Patent ID: 7367758

Claim:
A ceramic drill bit comprising: a cylindrical shank; and a shaped portion extending axially in line with the shank and having a free end forming the tip of the bit, the shaped portion being in the form of a truncated cone whose larger base is situated beside the tip of the bit, the tip comprising two main cutting edges and a central edge between the two main cutting edges, the shaped portion comprising two lips and two flutes extending in alternation around the axis of rotation of the bit, the lips and the flutes extending from the tip towards the shank, each lip including a land and each flute including a main cutting face adjacent to a land and to a main cutting edge, at least the shaped portion of the bit being made of ceramic material, the drill bit being wherein: the cutting angle of the bit is positive; a relief face extends from each main cutting edge at a relief angle lying in the range 4° to 10° approximately relative to a plane perpendicular to the axis of rotation of the bit; and two notches forming two secondary cutting faces extend from the central edge with positive cutting angles lying in the range 1° to 7° approximately relative to the axis of rotation of the bit; and wherein the taper angle of the shaped portion lies in the range 1° to 5° approximately.