Drill

Abstract

A drill, which is excellent in sharpness and strength, capable of preventing burrs at an exit of a machined bore and of suppressing an excessive enlargement of the machined bore size, and is low in manufacturing costs, and easy te re-grind. A rake face (30) is provided to improve sharpness of a single chisel edge (3) formed between the tip of the drill and a first main cutting edge (1), and a non-chisel-edge-forming portion (B.sub.1 OB.sub.2) is provided between the drill tip end and a second main cutting edge (2) to improve strength of the drill. A margin portion (5), provided in a peripheral portion of the drill tip end at the side close to the first main cutting edge and having a non-cutting-edge-forming portion (11), is disposed in slide contact with an inner peripheral surface of a machined bore to achieve a guide shoe function, thereby improving, during drilling process, stability of an outer peripheral cutting edge (6) formed in the peripheral portion of the drill tip end at the side close to the second main cutting edge. The outer peripheral cutting edge extends at an acute angle relative to the outer periphery of the drill as seen from the axial direction of the drill, to cause machined material to be directed to the inward of the machined bore, thereby preventing burrs. The rake face associated with the chisel edge is comprised of a twisted curved surface whose lead is the same as those of rake faces (10) of various drill portions, making it easy to produce the drill and perform re-grinding.

Dependencies are inferred from the claim text.