Patent Publication Number: US-10315290-B2

Title: Polishing brush

Description:
FIELD 
     The present invention relates to a polishing brush including a plurality of wire-shaped grinding elements extending from a grinding element holder in the direction of the axis of center of rotation. 
     BACKGROUND 
     A cup-shaped polishing brush is known in which the base end portions of a plurality of wire-shaped grinding elements arranged annularly are held by a grinding element holder. In such a polishing brush, when the polishing brush is rotated in polishing work, the tip ends of the wire-shaped grinding elements extending in the direction of the axis of center of rotation spread outward due to centrifugal force, and the contact position of the wire-shaped grinding elements on the workpiece becomes unstable. The polishing brush described in Patent Literature 1, therefore, is provided with a grinding element holder and a skirt (tubular member) covering the portions on the polishing holder side of the wire-shaped grinding elements on the outer peripheral side. The skirt prevents the spread of the wire-shaped grinding elements outward during rotation. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Patent Application Laid-open No. 2003-89067 
     SUMMARY 
     Technical Problem 
     Unfortunately, when the skirt covers the polishing brush and the outer peripheral side of the wire-shaped grinding elements, air or cutting fluid supplied from the outer peripheral side of the polishing brush hardly reaches a portion to be polished in the workpiece. For this reason, the polishing brush having a skirt is provided with a through hole passing through in the direction of the axis of center of rotation at the center of the grinding element holder. During polishing operation, this through hole is used to supply air or cutting fluid to the portion to be polished. 
     In view of the foregoing, the problem to be solved by the present invention is to provide a polishing brush capable of supplying cutting fluid or air to a portion to be polished in a workpiece from the outer peripheral side while preventing the spread of the wire-shaped grinding elements due to centrifugal force during polishing operation. 
     Solution to Problem 
     In order to solve the problem above, the present invention is characterized by including a grinding element holder, a plurality of wire-shaped grinding elements protruding from the grinding element holder in the direction of the axis of center of rotation, and a grinding element displacement-restricting member having an annular part surrounding the wire-shaped grinding elements from the outer peripheral side at a position between the tip ends of the wire-shaped grinding elements and the grinding element holder in the direction of the axis of center of rotation and at a distance away from the tip ends of the wire-shaped grinding elements and the grinding element holder. 
     According to the present invention, the grinding element displacement-restricting member has an annular part surrounding a plurality of wire-shaped grinding elements from the outer peripheral side, thereby preventing the spread of the wire-shaped grinding elements outward due to centrifugal force during polishing operation. Since the annular part is kept apart from the grinding element holder in the direction of the axis of center of rotation, the wire-shaped grinding elements are partially exposed on the outside between the annular part and the grinding element holder in the direction of the axis of center of rotation. Therefore, when air or cutting fluid is supplied from the outer peripheral side toward the exposed portions of the wire-shaped grinding elements, the air or cutting fluid reaches the polished portion of a workpiece easily compared with when the wire-shaped grinding elements are entirely covered on the polishing holder side. 
     In the present invention, it is preferable that the grinding element displacement-restricting member include: a shaft extending in the direction of the axis of center of rotation on the inner peripheral side of the annular part; and a connection part connecting the shaft with the annular part; the grinding element holder have a shaft hole passing through in the direction of the axis of center of rotation and be removably fixed to the shaft passing through the shaft hole, and the connection part connect the shaft with a circumferential portion of the annular part. In this configuration, the grinding element holder can be easily fixed to the grinding element displacement-restricting member. The position of the shaft to which the grinding element holder is fixed is changed in the direction of the axis of center of rotation, whereby the amount of protrusion of the wire-shaped grinding element from the annular part can be adjusted in the direction of the axis of center of rotation. In addition, since the coupling part is bridged from the shaft to a circumferential portion of the annular part, the grinding element holder-side portions of the wire-shaped grinding elements are not covered around the entire periphery. 
     In the present invention, the annular part and the connection part may be integrally formed, and the connection part may be removably attached to the shaft. With this configuration, when the tip ends of the wire-shaped grinding elements spreading outward due to centrifugal force come into contact with the annular part and wear the annular part, the annular part can be replaced with a new one together with the connection part. 
     In the present invention, the connection part may include an annular part-side connection portion extending continuously from the annular part and a shaft-side connection portion connecting the annular part-side connection portion with the shaft. The annular part-side connection portion and the shaft-side connection portion may be removably connected. With this configuration, for example, when the tip end portions of the wire-shaped grinding elements spreading outward due to centrifugal force come into contact with the annular part and wear the annular part, the annular part-side coupling portion and the annular part can be replaced with new ones. 
     In the present invention, it is preferable that the grinding element holder include: a first annular part having the shaft hole; a second annular part having an inner diameter size larger than the first annular part and disposed at a distance away from the outer peripheral side of the first annular part; and a holder-side connection part connecting a circumferential portion of the first annular part with a circumferential portion of the second annular part, the wire-shaped grinding elements be held in the second annular part and are disposed annularly around the axis of center of rotation, and when viewed from the direction of the axis of center of rotation, the holder-side connection part coincide with the connection part of the grinding element displacement-restricting member. In this configuration, air or cutting fluid can be supplied in the direction of the axis of center of rotation toward the inner peripheral side of the wire-shaped grinding elements held in the second annular part, through the opening of the grinding element holder formed between the first annular part and the second annular part and off the holder-side coupling portion. 
     In the present invention, it is preferable that the wire-shaped grinding elements be subdivided and bundled into a plurality of grinding element bundles, and the grinding element bundles be arranged annularly to be kept apart from each other. With this configuration, air or cutting fluid can be supplied to the inner peripheral side of the grinding element bundles held in the second annular part and arranged annularly, through the gap between the adjacent grinding element bundles. 
     In the present invention, it is preferable that a metal covering member cover the end portions on the tip end side of the wire-shaped grinding elements on the inner peripheral surface of the annular part, and at least the annular part of the grinding element displacement-restricting member be made of resin. When the annular part is made of resin, the weight of the polishing brush can be reduced compared with when the annular part is made of metal. This leads to reduction of power load of the machine tool to which the polishing brush is attached. In addition, when the annular part is made of resin, the production cost for the grinding element displacement-restricting member can be suppressed compared with when the annular part is made of metal. However, when the annular part is made of resin, the annular part may be worn when the tip end portions of the wire-shaped grinding elements spreading outward due to centrifugal force come into contact with the annular part. In this respect, covering the inner peripheral surface of the annular part with the covering member can prevent wear of the annular part. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a polishing brush according to a first embodiment of the present invention. 
         FIG. 2  is an exploded perspective view of the polishing brush in  FIG. 1 . 
         FIG. 3  is a perspective view of a grinding element holder. 
         FIG. 4  is a perspective view of an annular part and curved plate portions. 
         FIG. 5  is a perspective view of a grinding element displacement-restricting member in a modification. 
         FIG. 6  is a perspective view of a polishing brush according to a second embodiment of the present invention. 
         FIG. 7  is an exploded perspective view of the polishing brush in  FIG. 6 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention will be described 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. 
     First Embodiment 
       FIG. 1  is a perspective view of a polishing brush according to a first embodiment of the present invention.  FIG. 2  is an exploded perspective view of the polishing brush in  FIG. 1 .  FIG. 3( a )  is a perspective view of a grinding element holder viewed from above, and  FIG. 3( b )  is a perspective view of the grinding element holder viewed from below. As shown in  FIG. 1 , the polishing brush  1  in the first embodiment includes a brush-shaped grindstone  12  having a plurality of grinding element bundles  11  arranged annularly, and a grinding element displacement-restricting member  13  for restricting displacement of the grinding element bundles  11  outward. The brush-shaped grindstone  12  is removably attached to the grinding element displacement-restricting member  13  with setscrews  14 . 
     (Brush-Shaped Grindstone) 
     As shown in  FIG. 1  and  FIG. 2 , the brush-shaped grindstone  12  includes a grinding element holder  15  holding the base end portions (upper end portions) of the grinding element bundles  11 . Each of the grinding element bundles  11  protrudes downward from the grinding element holder  15  in the direction of the axis of center of rotation L. The grinding element holder  15  is made of resin or metal. In the first embodiment, the grinding element holder  15  is made of ABS resin. As shown in  FIG. 3 , the grinding element holder  15  includes a first annular part  17  having a holder-side shaft hole  16  at its center, a second annular part  18  disposed concentrically with the first annular part  17  on the outer peripheral side of the first annular part  17 , and a holder-side connection part  19  connecting a circumferential portion of the first annular part  17  with a circumferential portion of the second annular part  18 . As shown in  FIG. 3( b ) , on the lower surface of the second annular part  18 , a plurality of holding holes  20  for holding the grinding element bundles  11  are formed annularly at regular angular intervals. 
     The holder-side connection part  19  includes three holder-side arm portions  21  extending radially. The three holder-side arm portions  21  extend in the radius direction at regular angular intervals to connect the first annular part  17  with the second annular part  18  at three places in the circumferential direction. The grinding element holder  15  therefore has holder-side openings  25 . Each of the holder-side openings  25  is arranged between the first annular part  17  and the second annular part  18  and between the adjacent two holder-side arm portions  21 . The holder-side arm portions  21  have holder-side through holes  22  extending in the radius direction from the end surface on the outer peripheral side to reach the holder-side shaft hole  16  in the first annular part  17 . The inner peripheral surface of each of the holder-side through holes  22  has a screw portion that is female-threaded at least at a portion near the holder-side shaft hole  16 . 
     Each of the grinding element bundles  11  is a bundle of a plurality of wire-shaped grinding elements  27 . The wire-shaped grinding element  27  is formed of an assembly of inorganic filaments impregnated and hardened 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 first embodiment, the inorganic filaments are alumina filaments. The filament assembly is a group of 250 to 3000 alumina filaments with a fiber diameter of 8 to 50 μm. The diameter of the filament assembly is 0.1 mm to 2 mm. The filament assembly may be twisted. 
     The grinding element bundles  11  have respective base end portions inserted in the holding holes  20  in the grinding element holder  15  and fixed with an adhesive. A plurality of grinding element bundles  11  are thus held annularly in the grinding element holder  15 . 
     (Grinding Element Displacement-Restricting Member) 
     As shown in  FIG. 1 , the grinding element displacement-restricting member  13  has a shaft  32  having a shank portion  31  coupled to the head of a machine tool (drive device), an annular part  33  surrounding a portion in the direction of the axis of center of rotation L of the grinding element bundles  11  from the outer peripheral side, and a connection part  34  connecting the shaft  32  with the annular part  33 . 
     The shaft  32  is made of resin or metal. In the first embodiment, the shaft  32  is made of metal. When the shaft  32  is made of resin, the shaft  32  is formed of, for example, FRP resin to ensure its strength. As shown in  FIG. 2 , the shaft  32  is shaped like a cylinder and its upper portion is the shank portion  31 . At the lower portion of the shaft  32 , flat surfaces  35  are formed by cutting away a circumferential portion of the outer peripheral surface of the shaft  32  in parallel with the axis of center of rotation L. Three flat surfaces  35  are provided at regular angular intervals. 
     The annular part  33  and the connection part  34  are made of resin. In the first embodiment, the annular part  33  and the connection part  34  are made of ASB resin. The connection part  34  includes an annular portion  37  having a shaft hole  36 , three arm portions  38  extending radially outward in the radius direction from the outer peripheral surface of the annular portion  37 , and curved plate portions  39  each extending downward in the direction of the axis of center of rotation L from the end portion on the outer peripheral side of each of the arm portions  38 . The annular portion  37  and three arm portions  38  in the connection part  34  are integrally formed, and the curved plate portions  39  are separate. The curved plate portions  39  are formed integrally with the annular part  33 . 
     At the circumferentially central portion of the upper surface of each of the arm portions  38 , a groove  40  is provided to extend in the radius direction. The groove  40  reaches from the end of each of the arm portions  38  on the outer peripheral side to the outer peripheral surface of the annular portion  37 . As a result, parts of the outer peripheral surface of the annular portion  37  are exposed outward through the grooves  40 . At the portions on the outer peripheral surface of the annular portion  37  exposed outward through the grooves  40 , screw holes  41  are formed to pass through the annular portion  37  in the radius direction. The end surface of each of the arm portions  38  on the outer peripheral side has screw holes  42  recessed in the radius direction. 
     As shown in  FIG. 4 , each of the curved plate portions  39  extends with a certain width upward from a circumferential portion of the annular part  33 . The curved plate portions  39  are curved in the circumferential direction along the annular part  33 . The upper end portions of the curved plate portions  39  have through holes  43 . The curved plate portions  39  are removably coupled to the arm portions  38  with head screws  44  (see  FIG. 1 ) passing through the through holes  43  to be screwed into the screw holes  42  in each of the arm portions  38 . Below the through holes  43  in the curved plate portions  39 , guide holes  45  are provided, which are formed in the shape of grooves along the direction of the axis of center of rotation L. Each of the guide holes  45  has its lower end portion reaching a midway position in the direction of the axis of center of rotation L in the annular part  33 . 
     Here, as shown in  FIG. 2 , in the annular part  33 , the height dimension h 1  is constant where the curved plate portions  39  are not continuous upward. This height dimension h 1  is equal to or smaller than ½ of the protruding length of the unused grinding element bundles  11  protruding downward from the grinding element holder  15 . 
     A metal covering member  47  is attached to the grinding element displacement-restricting member  13 . As shown in  FIG. 4 , the covering member  47  is annular and covers the end portions on the tip end side of the wire-shaped grinding elements  27  on the inner peripheral surface of the annular part  33 . In the first embodiment, the covering member  47  is a metal adhesive tape. Alternatively, the covering member  47  may be a metal ring. 
     To assemble the grinding element displacement-restricting member  13 , the arm portions  38  of the connection part  34  are coupled to the curved plate portions  39  with head screws  44  to integrate the annular part  33  and the connection part  34 . The shaft  32  is passed through the shaft hole  36  in the annular portion  37  of the connection part  34 , and the connection part  34  is fixed to the shaft  32  with head screws  48  (see  FIG. 1 ) screwed in the screw holes  41  in the annular portion  37 . Here, when the grinding element displacement-restricting member  13  is assembled, the grinding element displacement-restricting member  13  has three large openings  50  each defined by an arc portion  33   a  not connected with the connection part  34  (curved plate portions  39 ) in the annular part  33 , two curved plate portions  39  adjacent to each other in the circumferential direction, the arm portions  38  extending toward the inner peripheral side from the two curved plate portions  39 , and the annular portion  37 . 
     To assemble the polishing brush  1 , the brush-shaped grindstone  12  is attached to the grinding element displacement-restricting member  13 . More specifically, as shown in  FIG. 2 , the grinding element displacement-restricting member  13  and the brush-shaped grindstone  12  are disposed concentrically, and the shaft  32  of the grinding element displacement-restricting member  13  is inserted into the holder-side shaft hole  16  of the brush-shaped grindstone  12 . The grinding element holder  15  and the grinding element bundles  11  are thus disposed on the inner peripheral side of the annular part  33 . 
     In addition, while the position of the brush-shaped grindstone  12  is adjusted in the direction of the axis of center of rotation L, the setscrews  14  are inserted into the holder-side through holes  22  of the grinding element holder  15  through the guide holes  45 , so that the grinding element holder  15  is fixed to the shaft  32  of the grinding element displacement-restricting member  13  with the setscrews  14 . As shown in  FIG. 1 , in a state in which the brush-shaped grindstone  12  is attached to the grinding element displacement-restricting member  13 , the annular part  33  surrounds the grinding element bundles  11  (the wire-shaped grinding elements  27 ) from the outer peripheral side at a position between the tip ends of the grinding element bundles  11  (the tip ends of the wire-shaped grinding elements  27 ) and the grinding element holder  15  in the direction of the axis of center of rotation L and at a distance away from the tip ends of the grinding element bundles  11  (the tip ends of the wire-shaped grinding elements  27 ) and the grinding element holder  15 . 
     Here, the setscrews  14  are inserted in the holder-side through holes  22  of the grinding element holder  15  through the guide holes  45 , whereby the grinding element holder  15  is positioned in the circumferential direction relative to the grinding element displacement-restricting member  13 . Thus, the flat surfaces  35  on the shaft  32  and the holder-side through holes  22  of the grinding element holder  15  are disposed at the overlapping positions as viewed in the radius direction. The tip ends of the setscrews  14  are screwed in the holder-side through holes  22 , and therefore, abut on the flat surfaces  35  of the shaft  32 . 
     When the grinding element holder  15  is positioned in the circumferential direction relative to the grinding element displacement-restricting member  13 , the three holder-side arm portions  21  of the grinding element holder  15  overlap the three arm portions  38  of the grinding element displacement-restricting member  13  as viewed from the direction of the axis of center of rotation L. Therefore, as shown in  FIG. 1 , the polishing brush  1  has a space continuous to an interior space  55  on the inside of the grinding element bundles  11  arranged annularly from the direction of the axis of center of rotation L, through the openings  50  in the grinding element displacement-restricting member  13  and the holder-side openings  25  of the grinding element holder  15 . Since the annular part  33  is kept apart from the grinding element holder  15  in the direction of the axis of center of rotation L, the portions on the side closer to the grinding element holder  15  of the grinding element bundles  11  held in the grinding element holder  15  are exposed outward, and the polishing brush  1  has a space continuous to the interior space  55  through the openings  50  of the grinding element displacement-restricting member  13  and between the adjacent grinding element bundles  11 . 
     (Work Operation) 
     When burring or grinding/polishing work is performed on a surface of a workpiece using the polishing brush  1 , the shank portion  31  is coupled to the head of a machine tool and rotated around the axis of center of rotation L, and the tip ends (the ends on the outer peripheral side) of the grinding element bundles  11  (the wire-shaped grinding elements  27 ) are pressed against the surface of the workpiece. 
     Here, the rotation of the polishing brush  1  allows the wire-shaped grinding elements  27  of each of the grinding element bundles  11  to spread outward. However, the tip end portions of the wire-shaped grinding elements  27  come into abutment with the annular part  33 , which restricts the displacement of the wire-shaped grinding elements  27  outward. The wire-shaped grinding elements  27  of each of the grinding element bundles  11  therefore can be accurately pressed against the polished position of the workpiece. In addition, the contact position of the wire-shaped grinding elements  27  on the workpiece can be stabilized. 
     During work operation, cutting fluid or air is supplied from above the polishing brush  1  or from the outer peripheral side to cool the polished portion of the workpiece. The supplied cutting fluid or air removes chips. 
     Here, the portions on the side closer to the grinding element holder  15  of the grinding element bundles  11  of the polishing brush  1  are exposed outward. The polishing brush  1  has a space continuous from the openings  50  of the grinding element displacement-restricting member  13  to the interior space  55  surrounded by the grinding element bundles  11  through the holder-side openings  25  of the grinding element holder  15 . The polishing brush  1  also has a space continuous to the interior space  55  surrounded by the grinding element bundles  11  through the openings  50  of the grinding element displacement-restricting member  13  and between the adjacent grinding element bundles  11 . Therefore, when cutting fluid or air is supplied from above the polishing brush  1  or from the outer peripheral side, the cutting fluid or air can reach the polished portion of the workpiece. This enables cooling of the polished portion of the workpiece and also enables removable of chips. 
     When the wire-shaped grinding elements  27  are worn out due to work operation and the protruding length of the wire-shaped grinding elements  27  from the opening end  33   b  of the annular part  33  of the grinding element displacement-restricting member  13  is reduced, the position of the brush-shaped grindstone  12  fixed to the shaft  32  is adjusted in the direction of the axis of center of rotation L, whereby the protruding length of the wire-shaped grinding elements  27  from the opening end  33   b  is adjusted. To perform such adjustment operation, the setscrews  14  are loosened, and then the brush-shaped grindstone  12  is moved in the direction of the axis of center of rotation L on the inside of the annular part  33 . The setscrews  14  are then tightened again. Here, when the brush-shaped grindstone  12  is moved in the direction of the axis of center of rotation L, the outer peripheral side-portions of the loosened setscrews  14  move inside the guide holes  45  along the guide holes  45  to allow the brush-shaped grindstone  12  to move in the direction of the axis of center of rotation L in such a state as to be positioned in the circumferential direction. 
     In the first embodiment, since the annular part  33  and the connection part  34  of the grinding element displacement-restricting member  13  are made of resin, the weight of the polishing brush  1  can be reduced compared with when they are made of metal. In addition, since the grinding element displacement-restricting member  13  has the three openings  50  in the circumferential direction, the weight of the polishing brush  1  can be reduced. This leads to reduction of power load of the machine tool to which the polishing brush  1  is attached. Moreover, since the grinding element displacement-restricting member  13  has the three openings  50  in the circumferential direction, the amount of resin used for producing the grinding element displacement-restricting member  13  can be reduced compared with when it does not have the openings  50 . This can suppress the production cost for the grinding element displacement-restricting member  13 . 
     Here, if the annular part  33  of the grinding element displacement-restricting member  13  is made of resin, the tip end portions of the wire-shaped grinding elements  27  spreading outward due to centrifugal force wear the annular part  33  when coming into contact with the annular part  33 . By contrast, in the first embodiment, the metal covering member  47  covers the inner peripheral surface of the annular part  33  and thus prevents the wear of the annular part  33 . In the first embodiment, since the annular part  33  is detachable from the polishing brush  1  together with the curved plate portions  39  of the connection part  34 , the annular part  33  and the curved plate portions  39  can be replaced with new ones, for example, when the covering member  47  and the annular part  33  are worn out. 
     (Modification of Grinding Element Displacement-Restricting Member) 
       FIG. 5  is a perspective view of a grinding element displacement-restricting member  13 A in a modification. The grinding element displacement-restricting member  13 A in the modification can be used in the same manner as the grinding element displacement-restricting member  13  of the polishing brush  1  in the first embodiment. The grinding element displacement-restricting member  13 A in the modification has a configuration corresponding to the grinding element displacement-restricting member  13  of the polishing brush  1  in the first embodiment, and the corresponding parts are denoted with the same reference signs and will not be further elaborated. 
     In the modification, the connection part  34  includes an annular portion  37 , arm portions  38 , and curved plate portions  39 , which are integrally formed. The annular part  33  is removably connected to the lower end portions of the curved plate portions  39 . More specifically, at the lower edge of each of the curved plate portions  39 , projections  61  protruding outward are provided at two places kept apart in the circumferential direction. Each of the projections  61  has a screw hole  62  passing through in the direction of the axis of center of rotation L. The annular part  33  has a constant height dimension h 2  and has projections  63  protruding outward at positions corresponding to the projections  61  of each of the curved plate portions  39 . Each of the projections  63  has a through hole  64  passing through in the axis of center of rotation L. The annular part  33  is removably fixed to the connection part  34  with head screws (not shown), which pass through the through holes  64  from below to be screwed in the screw hole  62  of the projection  61  of the connection part  34 . 
     When the grinding element displacement-restricting member  13 A is assembled, the grinding element displacement-restricting member  13 A has three large openings  50  each defined by an arc portion  33   a  not connected with the connection part  34  (curved plate portions  39 ) in the annular part  33 , two curved plate portions  39  adjacent to each other in the circumferential direction, the arm portions  38  extending toward the inner peripheral side from the two curved plate portions  39 , and the annular portion  37 . 
     Here, the height dimension h 2  of the annular part  33  is equal to or smaller than ¼ of the protruding length of the unused grinding element bundles  11  protruding downward from the grinding element holder  15 . On the inner peripheral surface of the annular part  33 , a metal covering member  47  is attached to cover the entire inner peripheral surface. 
     The polishing brush  1  having the grinding element displacement-restricting member  13 A in the modification also exerts the similar operation effects as in the polishing brush  1  in the first embodiment. 
     In the modification, the annular part  33  may be made of metal and the covering member  47  may be eliminated. That is, in the modification, the annular part  33  is a relatively small member and the annular part  33  is solely removable from the connection part  34 . Therefore, even when the annular part  33  is made of metal, an increase in weight of the polishing brush  1  can be suppressed, and the cost for replacement of the annular part  33  can be suppressed. 
     Here, the grinding element displacement-restricting member  13  and the grinding element displacement-restricting member  13 A have the guide holes  45  extending in the direction of the center axis of rotation. The guide holes  45 , however, may be eliminated. In this case, setscrews  14  are screwed into the holder-side through holes  22  through the openings  50  of the grinding element displacement-restricting member  13 A, so that the brush-shaped grindstone  12  is fixed to the shaft  32  of the grinding element displacement-restricting member  13 A. 
     Second Embodiment 
       FIG. 6  is a perspective view of a polishing brush  2  in a second embodiment of the present invention.  FIG. 7  is an exploded perspective view of the polishing brush  2  in  FIG. 6 . As shown in  FIG. 6 , the polishing brush  2  in the second embodiment includes a brush-shaped grindstone  12  having a plurality of grinding element bundles  11  arranged annularly, and a grinding element displacement-restricting member  13 B for restricting displacement of the grinding element bundles  11  outward. The brush-shaped grindstone  12  is removably attached to the grinding element displacement-restricting member  13 B with setscrews  14 . The brush-shaped grindstone  12  of the polishing brush  2  in the second embodiment is identical with the brush-shaped grindstone  12  of the polishing brush  2  in the first embodiment. The polishing brush  2  in the second embodiment has a configuration corresponding to the polishing brush  1  in the first embodiment, and the corresponding parts are denoted with the same reference signs and will not be further elaborated. 
     (Grinding Element Displacement-Restricting Member) 
     As shown in  FIG. 6 , the grinding element displacement-restricting member  13 B includes a shaft  32  having a shank portion  31  coupled to the head of a machine tool (drive device), an annular part  33  surrounding the portions in the direction of the axis of center of rotation L of the grinding element bundles  11  from the outer peripheral side, and a connection part  34  connecting the shaft  32  with the annular part  33 . 
     The shaft  32  is shaped like a cylinder and its upper portion is the shank portion  31 . As shown in  FIG. 7 , flat surfaces  35  are formed at the lower portion of the shaft  32 . Three flat surfaces  35  are provided at regular angular intervals. 
     The annular part  33  and the connection part  34  are made of resin. In the second embodiment, the annular part  33  and the connection part  34  are integrally formed. The connection part  34  includes an annular portion  37  having a shaft hole  36  and three arm portions  38  extending radially outward in the radius direction from the outer peripheral surface of the annular portion  37 . The ends on the outer peripheral side of three arm portions  38  are continuous to the inner peripheral surface of the annular part  33 , whereby the arm portions  38  connect a circumferential portion of the annular portion  37  with a circumferential portion of the annular part  33 . The thickness dimension in the circumferential direction of the arm portion  38  is smaller than the distance between the adjacent grinding element bundles  11  held annularly in the grinding element holder  15 . At a portion on the outer peripheral surface of the annular portion  37  between two adjacent arm portions  38 , a screw hole  41  is formed to pass through the annular portion  37  in the radius direction. 
     Here, as shown in  FIG. 7 , the annular part  33  and the connection part  34  have the identical height dimension h 3 . That is, the height dimension h 3  of the annular portion  37  and the arm portion  38  of the connection part  34  is identical with the height dimension h 3  of the annular part  33 . The height dimension h 3  of the annular part  33  is equal to or smaller than ¼ of the protruding length of the unused grinding element bundles  11  protruding downward from the grinding element holder  15 . On the inner peripheral surface of the annular part  33 , a metal covering member  47  is attached to cover the entire inner peripheral surface. 
     To assemble the grinding element displacement-restricting member  13 B, the shaft  32  is passed through the shaft hole  36  disposed in the annular portion  37  of the connection part  34 , and the connection part  34  and the annular part  33  are fixed to the shaft  32  with head screws  48  (see  FIG. 6 ) screwed in the screw holes  41  of the annular portion  37 . The connection part  34  and the annular part  33  are fixed at a position where the lower end of the annular part  33  coincides with the lower end of the shaft  32 . 
     To assemble the polishing brush  2 , the brush-shaped grindstone  12  is attached to the grinding element displacement-restricting member  13 B. More specifically, as shown in  FIG. 7 , the grinding element displacement-restricting member  13 B and the brush-shaped grindstone  12  are disposed concentrically, and the shaft  32  of the grinding element displacement-restricting member  13 B is inserted into the holder-side shaft hole  16  of the brush-shaped grindstone  12 . The arm portion  38  of the connection part  34  of the grinding element displacement-restricting member  13 B is inserted between the grinding element bundles  11  held at regular angular intervals in the brush holder. The grinding element holder  15  and the grinding element bundles  11  are thus disposed on the inner peripheral side of the annular part  33 . 
     In addition, while the position of the brush-shaped grindstone  12  is adjusted in the direction of the axis of center of rotation L, the setscrews  14  are inserted into the holder-side through holes  22  of the grinding element holder  15 , so that the grinding element holder  15  is fixed to the shaft  32  of the grinding element displacement-restricting member  13 B with the setscrews  14 . Here, in a state in which the brush-shaped grindstone  12  is attached to the grinding element displacement-restricting member  13 B, as shown in  FIG. 6 , the annular part  33  surrounds the grinding element bundles  11  (the wire-shaped grinding elements  27 ) from the outer peripheral side at a position between the tip ends of the grinding element bundles  11  (the tip ends of the wire-shaped grinding elements  27 ) and the grinding element holder  15  in the direction of the axis of center of rotation L and at a distance away from the tip ends of the grinding element bundles  11  (the tip ends of the wire-shaped grinding elements  27 ) and the grinding element holder  15 . 
     (Work Operation) 
     When burring or grinding/polishing work is performed on a surface of a workpiece using the polishing brush  2 , the shank portion  31  is coupled to the head of a machine tool and rotated around the axis of center of rotation L, and the tip ends (the ends on the outer peripheral side) of the grinding element bundles  11  (wire-shaped grinding elements  27 ) are pressed against the surface of the workpiece. 
     Here, the rotation of the polishing brush  2  allows the wire-shaped grinding elements  27  of each of the grinding element bundles  11  to spread outward. However, the tip end portions of the wire-shaped grinding elements  27  come into abutment with the annular part  33 , which restricts the displacement of the wire-shaped grinding elements  27  outward. The wire-shaped grinding elements  27  of each of the grinding element bundles  11  therefore can be accurately pressed against the polished position of the workpiece. In addition, the contact position of the wire-shaped grinding elements  27  on the workpiece can be stabilized. 
     During work operation, cutting fluid or air is supplied from above the polishing brush  2  or from the outer peripheral side to cool the polished portion of the workpiece. The supplied cutting fluid or air removes chips. 
     Here, the grinding element bundles  11  of the polishing brush  2  are merely surrounded by the annular part  33  at a position between the tip ends of the grinding element bundles  11  (the tip ends of the wire-shaped grinding elements  27 ) and the grinding element holder  15  in the direction of the axis of center of rotation L and at a distance away from the tip ends of the grinding element bundles  11  (the tip ends of the wire-shaped grinding elements  27 ) and the grinding element holder  15 . The grinding element holder  15  has holder-side openings  25  in communication with an interior space  55  surrounded by a plurality of grinding element bundles  11  between the first annular part  17  and the second annular part  18 . Therefore, when cutting fluid or air is supplied from above the polishing brush  2  or from the outer peripheral side, the cutting fluid or air can reach the polished portion of the workpiece. This enables cooling of the polished portion of the workpiece and also enables removable of chips. 
     The polishing brush  2  having the grinding element displacement-restricting member  13 B in the second embodiment also exerts the similar operation effects as in the polishing brush  2  in the first embodiment. 
     In the second embodiment, the annular part  33  and the connection part  34  may be made of metal. That is, in the second embodiment, the annular part  33  and the connection part  34  are formed integrally, and the annular part  33  is a relatively small member. Therefore, even when the annular part  33  and the connection part  34  are made of metal, an increase in weight of the polishing brush  2  can be suppressed, and the cost for replacement of the annular part  33  can be suppressed. 
     Other Embodiments 
     In the foregoing embodiments, each of the wire-shaped grinding elements  27  includes an assembly of inorganic filaments. Alternatively, the wire-shaped grinding element  27  may be formed of nylon, abrasive-containing nylon, abrasive-containing rubber, stainless steel, or brass. 
     The covering member  47  may be eliminated. Here, when the covering member  47  is eliminated, the lower end portion (the portion on the tip end side of each of the wire-shaped grinding elements  27 ) of the annular part  33  may be formed of a resin that has higher abrasion resistance and lower friction coefficient compared with other parts. 
     In the foregoing embodiments, the wire-shaped grinding elements  27  are subdivided and bundled into each of the grinding element bundles  11 , and the grinding element bundles  11  are arranged annularly to be kept apart from each other. Alternatively, the wire-shaped grinding elements  27  may not be formed into a bundle but may be held annularly in the grinding element holder  15 . Even in the polishing brush  2  with this configuration, at least the portions closer to the grinding element holder  15  of the wire-shaped grinding elements  27  are exposed outward. Therefore, when cutting fluid or air is supplied from above the polishing brush  2  or from the outer peripheral side, the cutting fluid or air can reach the polished portion of the workpiece. This enables cooling of the polished portion of the workpiece and also enables removable of chips.