Reamer

A reamer, which has a center axis and includes a single cutting edge, provided for a cutting part that is arranged at a leading end side, comprising:

• exactly four guide pad portions arranged at a distance from each other, and the cutting edge, around the cutting part;
• wherein
• each of the guide pad portions extends substantially parallel to the center axis;
• of the four guide pad portions, two adjacent guide pad portions define a first guide pad formed so as to project to the side almost opposite that where the single cutting edge is formed;
• a third guide pad portion defines a second guide pad arranged in one area of two areas, along a peripheral face of the cutting part, that are located between the first guide pad and the single cutting edge and that are directed toward sides opposite each other;
• a fourth guide pad portion defines a third guide pad arranged in the other area, different from the one area, of the two areas that are directed toward the sides opposite each other;
• when a direction in which the reamer is to be relatively rotated, about the center axis, relative to a workpiece is defined as a rotational direction, the second guide pad is positioned to the front, in the rotational direction, by employing the cutting edge as a reference, and the third guide pad is positioned to the rear in the rotational direction;
• when the cutting part is viewed from the leading end side along the center axis, a peripheral face of the first guide pad is larger than a peripheral face of the second guide pad, and is also larger than a peripheral face of the third guide pad;
• wherein the peripheral faces of the three guide pads extend along a cylindrical face that is defined as passing through the corner of the cutting edge about the center axis;
• a circumferential length of the peripheral face of the first guide pad is set within a range of 8% to 15% of a circumferential length of the cylindrical face;
• a circumferential length of the peripheral face of the second and third guide pads is each set within a range of 0.8% to 6% of a circumferential length of the cylindrical face;
• and
• wherein, when a half-plane that has a range determined by the center axis and that passes the corner of the cutting edge is defined as a reference half-plane, relative to the reference half-plane:
• i) an angle of 180° or greater, up to 230° or smaller, is formed, to the front in the rotational direction, by employing the reference half-plane as the origin, by a half-plane that has a range determined by the center axis and is defined as passing a circumferential midpoint of the peripheral face of the first guide pad,
• ii) an angle of 70° or greater, up to 130° or smaller, is formed, to the front in the rotational direction, by employing the reference half-plane as the origin, by a half-plane that has a range determined by the center axis and is defined as passing a circumferential midpoint of the peripheral face of the second guide pad, and
• iii) an angle of 225° or greater, up to 330° or smaller, is formed, to the front in the rotational direction, by employing the reference half-plane as the origin, by a half-plane that has a range determined by the center axis and is defined as passing a circumferential midpoint of the peripheral face of the third guide pad.