| 摘要 |
PROBLEM TO BE SOLVED: To prevent damage to a drill and to improve the chip dischargeability thereof by increasing a radial rake angle of a main cutting edge of the drill and by reducing the difference of a radial rake angle at the intersecting portion of a chisel and the main cutting edge. SOLUTION: The drill is formed with a flute 2 on the outer periphery of a drill body, and main cutting edges 5 formed at the tip end ridge of the wall surface of the flute 2 facing the rotational direction. The main cutting edges 5 have radial rake angles in a range from -5°to -20°in a range from 1/3 of the drill diameter to its outer periphery in an axial view from the tip of the drill with the drill axis as the center. Otherwise, the drill has the web thickness of the drill body in a range from 15 to 35% of the drill diameter and a radial rake angel in a range from -5°to -20°in a range from the web thickness to the outer periphery. In addition, the main cutting edges 5 of the drill have two or more straight lines, and the neighboring straight lines are connected by a curved line. COPYRIGHT: (C)2004,JPO
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