| 摘要 |
<p>[PROBLEMS] To provide a drill in which the lifetime can be prolonged by preventing wear of the cutting edge even in the case of high speed machining. [MEANS FOR SOLVING PROBLEMS] A cutting edge (5) consists of a convex arcuate main edge portion (51) having a radius of curvature (R1), and a central cutting edge (52) continuous to the main edge portion (51) and connecting it with a corner portion (71) on the drill center side of a thinning (7) opposing the main edge portion (51) in the shape of a convex arc having a radius of curvature (R2) on the side of rotational direction T of the drill (1). The radius of curvature (R1) of the main edge portion (51) is in the range of 0.25-1 times the drill diameter, the rake angle ? of the drill (1) in the radial direction at the outer circumferential portion (outer circumferential corner) of the main edge portion (51) is in the range of -15° to -50°, and the radius of curvature (R3) at the corner portion (71) of the thinning is in the range of 0.1 mm to 0.05 times the drill diameter. Consequently, wear resistance of the cutting edge is enhanced and cutting chips can be discharged smoothly.</p> |
