Cutting of Spur Gear

Cutting of Spur Gear

Cutting of Spur Gear - Milling, hobbing, shaping and shear cutting are the methods most commonly used for cutting teeth in spur gears.

Form milling, with the cutter ground to the desired shape of tooth space is a simple means of calling teeth in spur gears, Tooting cost is low, the process requires only a conventional milling machine, a form cutter and an indexing mechanism.

Except for low quantity production, milling is seldom used for cutting spur gears. This is because of lack of accuracy in tooth spacing. Moreover, form milling is much slower than hobbing etc. Further, one milling cutter is not universal for all numbers of teeth, as are bobs and gear shaping cutters.

Hobbing is the most widely used process for cutting teeth in spur gears. Hobbing has:

(i) Low cost,
(ii) Flexibility in quantity production,
(iii) Adaptability to work metals having higher than normal hardness,
(iv) High accuracy in a wide range of gear sizes.
Hobbing process has been explained in detail in section 12'10,

Shear cutting (Fig,) is a high production method for producing teeth in external spur gears. The process is not applicable to helical gears. In shear cutting, as in broaching, all tooth spaces are cut simultaneously and progressively (Fig).

The shear cutting head is mounted in a fixed position, and the gear blanks are pushed through the head. Cutting tools are fed radially into the head, a predetermined amount for each stroke, until the required depth of tooth space is reached.