PURPOSE: To machine a center hole easily and positively on the end face of a long-length round bar by making contact mutually between respective sides of a chuck means and the outer periphery of the end portion of a round bar work and then positioning the respective jointing points.
CONSTITUTION: The center of a rhomb constituting means 1 is always at the same point even when the jointing points 12a, 12b of the respective sides 11A, 11B move within guide portions 21a, 21b. In the state that the respective side 11A, 11B are in contact with the outer periphery of the end portion of a round bar work W, the center of the rhomb coincides with the axis of the work W. In this state, the respective jointing points 12a, 21b are positioned with a positioning handle 4 and then a drill tool 3 is advanced toward the end face of the work W, so that the tip 31 of the drill tool 3 reaches positively the center of the end face of the work W and thus a hole is machined at this portion. Accordingly, a center hole is machined easily and positively on the face of a long round bar work W.
SUGIURA TAKAYOSHI
KATO TAKAYOSHI
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