| 摘要 |
Since the ball end cutting edges (28a, 28b) of a throw-away tip (14) are smoothly curved helical teeth provided to project partially from the planar portion (26) in the plate thickness direction thereof and the projection angle a falls in the range of 20°-40°, the ball end cutting edges (28a, 28b) are projected significantly depending on the projection angle a while maintaining the plate thickness dimension t at the planar portion (26) of the throw-away tip (14) at the conventional level, and the helix angle is increased. Since the helix angle of the ball end cutting edges (28a, 28b) increases while controlling fall in strength or rigidity of the tool body (12) resulting from a fixing groove (20) or sharp increase in tip material, sharpness is enhanced furthermore and more excellent cutting performance is attained because the thickness dimension (dimension in the thickness direction at the planar portion (26)) of the ball end cutting edges (28a, 28b) is increased and thereby the rigidity is enhanced.
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