate of hot> is 0'05 to 0'375 mm per revolution of the gear blank.

The cutting process is continuous from one end of the gear blank to the other. Both gear blank and hob rotate during the entire process. Several cutting teeth of the hob are simultaneously in operation, the action of the hob tooth on the gear blank.

In their successive positions (1, 2, 3 etc.) the hob teeth gradually cut the tooth space of the gear while the hob rotates in timed relation with the blink. The profile obtained consists of series of flats formed by the teeth of the hob. These straight portions are superimposed on one another and are so short that practically constitute, not a broken line, but the curvilinear (involute) profile of the gear teeth.

As the gear blank is rotating, each successive hob tooth cuts a little deeper, first down into one side of the gear tooth and then up out of the other side. This process is caused generating a gear tooth profile. Gears can be cut either by climb hobbing or conventional hobbing.