Abstract: A bit (12) has a triangular drill portion (14), a frustoconical grinder portion (24), and a cylindrical reamer portion (28). The drill portion (14) has three longitudinal cutting edges (16) that define the angles of its triangular cross section. The grinder portion (24) extends axially inwardly from the drill portion (14) and has a minimum diameter less than and a maximum diameter greater than the maximum diameter of the drill portion (14). The reamer portion (28) is an axial continuation of the grinder portion (24). The outer surfaces of the grinder and reamer portions (24, 28) are plated with diamond grit (30) to enlarge and finish a hole produced by the drill portion (14). The relative diameters allow the grinder portion (24) to gradually engage the sidewall of a hole. The bit (12) is supported and centered in the hole by three point contact between the cutting edges (16) and the hole sidewall.

Abstract: The bit (1, 101, 201) includes a pointed tapered drill portion (10, 110, 210) with cutting edges (14, 114, 214), an abrasive frustoconical grinder portion (20, 120, 220), and an abrasive cylindrical reamer portion (30, 130, 230). The drill portion (10, 110, 210) produces a hole. The grinder portion (20, 120, 220) grinds and enlarges the hole. The reamer portion (30, 130, 230) finishes the hole. The drill portion (10, 110, 210) is carried by a shaft (12, 112, 212) that is received into an axial opening (40, 140, 240) through the grinder and reamer portions (20, 30, 120, 130, 220, 230). The drill portion (10) and grinder portion (20) may form a substantially continuous taper. In another embodiment, the drill portion (110) has an arrowhead configuration. In another embodiment, a radial slot (224) extends through the grinder portion (220), and the drill portion (210) extends axially and radially from the slot (224).