Patent ID: 7241085

Claim:
A drill, comprising: a shaft having a center axis; chip conveying flutes formed in the shaft; a drill head with at least two cutting inserts, each said cutting inserts being provided with at least one cutting edge, said at least one cutting edge being delimited between a chip-breaking surface and a first relief surface, said at least one cutting edge including an outer straight edge section, a curved cutting edge section in the proximity of the center axis of the shaft, and an adjacent enforcement bevel; said at least one cutting edge in direct proximity of said center axis and being terminated by a chisel edge between said cutting inserts in order to serve as centering means during drilling, wherein the curved cutting edge section is inwardly followed by a primary straight portion without an adjacent enforcement bevel in a direction that is oriented at an angle of between approximately 40–50° in relation to a horizontal line that extends through the center axis of the drill, wherein a radial linear distance between the intersection points between radially outer end points of the primary straight portions on either side of the center axis is approximately 0.17 to 0.21 times a diameter of the drill.