| 摘要 |
PROBLEM TO BE SOLVED: To provide a drill screw in which its strength is improved while machinability of its extremity is being maintained.SOLUTION: A drill part 13 is formed with a cutting edge 23 including a rake face 21 formed to face toward a rotating direction R of a drill screw 10 and a flank 22 formed at a rear side of the rake face 21. The rake face 21 includes a first rake face 21A formed at a band-like portion along an extremity edge of the cutting edge 23 and a second rake face 21B formed inside along the first rake face 21A. A first rake angle α formed by the first rake surface 21A is set to be larger than a second rake angle &bgr; formed by the second rake face 21B. Since the first rake angle α is large, a machinability is improved at a portion near the extremity edge of the cutting edge 23, and in turn due to low angle of the second rake angle &bgr;, cutting tool angle becomes large to enable a strength of the cutting edge 23 to be assured. |
