The productivity of bulb mandrel chamfering influences the part cost greatly. According to the part feature, a special machine tool for bulb mandrel chamfering was developed. Its structure and operating principle were introduced. The problems of sphere clamping, space of loading and unloading, part rotation etc were solved by adopting the co-clamping scheme of internal and external collet chuck. The high-efficiency machining of the bulb mandrel is achieved. The trial results of the prototype show that the special machine tool can be used to increase the productivity greatly. The machine can be made and rebuilt easily at a little cost with a compact structure.