| 摘要 |
PROBLEM TO BE SOLVED: To provide a twist drill restraining abrasion and chipping of an outer peripheral corner part, and chipping of a leading edge, in drilling work not using cutting fluid, in drilling work to spray a small quantity of cutting fluid on a drill or a drill head end flank, and in drilling work of an iron and steel product containing alloy steel SCM440. SOLUTION: The twist drill has: a pair of approximately straight-line central cutting blades 2 continued to an outer end part of a chisel 1; a pair of straight-line main cutting blade 3 continued to the outside of each of the central cutting blade 2; and a corner cutting blade 4 to retreat at an angle from an intermediate part of each of the main cutting blade 3. The angleα4 of the leading edge 7 is made to be obtuse angle, and a straight line or curved chamfering part 8 continued to the corner cutting blade 4 is provided on a leading edge 7. Length of the corner cutting blade 4 is 10 to 20% of a twist drill diameter. COPYRIGHT: (C)2007,JPO&INPIT
|
