| 摘要 |
PURPOSE:To prevent the inside surface of a hole from being scratched by chips made by a drill for soft metal such aluminum, by arc-curving the grooves of the drill, along which its cutting edges extend, to cause the chips to smoothly flow into the grooves directly. CONSTITUTION:Two grooves 12 with a prescribed twisting angle are provided on the peripheral surface of the body 11 of a drill. The part 121 of each groove 12, along which the cutting edge 13 extends, is shaped between the chisel edge 14 and the margin 15, in accordance with an arc, the radius R1 of curvature of which is equal to a half of the diameter of the drill body 11. The other part of the groove 12 is shaped up to the peripheral relief section of the drill, in accordance with an arc, the radius R2 of curvature of which is equal to seven sixths of the diameter of the drill body 11. As a result, when the drill is viewed in the diametral direction, the cutting edges 13, 13 are concave upwards and their cutting points 131 are acutely protruded. For that reason, a hole is drilled so that its inside surface is not scratched by the chips. |
