A drill may include a body which is extended along a rotation axis from a first end to a second end. The body may include a first cutting edge, a second cutting edge, a thinning surface, a flute, and an outer peripheral surface. The outer peripheral surface may include a first margin surface, a clearance surface, and a second margin surface. In a plan view of the first end, an imaginary straight line connecting the rotation axis and an end part on a side of an outer periphery in the first cutting edge may be a first straight line, and an imaginary straight line which passes through a center of the first straight line and is orthogonal to the first straight line may be a second straight line. The second straight line may intersect with the second margin surface.

The drill comprises a base body, which extends in the axial direction along an axis of rotation and rotates about the axis of rotation in a direction of rotation during operation. Into the base body are incorporated flutes and between consecutive flutes is formed a rear surface, which extends, in relation to the direction of rotation, from a leading flute to a trailing flute. On the rear surface in the region of the leading flute, a guide chamfer and a support chamfer spaced apart from it in the direction opposite the direction of rotation are formed, wherein the support chamfer, as radially outermost region, forms a support edge for a merely linear support.

Provided herein is a drill having less possibility of cracks in an inner periphery of a drilled workpiece and deformation of a workpiece upon penetrating with a drill, as well as delamination. A drill according to the present invention comprises two cutting blades which are formed symmetrical about an axis of rotation, wherein each of the cutting blades has a main cutting blade formed from a drill tip toward a peripheral side of the drill to become a shape with curves, a thinning cutting blade in a shape with curves formed in closer to the drill tip than the main cutting blade, and an U-shaped cutting blade in a shape with curves formed in closer to the periphery of the drill than the thinning cutting blade.

A cutting tool comprises at least one cutting edge and at least one relief surface adjacent thereto. The relief surface is arranged to provide clearance behind the cutting edge between the cutting tool and a workpiece and comprises one or more grooves arranged to communicate, in use, a cutting media across the relief surface.

In this small-diameter drill bit, two cutting blades having main cutting blades, of which a difference between lengths are 0.04 mm or less, are formed on a tip of a double-margin drill bit body having a diameter of 2 mm or less and a margin length/diameter ratio of 3 or more. Two tip flank faces are formed such that a first extension line extending from a linear first intersecting ridgeline between a first tip flank face and a second tip flank face of one of the flank faces to the linear first intersecting ridgeline of the other flank face is located on a side in the drill bit rotation direction with respect to the other linear first intersecting ridgeline. A distance between the first extension line and the linear first intersecting ridgeline is in a range of 0.04 mm-0.08 mm.

A drilling tool, in particular a spiral drill, has a drill longitudinal axis, at least two flutes extending at a twist angle with respect to the drill longitudinal axis, webs formed between the flutes, and lands formed on a lateral surface of the webs. Guide rings are at least partially formed on the lands. The guide rings extend at an angle different from the twist angle to the drill longitudinal axis. At least one guide chamfer is formed on at least one land in addition to the guide rings. The guide chamfer extends parallel to the twist angle and in front of the guide rings with respect to the direction of rotation of the drilling tool.

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.

A drilling tool, in particular a twist drill, has a substantially cylindrical main body formed with a shank portion, a cutting-edge portion having a drill diameter, and a drill end. The drilling tool is rotatable in a direction of rotation about a drill longitudinal axis. At least two flutes extend in a twisted manner along the drill longitudinal axis and are inclined with at least one helix angle. The flutes form a chip space. Webs are formed between the flutes with a web width. The chip space is formed with a chip space extension that enlarges the chip space in at least part of at least one of the flutes. The web width is reduced in the region of the chip space extension.

A small-diameter drill in which is a double margin having a diameter of 2 mm or less and a ratio of a margin length to a diameter of 3 or more, in which the margin length L in an axial direction from an outer peripheral end of a cutting edge to the rear ends of first and second margin parts and a ratio L/D to a diameter D are 3 or more, in which at least a surface of a chip discharge groove is provided with a hard coating made of nitride, in which a surface of the hard coating in the chip discharge groove has skewness (Ssk) defined in ISO25178 of less than 0, and in which the number of droplets having an equivalent circle diameter of 1.0 μm or more is 5 or less per 100 μm.sup.2 in cross-section observation of the hard coating.

The drill is rotatable about a central axis. The drill includes a central axis, a front end and a rear end opposite to each other in a direction along the central axis, an outer peripheral surface, a cutting edge formed at the front end and extending from the outer peripheral surface toward the central axis, a flank face contiguous with the cutting edge, a flute formed on the outer peripheral surface and extending spirally around the central axis from the front end toward the rear end, and a thinning rake face contiguous with the flute. The cutting edge has a main cutting edge extending from the outer peripheral surface and a thinning cutting edge contiguous with an end of the main cutting edge away from the outer peripheral surface. The flute includes a main rake face contiguous with the main cutting edge from the opposite side of the flank face.