Combined counter sinking bit for socket chamfering

A nest compound chamfering bit comprises a drill head and a drill rod, wherein a central drill is inserted in an empty cavity of the drill rod and the chamfering bit, and the drill head of the central drill detect the drill head of the chamfering bit. A coat body is arranged outside the drill rod, on which an inner surface of the guiding screw coat inosculating an outer surface of the coat body is arranged and a limiting rolling block coat is arranged outside the screw coat; a rolling sliding way and thrust bearing are arranged between the limiting rolling block coat and the screw coat; a steel ball and an adjusting mat are arranged in the sliding way and the left surface is filled with glycerin. A cage nut connected with the screw cut is arranged on the coat body and the limiting rolling block coat, with the cage nut and the limiting rolling block coat fixed by an adjusting nut. A sealing cover is arranged on the limiting rolling block coat and an adjusting mat is arranged between the sealing cover and the thrust bearing. The chamfering bit can find a position by shaft holes and key slots and be fixed by an adjusting bolt. The drilling rod inserted in the shaft holes can realize torque transmission through rotation to make the chamfering bit work stable which can finish the processing of a valve sealing nest one time and improve working precision and degree of finish of the sealing nest.