Patent ID: 7393163

Claim:
A drill comprising a generally solid shaft which defines a center line and includes: a rear mounting end portion; a front end portion disposed opposite the mounting end portion and provided with at least two cutting edges, each cutting edge including a main edge extending from an inner end to a peripheral end wherein the inner end is located closer to the center line, each cutting edge being inclined wherein the inner end is located axially forward of the peripheral end; and a plurality of flutes formed in an outer surface of the shaft, each flute extending from a respective cutting edge towards the rear mounting end portion for forming chips, wherein the main edge at the peripheral end has a curved shape, wherein said curved shape includes a plurality of circular segments having different radii, said plurality of segments including a front segment having a first radius, an intermediate segment having a second radius, and a rear segment having a third radius, said front segment having a radius which is smaller than the radius of the intermediate segment and greater than the radius of the rear segment, wherein the intermediate segment is a secondary cutting edge of the cutting edge, and has a wiper effect and wherein the second radius is larger than either the first radius or the third radius and wherein the intermediate segment is positioned between the front segment and the rear segment.