Abstract: A drill includes a body. The body includes a first cutting edge, and a second cutting edge apart from the first cutting edge to the back end side relative to the first cutting edge and formed in a recess traversing an outer peripheral portion of the body. In a side view of the body in a first direction in which a distance between a center axis of the body and a first outer end of the first cutting edge is seen the longest, a second outer end of the second cutting edge is located at the center axis side relative to the first outer end of the first cutting edge.

Abstract: A drill includes a body. The body includes a first cutting edge, and a second cutting edge apart from the first cutting edge to the back end side relative to the first cutting edge and formed in a recess traversing an outer peripheral portion of the body. In a side view of the body in a first direction in which a distance between a center axis of the body and a first outer end of the first cutting edge is seen the longest, a second outer end of the second cutting edge is located at the center axis side relative to the first outer end of the first cutting edge.

Abstract: A small diameter portion having an outside diameter smaller than a diameter of the drill is formed on a front end side of a body of the drill in which a cutting edge includes at least two portions, that is, a rotation center side cutting edge portion and an outer peripheral side cutting edge portion and point angles of the respective cutting edge portions reducing gradually from the rotation center side cutting edge portion to the outer peripheral side cutting edge portion. The cutting edge with the point angles varied is formed in the small diameter portion. A flat cutting edge having an inclination angle ? of 30° or less with respect to a line perpendicular to an axis of the drill is provided in a step portion formed between the small diameter portion and a large diameter portion.

Abstract: The problem of making it possible to shorten as much as possible the distance from a major margin to a minor margin of a two-edge double margin drill in an axial direction is addressed. An interval between major margins and respective minor margins, which are provided at outer peripheries of lands, are set at 80° to 100°, flank faces both include a flat second flank face and a flat third flank face, web thinning portions including web thinning surfaces having convex arcs in a direction of drill rotation in front view of the drill are formed at a central portion of an end, and an outer end of each web thinning surface in a radial direction is disposed behind an end of the corresponding minor margin in the direction of drill rotation and extends to the outer periphery of the corresponding land.

Abstract: A small diameter portion having an outside diameter smaller than a diameter of the drill is formed on a front end side of a body of the drill in which a cutting edge includes at least two portions, that is, a rotation center side cutting edge portion and an outer peripheral side cutting edge portion and point angles of the respective cutting edge portions reducing gradually from the rotation center side cutting edge portion to the outer peripheral side cutting edge portion. The cutting edge with the point angles varied is formed in the small diameter portion. A flat cutting edge having an inclination angle ? of 30° or less with respect to a line perpendicular to an axis of the drill is provided in a step portion formed between the small diameter portion and a large diameter portion.

Abstract: A flute spread angle ? in a drill axis-perpendicular section of a spiral flute is defined, a region of the flute taking part in chip treatment is formed along a first circle along an cutting edge of a concave curve and a second circle inscribed in this circle, both of the first circle and the second circle are circumscribed on a third circle expressing the web thickness, the radius R of the first circle and the radius R1 of the second circle are in the range of 0.40 D to 0.70 D and in the range of 0.15 D to 0.30 D respectively, and a drill rotational direction front portion of the spiral flute is formed on the second circle to be closer to the drill center than a fourth circle having a diameter of 0.65 D.

Abstract: A flute spread angle ? in a drill axis-perpendicular section of a spiral flute is defined, a region of the flute taking part in chip treatment is formed along a first circle along an cutting edge of a concave curve and a second circle inscribed in this circle, both of the first circle and the second circle are circumscribed on a third circle expressing the web thickness, the radius R of the first circle and the radius R1 of the second circle are in the range of 0.40 D to 0.70 D and in the range of 0.15 D to 0.30 D respectively, and a drill rotational direction front portion of the spiral flute is formed on the second circle to be closer to the drill center than a fourth circle having a diameter of 0.65 D.

Abstract: A molding die 1 is constituted by an upper die 1a and a lower die 1b which are made of a material transparent to an ultraviolet light, and has a cavity 3 constituted by grooves 2c, 2d, whereas a resin injection gate 4 and a resin exit gate 7 are provided so as to communicate with the cavity 3. A junction of an optical fiber 10 is inserted into the cavity 3. A UV-curable resin is injected into the cavity 3 surrounding an exposing portion of the glass optical fiber 11 from the resin injection gate 4 positioned at one of coating ends of the optical fiber 10, whereas a part thereof is discharged from the resin exit gate 7 positioned at the other coating end. The ultraviolet light is emitted through the lower die 1b so as to cure the resin, thereby forming a reinforcement resin coating. As a consequence, bubbles can be prevented from occurring due to the residual air within the reinforcement resin coating in the junction of the optical fiber 10.

Abstract: A molding die 1 is constituted by an upper die 1a and a lower die 1b which are made of a material transparent to an ultraviolet light, and has a cavity 3 constituted by grooves 2c, 2d, whereas a resin injection gate 4 and a resin exit gate 7 are provided so as to communicate with the cavity 3. A junction of an optical fiber 10 is inserted into the cavity 3. A UV-curable resin is injected into the cavity 3 surrounding an exposing portion of the glass optical fiber 11 from the resin injection gate 4 positioned at one of coating ends of the optical fiber 10, whereas a part thereof is discharged from the resin exit gate 7 positioned at the other coating end. The ultraviolet light is emitted through the lower die 1b so as to cure the resin, thereby forming a reinforcement resin coating. As a consequence, bubbles can be prevented from occurring due to the residual air within the reinforcement resin coating in the junction of the optical fiber 10.