| 摘要 |
PROBLEM TO BE SOLVED: To provide a twist drill excellent in scrap discharge even when flow- out speed for thickened scraps in a sheared shape each such as a long pitch and a jigzag shape, is low. SOLUTION: Let the groove widths 3 and 3' of a twisting groove 2 provided for the outer circumference 1a of a twist drill 1 be gradually increased toward the groove rear end part 6 side from the tip end part 5 side of the drill. The increasing ratio of a groove width ratio to be indicated by the angular ratioθ1/θ2 of each angleθ1 andθ2' at the groove part of the twisting groove to each angleθ1 and dθ2 'at the land part of a land, shall be 1.2 to 2.6, and the twisting angleθ2 at the heel 9 side is made smaller with respect to the twisting angleβ1 at the leading edge 8 side.
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