| 摘要 |
PURPOSE:To eccentrically rotate a tool part and drill a hole in larger diameter than that of a tool edge, by forming a chamfer in the peripheral edge of a front side edge ridge in a drill and providing a peripheral relief angle to a margin. CONSTITUTION:Two twisted chip discharge grooves 2 are provided in a tool main unit 1, and two front side edge ridges 4a, 4b are formed in horrow relation at a sloped angle beta=5 deg.-15 deg. internally of an end of the tool main unit 1. A chamfer in width C=0.5-1mm. is provided at a sloped angle alpha in the peripheral edge of the edge ridges 4a, 4b. A margin 6 is formed in the peripheral part of the tool main unit 1 to provide a relief angle gamma. The tool main unit 1 is mounted to a spindle so that its axial center may be located eccentrically by a distance delta, and a hole in diameter D+2delta can be drilled with diameter of the tool edge as D. |
