TWO-EDGE DOUBLE MARGIN DRILL

摘要

The present invention addresses the problem of making it possible to shorten as much as possible the distance from a major margin to a minor margin of a two-edge double margin drill in an axial direction and to keep the interval between the major margin and the minor margin within an ideal range. An interval (¸) between major margins (6) and respective minor margins (7), which are provided at outer peripheries of lands (5), are set at 80° to 100°, flank faces (8) both include a flat second flank face (8a) and a flat third flank face (8b), web thinning portions (4) including web thinning surfaces (4a) having convex arcs in a direction of drill rotation in front view of the drill are formed at a central portion of an end, and an outer end of each web thinning surface (4a) in a radial direction is disposed behind an end of the corresponding minor margin (7) in the direction of drill rotation and extends to the outer periphery of the corresponding land.