| 摘要 |
PROBLEM TO BE SOLVED: To provide a drill allowing substantial reduction of the cutting resistance and facilitating manual drilling work by using a hand drill or a boring machine.SOLUTION: A drill has two cutting edges formed symmetrically about the rotational axis, and its tip part is provided with thinning. When seen from the tip side of the drill, the cutting edges consist of a thinning cutting edge extending in a shape containing a curve from a chisel edge to the outer peripheral side of the drill and a main cutting edge extending linearly from the end of the thinning cutting edge to the outer peripheral end of the drill. With the length of the main cutting edge taken as A and the length of the thinning cutting edge as B, the lengths of the cutting edges in the extension direction of the main cutting edge meet the relationship 0<A≤B. |
