| 摘要 |
PROBLEM TO BE SOLVED: To secure strength particularly in the outer circumferential end side of a cutting edge 5 while suppressing the deterioration of sharpness of the whole of the cutting edge 5, and prevent the shortening of a tool life due to wear and breakage even in a harsh machining condition such as high-speed dry cutting. SOLUTION: In a drill, a chip discharge groove 3 extending toward a rear end side is formed in the tip part outer circumference of a drill body 1 rotated around an axis O, and the cutting edge 5 is formed in a crossing ridgeline part between an inner wall face 4 facing the drill rotating direction of the chip discharge groove 3 and a tip flank relief 2 of the drill body 1. The cutting edge 5 is formed so that a rake angleγin a cross section perpendicular to the cutting edge 5 is gradually increased from the inner circumference of the drill body 1 toward an outer circumference side until it reaches a transition point X on the cutting edge 5, and it is gradually decreased toward the outer circumference side from the transition point X. COPYRIGHT: (C)2003,JPO
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