Drill

Abstract

To provide a drill which inhibits occurrence of excessive burnishing while obtaining a good guide function during processing.SOLUTION: A drill includes: a shaft-like body which is rotated around a center axis; a chip discharge groove formed at the outer periphery of the body; a cutting blade formed at an intersection ridge line part between a wall surface directing the front side in a tool rotation direction of the chip discharge groove and the apical surface of the body; a first margin formed at a front end in the tool rotation direction of a land of the body and facing the radial outer side; a relieving surface located adjacent to the rear side in the tool rotation direction of the first margin; and a second margin which is located at the rear in the tool rotation direction of the relieving surface and located at the radial outer side relative to the relieving surface and the radial inner side relative to the first margin.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a drill.

Background Art

[0002] Conventionally, for example, Patent Document 1 discloses a so-called double margin type drill having a first margin and a second margin on the outer periphery of a drill body. The first margin is located on the land of the drill body and is disposed adjacent to a wall surface facing the drill rotation direction of the chip discharge groove. The second margin is located on the land on the rear side in the drill rotation direction than the first margin. In such a double margin type drill, a good guiding function can be obtained during machining by the first margin and the second margin slidingly contacting the inner peripheral surface of the machined hole of the workpiece, respectively.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in machining using a drill having a first margin and a second margin, since the first margin and the second margin rub against the inner peripheral surface of the machined hole of the workpiece, the temperature of the workpiece rises due to frictional heat. When the expansion coefficient of the workpiece is high, the workpiece may expand excessively due to the frictional heat between the workpiece and the first margin and the second margin. As a result, the distance between the inner peripheral surface of the machined hole and the outer peripheral surface of the drill body may be reduced, and excessive vanishing may occur. Therefore, it is desired to suppress the occurrence of excessive vanishing while obtaining a good guiding function during machining.

[0005] In view of the above circumstances, one of the objects of the present invention is to provide a drill that can suppress the occurrence of excessive vanishing while obtaining a good guiding function during machining.

Means for Solving the Problems

[0006] According to one aspect of the present invention, there is provided a drill including: a shaft-shaped body that rotates around a central axis; a chip discharge groove formed on an outer periphery of the body; a cutting edge formed at an intersection ridge line portion between a wall surface facing the front side in the tool rotation direction of the chip discharge groove and a tip surface of the body; a first margin formed at an end portion on the front side in the tool rotation direction of a land of the body and facing radially outward; a chamfered surface adjacent to the rear side in the tool rotation direction of the first margin; and a second margin located on the rear side in the tool rotation direction of the chamfered surface, radially outside the chamfered surface, and radially inside the first margin.

[0007] According to the above configuration, by providing the first margin and the second margin on the outer periphery of the body, the drill is suppressed from behaving radially during machining, and a good guiding function can be obtained. Further, since the second margin is located radially inside the first margin, the frictional heat between the second margin and the inner peripheral surface of the machined hole of the workpiece can be suppressed. Thereby, the temperature rise of the workpiece can be suppressed, so that the thermal expansion of the workpiece is suppressed and the reduction of the inner diameter of the machined hole is suppressed. As a result, while obtaining a good guiding function during machining, the occurrence of excessive vanishing can be suppressed.

[0008] The second margin may be configured to have a top portion that partially protrudes radially outward in a cross section orthogonal to the central axis on an outer peripheral surface of the second margin. In this case, by forming a top portion that protrudes radially outward in a part of the circumferential direction of the second margin, when the drill vibrates radially, the area of the surface of the second margin that contacts the inner peripheral surface of the machined hole can be reduced. Thereby, while maintaining the guiding function during machining, the occurrence of excessive vanishing can be more effectively suppressed.

[0009] The top portion may be configured to be formed at an end portion on the front side in the tool rotation direction on the outer peripheral surface of the second margin. Since the top portion is formed at the end portion on the front side in the tool rotation direction of the second margin, it is possible to suppress chips and sludge cut by the cutting edge from entering the gap between the second margin and the inner peripheral surface of the processing hole on the rear side in the tool rotation direction than the top portion. Thereby, it is possible to suppress an increase in frictional heat between the second margin and the inner peripheral surface of the processing hole due to chips and sludge, and to suppress the occurrence of excessive vanishing.

[0010] The top portion may be configured to be formed at an end portion on the rear side in the tool rotation direction on the outer peripheral surface of the second margin. Since the top portion is formed at the end portion on the rear side in the tool rotation direction of the second margin, the circumferential interval between the first margin and the top portion of the second margin is widened. Thereby, when the drill tends to behave in the radial direction during processing, the behavior can be stably suppressed, and the guide function can be further enhanced.

[0011] When the radial dimension centered on the central axis of the first margin is R1, the radial dimension centered on the central axis of the second margin is R2, and the radial dimension centered on the central axis of the chamfered surface is R3, it may be configured such that 0.1×(R1 - R3) ≦ (R1 - R2) ≦ 0.5×(R1 - R3). According to this configuration, it is possible to suppress the gap between the second margin and the inner peripheral surface of the processing hole from becoming excessively large. Thereby, it is possible to more effectively suppress the drill from behaving in the radial direction during processing.

[0012] When the radial dimension centered on the central axis of the first margin is R1 and the radial dimension centered on the central axis of the second margin is R2, it may be configured such that 0.8×R1 ≦ R2 ≦ 0.99×R1. According to this configuration, it is possible to suppress the gap between the second margin and the inner peripheral surface of the processing hole from becoming excessively large. Thereby, it is possible to more effectively suppress the drill from behaving in the radial direction during processing.

[0013] The second chamfered surface has an arcuate surface that forms an arc centered on the central axis, and a connecting surface that connects the arcuate surface and the second margin and extends radially outward as it goes rearward in the tool rotation direction. At the joint between the second chamfered surface and the second margin, the angle formed by the connecting surface and the front end portion of the second margin on the front side in the tool rotation direction may be an obtuse angle. If the angle formed by the connecting surface and the front end portion of the second margin on the front side in the tool rotation direction is an acute angle at the joint between the second chamfered surface and the second margin, this portion may function like a cutting edge. On the other hand, by making the angle formed by the connecting surface and the front end portion of the second margin on the front side in the tool rotation direction an obtuse angle, it is possible to suppress this portion from functioning like a cutting edge.

[0014] The outer peripheral surface of the second margin may be configured to be a convex curve protruding radially outward in a cross section perpendicular to the central axis. According to this configuration, it is possible to suppress a part of the second margin from locally contacting the inner peripheral surface of the processing hole. Thereby, even when the second margin contacts the inner peripheral surface of the processing hole, it is possible to suppress chipping or the like from occurring on the second margin.

[0015] The circumferential length of the outer peripheral surface of the second margin may be configured to be larger than the circumferential length of the outer peripheral surface of the first margin. According to this configuration, the strength of the second margin can be increased. Even when the second margin contacts the inner peripheral surface of the processing hole, it is possible to suppress chipping or the like from occurring on the second margin.

[0016] The tip portion on the front end side in the axial direction along the central axis of the second margin may be located on the rear end side in the axial direction rather than the tip portion on the front side in the axial direction of the first margin. By arranging the tip portion of the second margin on the rear end side in the axial direction rather than the tip portion of the first margin, from the initial stage of processing, the first margin and the second margin can suppress the drill from behaving radially during processing, and a good guiding function can be obtained.

[0017] The diameter dimension centered on the central axis of the first margin and the diameter dimension centered on the central axis of the second margin may be configured to gradually decrease from the front end side in the axial direction toward the rear end side in the axial direction. That is, each of the first margin and the second margin can be configured to have a so-called back taper.

Effect of the Invention

[0018] According to one aspect of the present invention, there is provided a drill that can suppress the occurrence of excessive vanishing while obtaining a good guiding function during machining.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0020] Hereinafter, a drill 1 according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a side view of the drill of the present embodiment. FIG. 2 is a partial side view showing an enlarged tip portion of the drill of the present embodiment. FIG. 3 is a front view of the drill of the present embodiment.

[0021] As shown in FIG. 1, the drill 1 of the present embodiment is a drill for deep hole machining. The drill 1 has a substantially cylindrical shape centered on the central axis O. The drill 1 has a shaft-shaped body 10 and a shank 11 that extend along the central axis O, respectively. The drill 1 perforates the workpiece by rotating around the central axis O with the tip surface of the body 10 facing the workpiece. The drill 1 of the present embodiment is a solid drill having a base material made of cemented carbide or the like. The drill 1 has a hard coating made of a metal nitride or the like that coats the surface of the base material.

[0022] The direction along the central axis O of the drill 1 (the direction in which the central axis O extends) is called the axial direction. Among the axial directions, the direction from the shank 11 toward the body 10 is called the tip side, and the direction from the body 10 toward the shank 11 is called the rear end side. The direction orthogonal to the central axis O is called the radial direction. Among the radial directions, the direction approaching the central axis O is called the inner radial side, and the direction away from the central axis O is called the outer radial side. The direction of orbiting around the central axis O is called the circumferential direction. Also, among the circumferential directions, the predetermined direction in which the body 10 rotates during drilling is called the front side in the rotation direction, and the opposite side is called the rear side in the rotation direction.

[0023] As shown in FIGS. 2 and 3, the body 10 has a pair of cutting edges 15, 15 and a pair of chip discharge grooves 14, 14 formed at intervals in the circumferential direction. The pair of cutting edges 15, 15 are located at the tip of the body 10. The pair of chip discharge grooves 14, 14 extend spirally along the outer circumference of the body 10 from the cutting edges 15, 15 toward the rear end side.

[0024] The drill 1 is formed with two coolant holes 9 symmetrically with respect to the central axis O from the rear end surface of the shank 11 toward the tip side, and twisted with the same lead as the chip discharge groove 14. These coolant holes 9 pass between the chip discharge grooves 14 in the body 10 and open to the tip relief surface 13, respectively. During drilling using the drill 1, coolant such as cutting oil or compressed air is ejected from the two coolant holes 9.

[0025] The chip discharge groove 14 is twisted rearward in the tool rotation direction T at a constant twist angle on the outer periphery of the body 10 as it extends from the cutting edge 15 toward the rear end side in the axial direction. The pair of chip discharge grooves 14, 14 are arranged symmetrically with respect to the central axis O. The drill 1 of the present embodiment is for deep hole machining, and the length along the axial direction of the chip discharge groove 14 is in the range of, for example, 8.0D to 50.0D with respect to the outer diameter D of the cutting edge 15 of the drill 1. Note that the outer diameter D of the cutting edge 15 is the outer diameter of the circle formed by the rotation locus around the central axis O at the outer peripheral end of the cutting edge 15, that is, the drill diameter.

[0026] The cutting edges 15, 15 are respectively formed at the intersection ridge line portions between the inner wall surfaces facing the front side in the tool rotation direction T of the pair of chip discharge grooves 14, 14 and the tip relief surface 13 (the tip surface of the body 10). The pair of cutting edges 15, 15 are arranged symmetrically with respect to the central axis O. The cutting edge 15 extends toward the rear end side as it goes toward the outer peripheral side (radially outward) of the body 10 and is provided with a tip angle.

[0027] The body 10 has lands 20, 20 between two circumferentially adjacent chip discharge grooves 14, 14 on the outer periphery of the body 10. A first margin 21 is provided at the front end side in the tool rotation direction T of the land 20. A second margin 22 is provided at the rear end side in the tool rotation direction T of the land 20. The first margin 21 and the second margin 22 are formed facing radially outward. The first margin 21 and the second margin 22 extend spirally along the edge of the chip discharge groove 14. The body 10 has a chamfered surface 23 recessed radially inward between the first margin 21 and the second margin 22.

[0028] The first margin 21 continuously extends rearward in the tool rotation direction T from the radially outer edge of the cutting edge 15. The outer peripheral surface 21a facing radially outward of the first margin 21 is arc-shaped centered on the central axis O in a cross section orthogonal to the central axis O. The second margin 22 is formed radially outside the chamfered surface 23. The second margin 22 is disposed radially inside the first margin 21. In the second margin 22, the outer peripheral surface 22a facing the radial outside is in a convex curve shape protruding toward the radial outside. In the case of the present embodiment, the outer peripheral surface of the second margin 22 is formed in an arc shape centered on the central axis O. Since the second margin 22 is formed convex radially outward, it is possible to suppress a part of the second margin 22 from locally contacting the inner peripheral surface of the machining hole. Thereby, even when the second margin 22 contacts the inner peripheral surface of the machining hole, it is possible to suppress chipping or the like from occurring in the second margin 22.

[0029] As shown in FIG. 3, the chamfered surface 23 has an arc-shaped surface 231 on the front side in the tool rotation direction T, a connecting surface 232 on the rear side in the tool rotation direction T with respect to the arc-shaped surface 231, and a connecting surface 233 on the front side in the tool rotation direction T with respect to the arc-shaped surface 231. The arc-shaped surface 231 is located radially inside the first margin 21. The arc-shaped surface 231 forms an arc shape centered on the central axis O when viewed from the axial direction.

[0030] The connecting surface 232 on the rear side in the tool rotation direction T connects the arc-shaped surface 231 and the second margin 22. The connecting surface 232 extends radially outward as it goes toward the rear side in the tool rotation direction T. The connecting surface 232 is a concave curved surface that is concave radially inward in a cross section perpendicular to the central axis O. With this configuration, the boundary between the chamfered surface 23 and the second margin 22 becomes clear, and it becomes easy to control both the depth of the chamfered surface 23 and the gap between the second margin 22 and the inner peripheral surface of the machining hole. The radius of curvature r of the connecting surface 232 is preferably in the range of, for example, 0.01×R1 [mm] < r < 0.8×R1 [mm].

[0031] At the joint between the chamfered surface 23 and the second margin 22, the angle α formed by the connecting surface 232 and the end portion on the front side in the tool rotation direction T in the second margin 22 is preferably an obtuse angle. The angle α is preferably in the range of 90° < α < 155°. If the angle α is an acute angle, there is a risk that this part will function like a cutting edge. On the other hand, by making the angle α formed by the connecting surface 232 and the end on the front side in the tool rotation direction T in the second margin 22 an obtuse angle, it is possible to suppress this part from functioning like a cutting edge. The angle α may be 100° or more, or 110° or more. The angle α may be 150° or less, or 140° or less.

[0032] The connecting surface 233 on the front side in the tool rotation direction T connects the arc-shaped surface 231 and the first margin 21. The connecting surface 233 extends radially outward as it goes toward the front side in the tool rotation direction T. The connecting surface 233 is a curved surface that is concave inward in the radial direction.

[0033] Also, when the radial dimension centered on the central axis O of the chamfered surface 23 is R3, the difference (R1 - R2) between the radial dimension R1 of the first margin 21 and the radial dimension R2 of the second margin 2 is preferably 0.1×(R1 - R3) ≦ (R1 - R2) ≦ 0.5×(R1 - R3), which is the difference between the radial dimension R1 of the first margin 21 and the radial dimension R3 of the chamfered surface 23, i.e., the chamfering depth (R1 - R3). Thereby, it is possible to prevent the gap between the second margin 22 and the inner peripheral surface of the processed hole from becoming excessively large. Therefore, it is possible to more effectively suppress the drill 1 from moving in the radial direction during processing. The difference (R1 - R2) may be 0.15×(R1 - R3) or more, or 0.2×(R1 - R3) or more. The difference (R1 - R2) may be 0.45×(R1 - R3) or less, or 0.4×(R1 - R3) or less.

[0034] When the radial dimension centered on the central axis O of the first margin 21 is R1 and the radial dimension centered on the central axis O of the second margin 22 is R2, the radial dimension R2 of the second margin 22 is preferably in the range that satisfies 0.8×R1 ≦ R2 ≦ 0.99×R1. Also in this case, it is possible to prevent the gap between the second margin 22 and the inner peripheral surface of the processed hole from becoming excessively large. Therefore, it is possible to more effectively suppress the drill 1 from moving in the radial direction during processing. The diameter dimension R2 of the second margin 22 may be 0.85×R1 or more, or 0.9×R1 or more.

[0035] The circumferential length W2 of the outer peripheral surface 22a of the second margin 22 is preferably larger than the circumferential length W1 of the outer peripheral surface 21a of the first margin 21. The circumferential length W2 may be the same length as the circumferential length W1. Thereby, even when the second margin 22 comes into contact with the inner peripheral surface of the processing hole, it is possible to suppress the occurrence of chipping or the like in the second margin 22. The circumferential length W2 of the outer peripheral surface 22a of the second margin 22 is preferably 1 time or more and 3 times or less the circumferential length W1 of the outer peripheral surface 21a of the first margin 21.

[0036] As shown in FIG. 2, the tip portion 22s on the axial front end side of the second margin 22 is preferably located on the axial rear end side with respect to the tip portion 21s on the axial front side of the first margin 21. The tip portion 22s on the axial front end side of the second margin 22 is preferably located on the axial rear end side within a range of, for example, 0.01×D [mm] to 0.5×D [mm] with respect to the tip portion 21s on the axial front side of the first margin 21. According to this configuration, from the initial stage of processing, the first margin 21 and the second margin 22 suppress the radial movement of the drill 1 during processing, and a good guiding function can be obtained.

[0037] The tool diameter of the drill 1 is gradually reduced from the axial front end side toward the rear end side, and a back taper is provided. Along with this, the diameter dimension R1 centered on the central axis O of the first margin 21 and the diameter dimension R2 centered on the central axis O of the second margin 22 gradually decrease from the axial front end side toward the axial rear end side. Also, as shown in FIG. 3, the tool diameters D1 at the positions of the first margins 21, 21 provided symmetrically with respect to the central axis O, and the tool diameters D2 at the positions of the second margins 22, 22 gradually decrease from the axial front end side toward the rear end side.

[0038] According to the drill 1 of the present embodiment described above, by providing the first margin 21 and the second margin 22 on the outer periphery of the body 10, it is possible to suppress the radial behavior of the drill 1 during machining and obtain a good guiding function. And since the second margin 22 is arranged radially inside the first margin 21, it is possible to suppress the frictional heat generated between the second margin 22 and the inner peripheral surface of the machined hole. By suppressing the temperature rise, it is possible to suppress the thermal expansion of the work material, so that it is possible to suppress the narrowing of the inner diameter of the machined hole and the rubbing against the first margin 21 and the second margin 22. As a result, it is possible to suppress the occurrence of excessive vanishing while obtaining a good guiding function during machining.

[0039] 〔Other configurations included in the present invention〕 Note that the present invention is not limited to the above-described embodiment, and modifications and the like of the configuration are possible without departing from the spirit of the present invention.

[0040] (First modification example) FIG. 4 is a front view showing a first modification example of the drill 1 described in the above embodiment. In this first modification example, as shown in FIG. 4, the second margin 22 has a top portion 225 that protrudes radially outward in a part in the circumferential direction. In this modification example, the top portion 225 is formed at the end portion on the front side in the tool rotation direction T of the second margin 22. In the second margin 22, the rear side in the tool rotation direction T with respect to the top portion 225 has a convex curved shape that protrudes radially outward.

[0041] The difference (R1 - R12) between the radial dimension R1 of the first margin 21 and the radial dimension R12 at the top portion 225 of the second margin 2 is preferably such that 0.1×(R1 - R3) ≤ (R1 - R12) ≤ 0.5×(R1 - R3). The difference (R1 - R12) may be 0.15×(R1 - R3) or more, or 0.2×(R1 - R3) or more. The difference (R1 - R12) may be 0.45×(R1 - R3) or less, or 0.4×(R1 - R3) or less.

[0042] According to the first modification example, by forming a top portion 225 that protrudes radially outward on a part of the circumferential direction of the second margin 22, even when the drill 1 swings radially, the area of the outer peripheral surface 22a of the second margin 22 that contacts the inner peripheral surface of the machining hole can be reduced. Thereby, while maintaining the guiding function during machining, the occurrence of excessive vanishing can be suppressed more effectively.

[0043] Also, since the top portion 225 is formed at the end portion on the front side in the tool rotation direction T of the second margin 22, chips and sludge generated by the cutting edge 15 can be prevented from entering the gap between the second margin 22 and the inner peripheral surface of the machining hole on the rear side in the tool rotation direction T with respect to the top portion 225. Thereby, it is possible to suppress an increase in frictional heat between the second margin 22 and the inner peripheral surface of the machining hole due to chips and sludge, and suppress the occurrence of excessive vanishing.

[0044] (Second Modification Example) FIG. 5 is a front view showing a second modification example of the drill 1 described in the above-described embodiment. In this second modification example, as shown in FIG. 5, the second margin 22 has a top portion 226 that protrudes radially outward on a part of the circumferential direction. In this modification example, the top portion 226 is formed at the end portion on the rear side in the tool rotation direction T of the second margin 22. In the second margin 22, the front side in the tool rotation direction T with respect to the top portion 226 has a convex curved shape that protrudes radially outward.

[0045] The difference (R1 - R22) between the radial dimension R1 of the first margin 21 and the radial dimension R22 at the top portion 226 of the second margin 2 is preferably such that 0.1×(R1 - R3) ≦ (R1 - R22) ≦ 0.5×(R1 - R3). The difference (R1 - R22) may be 0.15×(R1 - R3) or more, or 0.2×(R1 - R3) or more. The difference (R1 - R22) may be 0.45×(R1 - R3) or less, or 0.4×(R1 - R3) or less.

[0046] In the second modification example, by forming a top portion 226 that protrudes radially outward at a part of the second margin 22 in the circumferential direction, even when the drill 1 wobbles radially, the area of contact with the inner circumferential surface of the machined hole on the outer circumferential surface of the second margin 22 can be reduced. Thereby, while maintaining the guiding function during machining, the occurrence of excessive vanishing can be more effectively suppressed.

[0047] Further, since the top portion 226 is formed at the rear end portion of the second margin 22 on the rear side in the tool rotation direction T, the interval in the circumferential direction between the cutting edge 15 and the top portion 226 of the second margin 22 is increased. Thereby, when the drill 1 tends to behave radially during machining, its behavior can be stably suppressed, and the guiding function can be further enhanced.

[0048] In addition, within the scope not departing from the gist of the present invention, the respective configurations (components) described in the foregoing embodiments, modification examples, and supplementary notes may be combined, and addition, omission, substitution, and other changes of the configuration are possible. Further, the present invention is not limited by the foregoing embodiments, but is limited only by the scope of the claims.

Explanation of Reference Numerals

[0049] 1 Drill 10 Body 14 Chip discharge groove 15 Cutting edge 20 Land 21 First margin 21a Outer circumferential surface of the first margin 21s Tip portion 22 Second margin 22a Outer circumferential surface of the second margin 22s Tip portion 23 Chamfered surface 225, 226 Top portion 231 Arc-shaped surface 232, 233 Connecting surface

Claims

1. A shaft-shaped body that rotates around a central axis, A chip discharge groove formed on the outer periphery of the body, A cutting edge formed at the intersection ridge line portion between the wall surface facing the front side in the rotation direction of the chip discharge groove and the tip surface of the body, A first margin formed at the front end of the land of the body on the front side in the tool rotation direction and facing radially outward, A chamfered surface adjacent to the rear side in the tool rotation direction of the first margin, A second margin located behind the chamfered surface in the tool rotation direction, radially outside the chamfered surface, and radially inside the first margin, A drill comprising the above.

2. The second margin has a top portion that partially protrudes radially outward in a cross section perpendicular to the central axis on the outer peripheral surface of the second margin, The drill according to claim 1.

3. The top portion is formed at the front end of the outer peripheral surface of the second margin on the front side in the tool rotation direction, The drill according to claim 2.

4. The top portion is formed at the rear end of the outer peripheral surface of the second margin on the rear side in the tool rotation direction, The drill according to claim 2.

5. When the radial dimension of the first margin centered on the central axis is R1, the radial dimension of the second margin centered on the central axis is R2, and the radial dimension of the chamfered surface centered on the central axis is R3, 0.1×(R1 - R3) ≤ (R1 - R2) ≤ 0.5×(R1 - R3) is satisfied, The drill according to claim 1 or 2.

6. When the radial dimension of the first margin centered on the central axis is R1 and the radial dimension of the second margin centered on the central axis is R2, 0.8 × R1 ≤ R2 ≤ 0.99 × R1 is as follows The drill according to claim 1 or 2.

7. The chamfered surface is an arcuate surface that forms an arc centered on the central axis, and a connecting surface that connects the arcuate surface and the second margin and extends radially outward as it goes rearward in the tool rotation direction. It has At the joint between the chamfered surface and the second margin, the angle formed by the connecting surface and the end portion on the front side in the tool rotation direction of the second margin is an obtuse angle. The drill according to claim 1 or 2.

8. The outer peripheral surface of the second margin is a convex curved shape that protrudes radially outward in a cross section perpendicular to the central axis. The drill according to claim 1 or 2.

9. The circumferential length of the outer peripheral surface of the second margin is larger than the circumferential length of the outer peripheral surface of the first margin. The drill according to claim 1 or 2.

10. The tip portion on the front end side along the central axis of the second margin is located on the rear end side in the axial direction rather than the front end side in the axial direction of the first margin. The drill according to claim 1 or 2.

11. The diameter dimension centered on the central axis of the first margin and the diameter dimension centered on the central axis of the second margin gradually decrease from the front end side in the axial direction to the rear end side in the axial direction. The drill according to claim 1 or 2.

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