Patent ID: 6874979

Claim:
A throw-away tip for use with a drilling tool having a tool body rotatable about an axis, comprising: a tip body formed as a substantially polygonal plate, which has a rake face formed on one polygonal surface thereof and a cutting edge formed at a side ridge of the rake face where the rake face intersects a flank face, one end of said cutting edge being positioned adjacent the axis at a distal end of the tool body of the drilling tool and the other end of said cutting edge being positioned at an outer periphery of the distal end of the tool body such that said cutting edge has a first point angle proceeding toward a rear end of the tool as it proceeds toward the outer periphery of the tool and a second point angle disposed generally opposite to the first point angle and forming an acute angle at an intersection of the flank face and another side face as viewed in plan view, and that said rake face faces in a direction of rotation of the tool; a convexly curved surface formed on said rake face at least at a side of the one end of said cutting edge, which forms a curve toward the other polygonal surface of said tip body as it proceeds toward the side of the one end of said cutting edge; and a convexly curved cutting edge portion formed at a side ridge of said convexly curved surface coinciding with said side ridge of the rake face at the side of the one end of said cutting edge such that it forms a substantially arc shape projecting in the direction of rotation of the tool when said tip body is viewed from a distal end side in a direction of said axis, and when said tip body is viewed in a direction from a position closer to the other end of said cutting edge toward the inner periphery of the rear end of the tool.