Body and gun drill

Abstract

To provide a body and a gun drill capable of smoothly drilling a deep hole by suppressing abrasion of the inner peripheral surface of the drilled hole due to deflection occurring during drilling. [Solution] The body 10 of a gun drill 100 that is rotated in one rotational direction R around a central axis Ax to drill a hole has one insert pocket 11 provided at the tip end into which a cutting insert 50 is attached, multiple front guide pad pockets 21, 22 provided at the tip end into which guide pads 61, 62 are attached, one discharge groove 31 extending from the insert pocket 11 to the rear end side and at least a portion of which is formed spirally, and at least one rear guide pad pocket 41 provided at the rear end side of the positions of the front guide pad pockets 21, 22 and into which a guide pad 71 is attached.

Description

[Technical Field]

[0001] The present invention relates to a body and a gundrill. [Background technology]

[0002] Patent documents 1 to 3 show gun drills for drilling holes with a large depth-to-diameter ratio. These gun drills have multiple guide pads at the tip that slide against the inner periphery of the drilled hole to prevent the body from wobbling.

[0003] However, when using a gun drill to drill particularly small, deep holes, the bending moment generated by the guide pad sliding against the inner surface of the drilled hole can cause a large deflection in the center of the body, which can cause the body to scrape against the inner surface of the drilled hole.

[0004] For this reason, in Patent Document 4, a portion of the chip discharge groove is bent to provide a bent portion, thereby differentiating the direction in which the body bends due to the bending moment from the bending direction in which the second moment of area becomes smaller, thereby suppressing the deflection of the body. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Chinese Patent Application Publication No. 116551035 [Patent Document 2] US Patent Application Publication No. 20240269755 [Patent Document 3] U.S. Patent No. 10,994,346 [Patent Document 4] Patent No. 7515534 Summary of the Invention [Problem to be solved by the invention]

[0006] Incidentally, when manufacturing large molds used in processes such as Gigacast, which molds large parts in a single process, it has traditionally been possible to drill deep holes using gun drill machines with runout prevention mechanisms. However, in recent years, there has been an increasing need to drill deep holes in large molds using machining centers that do not have runout prevention mechanisms. For this reason, gun drills are required to be able to drill deep holes smoothly by further reducing deflection of the body during drilling.

[0007] The present invention has been made in consideration of the above circumstances, and aims to provide a body and a gun drill that can smoothly drill deep holes by suppressing abrasion on the inner surface of the drilled hole due to deflection that occurs during drilling. [Means for solving the problem]

[0008] A body according to one embodiment of the present invention is a gun drill body that is rotated in one direction around a central axis to drill holes, and has one insert pocket at the tip into which a cutting insert is attached, a plurality of front guide pad pockets at the tip into which guide pads are attached, one discharge groove extending from the insert pocket toward the rear end, at least a portion of which is formed spirally, and at least one rear guide pad pocket that is located rearward of the position of the front guide pad pocket and into which a guide pad is attached.

[0009] In a body with this structure, when the body deflects, the guide pad attached to the rear guide pad pocket slides against the inner surface of the drilled hole at the rear end of the body. Furthermore, because at least a portion of the body's discharge groove is spirally formed, the direction of deflection at the rear end of the body can be controlled, and the rear guide pad pocket can be positioned appropriately to allow the guide pad to slide smoothly against the inner surface of the drilled hole. Therefore, even when drilling deep holes, body wobble is suppressed, maintaining the diameter, straightness, and roundness of the drilled hole. Furthermore, rubbing of the body against the inner surface of the drilled hole is avoided, allowing for high-precision drilling.

[0010] The discharge groove may have a twisted portion at a portion of the tip end side that twists rearward in the direction of rotation during processing as it moves from the tip end side to the rear end side, and the rear guide pad pocket may be arranged on the outer peripheral surface between the tip end position and the rear end position of the twisted portion.

[0011] The front end of the rear guide pad pocket may be located axially rearward relative to the rear end of the front guide pad pocket.

[0012] The distance between the front end of the rear guide pad pocket and the rear end of the front guide pad pocket may be 3 mm or more.

[0013] When a plane formed by a perpendicular line parallel to the seating surface of the insert pocket and perpendicular to the central axis and the central axis is taken as a reference plane, the seating surface of the rear guide pad pocket may be positioned so that it has an angle relative to the reference plane that is different from the angle of the seating surface of the front guide pad pocket relative to the reference plane.

[0014] In a gundrill according to one aspect of the present invention, a cutting insert may be attached to the insert pocket of the body, and guide pads may be attached to the front guide pad pocket and the rear guide pad pocket, respectively.

[0015] The guide pad attached to the rear guide pad pocket may be positioned such that the point farthest from the central axis is located at a different position when viewed from the front of the body than the guide pad attached to the front guide pad pocket.

[0016] The guide pad attached to the rear guide pad pocket may have a point furthest from the central axis, when viewed from the front of the body, that is positioned between a first surface inclined 70° forward in the direction of rotation during machining and a second surface inclined 160° forward in the direction of rotation with respect to a reference plane formed by the central axis and a perpendicular line parallel to the seating surface of the insert pocket and perpendicular to the central axis.

[0017] A cutting insert having an arcuate cutting edge may be attached to the insert pocket.

[0018] A gun drill according to one embodiment of the present invention is a gun drill that is rotated in one direction around a central axis to drill a hole, and may have a body, a cutting edge provided at the tip of the body, a plurality of front guide portions provided at the tip of the body, a discharge groove extending from the cutting edge to the rear end of the body, at least a portion of which is formed in a spiral shape, and at least one rear guide portion provided at the rear end of the body relative to the position of the front guide portion.

[0019] The rear guide portion may be disposed at a position where the point farthest from the central axis is different from that of the front guide portion when viewed from the front of the body.

[0020] When viewed from the front of the body, the rear guide portion may have a distance from the central axis equal to the tool radius over part or all of the range of an angle between a first surface inclined 70° forward in the direction of rotation during machining and a second surface inclined 160° forward in the direction of rotation with respect to a reference plane formed by a perpendicular line parallel to the cutting edge and perpendicular to the central axis and the central axis. [Effects of the Invention]

[0021] According to the present invention, a body and a gun drill are provided that can smoothly drill deep holes by suppressing abrasion of the inner peripheral surface of the drilled hole due to deflection that occurs during drilling. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a perspective view of a body of a gun drill according to this embodiment. [Figure 2] FIG. 2 is a front view of the body of the gun drill according to this embodiment. [Figure 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a side view of the body of the gun drill according to this embodiment. [Figure 5] FIG. 5 is a cross-sectional view taken along line VV in FIG. [Figure 6] FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. [Figure 7] FIG. 7 is a cross-sectional view taken along line VII-VII in FIG. [Figure 8] FIG. 8 is a side view showing the entire gun drill. [Figure 9] FIG. 9 is a perspective view of a gun drill body according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0023] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a body and a gundrill according to the present invention will be described in detail below with reference to the drawings.

[0024] As shown in FIGS. 1 to 3, the body 10 according to this embodiment is the body of a gundrill 100. The body 10 of the gundrill 100 includes a cutting insert 50, front guide pads 61 and 62, and a rear guide pad 71. The gundrill 100 is used with the cutting insert 50 attached to the tip of the body 10. The gundrill 100 is a cutting tool that is rotated about a central axis Ax in one rotational direction R, and drills a hole in a workpiece with the cutting edge 51 of the cutting insert 50 attached to the tip of the body 10.

[0025] As shown in FIGS. 1 to 7 , the body 10 has a generally cylindrical shape. The body 10 is a member that constitutes substantially the entire gundrill 100 and is formed, for example, from steel. Alternatively, the body 10 is formed from cemented carbide. The body 10 has one insert pocket 11, a plurality of front guide pad pockets 21, 22, one discharge groove 31, and one rear guide pad pocket 41. The gundrill 100 according to this embodiment is a so-called "single-flute type" having one discharge groove 31, and correspondingly, the cutting insert 50 has only one cutting edge 51.

[0026] The insert pocket 11 is provided at the tip of the body 10. The insert pocket 11 functions as a mounting seat for mounting the cutting insert 50. The insert pocket 11 has a seat surface 12, and the cutting insert 50 is abutted against this seat surface 12 to be fixed.

[0027] A plurality of front guide pad pockets 21, 22 are provided at the tip of the body 10. These front guide pad pockets 21, 22 are arranged at intervals in the circumferential direction of the body 10. In this example, there are two front guide pad pockets 21, 22. Guide pads 61, 62 are attached to these guide pad pockets 21, 22, respectively.

[0028] The discharge groove 31 is formed in the body 10 so as to extend from the insert pocket 11 toward the rear end. This discharge groove 31 has a twisted portion 32 formed in a spiral shape in a portion of the front end of the body 10. This twisted portion 32 twists rearward in the rotation direction R during machining as it moves from the front end toward the rear end. The discharge groove 31 has a straight portion 33 that extends linearly in the axial direction toward the rear end of the body 10 from the twisted portion 32. The front end of the twisted portion 32 connects to the rear end of the insert pocket 11, and the rear end connects to the straight portion 33.

[0029] The discharge groove 31 has two inner surfaces 31a, 31b and is V-shaped in cross section. When a plane formed by the central axis Ax and a perpendicular line Lb, which is parallel to the seating surface 12 of the insert pocket 11 and perpendicular to the central axis Ax, is defined as a reference plane Sb, the twisted portion 32 of the discharge groove 31 has one inner surface 31a parallel to the reference plane Sb at a leading end position 32a, and the other inner surface 31b tilted forward in the rotational direction R from the reference plane Sb at an angle α (see FIG. 5). Furthermore, the twisted portion 32 of the discharge groove 31 has one inner surface 31a tilted backward in the rotational direction R with respect to the reference plane Sb at an angle β1, and the other inner surface 31b tilted forward in the rotational direction R with respect to the reference plane Sb at an angle β2 (see FIG. 6).

[0030] The rear guide pad pocket 41 is located closer to the rear end of the body 10 than the positions of the front guide pad pockets 21 and 22. The front end of the rear guide pad pocket 41 is located axially rearward of the rear ends of the front guide pad pockets 21 and 22. Specifically, the distance between the front end of the rear guide pad pocket 41 and the rear ends of the front guide pad pockets 21 and 22 is 3 mm or more. In addition, in a radial cross-sectional view, the rear guide pad pocket 41 is formed in a concave shape having a seat surface 41a, a side surface 41b on the front side in the rotational direction R, and a side surface 41c on the rear side in the rotational direction R (see FIG. 6). A guide pad 71 is attached to the rear guide pad pocket 41. The rear guide pad pocket 41 is located on the outer circumferential surface of the body 10 between the tip end position 32a and the rear end position 32b of the twisted portion 32 of the discharge groove 31. As described above, the rear guide pad pocket 41 is located closer to the rear end of the body 10 than the positions of the front guide pad pockets 21 and 22, and the front end of the rear guide pad pocket 41 is positioned axially rearward of the rear ends of the front guide pad pockets 21 and 22. This allows the rear guide pad pocket 41 to increase the thickness of the body 10 rearward in the rotational direction R compared to the rear side surface 41c of the rear guide pad pocket 41 in the rotational direction R, thereby stably restraining the guide pad 71 during cutting. In particular, the front end of the rear guide pad pocket 41 is positioned axially rearward of the rear ends of the front guide pad pockets 21 and 22 by 3 mm or more. Therefore, even if the inner surface 31b has a shape that is twisted forward in the rotational direction R as it extends axially forward, the effect of increasing the thickness of the body 10 rearward in the rotational direction R compared to the rear side surface 41b of the rear guide pad pocket 41 in the rotational direction R can be sufficiently obtained.

[0031] In a front view of the body 10, the rear guide pad pocket 41 has a seat surface 41a disposed above the reference plane Sb within the plane of FIG. 6 (see FIG. 6).

[0032] The seating surface 41a of the rear guide pad pocket 41 is disposed at an angle relative to the reference plane Sb that is different from the angle of the seating surfaces 21a, 22a (see FIG. 5) of the front guide pad pockets 21, 22 relative to the reference plane Sb.

[0033] In the gundrill 100, the front guide sections 63, 64, which have guide pads 61, 62 attached to the front guide pad pockets 21, 22, and the rear guide section 73, which has a guide pad 71 attached to the rear guide pad pocket 41, have different roles. Specifically, the front guide sections 63, 64 mainly serve to receive the cutting resistance generated in the cutting edge 51, and the rear guide section 73 serves to receive the deflection of the body 10 during machining.

[0034] In the body 10 of this example, by providing the twist portion 32, the direction in which cutting resistance occurs during machining differs from the direction in which the body 10 bends. For this reason, by arranging the seating surface 41a of the rear guide pad pocket 41 at a different angle relative to the reference plane Sb than the angle of the seating surfaces 21a, 22a of the front guide pad pockets 21, 22 relative to the reference plane Sb, the rear guide portion 73 is arranged at a different angular phase from the front guide portions 63, 64. This allows the front guide portions 63, 64 to absorb cutting resistance, while the rear guide portion 73 can absorb deflection of the body 10 during machining.

[0035] The cutting insert 50 attached to the insert pocket 11 of the body 10 is made of, for example, a superhard material. The cutting insert 50 has a cutting edge 51. The cutting insert 50 is placed in the insert pocket 11 of the body 10 with the cutting edge 51 facing the tip and in contact with the seat surface 12, and is fastened and attached to the body 10 by a screw 50a (see FIG. 1).

[0036] The cutting insert 50 attached to the insert pocket 11 has a cutting edge 51 that protrudes further toward the tip side from the tip of the body 10. When machining a workpiece, when the body 10 rotates in the rotation direction R, the cutting edge 51 comes into contact with the workpiece, cutting the workpiece and forming a hole in the workpiece.

[0037] The guide pads 61, 62 attached to the front guide pad pockets 21, 22 are components that slide against the inner circumferential surface of the machined hole during machining, thereby mainly suppressing wobble of the body 10 and maintaining the straightness and roundness of the machined hole. The guide pads 61, 62 are fitted into the front guide pad pockets 21, 22 and fastened and fixed to the body 10 with screws (not shown). By attaching the guide pads 61, 62 to the front guide pad pockets 21, 22, front guide portions 63, 64, to which the guide pads 61, 62 are attached, are provided at the tip of the body 10.

[0038] The guide pad 71 attached to the rear guide pad pocket 41 is a component that abuts against the inner circumferential surface of the machined hole in the body 10 during drilling, thereby suppressing abrasion of the inner circumferential surface of the machined hole in the body 10, mainly due to deformation such as bending of the body 100. The guide pad 71 is fitted into the rear guide pad pocket 41 and fastened and fixed to the body 10 with screws 71a (see FIGS. 1 and 3). Attaching the guide pad 71 to the rear guide pad pocket 41 provides a rear guide portion 73 on the body 10 that is located rearward of the positions of the front guide portions 63 and 64. In a front view of the body 10, a point P of the guide pad 71 attached to the rear guide pad pocket 41 that is farthest from the central axis Ax is located at a different position from points P1 and P2 of the guide pads 61 and 62 attached to the front guide pad pockets 21 and 22, respectively, that are farthest from the central axis Ax (see FIG. 2). Furthermore, the guide pad 71 attached to the rear guide pad pocket 41 has a point P that is farthest from the central axis Ax, when viewed from the front of the body 10, positioned within the range of an angle γ between a first surface S1 that is inclined 70° forward in the rotation direction R and a second surface S2 that is inclined 160° forward in the rotation direction R with respect to the reference plane Sb (see FIG. 3). Note that the guide pads 62, 63, 71 attached to the front guide pad pockets 21, 22 and the rear guide pad pocket 41 may have the same shape or different shapes.

[0039] 8, a gundrill 100 having a body 10 configured as described above is brazed to a shaft 82 made of steel and having a gripped portion 81 at its rear end that is gripped by a machine tool (not shown). The gundrill 100 may have a long body 10 that includes the shaft 82, in which case the entire long body 10 may be made of cemented carbide or steel.

[0040] The gun drill 100, which is equipped with the cutting insert 50 and the guide pads 61, 62, and 71, is rotated by a machine tool in one rotation direction R about the central axis Ax, so that a hole is drilled in a workpiece by the cutting edge 51 of the cutting insert 50 attached to the tip of the body 10. Chips generated by this drilling are discharged to the outside of the drilled hole through the discharge groove 31 of the body 10.

[0041] When drilling a hole using this gun drill 100, guide pads 61, 62 on front guide sections 63, 64 provided at the tip end of the body 10 come into sliding contact with the inner circumferential surface of the drilled hole during drilling. This reduces vibration of the body 10, allowing the gun drill 100 to drill a hole while maintaining the diameter, straightness, and roundness of the drilled hole.

[0042] However, when drilling a small-diameter, deep hole, the bending moment generated by the guide pads 61, 62 of the front guide portions 63, 64 sliding against the inner surface of the drilled hole may cause the body 10 to bend and scrape against the inner surface of the drilled hole.

[0043] In the body 10 according to this embodiment and the gundrill 100 equipped with the same, a rear guide pad pocket 41 is provided rearward of the positions of the front guide pad pockets 21, 22, and a guide pad 71 is attached to this rear guide pad pocket 41. As a result, when the body 10 deflects, the guide pad 71 of the rear guide portion 73 at the rear end of the body 10 slides against the inner circumferential surface of the drilled hole. Furthermore, by providing the discharge groove 31 of the body 10 with a helical twist portion 32, the direction of deflection at the rear end of the body 10 can be controlled, and by locating the rear guide pad pocket 41 in an appropriate position, the guide pad 71 of the rear guide portion 73 can slide smoothly against the inner circumferential surface of the drilled hole.

[0044] Therefore, with the body 10 according to this embodiment and the gun drill 100 equipped with it, even when drilling deep holes, the vibration of the body 10 is suppressed, maintaining the straightness and roundness of the drilled hole, and further, rubbing of the body 10 against the inner surface of the drilled hole is avoided, allowing for high-precision drilling.

[0045] In particular, the rear guide pad pocket 41, to which the guide pad 71 is attached and which serves as the rear guide portion 73, is disposed on the outer peripheral surface of the body 10 between a front end position 32a and a rear end position 32b of a twisted portion 32 of the discharge groove 31, which twists rearward in the rotation direction R during machining as it moves from the front end to the rear end in a portion of the front end of the body 10. The front end of the rear guide pad pocket 41 is disposed axially rearward of the rear ends of the front guide pad pockets 21, 22, and the distance between the front end of the rear guide pad pocket 41 and the rear ends of the front guide pad pockets 21, 22 is 3 mm or more. Furthermore, when the guide pad 71 is attached to the rear guide pad pocket 41, the point P of the guide pad 71 farthest from the central axis Ax is disposed between a first surface S1 inclined 70° forward in the rotation direction R during machining and a second surface S2 inclined 160° forward in the rotation direction R with respect to a reference plane Sb, as viewed from the front of the body 10.

[0046] By providing a rear guide pad pocket 41 in which the guide pad 71 is attached at such a position and attaching the guide pad 71 to this rear guide pad pocket 41, the position of the rear guide portion 73 can be set at an appropriate position taking into account the deflection direction of the rear end side of the body 10, and the guide pad 71 can be made to slide smoothly against the inner surface of the machined hole.

[0047] The gundrill 100 according to this embodiment is configured as a so-called "tip-replaceable" tool in which the cutting insert 50 having the cutting edge 51 is replaceable. Alternatively, the gundrill 100 may be configured such that the cutting edge 51 is brazed to the body 10 as an integral part. The gundrill 100 may also be configured such that the front guide portions 63, 64 and the rear guide portion 73 are integrally formed on the body 10 as guide pads 61, 62, 71. In this case, the point of the rear guide portion 73 farthest from the central axis Ax may be located at a different position from the point of the front guide portions 63, 64 farthest from the central axis Ax in a front view of the body 10. In addition, when viewed from the front of the body 10, the rear guide portion 73 may have a distance from the central axis Ax equal to the tool radius of the gun drill 100 over part or all of the range of an angle between a first surface inclined 70° forward in the direction of rotation R and a second surface inclined 160° forward in the direction of rotation R with respect to a reference plane formed by a perpendicular line parallel to the cutting edge 51 and perpendicular to the central axis Ax and the central axis Ax.

[0048] Next, a modified example will be described. Note that the same structural parts as those in the above embodiment are given the same reference numerals and the description thereof will be omitted.

[0049] As shown in FIG. 9, a gun drill 100A according to a modified example is suitably used, for example, when machining a hole so that the bottom of the hole has a hemispherical shape.

[0050] The gundrill 100A includes a body 10A having a spherically shaped peripheral edge at the tip. A cutting insert 80 having an arc-shaped cutting edge 81 is fastened and fixed by a screw 80a into an insert pocket 11 of the body 10. The cutting edge 81 of the cutting insert 80 attached to the insert pocket 11 of the body 10A is formed in an arc shape so that the center side of the body 10A protrudes toward the tip.

[0051] In a gundrill 100A equipped with a cutting insert 80 having an arc-shaped cutting edge 81 for machining a hemispherical hole bottom, the contact edge length when cutting into a workpiece during cutting is longer than that of a gundrill with a normal cutting edge. As a result, the cutting resistance acting on the cutting edge 81 is greater in this gundrill 100A than in a gundrill with the same tool diameter and tool length, making the body 10A more likely to deflect.

[0052] In this way, even in the gun drill 100A in which the cutting edge 81 is arc-shaped and therefore the body 10A is prone to deflection, by providing the rear guide pad pocket 41 on the body 10A having a spirally formed discharge groove 31 at the rear end side of the position of the front guide pad pockets 21, 22, and attaching guide pads 63, 64, 73 to the front guide pad pockets 21, 22 and the rear guide pad pocket 41, deflection of the body 10A during machining can be suppressed, and hole machining can be performed while maintaining the hole diameter, straightness, and roundness of the machined hole.

[0053] The present disclosure is not limited to the above specific examples, and designs that are appropriately modified by a person skilled in the art from these specific examples are also included within the scope of the present disclosure as long as they have the features of the present disclosure. The elements of the above specific examples, as well as their arrangement, conditions, shape, etc., are not limited to those exemplified and can be modified as appropriate. The elements of the above specific examples can be combined as appropriate as long as no technical contradictions arise. [Explanation of symbols]

[0054] 10,10A Body 11 Insert Pocket 12 Seat 21,22 Front guide pad pocket 21a, 22a seat 31 Discharge groove 32 Twisted section 32a Tip position 32b Rear end position 41 Rear guide pad pocket 41a Seat 50,80 cutting insert 51,81 cutting edge 61, 62, 71 Guide pad 63,64 Front guide section 73 Rear guide section 100,100A Gundrill Ax center axis Lb perpendicular R Rotation direction S1 1st page S2 side 2 Sb reference plane

Claims

1. A gun drill body that is rotated in one direction around a central axis to drill a hole, One insert pocket provided at the tip portion and into which a cutting insert is attached; a plurality of front guide pad pockets provided at the tip end and adapted to receive guide pads; one discharge groove extending from the insert pocket toward the rear end side and at least a portion of which is formed in a spiral shape; at least one rear guide pad pocket provided rearward of the front guide pad pocket and configured to accommodate a guide pad; and the discharge groove has a twisted portion that is twisted rearward in the rotation direction during machining as it moves from the tip end side to the rear end side in a part of the tip end side, and a linear portion that extends linearly in the axial direction rear end side of the twisted portion, The rear guide pad pocket is disposed on the outer peripheral surface between the leading end position and the rear end position of the twisted portion. body.

2. A front end of the rear guide pad pocket is disposed axially rearward relative to a rear end of the front guide pad pocket. The body of claim 1 .

3. The distance between the front end of the rear guide pad pocket and the rear end of the front guide pad pocket is 3 mm or more. The body of claim 2 .

4. When a plane formed by a perpendicular line parallel to the seating surface of the insert pocket and perpendicular to the central axis and the central axis is set as a reference plane, the seating surface of the rear guide pad pocket is arranged to have an angle with respect to the reference plane different from an angle of the seating surface of the front guide pad pocket with respect to the reference plane. The body of claim 1 .

5. A cutting insert is attached to the insert pocket of the body according to any one of claims 1 to 4, and guide pads are attached to the front guide pad pocket and the rear guide pad pocket, respectively. Gundrill.

6. The guide pad attached to the rear guide pad pocket has a point furthest from the central axis disposed at a different position from the guide pad attached to the front guide pad pocket when viewed from the front of the body. The gundrill of claim 5.

7. The guide pad attached to the rear guide pad pocket has a point furthest from the central axis, when viewed from the front of the body, disposed between a first surface inclined by 70° forward in a rotation direction during machining and a second surface inclined by 160° forward in the rotation direction with respect to a reference plane formed by the central axis and a perpendicular line parallel to the seating surface of the insert pocket and orthogonal to the central axis. The gundrill of claim 5.

8. The cutting insert having an arcuate cutting edge is attached to the insert pocket. The gundrill of claim 5.

9. A gun drill that is rotated in one direction around a central axis to drill a hole, Body and one cutting edge provided at a tip portion of the body; a plurality of front guide portions provided at a tip portion of the body; one discharge groove extending from the cutting edge to a rear end side of the body and at least a portion of which is formed in a spiral shape; at least one rear guide portion provided on the body rearward of the position of the front guide portion; and the discharge groove has a twisted portion that twists rearward in the rotation direction during machining from the tip end side toward the rear end side in a part of the tip end side of the body, and a linear portion that extends linearly in the axial direction rearward of the twisted portion, the rear guide portion is disposed on the outer circumferential surface of the body between the leading end position and the rear end position of the twisted portion. Gundrill.

10. The rear guide portion has a point farthest from the central axis disposed at a different position from the front guide portion when viewed from the front of the body. The gundrill of claim 9.

11. In a front view of the body, the rear guide portion has a distance from the central axis equal to the tool radius over a part or all of an angle range between a first surface inclined by 70° forward in the rotation direction during machining and a second surface inclined by 160° forward in the rotation direction with respect to a reference plane formed by a perpendicular line parallel to the cutting edge and perpendicular to the central axis and the central axis. The gundrill of claim 9.

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