Abstract: A rotary cutting tool according to the present disclosure is rotatable about an axial line and includes a rake face and a flank face. The flank face is contiguous to the rake face. A ridgeline between the rake face and the flank face constitutes a cutting edge. In a cross section perpendicular to the axial line, the rake face is constituted of a plurality of straight line portions.

Abstract: A tool tip is integral with or removably secured to a tool body and configured to machine a metal object. The tool tip has a tool tip diameter, a rotational axis and at least one coolant duct. The tool tip includes at least one major cutting edge formed at an intersection of a rake face and a first major flank. The rake face forms part of a chip flute. The coolant duct is configured to be in flow communication with discharge orifices located exclusively in the tool tip. The tool tip has an arrangement, such as a row of two or more discharge orifices located exclusively in the rake face of a major cutting edge. The arrangement extends at a non-zero angle relative to the rotational axis.

Abstract: A rotary cutting tool, in particular a drill, is described, which comprises a shank and an exchangeable cutting tip (14). For this purpose, a locking geometry having an undercut of a first type and a torque transmission geometry is provided on the shank. A locking projection having a torque transmission counter-geometry is provided on the cutting tip, wherein, in a mounted state, the locking projection engages in the undercut of the first type and the torque transmission counter-geometry abuts the torque transmission geometry. The rotary cutting tool further comprises a securing unit, which holds the cutting tip on the shank.

Abstract: A drill bit includes a drill bit head, a multi-strand helix made up of three or more helix ribs, and a shank end along a drill bit axis. The multi-strand helix is made up of a conveyance area, a helix gradient, and a pitch. The helix ribs extend parallel to the drill bit axis in a first area adjacent to the drill bit head and a second area adjacent to the shank end.

Abstract: A drill bit structure of a self-tapping screw is rotated clockwise to screw with a workpiece or is rotated counterclockwise to remove from the workpiece, and the self-tapping screw contains: a head, a shank, and a drill bit. The head is configured to connect with a tool. The shank integrally extends from the head. A conical face has a tip, two arcuate grooves, and two first cutting edges. Each of the first cutting edges is formed on a connection portion of each arcuate groove and the conical face. The drill bit includes two third cutting edges, and each third cutting edge is adjacent to the tip, shapes of the two first cutting edges correspond to shapes of the two third cutting edges respectively, and heights of the two first cutting edges are not less than the conical face. Each first cutting edge has a reinforcement portion.

Abstract: A drill may include a body extending from a first end toward a second end, and the body may include an outer peripheral surface and a cutting edge. The cutting edge may include a first cutting edge and a second cutting edge. The second cutting edge may be positioned closer to the second end and the outer peripheral surface than the first cutting edge. The second cutting edge may include a first part, a second part and a third part. The second part may be positioned closer to the outer peripheral surface than the first part and may be positioned closer to the second end as close to the first part. The third part may be positioned closer to the first cutting edge than the first part and may be positioned closer to the second end as close to the first part.

Abstract: A self-drilling screw includes a leading section having a drill body and opposite discharge grooves formed on the drill body. The drill body and the discharge grooves meet at cutting edges. On the drill body are formed two blade portions connected to the cutting edges and tapering at respective second tips. The blade portion has a second included angle of not more than 50 degrees. Between the blade portions is formed a drilling portion terminating at a first tip and having a first included angle of not more than 60 degrees. Two opposite concave surfaces each extend from the drilling portion to each blade portion. The first tip and the second tips are situated at different places. Accordingly, the end of the leading section presents a shape of a curved bow riser to cut quickly and help quick removal of chips, thereby decreasing resistance and preventing the cracking problem.

Abstract: A rotary cutting tool includes a tool shank, a replaceable cutting head mounted on the tool shank, a coupling pin, and an actuation member. In one embodiment, the coupling pin has a cylindrical portion with a reduced-diameter portion defined by a pair of angled side walls separated by a bottom surface for cooperating with a non-threaded portion at one end of the actuation member. In another embodiment, the coupling pin has a cylindrical portion with a notch with a pair of side walls for cooperating with a frustoconical member at one end of the actuation member. When assembled, a pair of V-shaped contact surfaces on the cutting head engage a pair of oppositely facing V-shaped contact surfaces on the tool shank to provide stability against the momentum created by cutting forces in two different directions and securely hold the cutting head in place during machining operations.

Abstract: A surgical bur is disclosed having cutting and trailing edges and associated flutes and lands. Each flute includes a cutting edge. Each of the trailing edges relatives in a selected dimension to a preceding cutting edge.

Abstract: Two discharge grooves (4) are formed in a drill (1). A cutting edge (5) is formed on a ridge section between an inner face (41) that faces a rotation direction (T) side of the discharge groove (4), and a flank (6). A thinning edge (7) is formed from an inner end (51) of the cutting edge (5) to the side of a chisel (9), by thinning processing, and further, a gash portion (8) is formed from an inner end (72) of the thinning edge (7), the gash portion extending in a circular arc shape and being connected to the discharge groove (4) further to an inner side in the radial direction than an outer peripheral surface (31). A circular arc groove (10) is formed in a section connecting a thinning face (71) and a gash face (81). The chips being cut by the thinning edge (7) are scooped up to the gash portion (8), are curled, and are discharged to the discharge groove (4). The chips are not likely to become caught by being provided with the circular arc groove (10).

Abstract: 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.

Abstract: A drill includes a drill body having a longitudinal axis, a front end, and a frontend portion and at least one flute in the front end portion. A cutting insert is mounted to the drill body in each flute of the at least one flute at the front end of the drill body. The at least one flute includes a plurality of grooves, concave surfaces of adjacent ones of the grooves intersecting to define a ridge separating the grooves.

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 surgical bur includes a body and a drill point. The body includes flutes and lands. Each of the flutes includes a cutting edge, a rake face, and a clearance surface. Each of the lands is convex-shaped and disposed between a pair of the flutes. The drill point includes axial relief surfaces. Each of the axial relief surfaces has a planar area, is distinct from the lands and borders (i) a distal portion of one of the cutting edges, (ii) one of the lands, and (iii) one of the clearance surfaces.

Abstract: 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.

Abstract: The drill has a rake face, a flank face, and an outer circumferential surface. The flank face is continuous to the rake face. The outer circumferential surface is continuous to both the rake face and the flank face. A ridgeline between the rake face and the flank face constitutes a cutting edge. A ridgeline between the rake face and the outer circumferential surface constitutes an outer circumferential end. A groove is provided cyclically in the rake face to extend at an angle relative to an axis of the drill, the angle being larger than a helix angle of the drill. The groove has a depth of more than or equal to 1.5 ?m.

Abstract: A method for producing a cutting tool, in particular a drill bit, is specified wherein the cutting tool has a front end (F) at the front and a rear end (R) toward the rear, wherein a tool tip is formed on the front end (F), a point thinning is ground at the tool tip with a grinding tool, the point thinning being ground to be narrower toward the front than toward the rear. The point thinning is ground with a constant point thinning angle (AW). Furthermore, a corresponding cutting tool is specified.

Abstract: A drill according to a non-limiting aspect may have a body, a cutting edge, a rake face, and a groove. The cutting edge may have a curved chisel edge, a pair of first cutting edges, and a pair of second cutting edges. The second cutting edge may have a first portion extending from the chisel edge and a second portion extending from the first portion toward the first cutting edge. The rake face may have a first region extending from the first portion and a second region extending from the second portion. A first rake angle of the first region may be zero or a negative value. A second rake angle of the second region may be a negative value. An absolute value of the second rake angle may be greater than an absolute value of the first rake angle.

Abstract: A drill including: a chip discharge groove formed in an outer periphery of an edge portion serving as a leading end side portion of a drill body; and a cutting edge formed in an intersecting edge between a rake surface of a leading end side region and a leading end flank of the edge portion. The drill having a margin portion, a shoulder portion and a web thinning portion. The cutting edge includes, in order from a rotation center, first cutting edge, second cutting edge, shoulder cutting edge, and margin cutting edge portions. Honing widths of the second cutting edge, the margin cutting edge, and the shoulder cutting edge portions satisfy a relation represented by expression (1), as follows: honing width of the shoulder cutting edge portion>honing width of the margin cutting edge portion?honing width of the second cutting edge portion.

Abstract: A surgical bur including primary flutes and auxiliary flutes. The primary flutes include (i) first clearance surfaces, and (ii) first rake surfaces with first cutting edges. The primary flutes extend from a proximal end of the surgical bur to a distal end of the surgical bur. The auxiliary flutes are localized in central regions or distal regions of the surgical bur. The auxiliary flutes include (i) second clearance surfaces, and (ii) second rake surfaces with second cutting edges. At least one of the auxiliary flutes is located between a pair of adjacent ones of the primary flutes.

Abstract: An orbital drill includes a drilling portion, a shank portion, and a neck portion between the drilling portion and the shank portion. The drilling portion includes one or more right-handed spiral flutes with cutting edges having a positive axial rake angle for positive cutting action while orbiting into a material. The right-handed spiral flutes have a positive radial and axial rake angle. The drilling portion also includes one or more left-handed spiral flutes located rearward of the one or more right-handed spiral flutes with cutting edges having a positive axial and radial rake angle for positive cutting action while orbiting back out of the material and removing any material left in the hole, thereby eliminating a separate reaming operation. A method of machining a workpiece using the orbital drill is also disclosed.

Abstract: A cutting tool according to an aspect of the present disclosure includes a cutting edge portion which contains at least one of cubic boron nitride and polycrystalline diamond. The cutting edge portion includes a flank face, a negative land contiguous to the flank face, and a cutting edge formed by a ridgeline between the flank face and the negative land. At least one of the negative land and the flank face is provided with a plurality of recesses and a projection. The projection is formed by arranging the edges of adjacent recesses in contact with each other.

Abstract: A drill structure includes a shank part and a flute part arranged on one end of the shank part. A chisel edge is formed on the front end of the flute part and two drill blades with tilt directions toward the shank part are symmetrically formed on the two sides of the chisel edge. Every drill blade includes: a primary relief surface with a cutting edge, a first connecting edge and a first chamfering edge, a secondary relief surface with a knife-back edge, a second connecting edge, a second chamfering edge and an outer edge, and an assist relief surface. The second connecting edge joins to the first connecting edge, and the second chamfering edge connects with the first chamfering edge. The assist relief surface, which tilts toward the shank part the, is extend from the first chamfering edge and the second chamfering edge. This drill structure can improve the surface finish of the drilling hole.

Abstract: The rotary tool has two coupling parts, namely a carrier and a cutting head having a front end face. The carrier has a pin seat into which a coupling pin of the cutting head is inserted. Effective stop faces are formed on the pin seat and on the coupling pin in the axial direction for axial pull-out protection. For a design that is as simple as possible, in particular in terms of grinding, a side face adjoins a respective stop face of the coupling pin and, when viewed in the axial direction, freely extends to the end face. In particular, the side face forms a torque face. For reliable clamping attachment, in particular with larger nominal diameters (D), a separating slot is made in the carrier and a clamping screw is inserted into it, both of which serve to fix the cutting head in the pin seat.

Abstract: A drill according to an embodiment includes a bar-shaped drill body extending along a rotation axis, a cutting edge located at a front end of the drill body, and a first flute extending spirally from the cutting edge toward a rear end of the drill body. The first flute includes a first region which is located close to the front end and has a helix angle ?1, and a second region which is located closer to the rear end than the first region and has a helix angle ?2 smaller than the helix angle ?1. The second region includes an elongated protruding part along the first flute.

Abstract: 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.

Abstract: A drill is provided with a body having a rod shape configured to rotate about a rotational axis, a cutting edge that is located at a tip portion of the body and extends from an outer periphery of the body toward the rotational axis when viewed from the tip portion, a flank located at the tip portion and disposed along the cutting edge, a covering layer that covers at least the tip portion of the body, and one or more recessed portions disposed on the flank at positions close to the cutting edge.

Abstract: A method is specified for producing a rotary tool (2) having a base body (4), which extends in a longitudinal direction (L) and in which at least one flute (6) is ground in by grinding in a first partial flute (12A) with a first helix angle (W1) in a first grinding step and by subsequently grinding in a second partial flute (12B) with a second helix angle (W2) in a second grinding step, the second helix angle differing from the first helix angle (W1) so that a flute (6) that expands in the longitudinal direction (L) is formed, wherein the two partial flutes (12A, 12B) are ground in using the same grinding wheel (11). In this way, a particularly quick production is realized. Furthermore, a corresponding rotary tool (2) is specified.

Abstract: A surgical bur including flutes and lands. Each of the flutes includes a cutting edge, rake surfaces and a clearance surface. The rake surfaces of one of the flutes are decoupled from each other. Each of the lands is disposed between a pair of the flutes.

Abstract: A drill bit including a shaft which has a pyramidal shaped end defining a drill tip with a plurality of edges defining the pyramidal shape. One or more recesses are provided for directing away debris produced while drilling, the at least one recess having a first portion extending along the shaft and a second portion having a first portion extending along the shaft and a second portion which extends along the drill tip; wherein the. The second portion which extends along the drill tip. The second portion of the at least one recess extends along an edge of the drill tip.

Abstract: 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.

Abstract: A drill includes a bar-shaped drill body, a major cutting edge which is located at a front end of the drill body and has a straight-line region in a front view, a rake surface located along the major cutting edge, and a chip discharge flute being extended spirally around a rotation axis of the drill body in a direction from the rake surface toward a rear end of the drill body. The rake surface has a flat region located along the straight-line region.

Abstract: A rotary tool comprising two coupling parts, namely a carrier and a cutting head in a front end surface. The carrier comprises a pin receptacle into which a coupling pin of the cutting head is inserted. In order to prevent pulling-out in an axial direction, stop surfaces are provided on the pin receptacle and on the coupling pin, said stop surfaces being effective in an axial direction. For a design that is as simple as possible, in particular with regard to grinding, each stop surface of the coupling pin is adjoined by a lateral surface which freely tapers off in the direction toward the end surface as viewed in the axial direction. In particular, the lateral surface constitutes a torque surface.

Abstract: The invention concerns a cutting tip (6) comprising: a core (10) that extends axially; and at least a first branch (12) and a second branch (14) that extend radially from the core (10), each comprising: a proximal portion (12a, 14a) connected to the core (10), a distal portion (12b, 14b), and a central portion (12c, 14c) connecting the proximal portion (12a, 14a) and the distal portion (12b, 14b); and a cutting edge (12d, 14d) extending at least along the distal portion (12b, 14b) and the central portion (12c, 14c); in which: the distal portion (12b) of the first branch (12) is arranged radially forward relative to the central portion (12c) of the first branch (12); and the central portion (14c) of the second branch (14) is arranged radially forward relative to the distal portion (14b) of the second branch (14).

Abstract: In order, in a drill tip (2) which is provided particularly for a modular drilling tool, to generate a ridge (18) with supporting chamfers (26, 28) in a simple way, a non-round grinding method is provided, in which, proceeding from a starting rotary position (30) which corresponds to a cutting corner position, the radius is first reduced and is subsequently increased again to form the supporting chamfer (28). There is therefore no need for a separate grinding step to form the supporting chamfers (26, 28). The supporting chamfers (26, 28) preferably extend parallel to the longitudinal mid-axis (22) in the axial direction (24) and intersect coiled chucking grooves (26).

Abstract: A hand drilling tool of one or more elements coupled therebetween comprising: a chuck (2) tightened in the spindle of a tool machine allowing the tool rotation; an elongated point body (3) with tool diameter (2) having at least four helical grooves developing longitudinally on the point body and defining at least two primary cutters, and at least two secondary cutters; said two primary cutters forming a tip angle; said secondary cutters having a discharge surface S; said discharge surface S is shaped so as to create an interruption between the secondary cutters and the primary cutters by contributing to reduce the operator's effort, to reduce the temperature and to promote the discharge of the worked material. Said point body (3) is formed by a substantially cylindrical first portion and a substantially conical second portion with taper towards the end of the tool.

Abstract: A surgical bur including primary flutes and auxiliary flutes. The primary flutes include (i) first clearance surfaces, and (ii) first rake surfaces with first cutting edges. The primary flutes extend from a proximal end of the surgical bur to a distal end of the surgical bur. The auxiliary flutes are localized in central regions or distal regions of the surgical bur. The auxiliary flutes include (i) second clearance surfaces, and (ii) second rake surfaces with second cutting edges. At least one of the auxiliary flutes is located between a pair of adjacent ones of the primary flutes.

Abstract: A surgical dissection tool for cutting bone and other tissue includes a cutting head having an outer surface having non-paired or an odd number of flutes formed therein. Each flute includes a rake surface intersecting with the outer surface to form a cutting edge, and a relief surface opposite the rake surface. The relief surface and the rake surface form a first angle. Each flute also includes a leading angled surface extending from the relief surface to a distal end portion of the cutting head, the leading angled surface and the rake surface forming a second angle substantially the same as the first angle.

Abstract: A drilling tool includes at least two chip flutes and a chisel edge with a thinned region. The thinned region merges continuously into the chip flutes in such a way that the thinned region forms the end of the respective chip flute in the region of the chisel edge.

Abstract: A method of making a cutting tap includes: providing an elongate tap body having an axial forward end, an axial rearward end and a central longitudinal axis; securing the axial rearward end of the tap body in a grinding machine; and forming in the axial forward end of the tap body a correction grind and a main flute in one continuous grinding operation. A cutting tap made by the invention is also provided.

Abstract: A cutting insert includes a body having an upper face, a lower face, a plurality of planar flank faces joining the upper and lower faces, and a plurality of curved flank faces joining the plurality of flank faces. A T-land is formed at a downward sloping angle with respect to the upper face. A cutting edge is formed at an intersection of a respective flank face and the T-land. A curved cutting edge is formed at an intersection of a respective curved flank face and the T-land. A micro-channel is formed in one of the flank faces, the curved flank faces and the T-land and proximate one of the cutting edge and the curved cutting edge.

Abstract: An endodontic instrument (20) for drilling root a canal within a tooth. The instrument has a working area (21) that is arranged so as to form, shape and/or cut the inner wall of the root canal. The instrument has a plurality of flutes wound around a central axis in the form of a spiral, within a conical envelope (25) so as to have a cross-section that becomes narrower from a first end (23) to the second end (26) of the instrument. The working area (21) is sub-divided into adjacent segments (13) such that the flutes alternately have a straight section and a section that is twisted in the form of a spiral and are arranged, in such a way, that the edges of the flutes are located either on the conical envelope (25) or inside the envelope on the straight sections or on the twisted sections.

Abstract: The invention relates to a rock drill comprising an insertion portion, a flute adjoined to the insertion portion, and a head portion adjoined to the flute, wherein the flute is of at least double-spiral configuration and correspondingly has at least two substantially spiral discharge grooves, to which respectively two substantially spiral flute webs forming the lateral groove walls are assigned. It is proposed that a constant spiral pitch is assigned to the first discharge groove, inclusive of the lateral groove walls thereof, along the drill longitudinal axis, and that at least one of the two flute webs assigned to the first discharge groove has or have along the drill longitudinal axis, at least in sections, a web spine width which changes, in particular, alternately.

Abstract: A drill head for deep-hole drilling includes cutting blade tips brazed to cutting chip discharge ports opened on a head distal end surface, guide pads mounted on a plurality of positions of the circumferential surface at the head distal end side, and a hollow inside portion made into a cutting chip discharge passage communicating with the cutting chip discharge ports. A guide pad portion having an arc surface that slide-contacts with the inner circumference of a cutting hole is formed on the outer end surface of the circumferential portion cutting blade tip.

Abstract: Disclosed is a cutting tool, including: a cutting edge including a coating from a rake face to a flank face, and has a relief angle of not less than 15 degrees, a material of the coating having a higher wear resistance than a base material of the cutting edge, and during cutting of a work, an edge of the coating on the rake face at a top of the cutting edge is worn by friction with the work; with a progress of a wear inward in a radial direction, an edge of the coating on the flank face at the top of the cutting edge is removed by friction with the work to expose the base material thereunder; and the exposed base material is worn by friction with the work to retract the flank face inward in the radial direction.

Abstract: A multi-lip drilling tool is described, in which main cutting edge transitions in the region of the drill into a center lip section, wherein a cooling duct that leads to the drill tip is formed in each drill web. The invention minimizes tensile stress spikes in the chip flute base, while at the same time ensuring that a hitherto unachievable coolant/lubricant quantity gets to the engaged main blade. This is ensured by selecting a duct cross sectional form similar to an unsymmetrical kidney, in which it is ensured the selected radii of curvature for the individual boundary curve sections causes as much coolant/lubricant as possible to arrive at the blade or in proximity thereto in the fastest way via the point thinning and its edges intersecting with drill core.

Abstract: A twist drill for drilling composite materials includes a shank; a drill body; a drill tip having a cutting edge, a chisel edge, and a secondary chisel edge, wherein the secondary chisel angle of the drill tip is 145° to 165 and the point angle is 70° to 100°; and a flute extending from the drill tip to the drill body. The flute has a constant helix, and the helix angle of the flute being selected from the range 45° to 55°. A method of drilling a composite material comprising fibers uses the twist drill of the present embodiment. Suitably, the composite material is carbon fiber reinforced plastic or glass fiber reinforced plastic, and optionally being a laminate material such that the method comprises stack drilling. Embodiments achieve a combination of good hole quality, good tool life and good hole size spread.

Abstract: A general-purpose multiple-cutting edge drill includes: a drill point (1); a drill body (2); margins (3) located on an outer wall of the drill body (2); two lips, wherein, if viewed from an axial direction, from out to inside, each of the two lips successively includes an outer cutting edge (11), an arc cutting edge (12) and an inner cutting edge (13); a chisel edge (14); outer peaks (15) formed by intersection of the outer cutting edges (11) and the arc cutting edges (12); a center peak (16) formed by intersection of two inner flank surfaces and two split surfaces. Moreover, an included angle between the inner cutting edges (13) ranges from 108° to 128°, an included angle between the outer cutting edge (11) ranges from 130° to 140°, and an included angle between the inner cutting edge (13) and outer cutting edge (11) ranges from 28° to 40°.

Abstract: A twist drill has a shaft and a flute portion, which extends between a drill tip and the shaft and has at least two flutes, which run helically around it at an angle of twist, are separated from one another by two webs and have a land extending between the flutes on the circumference of the flute portion. In order to provide a twist drill that has the features mentioned at the beginning, has better lubrication of the round bevels, less wear, improved guidance and improved concentricity, at least two round bevels that are spaced apart from one another are provided on each land and extend on the land at an angle of inclination in relation to the drill axis that is greater than the angle of twist but less than 90°.

Abstract: A small-diameter drill having a diameter of ?3 mm or less and an end that has undergone cross thinning is provided such that in a front view, a flute portion cutting edge is curved in concave with a degree of concavity with respect to an imaginary straight line in a range of 0.5 to 2% of a drill diameter, the imaginary straight line connecting the radially outer end of the flute portion cutting edge and the radially outer end of thinning portion cutting edge, the ratio of length of the thinning portion cutting edge to length of the flute portion cutting edge is set to 0.6 to 0.9:1, and in an axially perpendicular cross-sectional view, curvature radius of a heel-side flute surface of the flute is set to be smaller than curvature radius of a flute surface along the flute portion cutting edge.