| 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 or 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).
|
