| 摘要 |
A drill having a pair of cutting edges formed at one end of a shank and arranged symmetrically with respect to a point, each cutting edge comprising a central edge portion and an outer edge portion, the central and outer edge portions each extending substantially straight and being joined to each other with an obtuse angle formed therebetween when seen from below, the central edge portion being formed with a cutting face substantially parallel to the axis of the drill, the land portion of the two edge portions having a top face joined to the cutting face of the central edge portion and curved in a direction to give a large area to the cutting face; a method of grinding the drill with the outer periphery and a side surface of a rotary grinder; and a drill grinding apparatus for practicing the method comprising a holding frame for reciprocatingly moving the drill axially thereof, means for rotating the drill, a disklike rotary grinder, and posture changing means for altering the angle between the grinding portion of the grinder and the drill. |
