JP2007098511A - Boring bar and its machining method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent generation of a return mark by a cutting edge when retreating a boring bar after machining. <P>SOLUTION: This boring bar is provided with a chip 13 having the cutting edge 13a in a recessed part 11a of a chip pocket 11 on an outer periphery at a distal end of a shank part 1. The center of gravity on a boring bar distal end side is set to be an opposite side of the chip 13 across an axis O. A small diameter part 5a is formed to be a bending generation part on a base end side of the shank part 1. An internal face of a machining hole is cut by the cutting edge 13a since the boring bar is advanced, while being rotated. When the boring bar is retreated, while being rotated, after the machining, the boring bar is rotated at a higher number of rotation than that at the advancing time to increase bending amount to the opposite side of the chip 13 having the small diameter part 5a at the distal end of the boring bar as a starting point as compared with that at the machining time, and the cutting edge 13a is moved close to the axis O to be separated from the internal face of the hole. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a boring bar for boring a workpiece and forming a hole with a desired accuracy, and a machining method therefor.

  Conventionally, a boring bar has been used for boring the work material, and this boring bar is inserted into a prepared hole in the work material in advance to cut the inner peripheral surface of the prepared hole. The hole of desired accuracy is formed (for example, refer to Patent Document 1).

  The above-mentioned boring bar is equipped with a single throw-away tip (hereinafter abbreviated as a tip) for finishing at the tip of the cylindrical shank, and this tip is detachable so that it can be replaced when worn. When viewed from the front end of the shank portion, the cutting blade formed on the ridge line of the corner portion slightly protrudes from the outer peripheral portion of the front end of the shank portion.

  When such a boring bar is machined, the shank part advances around the work piece while rotating around the axis by a driving source, and the cutting edge of the insert is provided in the inner periphery of a prepared hole provided in advance in the work piece. By cutting the surface, a hole with a desired accuracy is formed.

Japanese Utility Model Publication No. 5-12009

  By the way, after cutting the hole with the above-mentioned cutting bar of the boring bar, if the shank part is moved back while being simply rotated, the cutting edge protrudes from the outer peripheral part of the tip of the boring bar. There is a possibility that a so-called return mark may be generated, with the hole finished with accuracy being scratched.

  In particular, when machining the valve lifter hole and cylinder bore inner surface of a vehicle engine that requires high accuracy, it is necessary to avoid it because it may adversely affect engine characteristics only by attaching a minute return mark. .

  Therefore, an object of the present invention is to prevent a return mark from being generated by a cutting edge when a boring bar is retracted after machining.

  The present invention provides a tip having a cutting edge on the outer periphery of the tip of a shank portion that rotates about an axis, and advances the shank portion with respect to the work material while rotating the shank around the axis, and the cutting edge allows the cutting to be performed by the cutting blade. A boring bar that cuts the inner surface of the hole of the material and retreats the shank part while rotating around the axis when the machining is finished, and when the shank part is retracted, the shank part is at the time of machining The main feature is that the shank portion is provided with a bending generation portion that bends the shank portion so that the cutting blade is rotated closer to the axis than in the processing by rotating at a different rotational speed. To do.

  According to the present invention, when the boring bar is retreated while rotating after machining, the shank portion is bent so that the cutting blade moves closer to the axis by rotating at a different rotational speed from that at the time of forward movement. When the boring bar is retracted after machining, the cutting blade will move away from the inner surface of the machining hole due to the bending of the shank starting from the bending generating portion, and a return mark is generated by the cutting blade. Can be avoided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a front view of a boring bar according to a first embodiment of the present invention, and FIG. 2 is a view taken in the direction of arrow A in FIG. In the boring bar of this embodiment, the shank portion 1 has a conical shape portion 3 whose diameter decreases in the lower side in FIG. 1, and a shaft-shaped portion 5 that continues from the end on the small diameter side of the conical shape portion 3 to the tip side. And a small-diameter portion 5a as a deflection generating portion is provided on the conical shape portion 3 side of the shaft-like portion 5. The small diameter portion 5 a is formed by providing a recess over the entire circumference of the shaft-like portion 5.

  A gripped portion 7 for gripping the shank portion 1 with an arm of an ATC (automatic tool changer) of a machine tool such as a machining center (not shown) is provided on the outer periphery of the upper rear end of the shank portion 1 in FIG. Is forming. Further, the rear end side of the gripped portion 7 is an arbor 9 for attaching the shank portion 1 to the drive shaft of the machine tool.

  The tip portion of the shank portion 1 is provided with a tip pocket 11 that opens to the outer periphery and the front, and a throw-away tip (hereinafter abbreviated as a tip) 13 having a cutting edge 13 a is attached to the tip pocket 11. The tip 13 is detachably attached to the recess 11 a provided in the tip pocket 11 with a mounting screw 15, and the cutting edge 13 a formed on the ridge line of the corner portion of the tip 13 has a radius from the outer peripheral portion of the tip end of the shank portion 1. It protrudes outward in the direction.

  The tip 13 is made of cemented carbide or cermet, and when the shank portion 1 moves downward in FIG. 1 while rotating around the axis O, the inner peripheral surface of a prepared hole provided in advance in a work material (not shown) is formed. Cutting to form holes with the desired accuracy. The work material is a cylinder head made of, for example, a vehicle engine (made of aluminum or an alloy thereof), and the inner surface of the valve lifter hole of the cylinder head is cut.

  1 having a structure in which the tip 13 is provided in the recess 11a provided in the tip pocket 11 described above, the center of gravity of the boring bar tip side is located on the left side in FIG. And

  The boring bar of this embodiment is configured as described above, and performs boring (finishing) as follows.

  First, in processing, the gripped portion 7 of the shank portion 1 is gripped by an arm of an ATC (automatic tool changer), and the arbor 9 is attached to the drive shaft of the machining center. At this time, when the shank portion 1 moves toward the lower hole of the workpiece (not shown) while rotating around the axis O by the drive shaft, the cutting edge 13a of the tip 13 provided at the tip of the shank portion 1 is lowered. By cutting the inner peripheral surface of the hole, a hole with a desired accuracy can be obtained from the lower hole.

  As described above, this boring bar has a structure in which the chip 13 is provided in the concave portion 11a of the chip pocket 11, so that the center of gravity on the tip side is located on the left side in FIG. . For this reason, when the boring bar is rotated, the side having the center of gravity on the left side in FIG. 1 opposite to the tip 13 is basically bent from the small diameter portion 5a in the direction away from the axis O due to centrifugal force. .

  Here, when the boring bar advances and processes, the machining center rotates the entire shank portion 1 at a low rotation speed (for example, about 10,000 to 3000 rpm). As described above, when the boring bar is rotated at a low rotation, the amount of bending to the left in FIG. 1 starting from the small diameter portion 5a is smaller than that when the boring bar is rotated at a higher rotation. Therefore, the cutting process is performed by contacting the inner peripheral surface of the prepared hole with the cutting edge 13a.

  After the hole having the desired accuracy is cut by the tip 13 as described above, the boring bar moves to a retreating process in which the boring bar retreats to the original position through the processed hole. The shank unit 1 is driven at a higher rotational speed (for example, about 15000 rpm) than the rotational speed at the time of processing.

  Thus, when the boring bar is moved backward, the shank portion 1 is rotated at a higher rotational speed than when moving forward (during machining), so that the centrifugal separation generated on the opposite side of the tip 13 with the axis O interposed therebetween. The force is larger than the centrifugal force generated during processing. For this reason, the amount of bending toward the opposite side of the tip 13 of the boring bar starting from the small diameter portion 5a becomes large, and the tip 13 located on the outer peripheral surface of the shank portion 1 is closer to the axis O than during processing. Since it moves, it can prevent reliably that the cutting blade 13a contacts the internal peripheral surface of a hole.

  That is, by providing the chip 13 in the recess 11a of the chip pocket 11, the center of gravity on the tip side of the boring bar is positioned on the left side in FIG. Thus, by making the number of rotations of the shank portion 1 at the time of retraction higher than that at the time of machining, the cutting blade 13a is moved closer to the axis O, thereby preventing the tip 13 from contacting the inner peripheral surface of the hole at the time of retraction.

  In addition, during machining, machining is performed at a low speed, and during backward movement, the shank unit 1 is moved backward only by increasing the number of rotations. Therefore, the rotation of the shank unit 1 is completely stopped although there is some loss time in the switching time of the number of rotations. Since it does not do, it can suppress that cycle time falls.

  As a result, it is possible to prevent a return mark from being generated by the cutting edge 13a while suppressing a decrease in work efficiency when the boring bar is retracted after processing, and it is possible to improve the reliability as a boring bar that performs boring finish. Thereby, the high-speed rotation and high cycle time peculiar to a machining center are realizable.

  FIG. 3 is a modification of the first embodiment shown in FIG. 1, FIG. 3 (a) is a front view showing a part of the tip side of the boring bar, and FIG. 3 (b) is FIG. 3 (a). It is BB sectional drawing of). In the boring bar according to this modification, instead of the small-diameter portion 5a in FIG. 1, a plurality of notch holes 5b serving as recesses as deflection generating portions are provided along the outer circumference of the shaft-like portion 5 in the shank portion 1 along the circumferential direction. A plurality (four at regular intervals) are provided.

  FIG. 4 is another modification of the first embodiment shown in FIG. 1, FIG. 4 (a) is a front view showing a part of the tip side of the boring bar, and FIG. 4 (b) is FIG. It is CC sectional drawing of (a). The boring bar according to this modification is provided with a notch recess 5 c serving as a recess as a deflection generating portion on the outer periphery of the shaft-like portion 5 in the shank portion 1 instead of the small-diameter portion 5 a in FIG.

  Also in the example of FIG. 3 and FIG. 4 described above, as in the first embodiment in FIG. 1, at the time of cutting, by reducing the rotation speed of the shank portion 1, the tip of the boring bar is moved away from the tip 13. While reducing the amount of bending of the boring bar after processing, by increasing the number of rotations of the shank portion 1 when the boring bar is retracted, it is opposite to the tip 13 starting from the notch hole 5b or notch recess 5c of the shank portion 1. By increasing the amount of bending to the side and making the turning radius of the tip 13 smaller than that during processing, contact with the inner peripheral surface of the hole of the cutting edge 13a during retraction is prevented, and generation of return marks is prevented. To do.

  The small-diameter portion 5a, the notch hole 5b, and the notch recess 5c described above may be further reduced in diameter or further increased in the notch hole when the amount of deflection of the shank portion 1 is insufficient when acting as a deflection generating portion. By taking measures such as these, a desired amount of deflection can be obtained.

  FIG. 5 is a front view of a boring bar according to the second embodiment of the present invention, and FIG. 6 is a view taken in the direction of arrow D in FIG. The boring bar of this embodiment is provided with a weight portion 17 at an upper position opposite to the tip 13 with respect to the axis O in the outer periphery of the tip end of the shank portion 1 with respect to the first embodiment shown in FIG. ing. Other configurations are the same as those of the first embodiment.

  As shown in FIG. 6, the weight portion 17 is composed of two screws 19 attached along the circumferential direction on the outer periphery on the front end side of the shank portion 1.

  These screws 19 are made of, for example, hexagon socket countersunk bolts. As shown in FIG. 6, the tip 19a is screwed into a female screw 5d provided on the outer periphery of the shank 1, and its head 19b is mounted. Is embedded in a head housing groove 5e provided continuously to the female screw 5d so as not to protrude from the outer periphery of the shank portion 1 to the outside.

  The screw 19 constituting the weight portion 17 is made of a material having a higher specific gravity than the shank portion 1 body and the chip 15.

  The second embodiment is different from the first embodiment in that the weight portion 17 is provided on the opposite side of the chip 13 with the axis O in between, thereby acting on the weight portion 17 side at the same rotational speed. When the centrifugal force to be increased increases and the shape of the small diameter portion 5a is made equal, the bending operation of the shank portion 1 starting from the small diameter portion 5a becomes more reliable.

  Therefore, in this case, in the structure of the small diameter portion 5a, the cutout hole 5b, and the cutout recess 5c, when the amount of bending of the shank portion 1 is insufficient, the diameter is further reduced as the bending generation portion, the cutout holes are further increased, etc. There is no need to do.

  Moreover, since the weight part 17 consists of the two screws 19 provided in the circumferential direction in the outer periphery of the shank part 1, it can be comprised easily. Moreover, since the two screws 19 are embedded in the outer periphery of the shank portion 1, there is no influence on surrounding obstacles.

  FIGS. 7 and 8 are modifications of the second embodiment shown in FIGS. 5 and 6 and differ from the second embodiment in that the weight of the entire weight portion 17 provided in the shank portion 1 is different. The point is that it can be adjusted.

  That is, as shown in FIG. 7, the weight portion 17 is on the outer periphery of the tip end of the shank portion 1 on the side opposite to the tip 13 with the axis O in between and on the rear end side of the shank portion 1 from the tip 13. In this example, a plurality are provided along the axis O direction, and a plurality are provided toward the axis O within a predetermined angle range as shown in FIG. In total, ten screws 21 are used.

  These screws 21 are, for example, hexagon socket head bolts, and as shown in FIG. 8 (a), the tip 21a is screwed into a female screw 5d provided in the shank 1, and its head 21b is The head is housed in a head housing groove 5e that is continuous with the screw 5d, and is embedded so as not to protrude outside from the outer periphery of the tip of the shank portion 1. FIG.8 (b) is F arrow view of Fig.8 (a).

  7 and 8, a plurality of weight portions 17 are provided on the outer periphery of the shank portion 1 on the rear end side of the shank portion 1 opposite to the chip 13 with the axis O interposed therebetween. Therefore, basically the same operational effects as those of the second embodiment shown in FIGS. 5 and 6 are obtained, and the following operational effects are obtained.

  That is, if the number of screws 21 constituting the weight portion 17 is increased, the difference in the magnitude of the centrifugal force generated in the weight portion 17 at the time of processing and retreating is increased. Conversely, if the number of screws 21 is decreased, the weight is increased. The difference in the magnitude of the centrifugal force generated in the weight portion 17 is reduced, and thus the radius of rotation of the tip 13 at the time of processing and at the time of retraction can be adjusted as appropriate.

  For this reason, the cutting edge 13a of the tip 13 draws a desired circular locus at the time of processing by adjusting the weight of the weight portion 17 and the difference in the rotational speed of the shank portion 1 between processing and retraction. At the time of retraction, the cutting edge 13a of the tip 13 can be reliably separated from the inner peripheral surface of the hole.

  Therefore, it is possible to accurately perform the machining advance movement for forming the hole with the desired accuracy and the backward movement without the return mark. Moreover, the number of screws 21 to be used can be selected based on the magnitude of the rotational speed at which the shank unit 1 is driven, and not only for machining centers that rotate at higher speeds, but also for driving devices that rotate at lower speeds. Can be used well.

  In the example shown in FIGS. 7 and 8, a hexagon socket head cap screw is used as the weight portion 17. However, the present invention is not limited to this, and a hexagon socket head cap screw as shown in FIGS. Of course.

  FIG. 9 is a front view of a boring bar according to the third embodiment of the present invention, and FIG. 10 is a view taken in the direction of arrow G in FIG.

  In both of the second embodiment shown in FIG. 5 and its modification (FIG. 7), the weight portion 17 is disposed on the outer periphery of the shank portion 1 on the opposite side of the chip 13 with the axis O interposed therebetween. Although provided on the rear end side of the shank portion 1, in this embodiment, the weight portion 17 is provided on the outer periphery of the shank portion 1 at the front end portion of the shank portion 1 on the opposite side of the chip 13 with the axis O interposed therebetween. Is provided.

  That is, as shown in FIG. 10, the weight portion 17 of this embodiment is provided along the axial direction at positions substantially opposite to the tip 13 along the radial direction on the tip surface of the shank portion 1. A screw 23 is screwed to make the portion opposite to the tip 13 heavy on the outer periphery of the shank portion 1.

  The screw 23 is composed of a hexagon socket head bolt as in the example of FIG. 7, and as shown in FIG. 9, the tip 23 a is screwed into a female screw 5 d formed in the axis O direction on the tip of the shank 1. At the same time, the head portion 23b is housed in a head housing groove 5e continuous with the male screw 5d. In this case, the two female screws 5 d and the head storage groove 5 e are provided along the radial direction on the tip surface of the shank portion 1.

  Also in the third embodiment described above, the center of gravity of the boring bar tip side is positioned on the left side in FIG. By making the rotational speed smaller than when retreating, the amount of bending of the tip of the boring bar at the opposite side of the tip 13 at the time of machining is reduced, while at the time of retreating, the rotational speed of the shank portion 1 is increased, The cutting edge 13a of the tip 13 is retracted by retracting the tip 13 from the small diameter portion 5a at the tip of the boring bar by increasing the amount of bending to the opposite side of the tip 13 and making the turning radius of the tip 13 smaller than that during processing. The contact with the inner peripheral surface of the hole is surely prevented.

  11 and 12 show a modification of the third embodiment shown in FIGS. In this example, the weight portion 17 is provided on the outer periphery of the shank portion 1 on the opposite side of the tip 13 with the axis O interposed therebetween, as in the third embodiment, and is also movable in the radial direction. Screwed.

  That is, as shown in FIG. 12A, which is a view from the direction of the arrow H in FIG. 11, the weight portion 17 has a rectangular slider 25 and a screw 27 through which the slider 25 is rotatably inserted. ing. As shown in FIG. 12B, which is a cross-sectional view taken along the line II of FIG. 12A, the slider 25 has a trapezoidal shape that gradually becomes wider from the surface side to the flange portion.

  On the other hand, on the front end surface of the shank portion 1, a dovetail groove 5 f that extends in the radial direction and fits with the slider 25 is provided at a position slightly opposite to the left side of the chip 13 as shown in FIG. . The dovetail groove 5f has a shape symmetrical to that of the slider 25 and opens at the front end surface of the shank portion 1, and a female screw portion 5g that engages with a screw 27 at a flange portion of the opening portion is formed in a groove shape along the radial direction. Provided.

  The weight portion 17 is attached to the front end surface of the shank portion 1 by screwing the screw 27 with the female screw portion 5g while fitting the slider 25 in the above-mentioned dovetail groove 5f, and the dovetail groove 5f The screw 27 can be screwed at an arbitrary position in the length along the radial direction, and the weight portion 17 can be set at an appropriate radial position on the front end surface of the shank portion 1.

  In this example, since the weight part 17 is provided so that the position of the weight part 17 can be adjusted in the radial direction, by adjusting the position of the weight part 17, the centrifugal force generated in the weight part 17 during processing and when the boring bar is retracted. Can be adjusted.

  That is, when the position of the weight portion 17 is adjusted so as to be close to the axis O, the centrifugal force generated in the weight portion 17 is reduced, and the weight portion 17 is positioned at a position separated from the axis O. When adjusted, the centrifugal force generated in the weight portion 17 increases.

  Thus, since the position of the weight part 17 can be adjusted, even when the rotational speed of the shank part 1 is changed during processing due to the material of the work material, the position of the weight part 17 is appropriately set. By adjusting, the cutting edge 13a of the tip 13 can be reliably separated from the inner peripheral surface of the hole when the boring bar is retracted.

  Therefore, various materials can be processed by adjusting the rotational speed of the shank portion 1 and the position of the weight portion 17 during processing according to the material of the material to be processed.

  Also in this example, since the weight portion 17 is provided with the weight portion 17 on the opposite side of the tip 13 on the outer periphery of the shank portion 1, at the time of processing, the weight portion 17 can move forward while rotating at a low rotational speed. The cutting blade 13a forms a hole with a desired accuracy, and when retracted, the centrifugal force is applied to the weight portion 17 by driving at a higher rotational speed than during machining, and the tip 13 is displaced toward the axis O side. It will be.

  For this reason, also in this example, the same operation and effect as the above-mentioned 3rd embodiment can be acquired.

  Further, in each of the above-described embodiments and modifications thereof, the cutting blade 13a forms a hole with a desired accuracy during processing, while the cutting blade 13a is displaced in the direction of the axis O during retraction, so The rotation speed of the boring bar is changed depending on the time. Strictly speaking, the above-described rotation speed is not only the weight of the entire boring bar to be used, but also the diameter of the portion where the tip 13 is mounted in the shank portion 1. Since it varies depending on the moment of inertia due to size, weight, etc., it is desirable to appropriately determine the rotational speed by taking these factors into consideration, and the present invention is not limited to the above embodiment.

  Furthermore, in each of the above-described embodiments and modifications thereof, an example in which the shank portion 1 is driven by the driving force of the machining center is shown, but the present invention is not limited thereto, and the hole is formed by being driven by another driving source other than that. Of course, it can be applied to all boring bars that can be finished by boring, and the same effect can be obtained.

  And in this invention, although the example which aimed at the cylinder head of the engine for vehicles as a work material was shown, it is applicable not only to this but all what performs high-precision hole processing, Of course, the following effects can be obtained.

  Further, in each of the above-described embodiments and modifications thereof, the center of gravity is set on the opposite side of the tip 13 with the axis O interposed therebetween at the tip of the boring bar. 5, the center of gravity of the tip of the boring bar may be set on the tip 13 side with the axis O interposed therebetween.

  When the center of gravity of the boring bar tip is set on the tip 13 side, contrary to the above-described embodiments and modifications thereof, when the boring bar moves forward and machining, the machining center has a high rotational speed (for example, , About 15000 rpm), the tip 13 of the cutting edge 13a of the tip 13 is rotated with a large turning radius by applying a large centrifugal force to the tip 13 so that the cutting edge 13a Cutting is performed in contact with the inner peripheral surface of the lower hole at a position spaced from the axis O.

  In the boring bar retraction process after cutting, the shank portion 1 is driven at a lower rotational speed (for example, about 10,000 to 3000 rpm) than the rotational speed at the time of the above processing, whereby the tip of the boring bar is bent toward the tip 13 side. By reducing the amount, the radius of rotation of the tip 13 positioned on the outer peripheral surface of the shank portion 1 is also smaller than that during processing, and the cutting edge 13a of the tip 13 contacts the inner peripheral surface of the hole during retraction. Is surely prevented.

1 is a front view of a boring bar according to a first embodiment of the present invention. It is A arrow directional view of FIG. The modification of 1st Embodiment is shown, (a) is a front view which shows a part of the front end side of a boring bar, (b) is BB sectional drawing of (a). In other modification of 1st Embodiment, (a) is a front view which shows a part of the front end side of a boring bar, (b) is CC sectional drawing of (a). It is a front view of the boring bar concerning the 2nd Embodiment of this invention. It is D arrow line view of FIG. It is a front view of the boring bar which shows the modification of 2nd Embodiment. (A) is an E arrow view of FIG. 7, (b) is an F arrow view of (a). It is a front view of the boring bar concerning the 3rd Embodiment of this invention. It is a G arrow line view of FIG. It is a front view of the boring bar concerning the modification of 3rd Embodiment. (A) is the H arrow directional view of FIG. 1, (b) is II sectional drawing of (a).

Explanation of symbols

1 Shank part 5a Small diameter part of shaft-like part (bending generation part)
5b Notch hole (flexure generating part, recess)
5c Notch recess (flexure generating part, recess)
13 Chip 13a Cutting edge of chip 17 Weight part 19, 21, 23, 27 Screw

Claims (11)

  A tip having a cutting edge is provided on the outer periphery of the tip of the shank that rotates about the axis, and the shank is advanced around the axis while rotating the shank around the axis of the work, and the inner surface of the hole of the work is cut by the cutting blade. Is a boring bar that retreats while rotating the shank part around an axis when the machining is completed, and when the shank part is retracted, the shank part is rotated at a different rotational speed from that during the machining. A boring bar characterized in that the shank portion is provided with a deflection generating portion that bends the shank portion so that the cutting blade is rotated and moved closer to the axis than during the processing.   2. The boring bar according to claim 1, wherein the deflection generating portion is formed by providing a concave portion on an outer periphery of the shank portion.   The tip is provided on the outer periphery of the tip of the shank portion, the opposite side of the tip is set to be heavy with respect to the tip side with the axis at the tip of the shank portion interposed therebetween, and the shank portion is retracted The boring bar according to claim 1 or 2, wherein the rotational speed is set higher than the rotational speed when the shank portion moves forward.   The boring bar according to claim 3, wherein a weight portion is provided on the opposite side of the tip with the axis at the tip of the shank portion interposed therebetween.   The boring bar according to claim 4, wherein the weight portion is provided along the axial direction with respect to the chip.   The boring bar according to claim 4, wherein the weight portion is provided along a circumferential direction with respect to the chip.   A weight portion is provided on the tip side with the axis at the tip of the shank portion interposed therebetween, and the tip side is set to be heavy with respect to the opposite side of the tip, and the rotation speed when the shank portion is retracted is set. The boring bar according to claim 1, wherein the boring bar is set lower than a rotation speed when the shank portion moves forward.   The boring bar according to any one of claims 4 to 7, wherein a plurality of the weight portions are provided, and the plurality of weight portions can be attached to and detached from the shank portion.   The boring bar according to claim 4 or 7, wherein the weight portion is provided so as to be movable in a radial direction on a tip surface of the shank portion.   The boring bar according to any one of claims 4 to 9, wherein the weight portion includes a screw that can be attached to and detached from the shank portion.   A tip having a cutting edge is provided on the outer periphery of the tip of the shank that rotates about the axis, and the shank is advanced around the axis while rotating the shank around the axis of the work, and the inner surface of the hole of the work is cut by the cutting blade. Is a boring bar machining method in which when the machining is completed, the shank portion is retreated while rotating around an axis, and the shank portion is different from the machining time when the shank portion is retracted. The boring bar is characterized in that the shank portion is bent by a bending generating portion provided in the shank portion so that the cutting blade is rotated at a rotation speed and the cutting blade moves closer to the axis than during the processing. Processing method.

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