Patent ID: 7267514

Claim:
An elongate drill bit with a longitudinal axis (X-X) comprising: a shank; a working end; and a fluted section located between the shank and the working end, the shank, the working end and the fluted section are all formed integrally in the drill bit, the working end comprises an outer cutting portion and a central pilot tip extending axially ahead of the outer cutting portion, the pilot tip is formed with at least one pair of minor cutting edges arranged on opposite sides of the axis, and the outer cutting portion is formed with a pair of major cutting edges arranged on opposite sides of the axis, the outer cutting portion has a major diameter (D) defined by the pair of major cutting edges and the pilot tip has a minor diameter (d) defined by the at least one pair of minor cutting edges, the fluted section has a pair of helical lands each with a respective inner surface extending axially rearward from one of the major cutting edges and from one of the minor cutting edges, said helical lands and respective inner surfaces formed with a helix angle with respect to said axis, said major cutting edges having a rake face angle equal to said helix angle, and the helical lands define a web and each helical land defines a respective helical flute, the helical lands have a pitch (S) and the web has a web thickness (K) at the pilot tip, the ratio of pitch to major diameter (S:D) falls within a range of about 380% to about 410% and the ratio of minor diameter to web thickness at the pilot tip (d:K) falls within a range of about 220% to about 380%.