Drill

Abstract

A drill of simple construction, using commercially available tips or tips obtained by simply modifying them, well balanced in cutting resistance, and capable of drilling small-diameter holes. A main cutting edge (12) of a center-side cutting edge 1 is situated on a base line VP of a circular cone having its vertex on a point V on a tool central axis OO and a half vertical angle .alpha.. An intermediate cutting edge (2) having a length substantially equal to 1/2 of the length of the main cutting edge (12) is arranged on a straight line V'Q', extending parallel to a base line VQ, which is symmetrical to the base line VP with respect to the tool central axis OO and advanced ahead of the base line VQ for a lip height t mm in the axial direction, so that a straight line connecting the respective middle points of the intermediate cutting edge (2) and the main cutting edge (12) intersect the tool central axis (OO) substantially at right angles. Since the intermediate cutting edge (2) is advanced only by the lip height t mm, a workpiece is cut by the intermediate cutting edge (2), and a portion of the main cutting edge (12) which corresponds to the intermediate cutting edge (2) is not used for cutting work, so that the cutting resistance is well balanced. Tips (20) and (21), which constitute the cutting edges individually, have a simple construction, and can be formed of commercially available tips or tips obtained by simply modifying them.

Dependencies are inferred from the claim text.