Groove processing device

Abstract

To provide a groove processing device that can achieve high-accuracy groove formation processing in an inner race of a constant-velocity joint.SOLUTION: A control part provided in a groove processing device controls relative movements so that a cutting part in rotation can continuously grind a processed region of a linear groove bottom part and a processed region of a curve groove bottom part along a forming direction of a ball groove, while inclining a rotating axial line of a ball end mill with respect to a normal line of a processed surface of a work-piece; and controls a posture of at least either of the work-piece and the cutting part so that an angle for linear processing that is an angle for processing in the processed region of the linear groove bottom part is smaller than an angle for curve processing that is an angle for processing angle in the processed region of the curve groove bottom part, in a center cross section, where the angle for processing is an angle formed by the normal line and the rotating axial line and is an inclination from the normal line, of the rotation axial line.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a groove machining device. [Background technology]

[0002] Conventionally, constant velocity joints (CVJs) capable of transmitting rotational force while maintaining speed have been used in the joints of drive shafts in automobiles, etc. A constant velocity joint is composed of an outer race with multiple grooves molded on its inner circumferential surface, an inner race with multiple grooves molded on its outer circumferential surface, and balls that fit into ball grooves molded in the outer and inner races.

[0003] The ball groove of the inner race has an approximately semicircular cross section in the axial direction, and is formed, for example, by cutting the outer periphery of a workpiece having an approximately cylindrical shape with a grinding wheel, as described in Patent Document 1. In some cases, the ball groove is formed by a ball end mill provided on an NC processing machine such as a five-axis machining center. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 6-39699 Summary of the Invention [Problem to be solved by the invention]

[0005] Constant velocity joints used in automobiles and the like are required to transmit driving force efficiently over a long period of time, so all of the components that make up the constant velocity joint must have high dimensional accuracy and wear resistance. However, there was a problem that conventional groove machining devices could not fully meet such high-precision requirements. [Means for solving the problem]

[0006] The present disclosure can be realized in the following forms.

[0007] (1) According to a first aspect of the present disclosure, there is provided a groove processing device for an inner race for a constant velocity joint, which molds ball grooves extending in the direction of a central axis on the outer peripheral surface of a workpiece for an inner race for a constant velocity joint, the inner race being a rotating body having a central axis. In this groove machining device, the ball groove includes a straight groove bottom portion having a straight groove bottom shape in a central cross section, which is a cross section in a plane including the central axis, and a curved groove bottom portion that is continuous with the straight groove bottom portion and has a curved groove bottom shape that is curved toward the central axis, and the ball end mill has a shaft that rotates around a rotation axis and a blade portion formed at a tip of the shaft, and the blade portion has a curved shape that is convex outward in a rotation trajectory shape in a plane including the rotation axis, and controls the relative movement of the blade portion with respect to the workpiece, and and a control unit that controls the attitude of at least one of the workpiece and the blade portion, and the control unit controls the relative movement so that the blade portion during rotation continuously grinds the machining area of ​​the straight groove bottom and the machining area of ​​the curved groove bottom along the molding direction of the ball groove in a state in which the rotation axis of the ball end mill is inclined with respect to the normal to the machining surface of the workpiece, and The above The straight line machining angle, which is the machining angle in the machining area, is the bottom of the curved groove. The above The posture is controlled so that the processing angle in the processing area is smaller than the curve processing angle. a gradual change section is provided in a portion of the machining area of ​​the curved groove bottom including a boundary with the machining area of ​​the straight groove bottom, and the posture is controlled so that a machining angle in the gradual change section is smaller than the curved machining angle in the machining area of ​​the curved groove bottom excluding the gradual change section and is larger than the straight machining angle. It is characterized by: According to the groove processing device of this embodiment, the linear machining angle is controlled to be smaller than the curved machining angle. By making the linear machining angle smaller than the curved machining angle, the difference in axial cross-sectional width between the linear groove bottom and the curved groove bottom can be reduced in the axial cross-section (cross-section perpendicular to the central axis) of the formed ball groove. That is, in the groove processing device of this configuration, the machining shape where the ball end mill contacts the workpiece is changed between the machining area of ​​the linear groove bottom and the machining area of ​​the curved groove bottom so that the difference in shape between the axial cross-section of the linear groove bottom and the axial cross-section of the curved groove bottom of the ball groove is reduced. Therefore, the axial cross-sectional width of the linear groove bottom and the curved groove bottom is stable along the forming direction, and high-precision groove forming processing can be realized in the inner race of the constant velocity joint. (2) In the above embodiment, the control unit is configured to: The above From the processing area to the bottom of the curved groove The above To the processing area or at the bottom of the curved groove The above From the machining area to the bottom of the straight groove The above The attitude may be controlled so that the processing angle gradually changes when the processing tool moves relatively to the processing region. According to this type of groove machining device, when the blade moves relatively from the machining area at the bottom of the straight groove to the machining area at the bottom of the curved groove, or from the machining area at the bottom of the curved groove to the machining area at the bottom of the straight groove, the machining angle changes gradually, i.e., in steps or incrementally, so that the occurrence of a step at the boundary where the machining area changes can be suppressed. As a result, in the completed constant velocity joint, the balls can move more smoothly in the ball grooves. (3) In the above embodiment, the blade portion may include an R-shaped portion having an R-shape centered on a central point that is not on the rotation axis, and the radius of curvature of the R-shaped portion may be greater than the radius of the shaft. According to the groove machining device of this embodiment, a ball groove is formed in which the groove bottom shape in the axial cross section is not a perfect circle but a part of an ellipse. The spherical balls that constitute the constant velocity joint and are interposed in the ball groove are in two-point contact with the ball groove. Therefore, according to the groove machining device of the above embodiment, it is possible to form a ball groove with reduced sliding resistance. [Brief description of the drawings]

[0008] [Figure 1] 1 is a perspective view showing a schematic configuration of a groove machining device according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a block diagram of a control unit. [Diagram 3] FIG. [Figure 4] 4 is a cross-sectional view of an inner race and a ball end mill during machining. FIG. [Diagram 5] 4 is a cross-sectional view of an inner race and a ball end mill during machining. FIG. [Figure 6] 1 is a diagram illustrating the machining angle of a ball end mill in each machining region. FIG. [Figure 7] 4 is an enlarged view of a ball groove portion of an inner race, illustrating the axial cross-sectional width of the ball groove; FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] A. First embodiment: A1. Overall configuration of the groove processing device: FIG. 1 is a perspective view showing a schematic configuration of a groove processing device 100 according to an embodiment of the present disclosure. FIG. 2 is a block diagram of a numerical control device 40 included in the groove processing device 100. FIG. 3 is a plan view showing an inner race 60 for a constant velocity joint after processing by the groove processing device 100. The groove processing device 100 is a groove processing device 100 for an inner race 60 for a constant velocity joint, and forms a ball groove 61 (see FIG. 3) extending in the direction of a central axis L of the workpiece W on the outer circumferential surface of the workpiece W. As shown in FIG. 3, the groove bottom shape of the ball groove 61 is not a perfect circle in an axial cross section, but describes a part of an ellipse. The workpiece W is a cylindrical member having a through hole 64 formed in the center. The inner race 60 of this embodiment has six ball grooves 61 at equal intervals in the circumferential direction.

[0010] As shown in Fig. 1, the groove machining device 100 is a three-axis machining center having two mutually orthogonal linear axes (X-axis and Z-axis) and one rotary axis (B-axis) as drive axes. The X-axis coincides with the vertical direction, and the Z-axis coincides with the horizontal direction. The groove machining device 100 includes a bed 10, a tool holding device 20, a workpiece holding device 30, and a numerical control device 40. The bed 10 is placed on the floor. A pair of Z-axis guide rails 12 extending in the Z-axis direction are provided on the upper surface of the bed 10.

[0011] The tool holding device 20 includes a column 21, a saddle 23, a tool headstock 24, a tool spindle 25, an X-axis servo motor 22, and a Z-axis servo motor 26. The column 21 is provided so as to be movable in the Z-axis direction while being guided by a pair of Z-axis guide rails 12. In addition, a pair of X-axis guide rails 27 extending along the X-axis direction are provided on the side surface of the column 21. The saddle 23 is capable of moving in the X-axis direction relative to the column 21 while being guided by the pair of X-axis guide rails 27.

[0012] The tool spindle stock 24 has a built-in motor 28 for rotating the tool spindle. The tool spindle stock 24 is attached to a saddle 23. The tool spindle 25 is supported by the tool spindle stock 24 so as to be rotatable around an O-axis parallel to the Z-axis direction with respect to the saddle 23. A ball end mill 50 used for machining the workpiece W is detachably attached to the tip of the tool spindle 25. The ball end mill 50 is held by the tool holding device 20 so as to be rotatable around the O-axis. The ball end mill 50 moves in the Z-axis direction in conjunction with the movement of the column 21, and moves in the X-axis direction in conjunction with the movement of the saddle 23.

[0013] Fig. 4 is a cross-sectional view of the inner race 60 (workpiece W) and the ball end mill 50 during machining, and is a diagram illustrating the groove bottom shape in the longitudinal direction of the ball groove 61 and the machining angle of the ball end mill 50. Fig. 4 is also a cross-sectional view in a plane including the central axis L of the inner race 60 (workpiece W) (hereinafter referred to as the "center cross section"), and shows the groove bottom shape in the longitudinal direction of the ball groove 61.

[0014] As shown in FIG. 4, the ball end mill 50 has a shaft 51 and a blade portion 52. In addition, in FIG. 4 and FIG. 5, the ball end mill 50 shows the rotation trajectory shape thereof simply and typically. The shaft 51 rotates around a rotation axis M. The rotation axis M coincides with the above-mentioned O-axis. The blade portion 52 is formed at the tip of the shaft 51. The ball end mill 50 of this embodiment is a solid type in which the shaft 51 and the blade portion 52 are integrated. The blade portion 52 has four cutting edges 53. Although detailed drawings are omitted, the four cutting edges 53 are provided at approximately equal intervals of 90 degrees around the rotation axis M in the circumferential direction of the tip of the blade portion 52.

[0015] The ball end mill 50 has a curved shape in which the blade portion 52 is convex outward in the shape of a rotation trajectory in a plane including the rotation axis M. Any one cutting edge 53 includes an R-shaped portion 54 having an R-shape with a radius of curvature R centered on a center point C that is not on the rotation axis M. The radius of curvature R is larger than the radius of the shaft 51. The other three cutting edges 53 have the same shape. The ball end mill 50 of this embodiment is configured as a so-called "elliptical end mill."

[0016] Referring again to FIG. 1, the workpiece holding device 30 includes a workpiece spindle indexing motor 31, a swivel table 32, a workpiece spindle table 33, a workpiece spindle 34, a support table 35, a swivel table indexing motor 36, a chuck device 37, and a swivel shaft 38. The swivel shaft 38 is connected to the swivel table 32 and supported by the support table 35. The chuck device 37 is attached to the workpiece spindle 34 and grips the workpiece W from its inner circumference. The swivel table indexing motor 36 is attached to the support table 35 and rotatably connected to the swivel shaft 38. The support table 35 is U-shaped in side view. The swivel table 32 is U-shaped in plan view. The center V of the B axis coincides with the center of the workpiece W.

[0017] As shown in Fig. 2, the numerical control device 40 includes a tool rotation control unit 41, a workpiece attitude control unit 42, and a position control unit 43. The numerical control device 40 corresponds to a "control unit." The tool rotation control unit 41 controls the drive of the tool spindle rotation motor 28 to rotate the ball end mill 50 attached to the tool spindle 25. The workpiece attitude control unit 42 controls the drive of the workpiece spindle index motor 31 and the swivel table index motor 36 to swing the workpiece W around the B axis while controlling the B axis. This controls the attitude of the workpiece W based on the ball end mill 50, in other words, the relative attitude between the workpiece W and the ball end mill 50.

[0018] The position control unit 43 controls the position of the workpiece holding device 30. Specifically, the position control unit 43 controls the drive of the Z-axis servo motor 26 to move the column 21 in the Z-axis direction, and controls the drive of the X-axis servo motor 22 to move the saddle 23 in the X-axis direction. As a result, the ball end mill 50 held by the tool holding device 20 moves relative to the workpiece W held by the workpiece holding device 30 in the X-axis direction and the Z-axis direction. In other words, the numerical control device 40 controls the relative movement of the blade portion 52 with respect to the workpiece W, and controls the attitude of the workpiece W and the blade portion 52.

[0019] A2.About ball groove machining: Next, ball groove machining by the groove machining device 100 will be described. First, the groove bottom shape of the inner race 60 after ball groove machining will be described. Like FIG. 4, FIG. 5 is a cross-sectional view of the inner race and the ball end mill during machining. However, as will be described later, the parts to be machined by the ball end mill 50 are different between FIG. 4 and FIG. 5. For the sake of convenience, FIG. 4 and FIG. 5 show the shape of the ball groove 61 after machining.

[0020] As shown in Figures 4 and 5, the ball groove 61 gently slopes from one axial end (the left end in Figures 4 and 5) to the other axial end (the right end in Figures 4 and 5). The ball groove 61 includes a straight groove bottom 62 and a curved groove bottom 63. The straight groove bottom 62 is located at one axial end, and the groove bottom shape in the central cross section is linear. The curved groove bottom 63 is located at the other axial end, and is continuous with the straight groove bottom 62 and curved toward the central axis L.

[0021] In this embodiment, the ball groove is formed from the curved groove bottom 63 toward the straight groove bottom 62. The ball groove machining in this embodiment is performed as a secondary finishing process on the workpiece W in which the ball groove has already been formed as a primary process. The shape of the workpiece W in FIG. 1 is illustrated in a simplified form. As shown in FIGS. 4 and 5, the ball groove is machined with the rotation axis M of the ball end mill 50 inclined with respect to the normals N1, N2 of the machining surface of the workpiece W. In this embodiment, the axis is inclined to the opposite side to the forming direction of the ball groove 61 (the relative traveling direction of the ball end mill 50 with respect to the workpiece W).

[0022] 6 is a diagram for explaining the machining angles of the ball end mill 50 in each of the machining regions S1, S2, and S3. The numerical control device 40 controls the relative movement so that the rotating blade portion 52 continuously grinds the machining region S1 of the curved groove bottom 63 and the machining region S2 of the straight groove bottom 62 along the forming direction of the ball groove 61. As shown in FIG. 6, in the machining region S1 of the curved groove bottom 63, a gradual change section S3 is provided in a portion including a boundary T with the machining region S2 of the straight groove bottom 62.

[0023] Here, in the central cross section, the angle between the normals N1, N2 and the rotation axis M, and the inclination of the rotation axis M from the normals N1, N2, is defined as the "machining angle." The numerical control device 40 controls the posture of at least one of the workpiece W and the blade portion 52 so that the linear machining angle θ2, which is the machining angle in the machining region S2 of the linear groove bottom 62, is smaller than the curved machining angle θc, which is the machining angle in the machining region S1 of the curved groove bottom 63. In this embodiment, the curved machining angle θc in the machining region S1 of the curved groove bottom 63 is θ2<θc<θ1 in the gradual change section S3, and is θ1 in the machining region S1 other than the gradual change section S3.

[0024] In this embodiment, the workpiece posture control unit 42 and the position control unit 43 control the machining angle to the above-mentioned machining angle. Furthermore, the machining angle in the gradual change section S3 is controlled by the numerical control device 40 to gradually change from the machining angle θ1 to the machining angle θ2. Note that "gradually" means in a multi-stage manner or a gradual manner.

[0025] The machining angle is determined by simulation based on data such as the dimensions and shape of the workpiece W, the shape of the ball end mill 50, and the dimensions and shape of the ball groove 61 to be formed, so that the axial cross-sectional width is constant from the machining area S1 to the machining area S2. The difference between the machining angle θ1 and the machining angle θ2 is approximately 5 degrees.

[0026] FIG. 7 is an enlarged view of the ball groove portion of the inner race 60, and is a view for explaining the axial cross-sectional width of the ball groove 61. As shown in FIG. 7, the ball groove 61 formed by the above control has a groove bottom shape in the axial cross section of the ball groove 61 that is not a perfect circle but a part of an ellipse. Therefore, a spherical ball (not shown) that constitutes a constant velocity joint and is interposed in the ball groove 61 comes into two-point contact with the ball groove 61. In addition, the axial cross-sectional width a of the ball groove 61 is approximately the same at the straight groove bottom 62 and the curved groove bottom 63. In addition, as shown in FIG. 4 and FIG. 5, the straight groove bottom 62 and the curved groove bottom 63 are smoothly continuous, and no step is formed at the boundary portion.

[0027] (1) As described above, the ball groove 61 has a straight groove bottom 62 whose groove bottom shape is a straight line and a curved groove bottom 63 whose groove bottom shape is curved in order to correspond to the specifications to which a constant velocity joint is applied. For example, when the ball groove 61 is machined by the ball end mill 50, if the machining angle of the ball end mill 50 is not changed, the straight groove bottom 62 and the curved groove bottom 63 have different axial cross-sectional widths (see axial cross-sectional widths a and b shown in FIG. 7). In FIG. 7, the axial cross-sectional width of the curved groove bottom when machined without changing the machining angle of the ball end mill 50 is illustrated as "b". In this way, if the axial cross-sectional width of the curved groove bottom becomes smaller than the axial cross-sectional width of the straight groove bottom, and the width of the ball groove changes, there is a risk that smooth movement of the ball will be hindered.

[0028] In this regard, according to the groove machining device 100 of the above embodiment, the machining angle of the ball end mill 50 is changed so that the linear machining angle θ2 is smaller than the curved machining angle θc in the machining area S1 of the curved groove bottom 63 and the machining area S2 of the straight groove bottom 62. By making the linear machining angle θ2 smaller than the curved machining angle θc, it is possible to reduce the difference in axial cross-sectional width between the straight groove bottom 62 and the curved groove bottom 63 in the axial cross-section (cross-section perpendicular to the central axis) of the formed ball groove 61.

[0029] That is, in the groove machining device 100 of this configuration, the machining shape where the ball end mill 50 contacts the workpiece W is changed in the machining area S2 of the straight groove bottom 62 and the machining area S1 of the curved groove bottom 63 so as to reduce the difference in shape between the axial cross section of the straight groove bottom 62 and the axial cross section of the curved groove bottom 63 of the ball groove 61. As a result, the axial cross-sectional width a of the straight groove bottom 62 and the curved groove bottom 63 is stable along the molding direction, and high-precision groove forming machining can be achieved in the inner race 60 of the constant velocity joint.

[0030] (2) Furthermore, according to the groove machining device 100 of the above-described embodiment, in the gradual change section S3, when the blade portion 52 moves relative to the workpiece W from the machining area S1 of the curved groove bottom 63 to the machining area S2 of the straight groove bottom 62, the machining angle gradually changes from the machining angle θ2 to the machining angle θ1.

[0031] When the machining angle is changed without gradually changing it, the feed speed temporarily slows down, reducing the pressure applied to the machining surface, changing the machining position of the blade 52 and cutting into the workpiece W. This may cause a step to occur, particularly in the cutting edge direction (direction perpendicular to the central axis L). In this regard, according to the above embodiment, by providing the gradual change section S3, it is possible to prevent a step from occurring at the boundary T between the straight groove bottom 62 and the curved groove bottom 63, particularly in the direction perpendicular to the central axis L.

[0032] (3) According to the groove machining device 100 of the above embodiment, the cutting edge 52 of the ball end mill 50 includes the R-shaped portion 54 centered on the central point C that is not on the rotation axis M, and the radius of curvature R of the R-shaped portion 54 is greater than the radius of the shaft 51. For this reason, the ball groove 61 is formed in the shape of a part of an ellipse that contacts the ball at two points in the axial cross section. That is, compared to a form in which the entire surface of the ball contacts the ball groove 61, a preferable ball groove 61 with reduced sliding resistance can be formed.

[0033] B. Other embodiments: (B1) In the above embodiment, the workpiece W is cylindrical, but it may be any other shape as long as it is a rotating body having a central axis L. Also, although it is assumed that the grooves are cut in advance in the primary process, they do not have to be cut.

[0034] (B2) In the groove machining device 100 of the above embodiment, the machining tool is an end mill with an elliptical blade 52, but the blade 52 may be a ball end mill with a spherical tip and a semicircular rotation trajectory. Also, the number of blades does not have to be four, but may be two or another number.

[0035] (B3) In the above embodiment, the groove machining device 100 is a three-axis machining center, but a machining center with another number of axes may be used as long as it is possible to control the relative movement of the blade portion 52 with respect to the workpiece W and to control the attitude of at least one of the workpiece W and the blade portion 52.

[0036] (B4) In the above embodiment, the groove machining device 100 is configured to form the ball groove 61 from the curved groove bottom 63 to the straight groove bottom 62. However, the ball groove 61 may be formed conversely, from the straight groove bottom 62 to the curved groove bottom 63.

[0037] (B5) In the groove machining device 100 of the above embodiment, the ball end mill 50 is inclined in the direction opposite to the forming direction of the ball groove 61, but it may be inclined toward the forming direction.

[0038] (B6) In the groove machining device 100 of the above embodiment, the gradual change section S3 is provided in the machining area S1 of the curved groove bottom portion 63, but this need not be provided.

[0039] The present disclosure is not limited to the above-mentioned embodiments, and can be realized in various configurations without departing from the spirit of the present disclosure. For example, the technical features in each embodiment corresponding to the technical features in each form described in the Summary of the Invention column can be appropriately replaced or combined in order to solve some or all of the above-mentioned problems or to achieve some or all of the above-mentioned effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted. [Explanation of symbols]

[0040] 10...bed, 12...Z-axis guide rail, 20...tool holding device, 21...column, 22...X-axis servo motor, 23...saddle, 24...tool headstock, 25...tool spindle, 26...Z-axis servo motor, 27...X-axis guide rail, 28...tool spindle rotation motor, 30...work holding device, 31...work spindle indexing motor, 32...swivel head, 33...work spindle head, 34...work spindle, 35...support base, 36...swivel head indexing motor, 37...chuck device, 38...swivel axis, 40...numerical control device, 41...tool Rotation control unit, 42...workpiece attitude control unit, 43...position control unit, 50...ball end mill, 51...shaft, 52...blade portion, 53...cutting edge, 54...R-shaped portion, 60...inner race, 61...ball groove, 62...straight groove bottom, 63...curved groove bottom, 64...through hole, 100...groove machining device, C...center point, L...center axis, M...rotation axis, N1, N2...normal, S1...machining area of ​​curved groove bottom, S2...machining area of ​​straight groove bottom, S3...gradual change section, T...boundary, W...workpiece, θ2...straight groove machining angle, θc...curved groove machining angle

Claims

1. 1. A groove machining device for an inner race for a constant velocity joint, which is a rotating body having a central axis, for forming ball grooves on an outer peripheral surface of a workpiece for the inner race for a constant velocity joint, the ball grooves extending in a direction of the central axis, the ball groove includes a straight groove bottom portion having a straight groove bottom shape in a central cross section, which is a cross section on a plane including the central axis, and a curved groove bottom portion continuing from the straight groove bottom portion and having a curved groove bottom shape curved toward the central axis, A ball end mill having a shaft that rotates around a rotation axis and a blade portion formed at a tip of the shaft, the blade portion having a curved shape that is convex outward in a rotation trajectory shape in a plane including the rotation axis; A control unit that controls the relative movement of the blade portion with respect to the workpiece and controls the attitude of at least one of the workpiece and the blade portion; The control unit includes: a control of the relative movement such that the blade portion during rotation continuously grinds the machining area of ​​the straight groove bottom and the machining area of ​​the curved groove bottom along a molding direction of the ball groove, while the rotation axis of the ball end mill is inclined with respect to a normal line of the machining surface of the workpiece; controlling the posture so that, when an angle between the normal line and the rotation axis in the central cross section and an inclination of the rotation axis from the normal line is defined as a processing angle, a linear processing angle which is the processing angle in the processing area of ​​the linear groove bottom is smaller than a curved processing angle which is the processing angle in the processing area of ​​the curved groove bottom; a gradual change section is provided in the machining area of ​​the curved groove bottom portion including a boundary with the machining area of ​​the straight groove bottom portion, and the posture is controlled so that the machining angle in the gradual change section is smaller than the curved machining angle in the machining area of ​​the curved groove bottom portion excluding the gradual change section and larger than the straight machining angle. Grooving equipment.

2. The control unit is The groove machining device of claim 1, wherein the posture is controlled so that the machining angle gradually changes when the blade portion moves relatively from the machining area at the bottom of the straight groove to the machining area at the bottom of the curved groove, or from the machining area at the bottom of the curved groove to the machining area at the bottom of the straight groove.

3. The blade portion is 3. The groove machining device according to claim 1, further comprising an R-shaped portion having an R-shape centered on a central point not on the rotation axis, the radius of curvature of the R-shaped portion being greater than a radius of the shaft.

Images