Single-edge drill for forming a deep hole

A single-edge drill for forming a deep hole comprising:

• a body including a cutting edge at a distal end of the body;
• and
• a shank connected to the body so as to be located rearward of the body,
• wherein in using the drill, an external oil supply method is used,
• wherein the body has, in an outer periphery of the body, a single chip discharge groove having a concave curved groove surface, and extending from a cutting tip of the drill toward the shank in a center axis direction,
• wherein the body includes:
• a large-diameter portion having a predetermined length from the distal end of the body toward the shank, and having an outer peripheral surface constituting a margin;
• and
• a small-diameter portion located between the large-diameter portion and the shank, and having a diameter smaller than a diameter of the large-diameter portion,
• wherein the large-diameter portion includes, in an outer periphery of the large-diameter portion, at least one coolant delivery groove twisted in a direction opposite a normal rotation direction of the drill,
• wherein, the chip discharge groove has a groove bottom including a first portion spanning either an entirety of the large-diameter portion or at least a distal end side portion of the large-diameter portion, and located at a position not beyond a rotation center of the drill, thereby providing a core thickness to the body at the first portion of the groove bottom,
• wherein, a second portion of the groove bottom other than the first portion of the groove bottom is located beyond the rotation center of the drill such that, at the second portion of the groove bottom, the body has no core thickness, and a cross section of the body perpendicular to the center axis direction has a crescent shape constituted by a combination of:
• an outer peripheral surface constituted by a first cutout circle larger than a cutout circle formed by cutting out ⅓ of a perfect circle;
• and
• a groove surface constituted by a second cutout circle having a diameter smaller than a diameter of the outer peripheral surface constituted by the first cutout circle, and
• wherein the drill is configured such that a supply path for coolant liquid is defined between an outer peripheral surface of the small-diameter portion and a radially inner surface of a hole being formed by the drill.