Abstract: The drill of the invention has: two cutting edges, each having a main cutting edge and a thinned cutting edge, wherein two relief surfaces formed symmetrically around rotation axis, first and second margin portions are formed, the first margin portions have a forward-end small-diameter portion with diameter smaller than the drill diameter, that is formed from the side of the drill forward-end toward the drill rearward-end, the second margin portions have a second forward-end small-diameter portion with diameter smaller than the first forward-end small-diameter portion, that is formed from the side of the drill forward-end toward the side of the drill rearward-end, the first forward-end small-diameter portion and the second forward-end small-diameter portion have inclination portions, the diameters of which gradually increase from the side of the drill forward-end toward the side of the drill rearward-end, and the inclination portions of the first forward-end small-diameter portion have relief surfaces.

Abstract: The problem to be solved is to provide a drill that is difficult to break and has a good cutting ability. The drill according to the present invention comprises: a first and a second cutting edge formed symmetrically with respect to a rotation axis; a first and a second relief surface formed symmetrically with respect to the rotation axis on back surfaces of the first and the second cutting edge, respectively; one chip-discharging groove formed from one of the first and the second cutting edge toward an outer peripheral side; and one or more arc-shaped grooves formed from another of the first and the second cutting edge toward the outer peripheral side.

Abstract: To design a novel tip end shape that performs most of the drilling process so as to prevent chips from entering the gap between the hollow drill bit and the small-diameter drill bit fitted into the hollow portion of the hollow drill bit as well as to provide a structure of the outer periphery so as to allow chips to be discharged toward the outer periphery and prevent them from entering the gap portion. A hollow drill bit for medical use of the present invention is characterized in comprising a hollow portion that penetrates the axial center in the axial direction from the tip end to the distal end; and four cutting edges at the tip end section, wherein arc-shaped outer peripheral grooves are helically formed in the cylinder-shaped outer peripheral portion.

Abstract: The drill of the invention has: two cutting edges, each having a main cutting edge and a thinned cutting edge, wherein two relief surfaces formed symmetrically around rotation axis, first and second margin portions are formed, the first margin portions have a forward-end small-diameter portion with diameter smaller than the drill diameter, that is formed from the side of the drill forward-end toward the drill rearward-end, the second margin portions have a second forward-end small-diameter portion with diameter smaller than the first forward-end small-diameter portion, that is formed from the side of the drill forward-end toward the side of the drill rearward-end, the first forward-end small-diameter portion and the second forward-end small-diameter portion have inclination portions, the diameters of which gradually increase from the side of the drill forward-end toward the side of the drill rearward-end, and the inclination portions of the first forward-end small-diameter portion have relief surfaces.

Abstract: [Problem] To provide a drill which enables a great reduction in cutting resistance and easy performance of a drilling operation by human power using a hand drill, a drilling machine, or the like. [Solution] A drill has two cutting edges formed symmetrically with respect to a rotation axis, and is subjected to thinning at the tip thereof. The cutting edge is configured from a thinned cutting edge (1) which extends in a shape including a curved line from a chisel edge to the outer peripheral side of the drill, and a main cutting edge (2) which extends from the end of the thinned cutting edge to the outer peripheral end of the drill when viewed from the tip side of the drill, and a thinned surface formed by the thinned cutting edge is formed into an approximately parabolic shape inclined in a drill axis direction when viewed from the front side of the drill.

Abstract: [Problem] To provide a drill which enables a great reduction in cutting resistance and easy performance of a drilling operation by human power using a hand drill, a drilling machine, or the like. [Solution] A drill has two cutting edges formed symmetrically with respect to a rotation axis, and is subjected to thinning at the tip thereof. The cutting edge is configured from a thinned cutting edge (1) which extends in a shape including a curved line from a chisel edge to the outer peripheral side of the drill, and a main cutting edge (2) which extends from the end of the thinned cutting edge to the outer peripheral end of the drill when viewed from the tip side of the drill, and a thinned surface formed by the thinned cutting edge is formed into an approximately parabolic shape inclined in a drill axis direction when viewed from the front side of the drill.