| 摘要 |
PROBLEM TO BE SOLVED: To restrain the wear of a margin part 6 by surely and efficiently feeding a cutting fluid to the margin part 6. SOLUTION: Chip evacuation slots 2 are formed in the circumference of a tip part of a nearly cylindrical drill body 1 rotated around an axis O, a cutting blade 4 is formed on the ridge part on the tip side of a wall surface 2A facing to the drill rotation direction T of each of the chip evacuation slots 2, the margin part 6 of which circumferential surface 6a forms a cross- sectionally circular arc centering the axis O with an outside diameter D nearly equal to the cutting blade 4 is formed on the edge part on the drill rotation direction T side of each land part 5 formed in the circumferential direction between the chip evacuation slots 2, and a feeding slot 11 of the cutting fluid is formed on the circumferential surface 6a of each of the margin parts 6.
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