Abstract:
A bolt assembly ( 100 ) enables a user to change a circular blade ( 160 ) on a power tool ( 200 ) without the use of tools. The bolt assembly includes a bolt body ( 110 ) that has a bolt head ( 132 ) and a shank ( 136 ) that extends axially from the bolt head. The bolt head has a shoulder and the shank has external threads that mate with a threaded bore ( 220 ) of a drive shaft ( 212 ) of the power tool. A grip body ( 130 ) is formed circumferentially around the bolt head to facilitate rotation of the bolt body by the user&#39;s hand. An upper washer ( 114 ), a needle roller thrust bearing ( 116 ), and a lower washer ( 118 ) are positioned on the bolt head and retained with a retaining clip ( 120 ). The bolt body is rotated to press the lower washer against a clamping surface of the circular blade. The bolt assembly permits rotation of the lower washer relative to the bolt body without rotating the bold body.

Description:
[0001]    This application claims the benefit of U.S. Provisional Application No. 61/908,423, filed Nov. 25, 2013, the entire contents of which are hereby incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The disclosure relates generally to a power tool and, more particularly, to a tool free bolt system for securing a circular blade to a power tool. 
       BACKGROUND 
       [0003]    A miter saw generally includes a circular blade having a centrally located hole for mounting the blade to a rotatable shaft. The blade is conventionally mounted to an end of the rotatable shaft in compression between an inner flange and outer flange or washer and held by a conventional arbor bolt threaded into a threaded bore in the shaft. 
         [0004]    Circular saw blades must be replaced periodically due to blade wear and to accommodate a variety of different cutting uses. In order to install or remove a blade, a wrench typically must be used to supply sufficient torque to remove the bolt from the shaft. Inconveniences are incurred by the use of a conventional bolt to mount a circular saw blade. For example, the task of obtaining an appropriate wrench can be time consuming, and using the wrench can be cumbersome. Additional inefficiencies can result if the wrench is misplaced between blade changes. 
         [0005]    Some existing tool free blade change systems suffer from problems during operation of the saw. A miter saw generates substantial torque when the saw blade rotationally accelerates or decelerates. Such acceleration or deceleration can occur, for example, when the rotating blade first contacts a material to be worked or when the blade first completes a cut and is no longer in contact with the material. In some instances, the saw can generate enough torque to self-tighten the blade change system holding the blade on the saw. It is therefore desirable to provide an improved mechanism for removing and replacing a circular saw blade. Additionally, it is desirable to provide a system that enables a quick and easy removal of the circular saw blade without additional tools. 
       SUMMARY 
       [0006]    A bolt assembly for securing a tool disc to a power tool, in one embodiment, includes a bolt body having a bolt head and a shank extending axially from the bolt head, the bolt head having a bearing surface that faces the shank and the shank having external threads that are matably receivable in a threaded bore of a shaft of the power tool, a grip body extending radially from and circumferentially about the bolt head, the grip body being configured to rotate the bolt body, a lower washer positioned between the bearing surface and the shank, the lower washer being rotatable about the bolt head and having a contact surface configured to be pressed against a clamping surface of the tool disc, and a bearing positioned between the bearing surface and the lower washer, the bearing being configured to allow the lower washer to rotate relative to the bolt body without rotation of the bolt body. 
         [0007]    A power tool, in one embodiment, includes a rotatable drive shaft having a threaded bore, a circular blade mounted to the end of the drive shaft, an inner blade washer and an outer blade washer mounted on the drive shaft, the inner blade washer positioned on an inner side of the circular blade and the outer blade washer positioned on an outer side of the circular blade, and a bolt assembly configured to press the outer blade washer against the circular blade and the inner blade washer so as to secure the circular blade to the drive shaft, the bolt assembly including a bolt body having a bolt head and a shank extending axially from the bolt head, the bolt head having a bearing surface and the shank having external threads that are matably receivable in the threaded bore of the drive shaft, a grip body extending radially from and circumferentially about the bolt head, the grip body being configured to rotate the bolt body, a lower washer positioned between the bearing surface and the shank, the lower washer being rotatable about the bolt head and having a contact surface configured to be pressed against the outer blade washer, and a bearing positioned between the bearing surface and the lower washer, the bearing being configured to allow the lower washer to rotate relative to the bolt body without rotation of the bolt body. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a top-perspective view of a tool free bolt system according to the disclosure; 
           [0009]      FIG. 2  is a bottom-perspective view of the tool free bolt system of  FIG. 1 ; 
           [0010]      FIG. 3  is an exploded view of the tool free bolt system of  FIG. 1 ; 
           [0011]      FIG. 4  is a section view of the tool free bolt system of  FIG. 1  along a line A-A; 
           [0012]      FIG. 5  is a side-perspective view of the tool free bolt system of  FIG. 1  securing a circular blade to a miter saw; 
           [0013]      FIG. 6  is a section view of the tool free bolt system and a portion of the miter saw of  FIG. 5  along a line B-B shown from a side perspective; and 
           [0014]      FIG. 7  is a section view of the tool free bolt system and a portion of the miter saw of  FIG. 5  along the line B-B. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the disclosure is thereby intended. It is further understood that the disclosure includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the disclosure as would normally occur to one skilled in the art to which this disclosure pertains. 
         [0016]      FIGS. 1-4  depict a tool free bolt system  100  according to the present disclosure. The bolt system  100  includes a main body  110 , a bolt  112 , an upper washer  114 , a thrust bearing  116 , a lower washer  118 , and a retaining ring  120 . With particular reference to the exploded view of  FIG. 3  and the section view of  FIG. 4 , the main body  110  includes an outer surface  122 , an inner cavity  124 , and an opening  126  extending from the inner cavity  124 . The inner cavity  124  is defined inside the main body  110 , and includes an annular inner surface  128 . The outer surface  122  is arranged around the outside of the main body  110  and is configured to enable a user to manually grip and twist the main body  110 . 
         [0017]    In the illustrated embodiment, the main body  110  may include a grip portion  130  surrounding a portion of the outer surface  122 . The grip portion  130  may be disposed about a periphery of the outer surface  122  along portions the main body  110  that a user would customarily grip in order to rotate the body about a longitudinal axis extending through bolt system  100 . In some embodiments, the grip portion  130  is a soft material with high surface friction, such as an elastomeric material, that enables the user to apply sufficient rotational force to the bolt system  100 . In other embodiments, the grip portion  130  includes grip features that are adhered onto or formed or cut into the portions of the outer surface  122 . The main body  110  and the grip portion  130  are sized and configured to be easily graspable and rotated by a user. In particular, the main body  110  is sized to produce a mechanical advantage to rotate the bolt  112 , as described herein. 
         [0018]    The bolt  112  includes a head  132 , which may include an internal hex  134 , and a threaded shank  136  extending from the head  132 . The head  132  includes an upper shoulder  138 , a lower shoulder  140 , an upper groove  142  spaced between the upper shoulder  138  and the lower shoulder  140 , and a lower groove  144  spaced from the lower shoulder  140 , as best seen in  FIG. 4 . The internal hex  134  is provided in the event the bolt  112  cannot be loosened by hand, in which case the user can loosen the bolt  112  with an appropriate tool or wrench. 
         [0019]    The lower groove  144  is configured to accommodate the retaining ring  120  and to hold the retaining ring  120  in a fixed position relative to the bolt  112 . The upper washer  114  is configured to contact the lower shoulder  140 , while the lower washer  118  is configured to contact the retaining ring  120 . The thrust bearing  116  is positioned between the upper and lower washers  114 ,  118 , and each of the upper washer  114 , the thrust bearing  116 , and the lower washer  118  are retained on the bolt  112  between the lower shoulder  140  and the retaining ring  120 . The retaining ring  120  may be in the form of a snap ring used to hold the bolt system  100  together. 
         [0020]    As best shown in  FIGS. 3 and 4 , the lower washer  118  includes an annular outer surface  146 , an upper recess  148 , a lower recess  150 , and a contact surface  151 . A portion of the lower washer  118  is configured to nest within the inner cavity  124  of the main body  110 . The overlapping portions of the annular outer surface  146  of the lower washer  118  and the annular inner surface  128  of the main body  110  are configured to slide freely relative to one another. In the illustrated embodiment, the upper washer  114  and the thrust bearing  116  may be positioned within the upper recess  148  of the lower washer  118 . The lower recess  150  is sized so that the lower surface  133  of the head  132  of the bolt  112  is to be flush with or beneath the contact surface  151  of the lower washer  118 . 
         [0021]    The main body  110  may be configured to be integral with portions of the head  132  of the bolt  112 . With particular reference to  FIG. 4 , and continuing reference to  FIGS. 1-3 , the wall forming the opening  126  of the main body  110  surrounds the upper groove  142 , the upper shoulder  138 , and portions of the head  132  above the upper shoulder  138  to form an interlocking connection between the main body  110  and the bolt  112 . In some embodiments, the head  132  may include one or more flat portions positioned about the periphery of the head  132  to enable further interlocking between the main body  110  and the bolt  112 . As a result of the integral, interlocking connection, the rotational motion of the main body  110  is transferred to the bolt  112  to enable the main body  110  and bolt  112  to rotate together so as to tighten the bolt  112  and to thereby produce the needed axial force to secure the blade against the inner blade washer  216  ( FIGS. 6 and 7 ). 
         [0022]      FIG. 5  shows the tool free bolt system  100  implemented to secure a circular blade  160  to an exemplary miter saw assembly  200 . The miter saw assembly  200  includes a base  202  and a turntable  204  that is rotatable on the base  202 . The miter saw assembly  200  further includes a cutting head  206  mounted on a cutting head support assembly  208 . The cutting head  206  (which may also be referred to herein as a “cutting assembly”) includes a motor  210  that is operable to rotate the circular saw blade  160  via a drive shaft  212  ( FIGS. 6 and 7 ). The cutting head support assembly  208  is attached to the turntable  204  and configured to support the cutting head  206  such that the cutting head  206  may move over the turntable  204  and perform cutting operations on a work piece supported by the turntable  204 . A rip fence  214  attached to the base  202  may be used to align a work piece thereon. 
         [0023]    The cutting assembly  206  includes a handle  226  to facilitate movement of the cutting assembly  206  in relation to the turntable  204 . The handle  226  is designed and dimensioned to be grasped by a human hand when performing a cutting operation. This allows the user to easily pivot the cutting assembly  206 . A switch (not shown) may be provided on the handle  226  to allow the user to easily energize and de-energize the electric motor  210  during a cutting operation. A lower blade guard  224  is rotatably mounted to the cutting head assembly  206 . The lower blade guard  224  is configured to rotate in a counterclockwise direction with respect to the cutting head assembly  206  when the cutting head assembly  206  is pivoted toward the turntable  204  thereby exposing the circular saw blade  160 . 
         [0024]      FIGS. 6 and 7  show section views of the tool free bolt system  100  and the miter saw assembly  200  through the longitudinal axis of the tool free bolt system  100 . With particular reference to  FIG. 7 , the circular blade  160  is mounted to the end of the drive shaft  212  of the miter saw assembly  200  between an inner blade washer  216  and an outer blade washer  218 . The threaded shank  136  of the bolt system  100  includes a plurality of threads configured to engage a threaded bore  220  of the drive shaft  212 . As explained in more detail below, the rotation of the threaded shank  136  of the bolt system  100  within the threaded bore  220  draws the contact surface  151  of the lower washer into compressive contact with the outer blade washer  218  and fixedly clamps the blade  160  between the inner and outer blade washers  216 ,  218 . 
         [0025]    In the illustrated embodiment, the threads of the bolt system  100  and of the bore  220  of the drive shaft  212  are arranged in a left-hand thread, by which is meant the bolt system  100  is tightened by turning the main body  110  counter-clockwise and loosed by turning the main body  110  clockwise. However, it should be appreciated that the system described herein can be applied to a bolt having a right-hand thread as well. It should further be appreciated that in a typical tool, the thread tightening direction of the threads is opposite to the direction of rotation of the drive shaft  212 , thereby producing a self-tightening effect. 
         [0026]    In operation, a blade  160  to be installed on the miter saw assembly  200  is positioned between the inner and outer blade washers  216 ,  218  on the drive shaft  212  of the miter saw assembly  200 . The tool free bolt system  100  is inserted into the threaded bore  220  of the drive shaft  212 . The user grasps the grip portion  130  of the main body  110  to turn the main body  110  in the counter-clockwise direction, or in the case of a left-hand thread, in the clockwise direction. 
         [0027]    The rotation of the threaded shank  136  of the bolt  112  within the threaded bore  220  moves the lower shoulder  140  of the bolt  112  in an axial direction towards the drive shaft  212 . The movement of the lower shoulder  140  urges the upper washer  114 , which in turn urges the thrust bearing  116 , which in turn bears against the lower washer  118  in the axial direction towards the drive shaft  212 . The continued rotation of the main body  110  of the bolt system  100  moves the contact surface  151  of the lower washer  118  into compressive contact with the outer blade washer  218  to secure the blade  160  in compression between the inner and outer blade washers  216 ,  218 . 
         [0028]    The tool free bolt system  100  disclosed herein has the advantage that no friction is generated between the lower surface  111  of the main body  110  and the outer blade washer  218  when the bolt system  100  is threaded into the drive shaft  212  because the main body  110  is offset by the lower washer  118 . If normal contact friction was to occur between the main body  110  and the clamping surface, such as in the case of some existing designs, at least some of the torque applied by the user would be offset by this friction. The user in this situation may not be able to generate enough torque to tighten the bolt with the proper pre-load, resulting in blade slippage between the blade washers during cutting. However, since the main body  110  of the bolt system  100  is spaced from the outer blade washer  218 , no friction is generated between the main body  110  and the blade washer, even when the lower washer  118  is compressed against the outer blade washer  218 . Moreover, the mating surfaces between the lower washer  118  and the main body  110  are configured for generally friction-free sliding, as described previously. 
         [0029]    The tool free bolt system  100  has the further advantage that the bolt system  100  is not prone to self-tightening. During cutting operations, the cutting force on the blade is transmitted via friction to the blade washer, which is then transmitted as torque to the bolt securing the blade on the saw. In some existing bolt systems, the torque transmitted to the bolt causes the bolt to self-tighten. When this occurs in a tool-free change system, the bolt can be tightened with significantly more torque than the user applied, making it very difficult or impossible to remove the bolt by hand. The thrust bearing  116  of the tool free bolt system  100  disclosed herein eliminates friction between the upper and lower washers  114 ,  118  and prevents the torque generated by the cutting load on the blade from being transferred to the bolt. In one embodiment, the thrust bearing  116  may include tapered rollers  117  that contact the upper and lower washers  114 ,  118 . The rollers  117  substantially eliminate any torque transmission between the two washers  114 ,  118 , whether during initial tightening of the bolt  112  or during operation of the saw assembly. 
         [0030]    In an alternative embodiment of the tool free bolt system, a low friction material may be used between the upper and lower washers  114 ,  118  in place of the thrust bearing  116 . The low friction material can include plastics such as Acetal (POM), Nylon (PA), or other polymers. The low friction material can also include metals such as brass or other oil impregnated sintered metals. In yet another embodiment of the tool free bolt system, a low friction coating, such as nickel or Teflon, is applied to the upper and lower washers  114 ,  118  to reduce the frictional contact therebetween and to substantially reduce or eliminate torque transmission between the washers  114 ,  118 . 
         [0031]    While the disclosure has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the disclosure are desired to be protected.