Patent ID: 11969803
Assignee: SUBARU CORPORATION
Field: Machine tools (Mechanical engineering)
Classification: CPC B | IPC B

Claim 16:
17. A drill comprising:
at least one first cutting edge for drilling a prepared hole to a workpiece, the at least one first cutting edge being formed in a tip side of the drill, a first point angle of the at least one first cutting edge at a tip position being more than 0 degrees and less than 180 degrees, the first point angle continuously or intermittently decreasing from the tip side toward a rear end side of the drill along a tool axis direction, a first relief angle of the at least one first cutting edge continuously or intermittently decreasing from the tip side toward the rear end side;
at least one second cutting edge for finishing the prepared hole, the at least one second cutting edge being formed at a position away in the rear end side from the at least one first cutting edge, the at least one second cutting edge having a second relief angle at a maximum diameter position of the at least one second cutting edge; and
a deflection reducer for reducing deflection of the at least one second cutting edge by being inserted into the prepared hole, the deflection reducer being formed between the at least one first cutting edge and the at least one second cutting edge,
and wherein a length L2 of the at least one second cutting edge, defined as a length, in the tool axis direction, from a forward position, at which the diameter of the at least one second cutting edge reaches the maximum diameter D1 of the at least one first cutting edge, to a rear position, at which the diameter of the at least one second cutting edge first becomes the maximum diameter D of the at least one second cutting edge, is greater than a length L1, with length L1 being defined as a length, in the tool axis direction, from the tip position to where the maximum diameter D1 is first reached in the at least one first cutting edge, and
wherein a length in the tool axis direction from a first position to a second position is not less than 0.7 times the maximum diameter D of the at least one second cutting edge and not more than 1.2 times the maximum diameter D of the at least one second cutting edge, an increasing diameter of the at least one second cutting edge becoming a maximum diameter D1 of the at least one first cutting edge at the first position, the increasing diameter of the at least one second cutting edge first becoming the maximum diameter of the at least one second cutting edge D at the second position, and
the maximum diameter D1 of the at least one first cutting edge is not less than 0.5 times the maximum diameter D of the at least one second cutting edge and not more than 0.7 times the maximum diameter D of the at least one second cutting edge.