| 摘要 |
<p>This invention relates to a drill with a tip part on which thinning is performed, comprising two cutting blades, thinning cutting blade and a thinning cutting blade, which are formed symmetrical about an axis of rotation, which enables a great reduction in cutting resistance and easy performance of a drilling operation by human power using a hand drill, a drilling machine, or the like. The cutting edge is configured from a thinned cutting edge (1) which extends in a shape including a curved line from a chisel edge to the outer peripheral side of the drill, and a main cutting edge (2) which extends from the end of the thinned cutting edge to the outer peripheral end of the drill when viewed from the tip side of the drill, and a thinned surface formed by the thinned cutting edge is formed into an approximately parabolic shape inclined in a drill axis direction when viewed from the front side of the drill, wherein a rake angle (¸ 1 ) formed by said thinning cutting blade and a rake angle (¸2) formed by said thinning cutting blade satisfy ¸1>¸2>0°, except for a part just below the chisel.</p> |
