Polishing brush

A polishing brush (4) includes a grinding element bundle (9) formed with a plurality of wire-shaped grinding elements (28) formed by impregnating and solidifying an assembly of inorganic filaments with resin, and a grinding element holder (7) having a holding hole (20) holding the base end portion of the grinding element bundle 9 on an outer peripheral side surface (7c) serving as a grinding element-holding surface. The grinding element bundle (9) has a front surface (9a) facing forward in a rotational direction (R1) and a back surface (9b) facing backward. The grinding element bundle (9) is held in the grinding element holder (7) such that the front surface (9a) and the back surface (9b) are inclined in the same direction relative to a virtual surface (30) that includes a center point (P) of a cross section (9d) of the grinding element bundle (9) cut across an outer peripheral side surface (7c) and the axis of center of rotation (L) of the grinding element holder (7) and extends in a radial direction. The wire-shaped grinding elements (28) included in the grinding element bundle (9) are easily displaced and can release excessive force applied thereto.

FIELD

The present invention relates to a polishing brush including a bundle of wire-shaped grinding elements formed by impregnating and solidifying an assembly of inorganic filaments with resin.

BACKGROUND

Patent Literature 1 describes a polishing brush in which a grinding element bundle formed with a plurality of wire-shaped grinding elements protrudes from the end surface in the direction of the axis of center of rotation or protrudes from the outer peripheral surface of the grinding element holder. Each of the wire-shaped grinding elements in this literature is formed by impregnating and hardening an assembly of alumina fibers, silicon carbide fibers, carbon fibers, silicon nitride fibers or glass fibers with binder resin. The wire-shaped grinding element composed of inorganic filaments has high hardness and thus has high grinding/polishing capability.

CITATION LIST

Patent Literature

SUMMARY

Technical Problem

In the polishing brush including a grinding element bundle formed with wire-shaped grinding elements composed of inorganic filaments, when the grinding element bundle becomes short due to wear, the wire-shaped grinding elements become so strong that the wire-shaped grinding elements easily break during grinding/polishing work.

In view of the foregoing, the problem to be solved by the present invention is to provide a polishing brush in which breaking of the wire-shaped grinding elements during work can be suppressed.

Solution to Problem

In order to solve the problem above, the present invention provides a polishing brush including a grinding element bundle formed with a plurality of wire-shaped grinding elements formed by impregnating and solidifying an assembly of inorganic filaments with resin, and a grinding element holder holding a base end portion of the grinding element bundle in a holding hole on a grinding element bundle-holding surface, characterized in that the grinding element bundle has a front surface facing forward in a rotational direction, the front surface being inclined relative to a virtual surface that includes a center point of a cross section of the grinding element bundle cut across the grinding element bundle-holding surface and an axis of center of rotation of the grinding element holder and extends in a radial direction.

In the present invention, when the polishing brush is rotated and the tip end of the grinding element bundle is pressed against a workpiece, the wire-shaped grinding elements included in the grinding element bundle are easily displaced, compared with a case in which the front surface of the grinding element bundle is not inclined relative to the virtual surface. Therefore, when excessive force is applied to the wire-shaped grinding elements, the force can be released. This can suppress the breaking of the wire-shaped grinding elements during work.

In the present invention, the grinding element bundle-holding surface may face toward an outer periphery.

In this case, the cross section of the grinding element bundle may have a flattened shape that has a smaller thickness dimension in the rotational direction than a height in the direction of the axis of center of rotation, and the front surface may be inclined in the rotational direction from one side toward the other side in the direction of the axis of center of rotation. With this configuration, when the polishing brush is rotated and the tip end of the grinding element bundle is pressed against a workpiece, the wire-shaped grinding elements are easily displaced in the direction of the axis of rotation and in the rotational direction. Here, the flattened shape includes a rectangle and an oval. When the cross section of the grinding element bundle has an oval shape, the state in which the front surface of the grinding element bundle is inclined relative to the virtual surface refers to a state in which the longer axis of the oval cross section is inclined relative to the virtual surface whereby the front surface is inclined.

In the present invention, the front surface may be inclined backward in the rotational direction from an inner periphery toward an outer periphery. With this configuration, when the polishing brush is rotated and the tip end of the grinding element bundle is pressed against a workpiece, the wire-shaped grinding elements are easily displaced backward in the rotational direction.

In the present invention, the grinding element bundle-holding surface may face in the direction of the axis of center of rotation.

In this case, the cross section of the grinding element bundle may have a flattened shape that has a smaller thickness dimension in the rotational direction than a length in the radial direction, and the front surface may be inclined in the rotational direction from an inner periphery toward an outer periphery. With this configuration, when the polishing brush is rotated and the tip end of the grinding element bundle is pressed against a workpiece, the wire-shaped grinding elements are easily displaced toward the outer periphery and backward in the rotational direction. Here, the flattened shape includes a rectangle and an oval. When the cross section of the grinding element bundle has an oval shape, the state in which the front surface of the grinding element bundle is inclined relative to the virtual surface refers to a state in which the longer axis extending from the inner periphery toward the outer periphery in the oval cross section is inclined relative to the virtual surface whereby the front surface is inclined.

In this case, the front surface may be inclined backward in the rotational direction as a distance from the grinding element holder increases in the direction of the axis of center of rotation. With this configuration, when the polishing brush is rotated and the tip end of the grinding element bundle is pressed against a workpiece, the wire-shaped grinding elements are easily displaced backward in the rotational direction.

In the present invention, it is preferable that the grinding element holder be made of resin. With this configuration, the flexibility of resin can absorb excessive force applied to the wire-shaped grinding elements. Therefore, compared with a case in which the inner peripheral end portions of the wire-shaped grinding elements are held by a grinding element holder made of metal, the breaking of the wire-shaped grinding elements can be suppressed during work.

In the present invention, it is preferable that the polishing brush include a plurality of the grinding element bundles, the grinding element holder have a plurality of the holding holes holding the grinding element bundles and a coupling hole connecting the holding holes in a circumferential direction, and each of the grinding element bundles of the wire-shaped grinding elements be fixed to the grinding element holder with an adhesive injected in the corresponding holding hole and the coupling hole. With this configuration, the grinding element bundles inserted in the adjacent holding holes can be affixed with each other with the adhesive filling the coupling hole. This ensures that the grinding element bundles are fixed to the grinding element holder. Since the fixing of the grinding element bundle to the grinding element holder is ensured, the depth dimension of the holding hole can be reduced. Therefore, in the case of a polishing brush in which the grinding element bundle protrudes from the grinding element holder toward the outer periphery, the size of the grinding element holder can be reduced in the radial direction, and the diameter of the polishing brush can be reduced. When the polishing brush has the same outer diameter dimension as conventional ones, the length of the grinding element bundle (the wire-shaped grinding elements) can be increased, thereby suppressing the breaking of the wire-shaped grinding elements during work. Similarly, in the case of a polishing brush in which the grinding element bundle protrudes from the grinding element holder in the direction of the axis of center of rotation, the height of the grinding element holder can be reduced, and the size of the polishing brush can be reduced. When the polishing brush has the same height as conventional ones, the length of the grinding element bundle (the wire-shaped grinding elements) can be increased, thereby suppressing the breaking of the wire-shaped grinding elements during work.

In this case, it is preferable that an inner peripheral surface of the holding hole have projections and depressions. With this configuration, the anchor effect brought about by the projections and depressions further ensures the fixing of the grinding element bundle to the grinding element holder with an adhesive.

In the present invention, it is preferable that the polishing brush include a shank removably attached to the grinding element holder. With this configuration, when the wire-shaped grinding elements are worn, the grinding element holder with the grinding element bundles alone can be replaced with a new one, whereas the shank serving as a mount for a machine tool can be reused. A plurality of shanks with different lengths may be prepared so that, by selecting any one of the shanks, it is possible to adjust the position of the grinding element bundle relative to the head when the polishing brush is coupled to the head of a machine tool.

DESCRIPTION OF EMBODIMENTS

The polishing brush that the present invention is applied to will be described below with reference to the drawings. In the following description, it is assumed that the top-bottom in the drawings is the top-bottom of the polishing brush for the sake of convenience.

FIG. 1(a)is a perspective view of a polishing brush according to a first embodiment of the present invention as viewed diagonally from above andFIG. 1(b)is a perspective view of the polishing brush as viewed diagonally from below.FIG. 2(a)is a perspective view of the brush body as viewed diagonally from above andFIG. 2(b)is an exploded perspective view of the brush body.

As shown inFIG. 1, the polishing brush1includes a shank member6having a shank portion (shank)5coupled to the head of a machine tool (drive device), an annular grinding element holder7through which the lower portion of the shank member6passes, and a locknut8screwed on the lower end portion of the shank member6. A plurality of grinding element bundles9protrude from the grinding element holder7toward the outer periphery. The grinding element holder7and the grinding element bundles9constitute the brush body10.

The shank member6is made of metal and includes a shank portion5, a collar11, and a bolt12from the top to the bottom. The bolt12has the same outer diameter dimension as the shank portion5and has a male thread on its outer peripheral surface to be screwed in the locknut8. The collar11stretches out toward the outer periphery from the shank portion5and the bolt12. The portion below the collar11of the shank member6is inserted into the center hole15(seeFIG. 2(a)) of the grinding element holder7, and the lower end portion of the bolt12protrudes downward from the grinding element holder7.

The grinding element holder7is made of resin. In the present embodiment, the grinding element holder7is made of ABS resin. The upper end surface7aof the grinding element holder7has an upper circular concave portion16at its central portion. The upper circular concave portion16is recessed downward in the axial direction. As shown inFIG. 2(a), an upper end opening17of the center hole15of the grinding element holder7is formed at the central portion of the bottom surface of the upper circular concave portion16. As shown inFIG. 1(b), the lower end surface7bof the grinding element holder7has a lower circular concave portion18at its central portion. The lower circular concave portion18is recessed upward in the axial direction. A lower end opening (not shown) of the center hole15of the grinding element holder7is formed at the central portion of the bottom surface of the lower circular concave portion18. The annular outer peripheral side surface7cof the grinding element holder7serves as a grinding element-holding surface. On the outer peripheral side surface7c, a plurality of holding holes20for holding the grinding element bundles9are formed at regular angular intervals in an annular shape. When the grinding element holder7is viewed from the radial direction, each of the holding holes20is shaped in a flat parallelogram longer in the direction of the axis of center of rotation L and shorter in the circumferential direction and is inclined relative to the axis of center of rotation L. The grinding element holder7has a rotation-symmetric shape that is identical when turned upside down.

As shown inFIG. 2(b), the grinding element holder7includes a holder body21and a cover22put on the holder body21from above and fixed to the holder body21with an adhesive. The holder body21has a plurality of holding grooves23to serve as holding holes20when covered with the cover22. Each of the holding grooves23(holding hole20) extends in the radial direction. The holder body21also has an annular coupling groove25, which connect the inner peripheral end portions of the holding grooves23. The coupling groove25is provided concentrically with the center hole15in the grinding element holder7. When the cover22is put on the holder body21, the coupling groove25serves as an annular coupling hole24. The holding grooves23(holding holes20) and the coupling groove25(coupling hole24) have the same height. The holding holes20and the coupling hole24have minute protrusions and depressions on their inner wall surfaces.

As shown inFIG. 2(b), each of the grinding element bundles9is formed by bundling a number of wire-shaped grinding elements28with the same length. Each of the wire-shaped grinding elements28is formed by impregnating and hardening an assembly of alumina filaments as inorganic filaments with thermosetting binder resin such as silicone resin, phenol resin, epoxy resin, polyimide resin, polymaleimide resin, unsaturated polyester resin, and urethane resin, or thermoplastic resin such as nylon. In the present embodiment, the filament assembly is a group of 250 to 3000 alumina filaments with a fiber diameter of 8 μm to 50 μm. The diameter of the filament assembly is 0.1 mm to 2 mm. The filament assembly may be twisted.

The inner peripheral end portion of the grinding element bundle9is inserted in a certain holding hole20and fixed to the grinding element holder7with an adhesive.

When the grinding element bundles9are fixed to the holding holes20, the holding grooves23and the coupling groove25in the holder body21are filled with an adhesive. An adhesive is applied also on the upper end surface of the holder body21. For example, a silicone resin-based or epoxy resin-based adhesive may be used. Concurrently, the wire-shaped grinding elements28with the identical length are held in the form of a bundle such that its cross-sectional shape is a parallelogram, using a jig or the like (not shown).

Next, the wire-shaped grinding elements28are inserted into the holding groove23filled with an adhesive. For example, as shown by the arrow inFIG. 2(b), the inner peripheral end portions of the wire-shaped grinding elements28are inserted into the holding groove23from above. Subsequently, the cover22is put on the holder body21and the adhesive is hardened. In this way, while the grinding element bundle9is formed, the inner peripheral end portion of this grinding element bundle9is fixed to the grinding element holder7. The wire-shaped grinding elements28(grinding element bundle9) may be inserted into the holding groove23from the outer periphery of the holder body21.

Inserting the grinding element bundle9into the holding hole20allows the grinding element bundle9to have a cross-sectional shape corresponding to the cross-sectional shape of the holding hole20. That is, the grinding element bundle9has a parallelogrammatic shape in cross section and has a front surface9afacing forward in the rotational direction R1and a back surface9bfacing backward.FIG. 3is a partial enlarged view of the brush body. InFIG. 3, the coupling hole24is not shown to facilitate understanding of the shape of the holding hole20.

As shown inFIG. 3, the front surface9aand the back surface9beach extend along the wire-shaped grinding element28from the inner periphery to the outer periphery and extend in the top-bottom direction. The front surface9aand the back surface9bare parallel to each other, and the thickness dimension of the grinding element bundle9is constant in the circumferential direction. The cross-sectional shape (the cross-sectional shape orthogonal to the direction in which the wire-shaped grinding elements28extend) of the grinding element bundle9is a flattened shape that has a smaller thickness dimension in the circumferential direction than the height in the direction of the axis of center of rotation L.

The grinding element bundle9is inclined from one side toward the other side in the direction of the axis of center of rotation L by a predetermined inclination angle θ1, relative to a virtual surface30that includes the center point P of a cross section9dof the grinding element bundle9cut across the grinding element bundle-holding surface (outer peripheral side surface7c) and the axis of center of rotation L and extends in the radial direction M orthogonal to the axis of center of rotation L. In other words, the grinding element bundle9is inclined such that the center line N1of the grinding element bundle9passing through the center point P and extending in the middle between the front surface9aand the back surface9bfrom the top to the bottom is inclined relative to the virtual surface30(relative to a virtual line O passing through the center point P on the virtual surface30and extending in the direction of the axis of center of rotation L) by the inclination angle θ1. Therefore, the front surface9aand the back surface9bof the grinding element bundle9are also inclined relative to the virtual surface30in the rotational direction R1from one side toward the other side in the direction of the axis of center of rotation L. In the present embodiment, the inclination angle θ1is 30°.

The locknut8is screwed from below onto the lower end portion of the bolt12protruding downward from the grinding element holder7. The locknut8is screwed on the bolt12until the locknut8and the collar11of the shank member6sandwich the grinding element holder7from opposite sides in the direction of the axis of center of rotation L. The grinding element holder7is thus fixed to the shank member6. In a state in which the grinding element holder7is mounted on the shank member6, the lower end portion of the collar11is inserted in the upper circular concave portion16, and the lower surface of the collar11abuts on the concave bottom surface. The upper end portion of the setscrew is inserted in the lower circular concave portion18, and the upper surface of the screw abuts on the concave bottom surface.

FIG. 4is an illustration of work operation by the polishing brush1in the present embodiment. When burring or grinding/polishing work on a surface is performed on a workpiece W using the polishing brush1, the shank portion5is coupled to the head of a machine tool and rotated around the axis of center of rotation L, and the tip end (the end on the outer periphery) of the grinding element bundle9(wire-shaped grinding elements28) is pressed against the surface of the workpiece W.

Here, in the polishing brush1in the present embodiment, the end surfaces (the front surface9aand the back surface9b) facing in the circumferential direction in the grinding element bundle9are inclined relative to the virtual surface30including the axis of center of rotation L. Therefore, compared with a case in which the end surfaces9aand9bare parallel to the virtual surface30(orthogonal to the rotational direction R1), the wire-shaped grinding elements28included in the grinding element bundle9are easily displaced in the direction of the axis of center of rotation L (the direction shown by the arrow Q1inFIG. 4: downward) when the polishing brush1is rotated and the tip end of the grinding element bundle9is pressed against the workpiece W. Therefore, when excessive force is applied to the wire-shaped grinding elements28, the force can be released. This can suppress the breaking of the wire-shaped grinding elements28.

In the present embodiment, when the polishing brush1is rotated and the tip end of the grinding element bundle9is pressed against the workpiece W, the wire-shaped grinding elements28included in the grinding element bundle9are displaced in the direction of the axis of center of rotation L, and this displacement improves the grinding/polishing capability.

The inclination angle θ1relative to the virtual surface30of the center line N1of the grinding element bundle9passing through the center point P and extending from the top to the bottom in the middle between the front surface9aand the back surface9bis preferably in the range of 15° or more to 60° or less. With this range of the inclination angle θ1, it is possible to suppress breaking of the wire-shaped grinding element28while suppressing reduction in contact surface of the grinding element bundle9on the workpiece W.

In the present embodiment, since the grinding element holder7holding the inner peripheral end portion of the grinding element bundle9is made of resin, the flexibility of the resin can absorb excessive force applied to the wire-shaped grinding elements28. Therefore, compared with a case in which the inner peripheral end portions of the wire-shaped grinding elements28are held by a metal grinding element holder7, the breaking of the wire-shaped grinding elements28can be suppressed during work.

In the present embodiment, the adjacent grinding element bundles9are affixed to each other with an adhesive injected to the coupling hole24. This ensures that the grinding element bundles9are fixed to the grinding element holder7. In addition, since the inner peripheral surfaces of the holding holes20and the coupling hole24to be filled with an adhesive have projections and depressions, the anchor effect ensures that the grinding element bundles9are fixed to the grinding element holder7. As a result, the radial dimension of the holding hole20can be reduced, so that the grinding element holder7can be reduced in the radial direction. Thus, the size of the polishing brush1can be reduced. When the polishing brush1has the same outer diameter dimension as conventional ones, the grinding element bundle9(wire-shaped grinding elements28) can be increased in length, thereby suppressing the breaking of the wire-shaped grinding elements28during work.

In the present embodiment, the shank member6and the brush body10are separate, and the shank member6is removable from the grinding element holder7. Therefore, when the wire-shaped grinding elements28are worn, the brush body10alone can be replaced with a new one and the shank member6can be reused. In addition, a plurality of shank members6having shank portions5with different lengths may be prepared so that, by selecting any one of the shank members6, it is possible to adjust the position of the grinding element bundle9relative to the head when the polishing brush1is coupled to the head of a machine tool.

The polishing brush1in the present embodiment may be rotated in any direction around the axis of center of rotation L as the rotational direction R1during work.

The grinding element holder7may be formed as a single member using, for example, a 3D printer. In this case, an adhesive is injected into the holding holes20from the outer periphery to fill the holding holes20and the coupling hole24with an adhesive. The wire-shaped grinding elements28(grinding element bundle9) are inserted into the holding hole20from the outer periphery of the holder body21to be fixed to the grinding element holder7.

Here, the cross-sectional shape of the grinding element bundle9may be a rectangle or an oval longer in the top-bottom direction and shorter in the rotational direction R1. In these cases, the holding hole20as viewed from the radial direction M is shaped in a rectangle or an oval inclined upward or downward in the rotational direction R1. The grinding element bundle9is then held in this holding hole20so that the front surface and the back surface of the grinding element bundle9are inclined relative to the virtual surface30. Here, when the cross section of the grinding element bundle9has an oval shape, the state in which the front surface and the back surface of the grinding element bundle9are inclined relative to the virtual surface30refers to a state in which the longer axis in the oval cross section is inclined backward in the rotational direction R1from one side toward the other side in the direction of the axis of center of rotation L whereby the front surface and the back surface of the grinding element bundle9are each inclined relative to the virtual surface30.

FIG. 5(a)is a perspective view of a polishing brush according to a second embodiment of the present invention as viewed diagonally from above andFIG. 5(b)is a perspective view of the brush body10of the polishing brush inFIG. 5(a)as viewed diagonally from above. The polishing brush2in the second embodiment has a configuration corresponding to the polishing brush1in the first embodiment, and the corresponding parts are denoted with the same reference signs and will not be further elaborated.

As shown inFIG. 5(a), the polishing brush2includes a shank member6having a shank portion (shank)5coupled to the head of a machine tool (drive device), an annular grinding element holder7through which the lower portion of the shank member6passes, and a locknut8screwed on the lower end portion of the shank member6. A plurality of grinding element bundles9protrude from the grinding element holder7toward the outer periphery. The shank member6and the locknut8are made of metal, and the grinding element holder7is made of resin. Each of the grinding element bundles9is formed with a bundle of a plurality of wire-shaped grinding elements28formed by impregnating and solidifying an assembly of inorganic filaments with resin. The grinding element bundles9have the identical length. The grinding element holder7and the grinding element bundles9constitute the brush body10. In the polishing brush2in the present embodiment, the direction of rotation during work is defined as the rotational direction R1.

The shank member6includes a shank portion5, a collar11, and a bolt12from the top to the bottom. The portion below the collar11of the shank member6is inserted into the center hole15in the grinding element holder7, and the lower end portion of the bolt12protrudes downward from the grinding element holder7.

The annular outer peripheral side surface7cof the grinding element holder7is the grinding element-holding surface. On the outer peripheral side surface7c, a plurality of holding holes20holding the grinding element bundles9are formed at regular angular intervals in an annular shape. When the grinding element holder7is viewed from the radial direction M, each of the holding holes20is shaped in a rectangle longer in the direction of the axis of center of rotation L and shorter in the circumferential direction. The grinding element holder7has a rotation-symmetric shape that is identical when turned upside down.

As shown inFIG. 5(b), each of the holding holes20is recessed in the direction inclined relative to the radial direction M. That is, each of the holding holes20is inclined forward in the rotational direction R1toward inner periphery. The grinding element holder7also has a coupling hole24, which connects the inner peripheral end portions of the holding holes20. The coupling hole24is provided concentrically with the center hole15in the grinding element holder7and has the same height as each of the holding holes20. The holding holes20and the coupling hole24have minute projections and depressions on their inner wall surfaces. Here, the grinding element holder7is constituted with a holder body21and a cover22as in the first embodiment, and the holder body21has holding grooves23serving as the holding holes20and a coupling groove25serving as the coupling hole24.

The inner peripheral end portion of the grinding element bundle9is inserted in the holding hole20and fixed to the grinding element holder7with an adhesive. When the grinding element bundle9is to be fixed to the holding hole20, the holding grooves23and the coupling groove25of the holder body21are filled with an adhesive. An adhesive is applied also on the upper end surface of the holder body21. Next, the wire-shaped grinding elements28with the identical length are held in the form of a bundle using a jig, and the inner peripheral end portions of the wire-shaped grinding elements28are inserted from above or from the outer periphery into the holding groove23. Subsequently, the cover22is put on the holder body21and the adhesive is hardened. In this way, while the grinding element bundle9is formed, this grinding element bundle9is fixed to the grinding element holder7.

Here, inserting the grinding element bundle9into the holding hole20allows the grinding element bundle9to have a cross-sectional shape corresponding to the cross-sectional shape of the holding hole20. That is, the grinding element bundle9has a rectangular cross-sectional shape and has a front surface9afacing forward in the rotational direction R1and a back surface9b.FIG. 6is a partial enlarged view of the brush body10. InFIG. 6, the coupling hole24is not shown to facilitate understanding of the shape of the holding hole20.

As shown inFIG. 6, the front surface9aand the back surface9beach extend along the wire-shaped grinding element28from the inner periphery to the outer periphery and extend in the top-bottom direction. The front surface9aand the back surface9bare parallel to each other, and the thickness dimension of the grinding element bundle9is constant in the circumferential direction. The cross-sectional shape (the cross-sectional shape orthogonal to the direction in which the wire-shaped grinding elements28extend) of the grinding element bundle9is a rectangle that has a smaller thickness dimension in the circumferential direction than the height in the direction of the axis of center of rotation L.

Since each of the holding holes20is inclined relative to the radial direction M, insertion of the grinding element bundle9into the holding hole20allows the grinding element bundle9to be inclined by a predetermined inclination angle θ2. In the present embodiment, the grinding element bundle9is inclined backward in the rotational direction R1from the inner periphery toward the outer periphery by the inclination angle θ2, relative to a virtual surface30that includes the center point P of a cross section9dof the grinding element bundle9cut across the grinding element bundle-holding surface (outer peripheral side surface7c) and the axis of center of rotation L and extends in the radial direction M. In other words, the center line N2of the grinding element bundle9passing through the center point P and extending in the middle between the front surface9aand the back surface9bfrom the inner periphery toward the outer periphery is inclined relative to the virtual surface30(relative to the virtual line S passing through the center point P on the virtual surface30and extending in the radial direction M) by the inclination angle θ2. Therefore, the front surface9aand the back surface9bof the grinding element bundle9are also inclined relative to the virtual surface30backward in the rotational direction R1from the inner periphery toward the outer periphery. In the present embodiment, the inclination angle θ2is 30°.

The locknut8is screwed from below on the lower end portion of the bolt12protruding downward from the grinding element holder7and holds the grinding element holder7together with the collar11of the shank member6.

FIG. 7is an illustration of work operation by the polishing brush2in the present embodiment. InFIG. 7, the front side in the drawing is the top side of the polishing brush2, and the back side is the bottom side. When burring or grinding/polishing work on a surface is performed on a workpiece W using the polishing brush2, the polishing brush2is rotated with the shank portion5coupled to the drive device of a grinder, and the tip ends (the ends in the outer periphery) of the wire-shaped grinding elements28(grinding element bundle9) are pressed against the surface of the workpiece W. During work, the polishing brush2is rotated in the rotational direction R1in which the front surface9aof the grinding element bundle9is inclined backward from the inner periphery toward the outer periphery.

Here, in the present embodiment, the surfaces facing in the circumferential direction (the front surface9aand the back surface9b) in the grinding element bundle9are inclined relative to the virtual surface30including the axis of center of rotation L. Therefore, compared with a case in which the end surfaces9aand9bare parallel to the virtual surface30(orthogonal to the rotational direction R1), the wire-shaped grinding elements28included in the grinding element bundle9are easily displaced backward in the rotational direction R1(the direction shown by the arrow Q2inFIG. 7) when the polishing brush1is rotated and the tip end of the grinding element bundle9is pressed against a workpiece W. Therefore, when excessive force is applied to the wire-shaped grinding elements28, the force can be released. This can suppress the breaking of the wire-shaped grinding elements28.

The inclination angle θ2relative to the virtual surface30of the center line N2of the grinding element bundle9passing through the center point P and extending from the inner periphery toward the outer periphery in the middle between the front surface9aand the back surface9bis preferably in the range of 10° or more to 60° or less. With this range of the inclination angle θ2, it is possible to suppress the breaking of the wire-shaped grinding elements28while suppressing reduction of the capability of the grinding element bundle9cutting a workpiece W.

Also in the present embodiment, since the grinding element holder7holding the inner peripheral end portion of the grinding element bundle9is made of resin, the flexibility of the resin can absorb excessive force applied to the wire-shaped grinding elements28. Also in the present embodiment, the adjacent grinding element bundles9are affixed to each other with an adhesive injected in the coupling hole24to ensure that the grinding element bundles9are fixed to the grinding element holder7. In addition, since the holding holes20and the coupling hole24to be filled with an adhesive have projections and depressions on their inner peripheral surfaces, the anchor effect ensures that the grinding element bundles9are fixed to the grinding element holder7.

Also in the present embodiment, the shank member6and the brush body10are separate, and the shank member6is removable from the grinding element holder7. Thus, the brush body10alone can be replaced with a new one. In addition, a plurality of shank members6having shank portions5with different lengths may be prepared so that, by selecting any one of the shank members6, it is possible to adjust the position of the grinding element bundle9relative to the head when the polishing brush2is coupled to the head of a machine tool.

Here, the cross-sectional shape of the grinding element bundle9may be an oval longer in the top-bottom direction and shorter in the rotational direction R1. Also in this case, the base end portion of the grinding element bundle9is held in the holding hole20inclined relative to the radial direction M, whereby the front surface and the back surface of the grinding element bundle9each can be inclined backward in the rotational direction R1from the inner periphery toward the outer periphery. In the present embodiment, the cross-sectional shape of the grinding element bundle9may be a circle. Also when the cross-sectional shape of the grinding element bundle9is a circle, the base end portion of the grinding element bundle9is held in the holding hole20inclined relative to the radial direction M, whereby the front surface and the back surface of the grinding element bundle9each can be inclined backward in the rotational direction R1from the inner periphery toward the outer periphery. In any case, the breaking of the wire-shaped grinding elements28can be suppressed during work.

(Modification to First Embodiment and Second Embodiment)

In the first embodiment, the grinding element bundle9may be held in the grinding element holder7in a state in which it is inclined in the circumferential direction relative to the virtual surface30. That is, each of the holding holes20in the grinding element holder7in the first embodiment is recessed in the direction inclined forward in the rotational direction R1relative to the radial direction M, in the same manner as each of the holding holes20in the second embodiment. The grinding element bundle9is then held in each of the holding holes20whereby the front surface9aand the back surface9bof the grinding element bundle9are inclined backward in the rotational direction R1from the inner periphery toward the outer periphery. In this way, when excessive force is applied, the wire-shaped grinding elements28are easily displaced in the direction of the axis of center of rotation L and backward in the rotational direction R1. This further suppresses the breaking of the wire-shaped grinding elements28.

FIG. 8is a perspective view of a polishing brush according to a third embodiment of the present invention as viewed diagonally from below.FIG. 9(a)is a perspective view of the grinding element holder as viewed from below andFIG. 9(b)is a longitudinal sectional view of the grinding element holder.FIG. 10is an illustration of work operation by the polishing brush3in the present embodiment.FIG. 10shows the polishing brush3as viewed from the shank portion5side in the direction of the axis of center of rotation L, in which the shank member6and the grinding element holder7are shown by dotted lines. InFIG. 10, the front side in the drawing is the top side of the polishing brush2and the back side is the bottom side. Here, the polishing brush3in the third embodiment has a configuration corresponding to the polishing brush1in the first embodiment, and the corresponding parts are denoted with the same reference signs and will not be further elaborated. In the polishing brush3in the present embodiment, the direction of rotation during polishing/grinding work is not defined, as is the case with the polishing brush1in the first embodiment. For the sake of convenience, it is assumed that the direction shown by the arrow inFIG. 8is the rotational direction R1.

As shown inFIG. 8, the polishing brush3includes a shank member6having a shank portion (shank)5coupled to the head of a machine tool (drive device), an annular grinding element holder7through which the lower portion of the shank member6passes, and a locknut8screwed on the lower end portion shank member6. A plurality of grinding element bundles9protrude from the lower end surface7bof the grinding element holder7in the direction of the axis of center of rotation L. The shank member6and the locknut8are made of metal, and the grinding element holder7is made of resin. Each of the grinding element bundles9is a bundle of a plurality of wire-shaped grinding elements28formed by impregnating and solidifying an assembly of inorganic filaments with resin. The wire-shaped grinding elements28have the identical length. The grinding element holder7and the grinding element bundles9constitute the brush body10.

The shank member6includes a shank portion5, a collar11, and a bolt12from the top to the bottom. The portion below the collar11of the shank member6is inserted in the center hole15in the grinding element holder7(seeFIG. 7), and the lower end portion of the bolt12protrudes downward from the grinding element holder7.

As shown inFIG. 9(a), the annular lower end surface7bof the grinding element holder7is the grinding element-holding surface, on which a plurality of holding holes20holding the grinding element bundles9are formed at regular angular intervals in an annular shape. Each of the holding holes20is recessed in the direction of the axis of center of rotation L. When the grinding element holder7is viewed from the direction of the axis of center of rotation L, the holding hole20is shaped in a rectangle longer in the radial direction M and shorter in the circumferential direction and is inclined relative to the radial direction M. That is, the holding hole20has a rectangular cross-sectional shape inclined backward in the rotational direction R1of the polishing brush3toward the outer periphery.

As shown inFIG. 9(b), the grinding element holder7also has a coupling hole24, which connects the upper end portions of the holding holes20. The coupling hole24is annular and provided concentrically with the center hole15in the grinding element holder7. The holding holes20and the coupling hole24have minute projections and depressions on their inner wall surfaces.

As shown inFIG. 8, the upper end portion of the grinding element bundle9is inserted in the holding hole20and fixed to the grinding element holder7with an adhesive. When the grinding element bundle9is to be fixed to the holding hole20, the holding holes20and the coupling hole24in the holder body21are filled with an adhesive. Next, the wire-shaped grinding elements28with the identical length are held in the form of a bundle using a jig and the upper end portions of the wire-shaped grinding elements28are inserted into the holding hole20. In this way, while the grinding element bundle9is formed, this grinding element bundle9is fixed to the grinding element holder7.

Here, inserting the grinding element bundle9into the holding hole20allows the grinding element bundle9to have a cross-sectional shape corresponding to the cross-sectional shape of the holding hole20. That is, the grinding element bundle9has a rectangular cross-sectional shape and has a front surface9afacing forward in the rotational direction R1and a back surface9b. The front surface9aand the back surface9beach extend along the wire-shaped grinding elements28in the top-bottom direction and extend from the inner periphery to the outer periphery. The front surface9aand the back surface9bare parallel to each other, and the thickness dimension of the grinding element bundle9is constant in the circumferential direction. The cross-sectional shape (the cross-sectional shape orthogonal to the direction in which the wire-shaped grinding elements28extend) of the grinding element bundle9is a flattened shape that has a smaller thickness dimension in the circumferential direction than the length from the inner periphery toward the outer periphery.

As shown inFIG. 10, since each of the holding holes20is inclined relative to the radial direction M, the grinding element bundle9is inclined backward in the rotational direction R1from the inner periphery toward the outer periphery of the radial direction M by an inclination angle θ3, relative to a virtual surface30that includes the center point P of a cross section9dof the grinding element bundle9cut across the grinding element bundle-holding surface (lower end surface7b) and the axis of center of rotation L and extends in the radial direction M. In other words, the center line N3of the grinding element bundle9passing through the center point P and extending in the middle between the front surface9aand the back surface9bfrom the inner periphery toward the outer periphery is inclined relative to the virtual surface30by the inclination angle θ3. Therefore, the front surface9aand the back surface9bof the grinding element bundle9are also inclined backward in the rotational direction R1from the inner periphery toward the outer periphery relative to the virtual surface30. In the present embodiment, the inclination angle θ3is 30°.

The locknut8is screwed from below onto the lower end portion of the bolt12protruding downward from the grinding element holder7and holds the grinding element holder7together with the collar11of the shank member6.

When burring or grinding/polishing work on a surface is performed on a workpiece W using the polishing brush3, the polishing brush3is rotated with the shank portion5coupled to the drive device of a grinder, and the tip ends (lower ends) of the wire-shaped grinding elements28(grinding element bundle9) are pressed against the surface of the workpiece W. As shown inFIG. 10, during work, the polishing brush3is rotated such that the front surface9aof the grinding element bundle9is inclined backward in the rotational direction R1from the inner periphery toward the outer periphery.

Here, in the present embodiment, the front surface9aand the back surface9bof the grinding element bundle9are inclined relative to the virtual surface30including the axis of center of rotation L. Therefore, compared with a case in which the front surface9aand the back surface9bare parallel to the virtual surface30(orthogonal to the rotational direction R1), the wire-shaped grinding elements28included in the grinding element bundle9are easily displaced toward the outer periphery (the direction shown by the arrow Q3inFIG. 10) when the polishing brush1is rotated and the tip end of the grinding element bundle9is pressed against a workpiece W. Therefore, when excessive force is applied to the wire-shaped grinding elements28, the force can be released. This can suppress the breaking of the wire-shaped grinding elements28.

The inclination angle θ3relative to the virtual surface30of the center line N3of the grinding element bundle9passing through the center point P and extending from the inner periphery toward the outer periphery in the middle between the front surface9aand the back surface9bis preferably in the range of 20° or more to 60° or less. With this range of the inclination angle θ, it is possible to suppress the breaking of the wire-shaped grinding elements28while suppressing reduction of the capability of the grinding element bundle9cutting a workpiece W.

Also in the present embodiment, since the grinding element holder7holding the upper end portion of the grinding element bundle9is made of resin, the flexibility of the resin can absorb excessive force applied to the wire-shaped grinding elements28. The adjacent grinding element bundles9are affixed to each other with an adhesive injected in the coupling hole24to ensure that the grinding element bundles9are fixed to the grinding element holder7. In addition, since the holding holes20and the coupling hole24to be filled with an adhesive have projections and depressions on their inner wall surfaces, the anchor effect ensures that the grinding element bundles9are fixed to the grinding element holder7. As a result, the dimension of the holding hole20can be reduced in the depth direction, so that the size of the grinding element holder7can be reduced in the direction of the axis of center of rotation L. When the polishing brush1has the same height as conventional ones, the grinding element bundle9(wire-shaped grinding elements28) can be increased in length, thereby suppressing the breaking of the wire-shaped grinding elements28during work.

Also in the present embodiment, the shank member6and the brush body10are separate, and the shank member6is removable from the grinding element holder7. Therefore, the brush body10alone can be replaced with a new one. In addition, a plurality of shank members6having shank portions5with different lengths may be prepared so that, by selecting any one of the shank members6, it is possible to adjust the position of the grinding element bundle9relative to the head when the polishing brush3is coupled to the head of a machine tool.

Here, the cross-sectional shape of the grinding element bundle9may be an oval longer in the radial direction M and shorter in the rotational direction R1. In this case, the holding hole20as viewed from the direction of the axis of center of rotation L is shaped in an oval inclined in the rotational direction R1from the inner periphery toward the outer periphery. The grinding element bundle9is then held in this holding hole20whereby the front surface and the back surface of the grinding element bundle9are inclined relative to the virtual surface30. Here, when the cross section of the grinding element bundle9has an oval shape, the state in which the front surface and the back surface of the grinding element bundle9are inclined relative to the virtual surface30refers to a state in which the longer axis in the oval cross section is inclined backward in the rotational direction R1from the inner periphery toward the outer periphery whereby the front surface and the back surface of the grinding element bundle9are each inclined relative to the virtual surface30.

FIG. 11(a)is a perspective view of a polishing brush according to a fourth embodiment of the present invention as viewed diagonally from below andFIG. 11(b)is a perspective view of the grinding element holder7as viewed diagonally from below.FIG. 12is a partial enlarged view of the brush body10as viewed from the radial direction M. InFIG. 12, the coupling hole24is not shown to facilitate understanding of the shape of the holding hole20. The polishing brush4in the fourth embodiment has a configuration corresponding to the polishing brush3in the third embodiment, and the corresponding parts are denoted with the same reference signs and will not be further elaborated. In the polishing brush4in the present embodiment, however, the direction of rotation during polishing/grinding work is defined as the rotational direction R1shown by the arrow inFIG. 11.

As shown inFIG. 11(a), the polishing brush4includes a shank member6having a shank portion (shank)5coupled to the head of a machine tool (drive device), an annular grinding element holder7through which the lower portion of the shank member6passes, and a locknut8screwed on the lower end portion of the shank member6. A plurality of grinding element bundles9protrude from the lower end surface7bof the grinding element holder7in the direction of the axis of center of rotation L. The shank member6and the locknut8are made of metal, and the grinding element holder7is made of resin. Each of the grinding element bundles9is formed of a bundle of a plurality of wire-shaped grinding elements28formed by impregnating and solidifying an assembly of inorganic filaments with resin. The grinding element holder7and the grinding element bundles9constitute the brush body10.

The shank member6includes a shank portion5, a collar11, and a bolt12from the top to the bottom. The portion below the collar11of the shank member6is inserted in the center hole15in the grinding element holder7(seeFIG. 11(b)), and the lower end portion of the bolt12protrudes downward from the grinding element holder7.

The annular lower end surface7bof the grinding element holder7is the grinding element-holding surface. On the lower end surface7b, as shown inFIG. 11(b), a plurality of holding holes20holding the grinding element bundles9are formed at regular angular intervals in an annular shape. When the grinding element holder7is viewed from the direction of the axis of center of rotation L, each of the holding holes20is shaped in a rectangle longer in the radial direction M and shorter in the circumferential direction. In each of the holding holes20, the opening of the rectangle extends in the radial direction M.

Each of the holding holes20is recessed in the direction inclined relative to the direction of the axis of center of rotation L. That is, each of the holding holes20is inclined forward in the rotational direction R1upward in the direction of the axis of center of rotation L. The grinding element holder7also has a coupling hole24, which connects the upper end portions of the holding holes20. The coupling hole24is provided concentrically with the center hole15in the grinding element holder7. The holding holes20and the coupling hole24have minute projections and depressions on their inner wall surfaces.

As shown inFIG. 11(a), the upper end portion of the grinding element bundle9is inserted in the holding hole20and fixed to the grinding element holder7with an adhesive. When the grinding element bundle9is to be fixed to the holding hole20, the holding holes20and the coupling hole24in the holder body21are filled with an adhesive. Next, the wire-shaped grinding elements28with the identical length are held in the form of a bundle using a jig, and one end portions of the wire-shaped grinding elements28are inserted into the holding groove23. In this way, while the grinding element bundle9is formed, this grinding element bundle9is fixed to the grinding element holder7.

Here, inserting the grinding element bundle9into the holding hole20allows the grinding element bundle9to have a cross-sectional shape corresponding to the cross-sectional shape of the holding hole20. That is, the grinding element bundle9has a rectangular cross-sectional shape and has a front surface9aand a back surface9bfacing forward in the rotational direction R1. The front surface9aand the back surface9beach extend along the wire-shaped grinding element28from the inner periphery to the outer periphery and extend in the top-bottom direction. The front surface9aand the back surface9bare parallel to each other, and the thickness dimension of the grinding element bundle9is constant in the circumferential direction. The cross-sectional shape of the grinding element bundle9(the cross-sectional shape orthogonal to the direction in which the wire-shaped grinding elements28extend) is a rectangle that has a smaller thickness dimension in the rotational direction R1than the length in the radial direction M.

Since each of the holding holes20is inclined relative to the radial direction M, as shown inFIG. 12, the insertion of the grinding element bundle9into the holding hole20allows the grinding element bundle9to be inclined by a predetermined inclination angle θ4. In the present embodiment, the grinding element bundle9is inclined backward in the rotational direction R1from the top to the bottom relative to a virtual surface30(seeFIG. 12) that includes the center point P (seeFIG. 11(a)) of a cross section9dof the grinding element bundle9cut across the grinding element bundle-holding surface (lower end surface7b) and the axis of center of rotation L and extends in the radial direction M. In other words, as shown inFIG. 12, the center line N4of the grinding element bundle9passing through the center point P and extending in the middle between the front surface9aand the back surface9bfrom the top to the bottom is inclined relative to the virtual surface30by the inclination angle θ4. Therefore, the front surface9aand the back surface9bof the grinding element bundle9are also inclined relative to the virtual surface30backward in the rotational direction R1as the distance from the grinding element holder7increases. In the present embodiment, the inclination angle θ4is 20°.

The locknut8is screwed from below on the lower end portion of the bolt12protruding downward from the grinding element holder7and holds the grinding element holder7together with the collar11of the shank member6.

When burring or grinding/polishing work on a surface is performed on a workpiece W using the polishing brush4, the polishing brush4is rotated with the shank portion5coupled to the drive device of a grinder, and the tip ends (lower ends) of the wire-shaped grinding elements (grinding element bundle9) are pressed against the surface of the workpiece W. During work, the polishing brush4is rotated such that the front surface9aof the grinding element bundle9is inclined backward in the rotational direction R1toward the tip end.

Here, in the present embodiment, the end surfaces (the front surface9aand the back surface9b) facing in the circumferential direction in the grinding element bundle9are inclined relative to the virtual surface30including the axis of center of rotation L. Therefore, compared with a case in which the end surfaces9aand9bare parallel to the virtual surface30(orthogonal to the rotational direction R1), the wire-shaped grinding elements28included in the grinding element bundle9are easily displaced backward in the rotational direction R1(the direction shown by the arrow Q4inFIG. 12) when the polishing brush4is rotated and the tip end of the grinding element bundle9is pressed against a workpiece W. Therefore, when excessive force is applied to the wire-shaped grinding elements28, the force can be released. This can suppress the breaking of the wire-shaped grinding elements28.

The inclination angle θ4relative to the virtual surface30of the center line N4of the grinding element bundle9passing through the center point P and extending from the top to the bottom in the middle between the front surface9aand the back surface9bis preferably within the range of 5° or more to 20° or less. With this range of the inclination angle θ2, it is possible to suppress the breaking of the wire-shaped grinding elements28while suppressing reduction of the capability of the grinding element bundle9cutting a workpiece W.

Also in the present embodiment, since the grinding element holder7holding the upper end portions of the grinding element bundles9are made of resin, the flexibility of the resin can absorb excessive force applied to the wire-shaped grinding elements28. The grinding element bundles9are fixed to the grinding element holder7with an adhesive injected to the holding holes20and the coupling hole24. The adjacent grinding element bundles9are thus affixed to each other to ensure that the grinding element bundles9are fixed to the grinding element holder7. In addition, since the holding holes20and the coupling hole24to be filled with an adhesive have projections and depressions on their inner peripheral surfaces, the anchor effect ensures that the grinding element bundles9are fixed to the grinding element holder7. As a result, the dimension of the holding hole20can be reduced in the depth direction, so that the size of the grinding element holder7can be reduced in the direction of the axis of center of rotation L. When the polishing brush4is formed with the same height as conventional ones, the length of the grinding element bundle9(wire-shaped grinding elements28) can be ensured, thereby suppressing the breaking of the wire-shaped grinding elements28during work.

Also in the present embodiment, the shank member6and the brush body10are separate, and the shank member6is removable from the grinding element holder7. Therefore, the brush body10alone can be replaced with a new one. In addition, a plurality of shank members6having shank portions5with different lengths may be prepared so that, by selecting any one of the shank members6, it is possible to adjust the position of the grinding element bundle9relative to the head when the polishing brush4is coupled to the head of a machine tool.

Here, the cross-sectional shape of the grinding element bundle9may be an oval having a cross-sectional shape longer in the radial direction M and shorter in the rotational direction R1. Also in this case, the base end portion of the grinding element bundle9is held in the holding hole20inclined in the top-bottom direction, whereby the front surface and the back surface of the grinding element bundle9each can be inclined backward in the rotational direction R1as the distance from the grinding element holder7increases. In the present embodiment, the cross-sectional shape of the grinding element bundle9may be a circle. Also when the cross-sectional shape of the grinding element bundle9is a circle, the base end portion of the grinding element bundle9is held in the holding hole20inclined in the top-bottom direction, whereby the front surface and the back surface of the grinding element bundle9each can be inclined backward in the rotational direction R1as the distance from the grinding element holder7increases. In any case, the breaking of the wire-shaped grinding elements28can be suppressed during work.

(Modification to Third Embodiment and Fourth Embodiment)

In the third embodiment, the grinding element bundle9may be inclined backward in the rotational direction R1as the distance from the grinding element holder7increases. That is, each of the holding holes20in the grinding element holder7in the third embodiment is recessed in the direction inclined forward in the rotational direction R1upward in the direction of the axis of center of rotation L, in the same manner as each of the holding holes20in the fourth embodiment. The grinding element bundle9is then held in each of the holding holes20whereby the front surface9aand the back surface9bof the grinding element bundle9are inclined backward in the rotational direction R1as the distance from the grinding element holder7increases. In this way, when excessive force is applied, the wire-shaped grinding elements28are easily displaced in the radial direction M and backward in the rotational direction R1. This can further suppress the breaking of the wire-shaped grinding elements28.

(Modification to Second Embodiment and Fourth Embodiment)

In the polishing brush2in the second embodiment and the polishing brush4in the fourth embodiment, a threaded portion to be screwed on the bolt12of the shank member6may be provided on the inner peripheral surface of the center hole15in the grinding element holder7, and the bolt12may be screwed into the threaded portion of the center hole15to removably couple the shank member6with the grinding element holder7. That is, in the polishing brush2in the second embodiment and the polishing brush4in the fourth embodiment, the direction of rotation in polishing/grinding work is defined as the rotational direction R1. Therefore, if the direction in which the bolt12is screwed in the threaded portion of the center hole15is set in an appropriate direction, the rotation of the polishing brush2,4causes neither loosening of the coupling between the shank member6and the grinding element holder7nor dropping off of the grinding element holder7from the shank member6. Thus, the provision of a threaded portion on the inner peripheral surface of the center hole15in the grinding element holder7can eliminate the nut8.

In the foregoing embodiments, the wire-shaped grinding elements28are inserted into the holding holes20formed in the grinding element-holding surface (the outer peripheral side surface7cor the lower end surface7b) of the grinding element holder7, and fixed in the holes with an adhesive to form each of the grinding element bundles9. Therefore, the shape of each of the holding holes20corresponds to the shape of each of the grinding element bundles9. That is, the shape of each of the holding holes20is the same as the shape of the base end portion of the grinding element bundle9inserted in the holding hole. In this respect, the holding hole20may be a hole larger than the base end portion of the grinding element bundle9.

In this case, before the wire-shaped grinding elements28are inserted into the holding hole20, the wire-shaped grinding elements28are bundled into the grinding element bundle9having a predetermined shape and gripped with a jig. Then, when the base end portion of the grinding element bundle9is inserted into the holding hole20filled with an adhesive, the front surface9aand the back surface9bof the grinding element bundle9are postured to be inclined relative to the virtual surface30that includes the center point P of the cross section9dof the grinding element bundle9inserted in the holding hole20cut across the grinding element bundle-holding surface and the axis of center of rotation L and extends in the radial direction M orthogonal to the axis of center of rotation L. The grinding element bundle9is thus affixed and fixed with this posture in the holding hole20. Before the wire-shaped grinding elements28are inserted into the holding hole20, the wire-shaped grinding elements28may be bundled into a grinding element bundle9having a predetermined shape, and the base end portion of the grinding element bundle9may be fixed with an adhesive.

This operation facilitates insertion of the wire-shaped grinding elements28into the holding hole20. Since the front surface9aand the back surface9bof the grinding element bundle9held in the holding hole20are inclined relative to the virtual surface30, the breaking of the wire-shaped grinding elements28can be suppressed during work.

In the foregoing embodiments, the grinding element-holding surface (the outer peripheral side surface7cor the lower end surface7b) of the grinding element holder7have the same number of holding holes20as the grinding element bundles9to be held by the grinding element holder7, and the grinding element bundles9are held in the holding holes20. Alternatively, the grinding element-holding surface may have a single annular holding hole20in the shape of a groove, and the grinding element bundles9may be held apart from each other in this single annular holding hole20.

In this case, before the wire-shaped grinding elements28are inserted into the holding hole20, the wire-shaped grinding elements28are bundled into the grinding element bundle9having a predetermined shape and gripped using a jig. The base end portions of the grinding element bundles9are then successively inserted at regular intervals into the annular holding hole20filled with an adhesive. Here, when the base end portions of the grinding element bundles9are inserted into the annular holding hole20, the front surface9aand the back surface9bof each of the grinding element bundles9are postured to be inclined relative to the virtual surface30that includes the center point P of the cross section9dof the grinding element bundle9inserted in the holding hole20, cut across the grinding element bundle-holding surface and the axis of center of rotation L and extends in the radial direction M orthogonal to the axis of center of rotation L. In this way, the grinding element bundles9are affixed and fixed with this posture at regular intervals in the holding hole20. The adhesive filling the holding hole20is interposed between the adjacent grinding element bundles9in the annular holding hole20. Before the wire-shaped grinding elements28are inserted into the holding hole20, the wire-shaped grinding elements28may be bundled into the grinding element bundle9having a predetermined shape, and the base end portion of the grinding element bundle9may be fixed with an adhesive.

This operation facilitates insertion of the wire-shaped grinding elements28into the holding hole20. Since the front surface9aand the back surface9bof the grinding element bundle9held in the holding hole20are inclined relative to the virtual surface30, the breaking of the wire-shaped grinding elements28can be suppressed during work.