Internal gear also often calls ring gears ,it’s mainly used in planetary gearboxes . The ring gear refers to the internal gear on the same axis as the planet carrier in the planetary gear transmission. It is a key component in the transmission system used to convey the transmission function. It is composed of a flange half-coupling with external teeth and an inner gear ring with the same number of teeth. It is mainly used to start the motor transmission system. Internal gear can be machined by,shaping ,by broaching ,by skiving ,by grinding.