Patent ID: 7632049

Claim:
A hole cutter comprising a blade cylinder having a rotational center line and a plurality of edge portions arranged side by side at intervals in a circumferential direction on an outer periphery of an end portion of the blade cylinder, wherein each edge portion includes a front cutting edge extending along a radial direction at one side of a circumferential direction, an inner lateral cutting edge extending along a rotational center line from a radially inner end portion of the front cutting edge, and an outer lateral cutting edge extending along the rotational center line from a radially outer end portion of the front cutting edge, wherein the front cutting edge includes an inner front cutting edge connected with the inner lateral cutting edge, and an outer front cutting edge connected with the outer lateral cutting edge, wherein each edge portion further includes a front flank corresponding to the front cutting edge, and wherein the front flank includes an inner front flank corresponding to the inner front cutting edge, and an outer front flank corresponding to the outer front cutting edge, and wherein an inner front clearance angle of the inner front flank is set at a larger value than an outer front clearance angel of the outer front flank, wherein when an imaginary plane perpendicular to the rotational center line is adopted as a perpendicular flat surface, as viewed from the radial direction, the inner front clearance angle is an inclined angle of the inner front flank relative to perpendicular flat surface, and as viewed from the radial direction, the outer front clearance angle is an inclined angle of the outer front flank relative to the perpendicular flat surface, wherein the ratio between the inner front clearance angle to the outer front clearance angle is set to 1.3:1.0, wherein the inner front clearance angle is set to twenty-three degrees, and the outer front clearance angle is set to eighteen degrees.