Twist drill

摘要

A rock drill has an axially elongated shank (1) with a hard metal drill head (2) secured at one end. The transverse cross-section of the drill head is basically rectangular with cutters located along each of two diagonals of its cross-section. The cutters remove drillings from rock. The cutters include a main cutter (4) and two auxiliary cutters (5, 6) having the same rotational envelope curve.