| 摘要 |
A drill comprising a shank part 11, which is adapted to be received in a drill holder of a drilling machine, and an opposite cutting end part 13. An intermediate fluted part 12 is provided, which defines at least one helical flute or channel 16 having a bottom surface 19 and a pair of opposite side surfaces 20 defined by the ribs or lands 17. The shape of a cross-section of said at least one flute or channel, taken at right angles to the course of the flute or channel, is such that the distance from a reference plane 24 to the bottom surface of the flute is decreasing from a central part 22 of the bottom surface towards the adjacent side surface 20 of the flute. Said reference plane is at right angles to a radial line 25 extending from the longitudinal axis of the drill and through the centre of the bottom surface width. A helically extending groove 21 is formed in the middle of the central part 22 of the bottom surface 19. |
