| 摘要 |
PROBLEM TO BE SOLVED: To provide a twist drill with an anti-chipping cutting edge which enables stable deep hole drilling, through hole drilling, and better chip curling process. SOLUTION: In the twist drill, a side close to the central cutting edge 21 of a major cutting edge 22 is formed as a straight line or a convex arc with larger radius R, and its outer circumference is shaped as a convex curved blade so that its radius R gradually becomes smaller up to the lower limit of 0.25 times as much as the drill radius as it approaches towards the outer circumference, to eliminate the inflection point of the major cutting edge and set the radial rakeθin the outer circumference to the range from -15°to -40°. COPYRIGHT: (C)2004,JPO
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