PURPOSE: To automatically provide the precise cut fringe of a portion to be welded by connecting lower blades to a moving unit with no play, and shifting the moving unit with a control device via a drive device.

CONSTITUTION: A wedge slider is inserted into the longitudinal groove of a lower blade support beam. The wedge slider is adjusted by a drive device operable from a control device 15, i.e., a hydraulic cylinder 9. Single or multiple lower blades 4 are pressed to an upper blade by adjusting screws and fastened by screws 11. A distance sensor 12 is adjusted so that the display device 22 of the control device 15 indicates '0'. The desired clearance can be adjusted by merely pushing a key 25. Control lines to the hydraulic cylinder 9 and the distance sensor 12 are shown by codes 26, 27.