DEBURRING TOOL AND DEBURRING METHOD
20250041953 ยท 2025-02-06
Inventors
Cpc classification
B23C5/10
PERFORMING OPERATIONS; TRANSPORTING
B23D79/00
PERFORMING OPERATIONS; TRANSPORTING
B23C3/12
PERFORMING OPERATIONS; TRANSPORTING
International classification
B23C3/12
PERFORMING OPERATIONS; TRANSPORTING
B23C5/10
PERFORMING OPERATIONS; TRANSPORTING
Abstract
A shaft (2) of a deburring tool (1) has a distal end surface (5) orthogonal to its axis L, an annular connecting surface (6) extending in an X2 direction from an outer peripheral end of the distal end surface (5) toward an outer peripheral side, and an annular outer peripheral surface (7) extending parallel to the axis L from an end in the X2 direction of the connecting surface (6). The shaft (2) also has notches (8) at four locations in a circumferential direction. Each of the notches opens to the distal end surface (5), the connecting surface (6), and the outer peripheral surface (7). Each of the notches (8) has an inner wall surface (10) having a pair of opposed surface portions (11) and (12) opposed to each other in the circumferential direction. Each of the pair of opposed surface portions (11) and (12) extends in a radial direction around the axis L. The edges of the pair of opposed surface portions (11) and (12) are cutting edges (25).
Claims
1. A deburring tool comprising a shaft, the shaft comprising a distal end surface orthogonal to an axis when visually observed, an annular connecting surface extending to a proximal end side from an outer peripheral end of the distal end surface toward an outer peripheral side, an annular outer peripheral surface extending parallel to the axis from an end on the proximal end side of the connecting surface, and a notch disposed at a portion of the shaft in a circumferential direction around the axis and opening to the distal end surface, the connecting surface, and the outer peripheral surface, the notch having an inner wall surface comprising a pair of opposed surface portions opposed to each other in the circumferential direction, each of the opposed surface portions extending in a radial direction, each of the opposed surface portions having an outer peripheral edge having a distal end edge portion continuous to the distal end surface in the circumferential direction, an outer peripheral end edge portion continuous to the outer peripheral surface in the circumferential direction, and a connecting end edge portion continuous to the connecting surface in the circumferential direction and connecting the distal end edge portion and the outer peripheral end edge portion, the distal end edge portion, the outer peripheral end edge portion, and the connecting end edge portion forming a cutting edge.
2. The deburring tool according to claim 1, wherein the connecting end edge portion is curved to the proximal end side from an end on the outer peripheral side of the distal end edge portion toward the outer peripheral side and continuous to an end on a distal end side of the outer peripheral end edge portion.
3. The deburring tool according to claim 1 or 2, wherein the inner wall surface of the notch has a connecting surface portion extending in the circumferential direction and in an axial direction along the axis and connecting end edges on an inner peripheral side of a pair of the opposed surface portions, and the distal end surface is continuous on the inner peripheral side of a distal end edge of the connecting surface portion.
4. The deburring tool according to claim 1, wherein the shaft has a plurality of the notches at equal angular intervals.
5. The deburring tool according to claim 4, wherein the plurality of notches of the shaft comprises four notches, a width dimension in the circumferential direction of a blade section located between two of the notches adjacent to each other in the circumferential direction is or more of a radius of the shaft, and an opening width in the circumferential direction of an outer peripheral-side opening in which each of the notches opens to the outer peripheral surface is or more of the radius of the shaft.
6. The deburring tool according to claim 1, wherein a length dimension in the axial direction of the notch is equal to or larger than a radius of the shaft.
7. The deburring tool according to claim 3, wherein the shaft has a through hole passing through a center of the shaft in the axial direction and opening to the distal end surface.
8. The deburring tool according to claim 1, wherein the distal end surface is orthogonal to the axis.
9. The deburring tool according to claim 8, wherein the distal end surface has a center portion with a protrusion having a shape that tapers toward a distal end side, and a distance in the axial direction between a distal end point located on a most distal end side in the protrusion and the outer peripheral end of the distal end surface is 50 m or less.
10. The deburring tool according to claim 1, wherein the distal end surface has a shape that tapers to a distal end side toward the axis, and a distance in the axial direction between a distal end point located on a most distal end side in the distal end surface and the outer peripheral end of the distal end surface is 50 m or less.
11. A deburring method comprising: attaching the deburring tool according to claim 1 to a machine tool via a floating holder; and while rotating the deburring tool around the axis, bringing the distal end surface into contact with a surface to be deburred of a workpiece and moving the distal end surface along the surface to be deburred to remove a burr on the surface to be deburred.
Description
BRIEF DESCRIPTION OF DRAWINGS
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DESCRIPTION OF EMBODIMENTS
[0044] A deburring tool and a deburring method according to embodiments of the present invention will be described below with reference to the drawings.
Example 1
[0045]
[0046] The shaft 2 has a distal end surface 5 orthogonal to its axis L, an annular connecting surface 6 extending in the X2 direction from an outer peripheral end of the distal end surface 5 toward the outer peripheral side, and an annular outer peripheral surface 7 extending parallel to the axis L from an end in the X2 direction of the connecting surface 6. The shaft 2 also has four notches 8 at four locations in the circumferential direction around the axis L of the shaft 2. The four notches 8 each open to the distal end surface 5, the connecting surface 6, and the outer peripheral surface 7. The four notches 8 are provided at equal angular intervals around the axis L. In this example, the distal end surface 5 is a flat surface.
[0047] As illustrated in
[0048] As illustrated in
[0049] The distal end edge portion 21, the outer peripheral end edge portion 22, and the connecting end edge portion 23 of each of the opposed surface portions 11 and 12 form a cutting edge 25 of the deburring tool 1. The opposed surface portion 11 is a rake surface of the cutting edge 25 at the outer peripheral edge of the opposed surface portion 11. The opposed surface portion 12 is a rake surface of the cutting edge 25 at the outer peripheral edge of the opposed surface portion 12. Here, each of the rake surfaces (each of the opposed surface portions 11 and 12) extends in the radial direction and parallel to the axis L. Thus, the rake angle of the cutting edge 25 is 90.
[0050] As illustrated in
[0051] Here, the distal end surface 5 is present on the inner peripheral side of each notch 8 and on the inner peripheral side of the connecting surface 6 in each blade section 26. The distal end surface 5 has a circular portion coaxial with the axis L and four protruding portions that protrude radially from the circular portion to the outside in the radial direction.
[0052] As illustrated in
(Deburring Method)
[0053]
[0054] Here, the floating holder 50 is a common one. The floating holder 50 holds the deburring tool 1 so as to advance and retract the deburring tool 1 in the axial direction between an advanced position and a retracted position in the X2 direction relative to the advanced position. The floating holder 50 biases the deburring tool 1 to the advanced position with a predetermined biasing force.
(Operation Effects)
[0055]
[0056] In the example illustrated in
[0057] As illustrated in
[0058] The burr 55 rising from the edge of the surface 54 to be deburred has higher rigidity at a root portion 55a of the burr 55 continuous to the surface 54 to be deburred than at a distal end portion 55b of the burr 55. Thus, when the high-strength burr 55 is removed, load tends to be exerted on the part of the cutting edge 25 that shears the root portion of the burr 55, and chipping tends to occur in this part.
[0059] In this respect, in this example, the deburring tool 1 is attached to the machine tool 51 via the floating holder 50, as illustrated in
[0060] In this example, the cutting edge 25 has the connecting end edge portion 23 between the distal end edge portion 21 and the outer peripheral end edge portion 22 that is curved to the proximal end side from an end on the outer peripheral side of the distal end edge portion 21 toward the outer peripheral side and continuous to an end on the distal end side of the outer peripheral end edge portion 22. In this configuration, the distal end edge portion 21 and the outer peripheral end edge portion 22 that constitute the cutting edge 25 do not intersect at the right angle. Thus, even when the shaft 2 is not perpendicular to the surface 54 to be deburred of the workpiece 53 during a deburring process, the surface 54 to be deburred can be prevented or suppressed from being damaged by the corner of the cutting edge 25 rotating around the axis L.
[0061] Furthermore, in this example, the inner wall surface 10 of the notch 8 has the connecting surface portion 13 that extends in the circumferential direction and the axial direction X and connects the end edges on the inner peripheral side of the pair of opposed surface portions 11 and 12. The distal end surface 5 is continuous on the inner peripheral side of the distal end edge of the connecting surface portion 13. In this way, the space between the pair of opposed surface portions 11 and 12 in the circumferential direction easily receives shavings of burrs. The shavings stored in this space are discharged to the outer peripheral side of the shaft 2 by rotation of the deburring tool 1. It is easy to prevent or suppress shavings from interfering with the cutting edge 25 when it shears the burr 55.
[0062] In this example, the shaft 2 has a plurality of notches 8 at equal angular intervals. In this configuration, a plurality of cutting edges 25 can be provided at equal angular intervals in the circumferential direction, so that the cutting edges 25 can be brought into contact with the burr multiple times in one rotation of the shaft 2.
[0063] In this example, the shaft 2 has four notches 8. The width dimension O in the circumferential direction of the blade section 26 located between two notches 8 adjacent to each other in the circumferential direction is or more of the radius R of the shaft 2. In this way, when four notches 8 are provided in the shaft 2 as in the deburring tool 1 in this example, it is easy to ensure the width dimension O in the circumferential direction of the blade section 26. Therefore, chipping of the blade section 26 can be prevented or suppressed.
[0064] Furthermore, in this example, when the shaft 2 has four notches 8, the opening width M in the circumferential direction of the outer peripheral-side opening 7a in which the notch 8 opens to the outer peripheral surface 7 is or more of the radius R of the shaft 2. In this way, it is easy to ensure the opening width M of the outer peripheral-side opening 7a of the notch 8. Here, ensuring the opening width M of the outer peripheral-side opening 7a of the notch 8 facilitates removal of shavings of burrs. In addition, when the deburring tool 1 is moved in a direction along the surface 54 to be deburred, the feeding speed of moving the shaft 2 can be increased.
[0065] In this example, the length dimension N in the axial direction of the notch 8 is twice or more of the radius E of the shaft 2. This configuration can ensure the length in the axial direction of the notch 8. Therefore, when the cutting power of the cutting edge 25 decreases, a new cutting edge 25 can be provided in the shaft 2 by cutting the shaft 2 in the middle of the notch 8 in the axial direction in a direction orthogonal to the axis L so that the cross section serves as a new distal end surface 5 of the deburring tool 1, and by cutting off the corner between the new distal end surface 5 and the outer peripheral surface 7 to form an annular connecting surface 6 extending to the proximal end side from the outer peripheral end of the distal end surface 5 toward the outer peripheral side between the new distal end surface 5 and the outer peripheral surface 7.
[0066] The opening width M of each notch 8 and the width in the circumferential direction of the blade section 26 may be changed from those of the above example. The number of notches 8 may be one, two, or three, or five or more.
Modifications
[0067]
[0068]
[0069] In the deburring tool 1B, the shaft 2 has four notches 8 at equal angular intervals in the circumferential direction. As illustrated in
[0070] The distal end edge portion 21, the outer peripheral end edge portion 22, and the connecting end edge portion 23 of each of the opposed surface portions 11 and 12 form a cutting edge 25. The opposed surface portion 11 is a rake surface of the cutting edge 25 at the outer peripheral edge of the opposed surface portion 11. The opposed surface portion 12 is a rake surface of the cutting edge 25 at the outer peripheral edge of the opposed surface portion 12. Here, each of the opposed surface portions 11 and 12 extends in the radial direction and parallel to the axis L. Thus, the rake angle of the cutting edge 25 is 90. An angle 2 formed by the tangent line of the shaft 2 passing through the point of contact with the burr 55 and each of the opposed surface portions 11 and 12 is 90 at the point in time when the blade section 26 leaves the burr 55.
[0071] The notch 8 has a depth increasing in the X2 direction from the center of the shaft 2 toward the outer peripheral side. Between two notches 8 adjacent to each other in the circumferential direction is a blade section 26 with cutting edges 25 on the outer peripheral edge on one side and on the outer peripheral edge on the other side in the circumferential direction. The distal end surface 5 is located on the inner peripheral side of the connecting surface 6 in each blade section 26. The distal end surface 5 consists of four fan-shaped portions arranged radially.
[0072] When the deburring tool 1 in this example is used to perform deburring, the deburring tool 1 is also connected to the machine tool 51 via the floating holder 50. Chipping of the cutting edge 25 and the blade section 26 can be suppressed even when the deburring tool 1 in this example is used.
Modifications
[0073]
[0074] In this example, the connecting surface 6 has an annular curved surface portion 41 that is curved in the X2 direction from the outer peripheral edge of the distal end surface 5 toward the outer peripheral side, and an annular tapered surface portion 42 that is inclined in the X2 direction from an end edge on the outer peripheral side of the curved surface portion 41 toward the outer peripheral side. The end edge on the outer peripheral side of the tapered surface portion 42 is continuous to the outer peripheral surface 7. Thus, in the cutting edge 25, the connecting end edge portion 23 connecting the distal end edge portion 21 and the outer peripheral end edge portion 22 has a curved portion 45 that is curved in the X2 direction from an end on the outer peripheral side of the distal end edge portion 21 toward the outer peripheral side, and an inclined portion 46 that is inclined in the X2 direction from an end on the outer peripheral side of the curved portion 45 toward the outer peripheral side, in conformity with the cross-sectional profile of the connecting surface 6. An end on the outer peripheral side of the inclined portion 46 is continuous to the outer peripheral end edge portion 22.
[0075] Also in the deburring tool 1C in Modification 3, if load is exerted on the cutting edge 25 from the root portion 55a of the burr 55 when the cutting edge 25 shears the root portion 55a of the burr 55, the vector F1 of the load points to the X2 direction. As a result, the force in the X2 direction is exerted on the floating holder 50, so that the floating holder 50 functions to allow the deburring tool 1 to retract in the X2 direction from the surface 54 to be deburred. Accordingly, chipping of the cutting edge 25 can be prevented or suppressed.
[0076] The distal end edge portion 21 and the outer peripheral end edge portion 22 that constitute the cutting edge 25 do not intersect at the right angle. Thus, even when the shaft 2 is not perpendicular to the surface 54 to be deburred of the workpiece 53 during a deburring process, the surface 54 to be deburred can be prevented or suppressed from being damaged by the corner of the cutting edge 25 rotating around the axis L.
[0077] The connecting surface 6 can be a tapered surface that extends to the outer peripheral side toward the outer peripheral surface 77. In other words, in the deburring tool 1C in Modification 3, the connecting surface 6 does not have the curved surface portion 41 but has the tapered surface portion 42 alone. In this case, in the cutting edge 25, the connecting end edge portion 23 connecting the distal end edge portion 21 and the outer peripheral end edge portion 22 is inclined in the X2 direction from an end on the outer peripheral side of the distal end edge portion 21 toward the outer peripheral side and connected to the outer peripheral end edge portion 22, in conformity with the cross-sectional profile of the connecting surface 6. Also in this configuration, if load is exerted on the cutting edge 25 from the root portion 55a of the burr 55 when the cutting edge 25 shears the root portion 55a of the burr 55, the vector of the load points to the X2 direction. Thus, when load is exerted on the cutting edge 25 from the root portion 55a of the burr 55, the floating holder 50 functions to allow the deburring tool 1 to retract in the X2 direction from the surface 54 to be deburred. Accordingly, chipping of the cutting edge 25 can be prevented or suppressed. The distal end edge portion 21 and the outer peripheral end edge portion 22 that constitute the cutting edge 25 do not intersect at the right angle. Thus, even when the shaft 2 is not perpendicular to the surface 54 to be deburred of the workpiece 53 during a deburring process, the surface 54 to be deburred can be prevented or suppressed from being damaged by the corner of the cutting edge 25 rotating around the axis L.
Example 2
[0078]
[0079] In the deburring tool 1D in Example 1, the distal end surface 5 of the shaft 2 is a flat surface orthogonal to the axis L. In contrast, in the deburring tool 1D in this example, the distal end surface 5 of the shaft 2 has a minute protrusion 60 at the center portion. Here, the deburring tool 1D in Example 2 has the same configuration as Example 1, except that the distal end surface 5 has the protrusion 60. Thus, in the description of Example 2, the configuration corresponding to that of Example 1 is denoted by the same sign and will not be further elaborated. The deburring method for removing burrs on the surface to be polished of the workpiece 53 using the deburring tool 1D in Example 2 is the same as the deburring method in Example 1. Thus, the deburring method using the deburring tool 1D in Example 2 will not be further elaborated.
[0080] As illustrated in
[0081] Each of the pair of opposed surface portions 11 and 12 extends in the radial direction around the axis L. The pair of opposed surface portions 11 and 12 each have a distal end edge portion 21, an outer peripheral end edge portion 22, and a connecting end edge portion 23. The distal end edge portion 21, the outer peripheral end edge portion 22, and the connecting end edge portion 23 form a cutting edge 25 of the deburring tool 1D. The opposed surface portion 11 is a rake surface of the cutting edge 25 at the outer peripheral edge of the opposed surface portion 11. The opposed surface portion 12 is a rake surface of the cutting edge 25 at the outer peripheral edge of the opposed surface portion 12. Here, each of the rake surfaces (each of the opposed surface portions 11 and 12) extends in the radial direction and parallel to the axis L. Thus, the rake angle of the cutting edge 25 is 90.
[0082] The distal end surface 5 has a circular protrusion 60 at the center portion when viewed from the axial direction X. As illustrated in
[0083] Here, the distance U in the axial direction X (height dimension of the protrusion 60) between the distal end point 61 and the outer peripheral end 5a of the distal end surface 5 is 50 or less. Thus, the presence of the protrusion 60 can be confirmed by measuring the shape of the shaft 2 using a micrometer-order shape measuring machine. However, an observer who visually observes the deburring tool 1D is unable to recognize the presence of the protrusion 60. Therefore, it can be said that the shaft 2 has the distal end surface 5 orthogonal to the axis L when visually observed.
(Operation Effects)
[0084] The same operation effects as when the deburring tool 1 in Example 1 is used can be achieved when the deburring tool 1D in this example is used.
[0085] When the deburring tool 1D in this example is used, the biting of the cutting edge 25 of the deburring tool 1D on the surface 54 to be deburred of the workpiece 53 can be prevented or suppressed in a deburring process.
[0086]
[0087] The biting of the cutting edge 25 on the surface 54 to be deburred can occur in the deburring tool 1 when the positional relationship between the axis L and the surface 54 to be deburred of the workpiece 53 deviates from the perpendicular. As used herein the positional relationship between the axis L of the deburring tool 1D and the surface 54 to be deburred of the workpiece 53 deviates from the perpendicular refers to a case where the attachment posture of the deburring tool 1D is inclined relative to an ideal attachment posture when the deburring tool 1D is attached to the machine tool 51, or a case where the installation posture of the workpiece 53 arranged so as to be opposed to the deburring tool 1D is inclined relative to an ideal installation posture. The biting of the cutting edge 25 on the surface 54 to be deburred occurs also when the deburring tool 1D is connected to the machine tool 51 using the floating holder 50.
[0088] When the positional relationship between the axis L of the deburring tool 1 and the surface 54 to be deburred of the workpiece 53 deviates from the perpendicular, as illustrated in the area enclosed by the dotted line in
[0089] For such biting of the cutting edge 25, the deburring tool 1D in this example has the protrusion 60 on the distal end surface 5. Thus, when the distal end surface 5 of the deburring tool 1D is brought into abutment with the surface 54 to be deburred of the workpiece 53, the outer peripheral end portion of the distal end surface 5 (the outer peripheral end portion of the distal end edge portion 21 of the cutting edge 25) is not in intimate contact with the surface 54 to be deburred. Accordingly, as illustrated in
[0090] The protrusion 60 is minute. Thus, even when the outer peripheral end portion of the distal end surface 5 is not in intimate contact with the surface 54 to be deburred when the distal end surface 5 of the deburring tool 1D is brought into abutment with the surface 54 to be deburred of the workpiece 53, the burr 55 rising from the surface 54 to be deburred is less likely to be left unshaved.
[0091] If the distance U in the axial direction X between the distal end point 61 of the protrusion 60 and the outer peripheral end 5a of the distal end surface 5 exceeds 50 m, more burrs 55 are likely to be left unshaved during a deburring process. Thus, the distance U (height dimension of the protrusion 60) in the axial direction X between the distal end point 61 of the protrusion 60 and the outer peripheral end 5a of the distal end surface 5 is preferably 50 m or less, and more preferably 30 m or less. To avoid the biting of the cutting edge 25, it is preferable that the distance U (height dimension of the protrusion 60) in the axial direction X between the distal end point 61 of the protrusion 60 and the outer peripheral end 5a of the distal end surface 5 is 10 m or more.
[0092]
Example 3
[0093]
[0094] In the deburring tool 1E in Example 3, the distal end surface 5 of the shaft 2 has a shape that tapers toward the X1 direction (the distal end side). The deburring tool 1E in Example 3 has the same configuration as Example 1, except for the shape of the distal end surface 5. Thus, in the description of Example 3, the configuration corresponding to that of Example 1 is denoted by the same sign and will not be further elaborated. The deburring method for removing burrs on the surface to be polished of the workpiece 53 using the deburring tool 1E in Example 3 is the same as the deburring method in Example 1. Thus, the deburring method using the deburring tool 1E in Example 3 will not be further elaborated.
[0095] As illustrated in
[0096] Each of the pair of opposed surface portions 11 and 12 extends in the radial direction around the axis L. The pair of opposed surface portions 11 and 12 each have a distal end edge portion 21, an outer peripheral end edge portion 22, and a connecting end edge portion 23. The distal end edge portion 21, the outer peripheral end edge portion 22, and the connecting end edge portion 23 form a cutting edge 25 of the deburring tool 1E. The opposed surface portion 11 is a rake surface of the cutting edge 25 at the outer peripheral edge of the opposed surface portion 11. The opposed surface portion 12 is a rake surface of the cutting edge 25 at the outer peripheral edge of the opposed surface portion 12. Here, each of the rake surfaces (each of the opposed surface portions 11 and 12) extends in the radial direction and parallel to the axis L. Thus, the rake angle of the cutting edge 25 is 90.
[0097] As illustrated in
[0098] Here, the distal end surface 5 as a whole has a shape that tapers toward the X1 direction. However, in the distal end surface 5, the distance V in the axial direction X between the distal end point 71 at a most distal location in the X1 direction and the outer peripheral end 5a of the distal end surface 5 is 50 m or less. Thus, the shape of the distal end surface 5 can be confirmed by measuring the shape of the shaft 2 using a micrometer-order shape measuring machine. However, an observer who visually observes the deburring tool 1E is unable to recognize the shape of the distal end surface 5. Therefore, it can be said that the shaft 2 has the distal end surface 5 orthogonal to the axis L when visually observed.
(Operation Effects)
[0099] The same operation effects as when the deburring tool 1 in Example 1 is used can be achieved when the deburring tool 1E in this example is used. When the deburring tool 1E in this example is used, even if the positional relationship between the axis L of the deburring tool 1E and the surface 54 to be deburred of the workpiece 53 deviates from the perpendicular in a deburring process, the biting of the cutting edge 25 on the surface 54 to be deburred can be prevented or suppressed, in the same manner as when the deburring tool 1D in Example 2 is used.
[0100] In other words, when the deburring tool 1E in this example is employed, the outer peripheral end portion of the distal end surface 5 (the outer peripheral portion of the distal end edge portion 21 of the cutting edge 25) is not in intimate contact with the surface 54 to be deburred when the distal end surface 5 of the deburring tool 1E is brought into abutment with the surface 54 to be deburred of the workpiece 53. Thus, even if the positional relationship between the axis L of the deburring tool 1E and the surface 54 to be deburred of the workpiece 53 deviates from the perpendicular in a deburring process, the biting of the outer peripheral portion of the distal end edge portion 21 and the distal end portion of the connecting end edge portion 23 in the cutting edge 25 on the surface 54 to be deburred of the workpiece 53 can be prevented or suppressed. The distance V in the axial direction X between the distal end point 71 in the distal end surface 5 and the outer peripheral end 5a of the distal end surface 5 is 50 m or less. Thus, even when the outer peripheral end portion of the distal end surface 5 is not in intimate contact with the surface 54 to be deburred when the distal end surface 5 of the deburring tool 1E is brought into abutment with the surface 54 to be deburred of the workpiece 53, the burr 55 rising from the surface 54 to be deburred is less likely to be left unshaved.
[0101]
[0102] Also in this example, if the distance V in the axial direction X between the distal end point 71 of the distal end surface 5 and the outer peripheral end 5a of the distal end surface 5 exceeds 50 m, more burrs 55 rising from the surface 54 to be deburred are likely to be left unshaved during a deburring process. Thus, the distance V in the axial direction X between the distal end point 71 of the protrusion 60 and the outer peripheral end 5a of the distal end surface 5 is preferably 50 m or less, and more preferably 30 m or less. To avoid the biting of the cutting edge 25, it is preferable that the distance V in the axial direction X between the distal end point 71 of the protrusion 60 and the outer peripheral end 5a of the distal end surface 5 is 10 m or more.
[0103] Here, the shape of the distal end surface 5 illustrated in