Machining method of combined herringbone gear and single helical gear with key groove in inner hole

The invention discloses a machining method of a combined herringbone gear and single helical gear with a key groove in an inner hole. The machining method of the combined single helical gear comprises the following steps of machining the inner hole, an end surface and a tooth surface of the single helical gear, and roughly and finely inserting or roughly and finely milling the key groove of the single helical gear; mounting a pressing plate; detecting the tooth space center at the middle section of a part, calculating to obtain an upper end face reference tooth space center, enabling the connecting line of the upper end face reference tooth space center and a part inner hole center to be perpendicular to the long edge of the pressing plate, and fastening the pressing plate and the part; detecting an alignment error between a key groove center and the connecting line of the upper end surface reference tooth space center and the inner hole center of the part; aligning the inner hole and the end face of the part