| 摘要 |
PROBLEM TO BE SOLVED: To provide a drill to keep chip discharge performance well. SOLUTION: A cutting edge 12 has a grinding allowance part 16 having an approximately constant core thickness along the axis line O direction, a back taper part 17 which continues to the rear end of the grinding allowance part 16, and has the core thickness gradually reduced as the core thickness heading toward the rear end side of the axis line O direction, and a straight part 18 which has an approximately constant core thickness along the axis line O direction. The core thickness at the tip end of the back taper part 17 is set within a range of 0.25D to 0.40D relative to outside diameters D of the cutting edges 15, 15. The core thickness at the rear end of the back taper part 17 is set within a range of 0.20D to 0.25D relative to the outside diameters D of the cutting edges 15, 15. COPYRIGHT: (C)2005,JPO&NCIPI
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