Importance

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Abstract

An elongate drill bit (20) with a longitudinal axis (X-X) has a shank (28), a working end (24), and a fluted section (26) 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 has an outer cutting portion (34) and a central pilot tip (36) which extends axially ahead of the outer cutting portion. The pilot tip is formed with at least one pair of minor cutting edges (40, 42; 44, 46) arranged on opposite sides of the axis. The outer cutting portion is formed with a pair of major cutting edges (70, 72) arranged on opposite sides of the axis. The outer cutting portion has a major diameter (D) defined by the pair of major cutting edges. 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 (32) each with a respective inner surface (92) extending axially rearward from one of the major cutting edges and from one of the minor cutting edges. The helical lands define a web (94). Each helical land defines a respective helical flute (30). The helical lands have a pitch (S) and the web has a web thickness (K) at the pilot tip such that the ratio of the pitch to the major diameter (S:D) falls within a range of about 380% to about 410%. Also, the ratio of the minor diameter to the web thickness at the pilot tip (d:K) falls within a range of about 220% to about 380%.

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First Claim