PURPOSE:To obtain a drum that withstands high coiling force and does not cause segment mark by providing a device that expands a segment of a coil winding drum divided into plural sections and wedges that fix the segment to the direction of diameter. CONSTITUTION:When a piston united to an axis 25 of winding drum is moved to the left in axial direction by supplying pressurized oil to the cylinder, the axis 25 of the winding drum moves to the left. Consequently, the segment 21 which is in wedge-like contact with the axis 25 of winding drum expands in radial direction. On the other hand, when the piston moves to the left in axial direction, a rod 29 united to the piston, a connector 30 and a lower wedge 27 move to the left. In consequence, an upper wedge 28 which is in wedge-like connection with the lower wedge 27 expands in radial direction and push the upper wedge against a gap at the end face of adjoining segment 21. Accordingly, the segment 21 and upper wedge 28 from an even, truly circular drum and prevents generation of segment marks.
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