Drill bit and insert for drill bits with improved centering capability and cutting performance

Abstract

Drill (310;350;371;373) with a rotary axis (X) and a plurality of cutting parts and flutes (313) which are formed alternately, wherein the drill (310;350;371;373) has: Cutting parts (311a, 311b) having central clearance surfaces (407, 409) that are in contact with a chisel edge (401) and are machined as flat surfaces, and outer circumferential clearance surfaces (411, 413) formed by extending from the central clearance surfaces (407, 409) in directions towards an outer circumferential surface (405) of the drill (310; 350; 371; 373) and being formed as curved surfaces, each of the curved surfaces having at least one radius, wherein a peak angle (θ4) between the outer perimeter free areas (411,413) in contact with the central free areas (407,409) is the same as a central peak angle (θ3) between the central free areas (407,409), where the central peak angle (θ3) is a constant angle defined by the central free areas (407,409) which define a central free area section (SR) represented as a straight line, characterized by the fact that The outer circumferential free surfaces (411,413) between the contact with the central free surfaces (407,409) and the outer circumferential surface (405) define an outer circumferential free surface section (CR), which is represented as a curve such that the outer circumferential tip angle (θ4) gradually increases in the radial direction to the outer circumferential surface (405) from the axis of rotation (X).

Description

Technical area

[0001] The present disclosure relates to a drill and an insert for a drill, in which flat relief surfaces are formed on the central part of the drill so that a point angle between the flat relief surfaces is constant to improve the centering ability of the drill, and curved relief surfaces are formed on the outer peripheral part of the drill to solve problems caused by an abrupt change in the point angle, thereby minimizing the generation of drill vibrations and burrs. State of the art

[0002] A drill as a rotating tool, such as an end mill, includes a cutting part provided at its distal end and having cutting teeth machined along its central axis, which is a rotation axis, and a spindle body provided at and extending from a rear end of the cutting part.

[0003] A drill is divided into an integrated solid drill and an indexable insert drill, which is used by inserting an insert into a drill tip of the drill. The solid drill cannot be used when a cutting part of the distal end part of the solid drill is worn out, and therefore the entire solid drill must be replaced with a new one. On the other hand, the indexable insert drill is a drill in which a cutting part and a spindle body are manufactured separately. The cutting part, as an insert type, is used by combining it with the spindle body and held therein by several retainers. When the service life of the cutting part ends, the cutting part can be removed from the spindle body and replaced.

[0004] A drill includes a cutting part formed along its central axis and a spindle body provided at the rear end of the cutting part. The cutting part includes a web portion with a cutting tooth formed along a longitudinal direction of its outer circumference and a chip removal groove. The web portion and the chip removal groove are alternately formed. The spindle body is combined with a drilling machine by supporting a drill shank on the machine. Fig. 1 is a view showing a head of a conventional twist drill in which two cutting parts are arranged symmetrically to each other and two chip flutes are arranged symmetrically to each other with respect to a drill tip of the conventional twist drill. Fig. 2(a), Fig. 2(b) and Fig. 2(c) show sections along the line AA of Fig. 1. Each of the sections of AA is a section taken along a boundary line of reliefs of the two symmetrically arranged cutting parts, crossing the drill tip 11. Fig. 2(a) is an example of a clearance surface designed as a flat surface, in which a line extending from the drill tip 11 to the outer peripheral surface 12 of the drill is shown as a straight line 13. Fig. 2(b) shows an example in which a relief extending from the drill tip 11 to the outer peripheral surface 12 is configured to have two flat surfaces, the relief being represented as two straight lines 14 and 15. Fig. Fig. 2(c) shows an example of a relief surface configured as a curved surface, wherein a line extending from the drill tip 11 to the outer peripheral surface 12 is shown as a curved line. Fig. 2(b) and Fig. 2(c) illustrate examples in which a central part 16 adjacent to the drill tip 11 and an outer peripheral part 17 connected to the central part 16 are machined to have different tip angles from each other.

[0005] Since the drill bit has a tip angle as in Fig. 2(a), is easy to machine, is relatively inexpensive, and is widely used. A normal tip angle θ1 of a conventional drill is 118° ∼ 150°, and an optimal angle is applied thereto according to requirements. The drill 10 with a small tip angle has excellent centering ability, so that the movement of a center point of a hole formed during penetration of a workpiece is prevented, but many burrs are generated at the entrance and exit of the penetrated hole. However, in a case where a drill with a large tip angle is used, the center point of the rotating drill 10 moves when it is operated in a state where the rigidity of the equipment is weak or the state of supporting a workpiece is uncertain, and therefore vibrations may occur between the workpiece and the drill 10.Such vibrations lead to drill bit breakage and poor hole quality. Especially when machining a thin plate, due to the elasticity of the thin plate, in addition to the cutting resistance encountered during drilling, external forces caused by the springback of the thin plate are very likely to occur, which may cause the drill bit to break and generate a relatively large amount of burrs.

[0006] The drill in Fig. 2(b), the tip angle θ1 of the central part 16 of the drill is less than 140°, and the tip angle θ2 of the outer peripheral part 17 extending from the central part 16 toward the outer peripheral surface 12 is greater than 140°, so that the problem of the drill from Fig. 2(a) can be solved to some extent. Due to the small size of a central tip angle θ1, the drill exhibits excellent centering ability during hole drilling, and due to the large size of an outer peripheral tip angle θ2, a relatively small amount of burrs is generated in the drilled hole.

[0007] When drilling from Fig. 2(b), the relief of the outer peripheral part 17 is machined as a flat surface, so that despite a change in the outer diameter of the drill, the outer peripheral tip angle θ2 remains the same as in the drill of Fig. 2(a) can be kept constant.

[0008] The problem of the drill in Fig. However, the angle of the drill bit in Figure 2(b) lies within its two apex angles. After the central portion 16 of the drill bit penetrates a workpiece, the outer peripheral portion 17 of the drill bit contacts the workpiece and begins drilling. The problem is that the apex angle of the drill bit changes when the outer peripheral portion 17 begins drilling. This means that the torque and thrust of the drill bit change abruptly, which can cause vibration of the drill bit and make the cutting mechanism of the drill bit unstable. As a result, the quality of a hole to be drilled may deteriorate or the drill bit may break.

[0009] On the other hand, to improve the centering of a drill, when drilling a hole with the Fig. 2(b) after first drilling a pilot hole with the drill bit shown in Fig. 2(a) with the same outer diameter, the outermost point of the outer peripheral portion 17 of the workpiece will be ahead of the center portion 16 of the drill and may start cutting. As a result, it is impossible to perform stable centering of the drill.

[0010] In the Fig. In the drill shown in Figure 2(c), the entire flank surface is formed as a curved surface. Fig. The section of the flank surface 18 shown in Fig. 2(c) is a curve having one radius or a plurality of radii from the drill tip 11 to the outer peripheral surface 12. When the flank surface 18 is a curve, the apex angle of the central part 16 and the apex angle of the outer peripheral part 17 are different from each other, as in the case of the section shown in Fig. 2(b), so that a similar effect to that of the drill of the Fig. 2(b). In addition, the change between the two tip angles is not abrupt, so that no problems arise from abrupt changes in torque and thrust. The drill bit of Fig. However, Figure 2(c) has an outer circumferential tip angle θ2 that changes according to the outer diameter of the drill, so that even if drills with the same shapes are used, it is difficult to obtain a constant quality of a hole according to the size of the hole to be drilled.

[0011] A prior art indexable insert drill is known, for example, from Korean patent application No. 10-2009-0096230.

[0012] US 2003 / 0077134 A1 shows a drill according to the preamble of claim 1. RevelationTechnical Problem

[0013] The present disclosure aims to propose a drill and an insert for a drill in which flat relief surfaces are formed on the central part of the drill such that a point angle between the flat relief surfaces is constantly small to improve the centering ability of the drill, and in which curved relief surfaces are formed on the outer peripheral part of the drill to solve problems caused by an abrupt change in the point angle, thereby minimizing the generation of drill vibrations and burrs.

[0014] Furthermore, the present disclosure aims to provide a drill and an insert for a drill in which the outer peripheral flank surfaces are formed as curved surfaces and the tip angles of the outer peripheral part of the drill in contact with a hole to be drilled are constant regardless of the size of the outer diameter of the drill. Technical solution

[0015] Accordingly, the invention proposes a drill having the features of claim 1, as well as a use of such a drill as a corresponding insert part according to claim 5.

[0016] According to an embodiment of the present disclosure, the central flank surface and the outer peripheral flank surface may be divided into a first flank surface in contact with a cutting edge and a second flank surface extending from the first flank surface and having a larger relief angle than the relief angle of the first flank surface.

[0017] According to an embodiment of the present disclosure, a central apex angle between the central flanks of the plurality of cutting parts may be set to 140° or less, and an outer circumferential apex angle between the outer circumferential flanks of the plurality of cutting parts may be set to 140° or more, wherein the outer circumferential apex angle may be defined by tangential lines of the outer circumferential flanks that meet the outer circumferential surface.

[0018] On the other hand, the outer peripheral tip angle can be kept constant despite a change in the size of an outer diameter of the drill by changing at least the radius of the curved surface of each of the outer peripheral flanks or the length of each of the central flanks in a direction toward the outer peripheral surface.

[0019] The present disclosure also applies to an insert attached to an insert portion of the drill. The insert includes the plurality of cutting portions that meet at the bit edge, each of the cutting portions including the central clearance surface and the outer peripheral clearance surface described above. Beneficial effects

[0020] The drill according to the present disclosure has a small tip angle at its central part and a relatively large tip angle at the outer peripheral part of the drill, thereby improving the centering ability of the drill and minimizing the generation of drill vibrations and burrs.

[0021] Furthermore, in the drill of the present disclosure, the outer peripheral relief surface is configured as a curved surface, so that the angle of a portion where the center portion extends to the outer peripheral portion does not change abruptly, thereby mitigating changes in torque and thrust of the drill and minimizing vibration of the drill. In particular, the drill of the present disclosure has excellent centering ability and allows a machined surface of a workpiece to remain clean, so the drill is advantageous even for machining a thin plate where kickback may occur during drilling due to the elasticity of the thin plate.

[0022] The drill of the present disclosure machines a workpiece with a constant outer circumferential tip angle of the drill regardless of the size of the outer diameter of the drill, thereby realizing consistent performance of the drill despite changes in the outer diameter of the drill. Description of the drawings Fig. 1 is a plan view showing a drill tip part of a conventional drill; Fig. 2(a), Fig. 2(b) and Fig. 2(c) show various examples of a section along the line AA of the drill bit part of the drill of Fig. 1; Fig. 3(a), Fig. 3(b), Fig. 3(c) and Fig. 3(d) are views showing examples of various types of drills to which the technology of the present disclosure is applied; Fig. 4 is a perspective view of an insert for an indexable insert drill according to an embodiment of the present disclosure; Fig. 5 is a plan view of the insert for each drill of the Fig. 3(a), Fig. 3(b), Fig. 3(c) and Fig. 3(d); and Fig. Figure 6 is a sectional view along line BB of the insert for each of the drills of the Fig. 3(a), Fig. 3(b), Fig. 3(c) and Fig. 3(d). Implementation of the invention

[0023] Hereinafter, the present disclosure will be described in detail with reference to the accompanying drawings.

[0024] The insert of the present disclosure is applied to a regular solid drill and an indexable insert drill. An insert for the indexable insert drill, such as an insert for a spade drill, has a variety of shapes according to a fastening method thereof, but any shape of the indexable insert drill can be applied. Fig. 3(a) shows an example of a normal solid drill or a welding drill, Fig. 3(b) shows an example of the indexable insert drill, and the Fig. 3(c) and Fig. 3(d) show examples of a spade drill.

[0025] With reference to the Fig. 3(a) and Fig. 3(b), the drill of the present disclosure includes a drill tip portion 310 formed at its distal end along a rotation axis X, and a spindle body 330 provided at a rear end of the drill tip portion 310. The technology of the present disclosure can be applied to a drill itself due to an embodiment thereof embodied in the drill tip portion 310 of the drill, and can be applied to the insert 350 for an indexable insert drill or to an insert such as an insert 371 or 373 for a spade drill. Meanwhile, the technology of the drill according to the present disclosure can be applied to the insert having two cutting parts as shown in FIGS. Fig. 3(a), Fig. 3(b), Fig. 3(c) and Fig. 3(d), and can even be used in an insert with at least three cutting parts.

[0026] The drill bit portion 310 has a plurality of cutting parts and flutes 313 formed alternately. Generally, two or three cutting parts and flutes are arranged in the drill bit portion, and the Fig. 3(a) and Fig. 3(b) show a twist drill with two cutting parts 311a and 311b and two chip flutes 313. The plurality of cutting parts are arranged such that they are opposite one another relative to the rotational axis of the drill and meet at a chisel edge and are spaced at equal intervals from one another. For example, in the Fig. 3(a) and Fig. 3(b) the two cutting parts 311a and 311b of the insert 350 are arranged symmetrically to each other and meet at the chisel edge.

[0027] In the following, the present disclosure will be described by referring to the Fig. 3 (b) , Fig. 4 and Fig. 6 shown insert for an indexable insert drill 350. First, with reference to Fig. 3(b), an insert part 331 is provided in the spindle body 330 of the drill, into which the insert 350 can be inserted. To hold the insert 350 inserted into the insert part 331, retaining holes are formed in the spindle body 330 and the insert 350 such that the retaining holes correspond to each other. A retaining element 333 is inserted into the retaining holes so that the retaining element passes through the spindle body 330 and is inserted into the insert 350, thus securing the insert 350 to the spindle body 330.

[0028] As described above, 350 of Fig. 4, the two cutting parts 311a and 311b are arranged symmetrically to each other and are in contact with each other at the chisel edge 401. Each of the cutting parts 311a and 311b has the same shape and configuration and can be described in the same way.

[0029] Each of the two cutting parts 311a and 311b comprises the central flank surface 407 or 409 and the outer peripheral flank surface 411 or 413, which extends radially from the rotation axis X toward the outer peripheral surface 405 of the insert. A cutting edge 415 is formed on one side of the central flank surface 407 or 409 and the outer peripheral flank surface 411 or 413, which are in contact with the chip groove 313. The central flank surfaces 407 or 409 of the two cutting parts 311a and 311b become thinner toward the drill tip due to a thin web arranged therebetween, so that the central part of the drill is tapered. The cutting edge 415, which adjoins the central flank 407 or 409 from the outer peripheral flank 411 or 413, is connected to a thinning edge 417 of the center section of the drill. In the thinning edge 417, the central flank 407 or 409 meets the gap formed between the central flank 407 or 409.409 and a central free surface 407 or 409 of another cutting part arranged web thickness 421.

[0030] The central flank surface 407 or 409 and the outer peripheral flank surface 411 or 413 represent “a flank surface of a cutting part” in contact with the entirety of the cutting edge 415. As in Fig. Meanwhile, as shown in Figure 4, the relief of a cutting part may include a first flank surface 407 and 411 in contact with the cutting edge 415 and a second flank surface 409 and 413 connected to the first flank surface 407 and 411 relative to a boundary line 419 that crosses the central flank surfaces 407 and 409 and the outer peripheral flank surfaces 411 and 413 in a radial direction. The second flank surface 409 and 413 has a larger relief angle than the first flank surface 407 and 411, thereby reducing the risk of breakage of the cutting edge 415 during a cutting operation and preventing a portion of the flank surfaces from excessively contacting a workpiece during rapid rotation of the drill.Accordingly, each of the cutting parts 311a and 311b includes four flank surfaces 407, 409, 411 and 413, which consist of a first central flank surface 407 and a second central flank surface 409 forming the central flank surfaces 407 and 409, and a first outer peripheral flank surface 411 and a second outer peripheral flank surface 413 forming the outer peripheral flank surfaces 411 and 413.

[0031] One in the Fig. 3(a) and the solid drill shown in the Fig. 3(c) and Fig. In contrast, the inserts 371 and 373 for a spade bit shown in Figure 3(d) contain the central flank and the outer peripheral flank. However, due to the properties of the spade insert, a chip breaker is formed on each flank.

[0032] As for the features of the present disclosure, the central flank surface 407 or 409, which is in contact with the chisel edge 401, is formed as a flat surface, and the outer peripheral flank surface 411 or 413, which extends from the central flank surface 407 or 409 toward the outer peripheral surface 405, is formed as a curved surface. Here, as in the Fig. 6, the curved surface of the outer peripheral flank surface 411 or 413 means that a line extending from the rotation axis X toward the outer peripheral surface 405 is a curve. Furthermore, the curve of the outer peripheral flank surface 411 or 413 is generally a curve with one or more radii, but is not limited thereto. The curve of the outer peripheral flank surface 411 or 413 is, for example, an Archimedean spiral, a cycloid spline, a trochoidal spiral, a sine curve, or even a curve (i.e., a free curve) that cannot be defined to have a plurality of radii, such as an involute curve. The same also applies to a spade insert 371 or 373.

[0033] Fig. 6 shows a section (a section along the line BB of Fig. 5), which intersects the central flank surfaces 407 and 409 and the outer peripheral flank surfaces 411 and 413 by intersecting the rotational axis X of the insert 350, and indicates whether the central flank surfaces 407 and 409 and the outer peripheral flank surfaces 411 and 413 are flat surfaces or curved surfaces. Referring to Fig. 6, since each of the central relief surfaces 407 and 409 is machined as a flat surface, the central relief surface portion SR is represented as a straight line, and since each of the outer peripheral relief surfaces 411 and 413 is machined as a curved surface, the outer peripheral relief surface portion CR is represented as a curved line.

[0034] The BB line from Fig. 5 coincides with the boundary line 419, and when one of the first flanks 407 and 411 and / or the second flanks 409 and 413 is viewed in the direction of the rotation axis X, the central flank portion SR is represented as a straight line, and the outer peripheral flank portion CR is represented as a curve. As described above, the curved surface of the outer peripheral flank 411 or 413 means that a line extending from the rotation axis X to the outer peripheral surface 405 is a curve. Accordingly, the portion of the outer peripheral flank 411 or 413 is represented as a straight line in a section along the line CC perpendicular to a section along the line BB.

[0035] The curve of the outer peripheral flank portion CR may have a radius and be formed as an arc, but it may also be formed as a curve with at least two radii. The radius of the curve of the outer peripheral flank portion CR, which extends to the outer peripheral surface 405, increases with the size of the outer diameter ØD of the drill and is preferably at least approximately 1.5 times the outer diameter ØD of the drill.

[0036] On the other hand, the shape of the thinning edge 417 and the shape of the cutting edge 415 of the insert 350, when viewed in a direction perpendicular to the thickness surface 423 of the insert in Fig. 4, may not be the same as the shape of the straight line of the central flank section SR or the shape of the curved line of the outer peripheral flank section CR in Fig. 6, corresponding to the shape of the chip groove 313 and the shape of the web thickness 421.

[0037] Referring to Fig. 6, a central tip angle θ3, which is defined by the central flank surfaces 407 and 409, respectively, and an outer circumferential tip angle θ4, which is defined by the outer circumferential flank surfaces 411 and 413, respectively, are all designed as obtuse angles. Preferably, the central tip angle θ3 is set to 115° to 135°, i.e., less than 140°, and the outer circumferential tip angle θ4 is set to an angle greater than 140°. Here, the central tip angle θ3 is an angle defined by the central flank surfaces 407 and 409, respectively, relative to the rotation axis X, and the outer circumferential tip angle θ4 is an angle defined by tangential lines at the outermost points of the outer circumferential flank surfaces 411 and 413, respectively, which meet the outer circumferential surface 405. When a drill bit (or an insert) with the two in Fig. 4, the central tip angle θ3 of the drill is an angle between the central flank surfaces 407 and 409 of the two cutting parts 311a and 311b, respectively, and the outer circumferential tip angle θ4 is an angle between the tangential lines at the outermost points of the outer circumferential flank surfaces 411 and 413 of the two cutting parts 311a and 311b, respectively. When a drill is a drill (or an insert) with at least three cutting parts, the central tip angle θ3 of the drill is twice the flare angle of each of the central flank surfaces relative to the rotation axis X, and the outer circumferential tip angle θ4 of the drill is twice the flare angle of each of the tangential lines at the outermost points of the outer circumferential flank surfaces relative to the rotation axis X.

[0038] Since the central flank section SR is represented as a straight line, the central tip angle θ3 in the central flank section SR is constant and is formed to be less than 140°, so that the centering ability of the drill as a whole can be excellently maintained.

[0039] On the other hand, since the outer circumferential flank portion CR is shown as a curve, the outer circumferential apex angle in the outer circumferential flank portion CR is not constant. That is, the outer circumferential apex angle gradually increases in the radial direction toward the outer circumferential surface 405 from the rotation axis X and becomes the largest angle when the outer circumferential flank portion CR meets the outer circumferential surface 405. Accordingly, as shown in Fig. 6, the outer peripheral tip angle θ4 can be obtained by an angle between the tangential lines of the outer peripheral flank surfaces 411 and 413 in contact with the outer peripheral surface 405, respectively. In the drill, the central tip angle θ3 and the outer peripheral tip angle θ4 are important factors that determine the performance of the drill. Accordingly, even though the outer diameter ∅D of the drill increases, the outer peripheral tip angle θ4 is preferably set constant. In order to maintain the constancy of the outer peripheral tip angle θ4 regardless of the increase in the outer diameter ØD of the drill, the radius of the curve of the outer peripheral flank portion CR and the length of the central flank surface 407 and 409 toward the outer peripheral surface can be changed according to the size of the outer diameter ØD of the drill.

[0040] The tip angle between the outer peripheral flank surfaces 411 and 413, respectively, which are in contact with the central flank surfaces 407 and 409, respectively, is defined to be equal to the central tip angle θ3, so that the difference between the tip angle between the central flank surfaces 407 and 409 and the tip angle between the outer peripheral flank surfaces 411 and 413 is not large. Accordingly, abrupt changes in the torque and thrust force of the drill bit do not occur. The outer peripheral tip angle θ4 has an angle of more than 140°, so that burrs generated in the drilled hole can be minimized.

[0041] However, since the clearance angle of the first flank surface 407 and 411 and the clearance angle of the second flank surface 409 and 413 are different from each other, the outer circumferential tip angle θ4 may change slightly even in the same insert 350 when the line BB is at a position different from the position of the boundary line 419.

[0042] On the other hand, a part extending from the chisel edge of the drill bit to the outermost point of the cutting edge is preferably machined so that the height of the outermost point of the cutting edge is the same as the height of the outermost edge part of the drill bit from Fig.2(a). This is because, when selecting the drill bit of the present disclosure, if a drill bit with the same outer diameter as the outer diameter of the conventional drill bit 10 is selected, a hole of the same depth and size can be drilled. Accordingly, it is not necessary to change other settings of a tool even though the drill bit of the present disclosure is selected instead of the conventional drill bit.

[0043] In the foregoing, the exemplary embodiment of the present disclosure has been shown and described, but the present disclosure is not limited to the specific embodiment described above. Of course, various modifications of the embodiment can be implemented by a person having ordinary skill in the technical field to which the present disclosure belongs, without departing from the gist of the present disclosure as claimed in the claims. Such modified embodiments should not be individually understood from the technical idea or perspective of the present disclosure.

Claims

[1] Drill (310;350;371;373) having a rotational axis (X) and a plurality of cutting parts and flutes (313) formed alternately, the drill (310;350;371;373) comprising: Cutting parts (311a, 311b) having central flanks (407, 409) in contact with a chisel edge (401) and machined as flat surfaces, and outer peripheral flanks (411, 413) formed by extending from the central flanks (407, 409) in directions toward an outer peripheral surface (405) of the drill (310; 350; 371; 373) and formed as curved surfaces, each of the curved surfaces having at least one radius, wherein an apex angle (θ4) between the outer peripheral flanks (411,413) in contact with the central flanks (407,409) is the same as a central apex angle (θ3) between the central flanks (407,409), the central apex angle (θ3) being a constant angle defined by the central flanks (407,409) defining a central flank section (SR) shown as a straight line, characterized by , that the outer circumferential clearance surfaces (411,413) define an outer circumferential clearance surface section (CR) between the contact with the central clearance surfaces (407,409) and the outer circumferential surface (405), which is shown as a curve such that the outer circumferential tip angle (θ4) gradually increases in the radial direction to the outer circumferential surface (405) from the axis of rotation (X). [2] A drill (310; 350; 371; 373) according to claim 1, wherein each of the central relief surfaces (407, 409) and each of the outer peripheral relief surfaces (411, 413) is divided into a first relief surface (407; 411) in contact with a cutting edge (415) and a second relief surface (409; 413) extending from the first relief surface (407; 411) and having a larger relief angle than the relief angle of the first relief surface (407; 411). [3] A drill (310; 350; 371; 373) according to claim 1, wherein the central tip angle (θ3) between the central flank surfaces (407, 409) of the plurality of cutting parts (311a, 311b) is set to 140° or less, and an outer peripheral tip angle (θ4) between the outer peripheral flank surfaces (411, 413) of the plurality of cutting parts (311a, 311b) is set to 140° or more. [4] A drill (310;350;371;373) according to claim 3, wherein despite a change in the size of an outer diameter (ØD) of the drill (310;350;371;373), the outer peripheral tip angle (θ4) is kept constant by changing at least one of a radius of the curved surface of each of the outer peripheral flanks (411,413) and a length of each of the central flanks (407,409) in a direction toward the outer peripheral surface (405). [5] Use of a drill according to one of the preceding claims 1 to 4 as an insert (350; 371; 373) in an insert part (331) of a spindle body (330).

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