| 摘要 |
A tool main cutting edge extends rearward in a rotating direction as it approaches a rear end at the outer periphery. The main cutting edge is a convexly curved line protruding toward the outside of a rake face viewed from the top and another convexly curved line extending toward the seat face, convexly curving from one end of the main cutting edge to the other, viewed from the side. When mounted, an inclination angle defined by the rake face gradually decreases from one end toward the other, and a projection line of a rotation about a rotation axis of the tool forms a convex arc smoothly coming, at a middle portion of the main cutting edge, into contact with a cylindrical surface about the axis and gradually retreats inward from the cylindrical surface as it approaches both ends of the main cutting edge.
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