| 摘要 |
<p>A drill for forming a hole, being excellent in cutting performance and cutting accuracy, comprises: main cutting edges (1, 2) extending radially and outwardly of the drill from vertices (E, F) of cutting edges which are disposed symmetrically with each other with respect to the axis (00) of the drill in the radially intermediate portion of the forward end face of the drill toward the outer peripheral ends (C, D) of the drill; and central cutting edges (3, 4) extending radially and inwardly of the drill from the vertices (E, F) of the cutting edges toward a center point (Q) of the forward end face of the drill on the axis (00) of the drill. The main cutting edges (1, 2) and the central cutting edges (3, 4) extend to the sides opposite to the vertices of the cutting edges in the axial direction of the drill and obliquely with respect to the axis of the drill. During the formation of the hole, eccentricity of the drill is not caused, the main cutting edges and the central cutting edges replacing the conventional chisel edges can cut the portions of a work to be cut, which correspond to the outer peripheral portion and the central portion of the hole, highly efficiently and accurately.</p> |
