| 主权项 |
1. A drill, comprising:
a substantially cylindrical cutting portion comprising
a first region located at a front end portion, anda second region which has a step whose diameter increases as going from the first region to a rear end in a sectional view perpendicular to a rotation axis, and which is continuous with the first region in an end of the second region on a side of the step,wherein the first region comprises
a plurality of first cutting edges located at a front end,a first outer peripheral portion located at an outer peripheral portion of the cutting portion,a plurality of first flutes spirally located in the first outer peripheral portion from rear ends of the plurality of first cutting edges toward the rear end of the cutting portion, anda plurality of first rake surfaces located between the plurality of first cutting edges and the plurality of first flutes and not abutting the rotation axis,each of the plurality of first rake surfaces comprising
a first central surface, which is connected to an inner end of one of the plurality of first cutting edges, anda first outward surface which is located closer to the first outer peripheral portion than the first central surface and is connected to an outer end of the one first cutting edge,wherein, in the first central surface, a length of the first rake surface in a direction parallel to the rotation axis increases as going inward from the first outer peripheral portion, andwherein, in the first outward surface, the length of the first rake surface increases, as going to the first outer peripheral portion, the second region comprisesa plurality of second cutting edges located at the step,a second outer peripheral portion located at the outer peripheral portion of the cutting portion,a plurality of second flutes spirally located in the second outer peripheral portion from rear ends of the plurality of second cutting edges toward the rear end of the cutting portion, anda plurality of second rake surfaces located between the plurality of second cutting edges and the plurality of second flutes and not abutting the rotation axis,each of the plurality of second rake surfaces comprising
a second central surface, which is connected to an inner end of one of the plurality of second cutting edges, anda second outward surface which is located closer to the second outer peripheral portion than the second central surface and is connected to an outer end of the one second cutting edge,wherein, in the second central surface, a length of the second rake surface in a direction parallel to the rotation axis decreases as going to the second outer peripheral portion, andwherein, in the second outward surface, the length of the second rake surface increases as going to the second outer peripheral portion, wherein the second rake surface does not have a surface closer to the rotation axis than the second central surface, wherein a rear end of the first central surface is located closer to the rear end of the cutting portion than a rear end of the first outward surface, and wherein a rear end of the second outward surface is located closer to the rear end of the cutting portion than a rear end of the second central surface, wherein, for each of the plurality of first rake surfaces, in a direction parallel to a corresponding one of the plurality of first cutting edges and in a portion most adjacent to the corresponding first cutting edge, a width of the first central surface is smaller than a width of the first outward surface, and wherein, for each of the plurality of second rake surfaces, in a direction parallel to a corresponding one of the plurality of second cutting edges and in a portion most adjacent to the corresponding second cutting edge, a width of the second central surface is larger than a width of the second outward surface. |
