A drill has a helical flute surface, a flank face, and a thinning face. A ridgeline between the thinning face and the flank face constitutes a thinning cutting edge. The thinning cutting edge has a curved thinning cutting edge portion and a straight thinning cutting edge portion. The curved thinning cutting edge portion protrudes forward in the rotation direction. The straight thinning cutting edge portion is contiguous to the curved thinning cutting edge portion. The curved thinning cutting edge portion has a first end portion and a second end portion. The first end portion is a boundary between the curved thinning cutting edge portion and the straight thinning cutting edge portion.

In a drill, a negative land is provided on a rake face, and a ridge line at an intersecting position of the negative land and a flank face, a ridge line at an intersecting position of the flank face and a margin, and a ridge line at an intersecting position of the negative land and the margin are convex faces in a longitudinal rectangular cross section. When a curvature radius of the convex face of a first ridge line at the intersecting position of the flank face and the negative land is 1, at curvature radius of the convex face of a second ridge line at the intersecting position of the flank face and the margin is 0.8 to 1.5 times the curvature radius of the first ridge line, and a curvature radius of the convex face of a fourth ridge line at the intersecting position of the negative land and the margin is 1.5 to 3.0 times the curvature radius of the first ridge line.

A cutting tool for cutting a hole into a fluid transportation pipe and for retaining a cutting chip is provided. The tool (1) comprises a main body (2) having an end which is prolonged by a tapered part (3), the tool (1) further comprising an accommodation space (11), the tool being configured to receive a cutting chip in the accommodation space (11) via an opening (10) which extends at least from a geometrical apex (5) of the tapered part (3) to the periphery of the main body (61), and the tool (1) further has a cutting edge (4) extending at least from the geometrical apex (5) of the tapered part (3) to the periphery of the main body (2) of the cutting tool (1). The main body (2) is made of a material that differs from a material of which the cutting edge (4) is made.

The drill of the present invention includes: a drill main body; a chip discharge flute extending from a tip flank face of the drill main body toward a rear end side of the drill main body and formed on an outer circumference of a tip part of the drill main body; a margin formed at an opposite side of the chip discharge flute in the drill rotation direction; and a body clearance formed at an opposite side of the margin in the drill rotation direction and having an outer diameter smaller than that of the margin. A surface roughness of the body clearance at least along a circumferential direction is equal to or less than a surface roughness of the margin.

A drill has a thinning rake face formed in the front end. An intersection ridgeline between the thinning rake face and the tip flank face is the thinning edge. On the opposite side of the rotation direction, the first and second thinning wall surfaces (6b, 6c) and are formed. Viewed from the front, an intersection angle between the thinning edge (4a) and the first thinning ridgeline is larger than 95. The second thinning ridgeline (L2) is bent to the opposite side of the rotation direction. The thinning edge and the first thinning ridgeline are connected via a concave curve line. The first and second thinning wall surfaces are connected via a concave surface, and a curvature radius of the concave curve line is smaller than a curvature radius of the concave surface.

A drill includes a cutting edge. The cutting edge has a point angle which is continuously decreased from a center-position point angle A (herein, 0<A<180) at a center position to a maximum-diameter-position point angle of 0 at a maximum diameter position. The cutting edge has a relief angle which is continuously decreased from the center position to the maximum diameter position. The cutting edge of the drill has a relief angle at the maximum diameter position. Hence, the cutting edge also serves as a cutting edge for reaming. The ridgeline and relief face of the cutting edge have no corner, thereby providing good wear resistance.

In an embodiment, an insert includes an upper surface including a corner part, a lower surface, a side surface, and a cutting edge. The side surface is between the upper surface and the lower surface. The cutting edge is at least at a part of a first region in which the upper surface intersects with the side surface. The cutting edge includes a first cutting edge at the corner part, a second cutting edge, a third cutting edge, and a fourth cutting edge. The second cutting edge is next to the first cutting edge, and also next to the third cutting edge. The third and fourth cutting edges: each have a convex curvilinear shape with first and second radii of curvature, respectively; and extend downward and upward, respectively, in a side view as going farther from the second cutting edge. The second radius smaller than the first radius.

The present invention relates to a drilling tool and method for modifying a blind hole in a blade root insert of a wind turbine. The invention further relates to an apparatus and method for cleaning a blind hole. The method for modifying a blind hole comprises: removing a blade screw located in the blind hole, inserting a drilling tool into the blind hole, fixing the drilling tool in a drill, recessing the blind hole by a predetermined depth, with a maximum diameter of the end section and of the hole bottom after recessing being smaller than or equal to a diameter of the end section prior to recessing and a transition from the end section to the hole bottom being round after recessing, removing the drilling tool and the drill, mounting the blade screw in the modified blind hole.

A drill of the present invention includes: a drill main body; a plurality of convex-arc cutting edges which are formed on a tip side of the drill main body from an outer periphery of the drill main body to a chisel edge provided near to a rotational axis; second faces which are each formed in an approximately band shape and are each formed along each of the convex-arc cutting edges on a back side of the convex-arc cutting edge in the rotational direction; third faces which are each formed to be continuous with a back side of each of the second faces in the rotational direction; and fourth faces which are each formed to be continuous with a back side of each of the third faces in the rotational direction.

A three-flute drill includes: three chip discharge flutes; and three cutting edges each having concavely-curved and convexly-curved cutting edge portions, an axially perpendicular cross-sectional view orthogonal to an axial center having first convex and concave curves respectively corresponding to the convexly-curved and concavely-curved cutting edge portions intersecting each other, in the axially perpendicular cross-sectional view, a concave amount of the first concave curve being within a range of 0.01D to 0.05D in terms of a drill cutting diameter relative to a reference line connecting an outer circumferential point, at which a drill outer circumferential portion intersects with the first convex curve, and the axial center, and in the axially perpendicular cross-sectional view, a rake chamfer width being a distance from an intersection between a straight line through the intersection and orthogonal to the reference line and the reference line, to the outer circumferential point, and being within 0.005D to 0.06D.