Cutting of Internal Gears

Cutting of Internal Gears

Cutting of Internal Gears - The following methods are most frequently used for cutting of internal gears:

(i) Broaching

(ii) Shear cutting

(iii) Shaping.

(i) Broaching can cut both external and internal gear teeth, spur or helical, but conventional broaching is usually confined to cut teeth in internal gears. Fig. shows progressive broach steps in cutting an internal spur gear. The form of the space between broached gear teeth corresponds to tbe form of the broach teeth.

Each cross section of tbe broach has as many teeth as there are tooth spaces on the gear. The diameter of each section increase; progressively to the major diameter that completes tbe tooth form on the workpiece.

Broaching is an extremely fast and accurate means of machining internal gears, but tooling cost is high; therefore broaching is practical only for high volume production, . Broaching, however, is restricted to workpieces having configurations that permit the broach to pass completely through the workpiece,

Broaching of Internal Gears

(ii) Shear cutting is applicable to internal gears also, The principal involved is same as illustrated in Fig, for cutting external gears, except that the cutting edges and direction of radial feed are reversed.

(iii) Shaping involves a lower tooling cost than broaching and shear cutting, therefore it is applicable to low volume production. Shaping is often the only practical method for cutting teeth in large internal gears because the cost of large broaches or shear cutting tools is prohibitive.