| 摘要 |
PURPOSE:To keep off any clogging of chips due to wear in a curved surface at the tool body side by forming a part coming nearer to a chip discharge groove wall on a tip rake face into a sectional circular concave surface to be gradually projected, and situating a chip discharge groove at the outside of the circular arc. CONSTITUTION:Since growth of chips is speedier at the outer circumferential side than the inner circumferential side of a cutting edge 3b, the chips extend in the direction of an arrow P along a rake face 3a and they are bent on a concave surface 4. A wall part 2a is formed into a curved surface of a radius of curvature R0 larger than another radius of curvature R1 of this concave surface 4, and it is situated at the outside of a circular arc inclusive of the concave surface 4, while an interval between the concave surface 4 and the wall part 2a is formed into a flat part 5 and the width T is set to 0.08D<=T<=0.3D as setting a drill diameter down to D, and the chips extend toward the base end side of a tool body 1 spirally without being reached to the wall part 2a. The radius of curvature R0 is set to be larger than that R1, whereby capacity of a chip discharge groove 2 is large enough, and the wall part is covered with a hard layer, thus it is excellent in chip dischargeability and abrasion resistance.
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