borrskruv med skaerkant, var och i bildande i baoge, som kroeker sig mot huvudstycker.

摘要

PURPOSE:To prevent deflective turning travel and improve cutting performance by furnishing cutting edges which adjoin both ends of a chisel located in the center of the tip of a drill portion, with a shape which is arc-formed and curved backward in the axial direction. CONSTITUTION:The shape of a chisel 21 is arc-formed and curved backward in the axial direction, and the shape of cutting edges 22 and 23 which adjoin ends 21a and 21b and extend toward the outside surface 26 of drill screw is arc-formed and curved backward in the axial direction and also arc-formed and curved backward in the rotating direction. Consequently, both the ends 21a and 21b of the chisel 21 are steeply rising in the outward direction, which decreases cutting load applied to the cutting edges, improves cutting performance and prevents irregular travel.