Patent Publication Number: US-8109183-B2

Title: Impact resistant tool bit and tool bit holder

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority, under 35 U.S.C. §119(e), to U.S. Provisional Application No. 61/059,363, filed Jun. 6, 2008, titled “Screwdriving Tool with Damper,” and U.S. Provisional Application No. 61/103,352, filed Oct. 7, 2008, titled “Tool Holder”, which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This application relates to accessories for power tools and, more specifically, to a tool bit and/or tool bit holder that includes a damper to make the bit or bit holder resistant to breakage when used in an impact driver. 
     BACKGROUND 
     When an impact driver is utilized to drive fasteners, such as screws, into a workpiece, a large driving torque (e.g., approximately 500 inch-lbs) is generated in rapid cycles (e.g., approximately every 2 milliseconds). Due to the large driving torque and the rapid cycling, current tool bits (e.g., screwdriving bits) and/or bit holders often fail when used with impact drivers. This may be due to the fact that the tool bits and bit holders often have a lower torque rating (e.g., approximately 200 inch-lbs) than the torque rating of the impact driver. It would be desirable to have a tool bit or a holder for a screwdriving bit that can withstand the torque loading of an impact driver. 
     SUMMARY 
     This application discloses a tool bit and/or a bit holder with a damper, which enables the tool bit and/or bit holder to dissipate large and dynamic torque loading from an impact driver, while smoothly delivering torque, e.g., to a fastener such as a screw. The tool bit or bit holder dissipates a sufficient amount of energy to prevent the peak torque from exceeding the strength of the tool bit or bit holder, without breaking the tool bit or bit holder. 
     It is an aspect of the present disclosure to provide a tool bit holder that comprises a tool holder body defining an axis and having a first and second end. The first end has a tool receiving bore and the second end has a shank receiving bore. The holder body includes a pocket between the first and second ends. The pocket receives a damping mechanism. The pocket is defined by a plurality of walls that define an overall rectangular bore. At least one wall includes a recess portion. The recess portion receives material from the damping mechanism during deformation of the damping mechanism caused by dynamic torque loading from an impact driver onto the tool bit holder. A shank defines an axis. The shank has a first and second end. The first end of the shank has a mating configuration with the tool holder shank receiving bore and is received in the shank receiving bore of the holder body. The shank first end is rotatable in the shank receiving bore. The shank second end includes a configuration to mate with a chuck or the like of a power tool. A pocket is formed in the shank between the first and second ends. The pocket receives a portion of a damping mechanism. The pocket is defined by a plurality of walls that define an overall rectangular bore. At least one wall includes a recess portion to receive material from the damping mechanism during deformation. A rotation limiting mechanism is coupled with the holder body and the shank. The rotation limiting mechanism limits rotation of the holder body and shank with respect to one another. The rotation limiting mechanism includes at least one pin positioned in a recess, in the holder body and the shank. A damping mechanism is received in the holder body and shank pockets. The damping mechanism has a rectangular configuration that fits into the pockets rectangular bores. The damping mechanism is made from a shape memory material, such as a nitinol alloy. The recess portions are defined by at least one surface extending away from one of the walls. The surface forms an acute angle with respect to one of the walls forming a wedge shaped void to receive the deformed material. 
     In accordance with a second aspect of the disclosure, an impact resistant tool comprises an active end to drive a fastener. The active end includes a body defining an axis. A bore is in the body to receive a shank. A pocket is formed in the body to receive a damping mechanism. A shank is to be secured with a power tool. The shank includes an end to engage the bore in the body. The shank includes a pocket to receive the damping mechanism. The shank has a limited rotation with respect to the body. A damping mechanism is positioned in the pockets to provide dampening between the body and the shank caused by dynamic torque loading of the tool. The active end may include a tool bit or tool bit holder. The active end may include a fastening bit, including a bit having a flat head, a socket head, a Phillips head, a Torx® head, a star head, a socket head or the like, or a drilling bit. The holder may include, e.g., a pivoting holder, a quick release holder, a drop and load holder, all including a receiving bore. The pockets further comprise at least one transition zone to receive material from the damping mechanism as it deforms in response to dynamic torque applied onto the tool. A mechanism for limiting rotation of the body with respect to the shank is coupled with the body and the shank. 
     According to a third aspect of the disclosure, a tool bit holder includes a shanking end to couple it with a powered driver. A body is coupled with the shanking end. A tool bit receiver is coupled with the body. The tool bit receiver includes a mechanism to receive a tool bit. A damping mechanism is internally positioned within the body. The damping mechanism provides torsional dampening between the shanking end and the tool bit receiver. The damping mechanism is coupled between the body and the tool bit receiver. The damping mechanism is of a shape memory material, e.g., a nitinol alloy. The damping mechanism enables torsional twisting with respect to one another. A bearing is positioned between the body and the tool bit receiver. 
     According to a fourth aspect of the disclosure, a screwdriving tool or holder includes an active end and a shanking end separated by a damping mechanism. The active end may include a fastening end, including an end having a flat head, a socket head, a Phillips head, a Torx® head, a star head, a socket head or the like, a drilling end, or a receptacle for receiving a fastening or drilling bit. The shanking end may be hexagonal with a groove to be received in an impact driver. The damping mechanism is a torsional biasing member. The biasing member may include a helical torsion spring, an energy absorbing material, a memory shape metal, or the like. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a perspective view of an impact resistant tool bit holder. 
         FIG. 2  is an exploded view of  FIG. 1 . 
         FIG. 3  is a cross-section view of  FIG. 1  along line  3 - 3  thereof. 
         FIG. 4  is a view like  FIG. 3  with the damping bar removed. 
         FIG. 5  is a perspective view along arrow  5  of  FIG. 2 . 
         FIG. 6  is a cross-section view of  FIG. 4  along line  6 - 6  thereof. 
         FIG. 7  is a cross-section view of  FIG. 4  along line  7 - 7  thereof. 
         FIG. 8  is a cross-section view of  FIG. 4  along line  8 - 8  thereof. 
         FIG. 9  is a cross-section view of  FIG. 4  along line  9 - 9  thereof. 
         FIG. 10  is a cross-section view of  FIG. 4  along line  10 - 10  thereof. 
         FIG. 11  is a cross-section view of  FIG. 4  along line  11 - 11  thereof. 
         FIG. 12  is a perspective view of a tool holder in accordance with the present disclosure. 
         FIG. 13  is a cross section view of  FIG. 12 . 
         FIG. 14  is an exploded perspective view of  FIG. 12 . 
         FIG. 15  is a plan view along arrow  15 . 
         FIG. 16  is a plan view of the tool bit receiver along arrow  16 . 
         FIG. 17  is a view like  FIG. 13  of a second embodiment. 
         FIG. 18A  is a perspective view of a screwdriver tool in accordance with the present disclosure. 
         FIG. 18B  is another perspective view of a screwdriver tool in accordance with the present disclosure. 
         FIG. 19  is a perspective view of a second embodiment of a screwdriving tool in accordance with the present disclosure. 
         FIG. 20A  is an exploded perspective view of another embodiment of a screwdriving tool. 
         FIG. 20B  is a cross section view along the embodiment of  FIG. 20A . 
         FIG. 21A  is an additional embodiment of a screwdriving tool in accordance with the present disclosure. 
         FIG. 21B  is a cross section view through  FIG. 21A . 
         FIG. 22  is a cross section view of an additional embodiment of a screwdriving tool in accordance with the present disclosure. 
         FIG. 23  is a graph of torque versus time. 
         FIG. 24  is a graph showing torque versus angle of twist for a damping mechanism. 
     
    
    
     DETAILED DESCRIPTION 
     Turning to  FIG. 1 , an impact resistant tool bit holder is illustrated and designated with the reference numeral  10 . The tool bit holder  10  includes an active end  12  and a shanking end  14 . The active end  12  may include a tool holder body  16  as illustrated or a tool may be unitarily formed with the holder body  16 . The shanking end  14  includes a shank  18  that has an overall hexagonal cross-section as well as a groove  20 . The shank  18  enables tool  10  to be positioned into a chuck or the like of a power tool or impact driver. 
     The holder body  16  has an overall cylindrical configuration illustrated with a hex shaped outer surface. The holder body  16  includes a first end  22  and a second end  24 . Also, the holder body  16  defines an axis  26  extending through the body. The first end  22  includes a bit receiving bore  28 . Likewise, the second end  24  includes a shank receiving bore  30 . The bit receiving bore  28  has a first portion  32  designed to receive a cylindrical magnet  34 . A second portion  36  is defined by hexagonal walls to receive a tool bit. Additionally, a groove  38  is positioned toward the end  22  to receive a ring  40 . The ring  40  cooperates with detents on the tool bits to maintain the tool bits in the second bore portion  36 . It should be understood that, the first end may instead have a bit retention mechanism such as a pivoting holder, a quick-release holder, or a drop and load holder, e.g., as illustrated in Assignee&#39;s U.S. Des. Pat. No. D589,319, issued Mar. 31, 2009, entitled “Pivoting Bit Holder” and Assignee&#39;s U.S. patent application Ser. No. 11/322,183, filed Dec. 29, 2005, entitled “Universal Tool Bit Shank, which are hereby incorporated by reference 
     The shank receiving bore  30  is defined by a right cylindrical wall  42  to receiving a portion of the shank  18 . The bores  28  and  30  terminate inside of the body  16 . A pocket  44  is formed between the bores  28  and  30 . The pocket  44  may be a blind pocket or it may extend from one bore to the other. The pocket  44  is defined by a plurality of walls  46 . The walls  46  are substantially identical and define a polygonal cross-section  48 , e.g., a rectangular or square cross-section. The pocket  44  receives a portion of the damping mechanism  50 . The walls  46  include recesses or transition portions  52 , which will be described in more detail below. The pocket  44  extends from a desired point along the wall  42  toward the second bore  30  as seen in  FIGS. 4 and 5 . 
     Additionally, the second end includes a receiving portion  58  to receive a cap  60  that holds the shank  18  and holder body  16  together. Also, the receiving portion  58  includes a pair of apertures  62  and  64  that receive pins  66  that couple with the shank  18  to limit the rotation of the shank  18  in the holder body  16 . 
     The shank  18  includes a first end  68  and the shanking end  14 . The first end  68  has an overall cylindrical outer surface in the shape of a right cylinder. The cylinder  70  includes a pair of smaller cylindrical portions  72  and  74  that receive bearing sleeves  76 . The bearing sleeves  76  enhance the rotation of the shank  18  with respect to the holder body  16 . The first end  68  includes a pocket  78 . The configuration of pocket  78  is like that of pocket  44 . Accordingly, pocket  78  includes walls  80  that define a bore of polygonal cross-section, e.g., rectangular or square. The pocket receives  78  a portion of the damping mechanism  50 . The walls  80  include recesses or transition portions  82 , which will be described in more detail below. The pocket  78  extends from a desired point along the wall toward the first end  68 . 
     Additionally, the cylindrical portion  74  includes a pair of recesses or stops  88 . The recesses  88  receive the pins  66  to limit the rotation of the shank  18  with respect to the body  16 . The recesses  88  act like a stop to prohibit movement once they encounter the pins  66 . Thus, the pins  66  and recesses  88  act as a rotational limiting device. 
     The damping mechanism  50  comprises a damping bar having a cross-sectional shape that is substantially similar to the cross-sectional shape of pockets  44  and  78 , e.g., substantially rectangular or square. The bar has a length set as a minimum that maintains the required cycled life. The damping mechanism  50  has surfaces  90  that are substantially flat planar surfaces. The damping mechanism  50  is positioned into the pockets  44  and  78  as illustrated in  FIG. 3 . In this position, the damping mechanism  50  maintains the shank  18  and holder body  16  together. The damping mechanism  50  is made of a material that provides for damping of the torsional forces that are applied to the holder  10 . For example, the damping mechanism  50  can be manufactured from a shape memory material, such as a nitinol alloy, an elastomeric material, a resin material, or a spring, such as a helical spring, leaf spring or the like. The damping mechanism enables the dissipation of stored energy as the mechanism returns to its original shape. 
     For example, if the bar is made from nitinol alloy, the energy may be dissipated as the material transitions from austentite to martensite and back to martensite. Initially, the crystal structure is in an austenite phase. When stress develops, the material transitions to martensite. Martensite is unstable and when the stress is removed it returns to the austenite phase. A torque versus angle of twist graph shows a typical nitinol torsion bar as it is twisted to some arbitrary angle (see  FIG. 24 ). It is then allowed to return to its original state. The area under the curve represents the energy required to twist the bar. Since the area under curve is greater during the twisting portion of the cycle than during the un-twisting portion, the energy has been dissipated. 
     The transition portions  52 ,  82  reduce the stress concentrations that develop in the torsion bar at the bar-shank interface and bar-holder interface. The gradual transitions from the rigidly mounted ends to the free section of the bar help support the bar as it is twisted to its maximum angle. Without the transition portions  52 ,  82 , the same region will take the entire load as it is twisted. But, with this type of support, the load is distributed over a much larger area. 
     The pocket walls  46  each include a recess or transition portion  52 . The recesses  52  are defined by a pair of surfaces  54  and  56 . The surfaces  54  and  56  extend outwardly from the axis of the holder body  16 . Surface  54  has an overall triangular shape and is positioned at the vertex of adjoining walls  46 . Surface  56  has an overall rectangular shape. It should be realized that other surface shapes may be used as long as they provide an increased surface area. The surfaces  54  and  56  are angled at acute angles with respect to the axis and walls  46 . The distance from the walls  46  to the surfaces  54 ,  56  increases towards the open end of the pocket as illustrated in  FIGS. 7 and 8 . Thus, the recess  52  defines a wedge shape void or transition space or zone. Accordingly, when dynamic torque is applied to the tool, the damping mechanism  50  twists. As this occurs, the damping mechanism  50  deforms so that the wedge shaped transition space  52 ,  82  receives material from the damping mechanism  50 . Thus, due to the increased surface area provided by the surfaces of the transition recesses or wedges  52 ,  82 , they prevent stress concentration to prevent prematurely breaking of the damping mechanism. 
     The pocket walls  80  each include a recess or transition portion  82 . The recesses  82  are defined by a pair of surfaces  84  and  86 . The surfaces  84  and  86  extend outwardly from the axis of the holder body  16 . Surface  84  has an overall triangular shape and is positioned at the vertex of adjoining walls  80 . Surface  86  has an overall rectangular shape. It should be realized that other surface shapes may be used as long as they provide an increased surface area. The surfaces  84  and  86  are angled at acute angles with respect to the axis and walls  80 . The distance from the wall  80  to the surfaces  84 ,  86  increases towards the open end of the pocket as illustrated in  FIGS. 9 and 10 . Thus, the recess  82  defines a wedge shape void or transition space or zone. Accordingly, when the dynamic torque is applied to the tool, the damping mechanism twists. As this occurs, the damping mechanism  50  deforms so that the wedge shaped transition space  52 ,  82  receives material from the damping mechanism  50 . The transition recesses or wedges  52 ,  82  prevent stress concentration to prevent prematurely breaking the bar. 
     Turning to the figures,  FIG. 12  illustrates a perspective view of another embodiment of a tool holder designated with the reference numeral  110 . The tool holder  110  includes a shanking end  112 , a body  114  and a tool bit receiving member  116 . The shanking end  112  has a generally hexagonal cross-sectional shape with a groove  118 . The shanking end  112  is to be received into an impact driver or drill motor. The body  114 , as well as the bit receiving member  116 , has an overall right circular cylindrical shape; however, any type of right cylindrical shape may be utilized. 
     The body  114  may be welded or connected with the shanking end  112 . Alternatively, the body  114  and shanking end  112  may be a unitary single piece. The body  114  includes a projecting portion  120 . The projecting portion  120  has a right cylindrical shape having a smooth outer surface. A circular bore  122  is formed into the projecting member  120 . The bore  122  extends through the projecting member  112  into the body  114  as shown in  FIG. 13 . At the terminus of bore  122 , a second bore  124  extends from it. The extending bore  124  has a polygonal, e.g., rectangular or square, cross-sectional shape. The polygonal cross-sectional shape receives a damper bar  126 . 
     The damping mechanism  126  has an overall polygonal, e.g., rectangular or square, cross-sectional shape with chamfered corners  128 . The damping mechanism  126  has a desired length as well as height and width. The damping mechanism  126  cross sectional dimension is sized so that it is press fit into the extending bore  124  to secure the damping mechanism  126  and the holder body  114  together. The damping mechanism  126  provides torsional twisting movement. The damping mechanism  126  is manufactured from a memory metal material, such as nitinol. This material provides desired dampening characteristics. The memory metal material provides plastic deformation when torque is present. It provides damping from the impact driver to the tool bit. When the torque is removed, the memory metal material springs back to its original position. 
     Further, other dampers may be utilized to provide the desired characteristics. These dampers may be springs of various types, such as helical, leaf or the like. Additionally, polymeric materials may be used. 
     The tool bit receiving member  116  has an overall right circular cylindrical shape. The tool receiving member  116  includes two bores  130  and  132 , one on each end of the tool bit receiving member  116 . The bore  130  is like the bore  122  including a circular cross-section bore. A polygonal, e.g., rectangular or square, shaped bore  134  extends from the terminus of the bore  30  (see  FIGS. 13 and 15 ). The polygonal shape bore  134  receives the damping mechanism  126  which is press fit into the bore  134 . Thus, the damping mechanism  126  secures the body  114  with the bit receiving member  116  and provides torsional twisting movement between the two. The bore  132  has an overall hexagonal cross section to receive a tool bit (see  FIG. 16 ). Additionally, a second larger bore  138  is formed at the end of the hexagonal bore  132 . The second bore  138  receives a C clip  36  that helps to retain the tool bit inside of the hexagonal bore  132 . 
     Additionally, other shaped bores may be used to receive the damping mechanism. The damping mechanism could be a right circular cylinder press fit into circular bores. Further, the damping mechanism could be a flat rectangular bar or leaf, press fit into a mating rectangular shaped bore. 
     A bearing sleeve  140  is positioned on the projecting portion  120  between the body  114  and the bit receiving member  116 . The bearing sleeve  140  is manufactured from an oil impregnated material such as bronze. However, it could be manufactured from various types of plastics or metal material depending upon the design. The bearing sleeve  140  provides for smooth rotation of the bit receiving member  116  with respect to the body  114 . The bearing sleeve  40  fits into the bore  130  of the bit receiving member  116 . 
     The damping mechanism  126  is positioned within the body and bit receiving member  116 . The damping mechanism  126  is press fit into the bore  124  of body  114  and bore  134  bit receiving member  116 . The damping mechanism  126  holds the two members together as illustrated in  FIGS. 12 and 13 . Additionally, the damping mechanism bar  26  provides torsional twisting movement between the two. While a press fit is used to hold these two members together, other types of mechanisms may be utilized to hold the two members together with respect to one another. The mechanism enables rotation of the body  114  and tool receiving member  116  with respect to one another while enabling a damping mechanism  126  or the like to provide the torsional spring to absorb the energy from the impact driver or drill motor. 
       FIG. 17  is a cross-section view like  FIG. 13  of a third embodiment of the disclosure. The tool holder  110  is the same as that of the second embodiment except the front bore  132  in the tool receiving member  116 ′ has been replaced with a unitary tool bit head  150 . The tool bit head  150  is illustrated as a Phillips bit, however, any type of bit such as a torque, flat, socket or the like could be positioned on the bit member  16 ′. The remaining elements have been identified with the same reference number since they are the same. 
       FIG. 18  illustrates a another embodiment of a screwdriving tool bit with a damper illustrated with reference numeral  210 . The screwdriving bit  210  includes an active end  212 , a shanking end  214  and a damping mechanism  216 . The active portion  212  is illustrated as a Phillips head screwdriver. It is understood that the Phillips head could be a flat head, Torx®, square, hexagon, star, socket, retaining member or the like tool bit head. The shanking end  214  is generally hexagonal shape with a groove  218  to be received into an impact driver or drill motor. 
     The damping mechanism  216  is illustrated as a torsional spring. The damping mechanism  216  is secured at one end to the active end  212  and at its other end to the shanking end  214 . The damping mechanism  216  is a discreet member and has desired characteristics to provide dampening to dissipate energy from the impact driver to the tool bit. The damping mechanism may be secured to the active end  212  and shanking end  214  by welding, adhesives, interference fit, crimping, or fitting as described above or the like. 
     Additionally, the damping mechanism  216 ′ could be manufactured from memory metal material, such as nitinol, that provides desired dampening characteristic. In this event, the nitinol portion is secured between the active end  212  and the shanking end  214  as illustrated in  FIG. 18B . The memory metal material provides plastic deformation when torque is present to provide dampening from the impact driver to the tool bit. When the torque is removed, the memory metal springs back to its original position. 
     Turning to  FIG. 19 , another embodiment like that of  FIG. 18A  is illustrated. Here, the screwdriving tool includes an active end  222 , a shanking end  224 , and a damping mechanism  226 . The damping mechanism  226  is like those previously discussed. Here, the active end  222  includes a retention member, such as a hex head socket. Additionally, the damping mechanism  226  may be secured to securement members  228  which, in turn, are secured with the shanking end  224  and the active end  222 . 
     Turning to  FIG. 20 , an additional embodiment is shown. Here, the embodiment includes a shanking end  234 , an active end  232  and a damping mechanism  236 . The shanking end  234  includes a bore  238 . Raised portions  242  divide the bore  238 . A series of valleys  244  are formed between the raised portions  242 . 
     The damping mechanism  236  has a plurality of ears  246  that fit into the valleys  244  so that the damping mechanism  236  meshes in the bore  238 . The body  248  of the damper includes a bore  250  to receive the active end  232 . The damping mechanism  236  is manufactured from a soft elastic material, such as rubber, to enable it to absorb and dissipate the energy. Thus, as the impact driver is activated and the shanking end rotates, the damping mechanism  236  is compressed to absorb the energy. Additionally, torque may be applied to the active end  232  when the driven fastener bottoms out into the workpiece. Accordingly, after the torque is released, the damping mechanism  236  rotates and returns to its original shape. 
     Moving to  FIG. 21 , an additional embodiment is illustrated. Here, the screwdriver tool includes a shanking end  252 , a sleeve  254 , and a damping mechanism  256 . The sleeve  254  includes a bore  258  to receive a screwdriver bit  60  as well as the damping mechanism  256 . The damping mechanism  256  includes an external configuration to fit within the sleeve bore  258 . The damping mechanism  256  includes two D-shaped ears  262  connected by a body  264 . The D-shaped ears  262  compress when torque is applied. The damping mechanism  256  also includes a bore  264  to receive the shanking end  252 . The shanking end  252  includes an elongated member  266  with two D-shaped members  268  that fit inside of the damping mechanism  256 . Thus, as the shanking end  252  or active end is rotated, the damping mechanism  256  absorbs and dissipates the energy to the sleeve  254 . 
       FIG. 22  illustrates an additional embodiment of the screwdriving tool. The tool includes a shanking end  272  and a body portion  274 . The shanking end  272  is unitarily formed with the body portion  274 . The body portion  274  includes a bore  276 . The bore  276  receives a helical spring  280 . Additionally, a helical thread  282  is formed in the wall of the bore  276 . A screwdriver bit  284 , with at least one projection  286  seated in the helical thread  282 , is positioned in the bore  276 . Thus, as the impact driver imparts torque onto the shanking end  272 , the shanking end  272  rotates which, in turn, rotates the body  274  to enable the screwdriver bit  284  to rotate. As this occurs, the projection  286  rides in the thread  282  so that the screwdriver bit  284  compresses the spring  280  dampening the torque. Additionally, torque may be applied to the screwdriver bit  284  when the driven fastener bottoms out into the workpiece. Accordingly, the screwdriver bit  284  would rotate along the thread  282  into the body portion  274 . Once the torque is released, the spring  280  forces the screw driver bit  284  outward, rotating the projection  286  along the helical path of the thread  282 , until the screwdriver bit reaches its original position. 
       FIG. 23  is a graph of torque versus time for the impact-driver, impact-driver after damping, and material breaking torque. The large peaks illustrates (solid line) the large driving torque from an impact driver in the range of 500 inch-lbs that cycles about every 2 milliseconds. The dashed line is the torque rating of the tool holder and tools in the range of about 200 inch-lbs. The lower peak (dot and dash line) is the drive torque with a tool holder or tool as described above on the impact driver cycling every 2 milliseconds. The peak torque does not exceed the torque rating of the tool or tool holder. Accordingly, the disclosed tool holder or tool reduces breakage of the tools or tool holders. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.