| 摘要 |
PURPOSE:To form the large-diameter part of a supporting part and the small- diameter part of an attaching part by cold-pressing by enclosing the central part of shaft stock corresponding to the supporting part with stationary dies and compressing both ends of the shaft stock corresponding to the attaching part with movable dies in the axial direction. CONSTITUTION:The central part of the shaft stock cut to the prescribed length is enclosed with the stationary dies 6 consisting of an upper die 4 and a lower die 5 and the movable dies 7, 7 are set at both ends. The stock is pressed and held from a vertical direction by the dies 6; at the same time the movable dies 7, 7 at both ends compress axially the shaft stock. Then tapered parts 8 are formed at both ends of the stock 1 and large-diameter flange parts 9, 9 are formed in the central part. A crank shaft 10 is thus formed. The central part near the flange parts 9 acts as the supporting part to be supported freely rotatably by the body of a bicycle and the tapered parts 8 at both ends act as the attaching part to be fitted with crank arms. |
