Abstract: A throwaway ball end mill comprising an end mill body and a tip pressed by a clamp screw onto a cutout formed at the forward end of the end mill body. The cutout is formed in a longitudinal direction with respect to the end mill body, and a pair of lateral regions forked by the cutout have opposite flat surfaces, the lateral regions have clamp holes formed in a direction making a right angle with the cutout, one clamp hole has a conical surface extending toward the periphery of the corresponding lateral region, and the other clamp hole has a female thread formed therein,the centerline of the conical surface is deviated from that of the clamp holes toward the base end of the end mill body. When the clamp screw is tightened with the tip inserted in the cutout, the tip is pressed against the end of the cutout accordingly, and at the same time one lateral region is bent toward the other lateral region.

Abstract: An insert rotary cutter for processing a metal workpiece includes a cutter body of a generally circular cross-section having an axis of rotation therethrough. The cutter includes one or more cutter inserts releasably mounted on a periphery of the cutter body. The insert includes a generally quadrilateral plate defined by a front face, a rear face disposed generally parallel to the front face and four side faces. The insert has a pair of main cutting edges defined by the front face and one pair of the opposite side faces. The pair of opposite side faces serve as respective rake surfaces for the main cutting edges. Each of the rake surfaces is convexly curved in such a manner that the width of the insert between the rake surfaces is larger at a central portion of each main cutting edge than at opposite ends of the main cutting edge.