Abstract:
Embodiments of the present invention include a locking assembly for a power miter saw of the type which has a base and a table that is rotatably mounted on the base about a center pivot axis, comprising a pair of oppositely facing arcuate surfaces on the base spaced from and being concentric with the center pivot axis, a clamp attached to the table for engaging the arcuate surfaces to lock the table from rotating relative to the base by applying a clamping force to the arcuate surfaces and not to the center pivot axis, and an actuating mechanism for operating the clamp.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention generally relates to power tools that have a table that is rotatable on a base, and more particularly to a locking assembly for locking the table. 
         [0002]    Power miter saws have long been used to cut work pieces such as trim, molding and the like where precise angled cuts are made. Such miter saws generally have a base on which a rotatable table is mounted, the table being adjustable around a center pivot axis. A user can adjust the angle of the table relative to a fence, and a blade and motor assembly is generally attached to the table and can be lowered into a cutting position. It is common for the table to have angular indicia so that a user can quickly rotate the table to a desired angular position so that cuts can be made. 
         [0003]    Such miter saws have detents for commonly used angular positions such as 22½°, 45°, as well as others, and also have locking mechanisms for locking the table in a preferred predetermined position. 
         [0004]    All known miter saw locks have at least one of three undesirable characteristics. First, locking the miter angle can cause the table itself to bend, which can detrimentally affect the accuracy of miter cuts made by the saw. Second, locking the table can cause the preset miter angle to move, which can also affect the accuracy of the cut. Third, locking the table may cause the top surface of the table to go out of plane relative to the base. Any one of the three characteristics can have an adverse effect on the quality of the cuts made by the miter saw. 
         [0005]    With regard to the characteristic of the table bending, the location of the opposing forces that are produced during the locking action is the main cause of this. Moving the locking mechanism components closer to one another by reducing the span on the table can effectively reduce this characteristic. With regard to the miter angle movement, it is a common characteristic of many locking mechanisms to lock the miter angle by turning the screw against a stationary wall. This can cause the miter angle to move as the screw tightens. Tightening the lock knob will generally cause the table to rotate slightly in the counterclockwise direction, which can detrimentally affect precision cuts. An acceptable solution to overcome this characteristic is to have the screw tighten against an intermediate piece, which is effective if the piece is not allowed to rotate. Other designs have addressed this problem by using linkages and cams instead of screws to lock the miter angle. 
         [0006]    With regard to the out of plane table movement, there are no known locking assemblies that effectively address this problem or characteristic. All known miter lock designs utilize the pivot point of the table to the base to provide the opposing force when the miter locking assembly is engaged. For a freely moving pivot connection, there must be clearances in the pivot joint. When the miter lock assembly is engaged, the pivot joint is pushed to one side of the clearance, and that causes the table to move out of plane, relative to the base. 
       SUMMARY OF THE INVENTION 
       [0007]    Embodiments of the present invention include a locking assembly for a power miter saw of the type which has a base and a table that is rotatably mounted on the base about a center pivot axis, comprising a pair of oppositely facing arcuate surfaces on the base spaced from and being concentric with the center pivot axis, a clamp attached to the table for engaging the arcuate surfaces to lock the table from rotating relative to the base by applying a clamping force to the arcuate surfaces and not to the center pivot axis, and an actuating mechanism for operating the clamp. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a left front perspective view of a power miter saw which incorporates a first preferred embodiment of the present invention, and is shown with portions broken away to show a motor in a motor housing; 
           [0009]      FIG. 2  is a perspective view of the underside of the table of the saw shown in  FIG. 1 , particularly illustrating the first preferred embodiment of the locking assembly of the present invention; 
           [0010]      FIG. 3  is a view similar to  FIG. 2 , exploded to illustrate the components of the locking assembly; 
           [0011]      FIG. 4  is a perspective view similar to  FIG. 3  with components removed to reveal other portions of the structure of the locking assembly; 
           [0012]      FIG. 5  is a plane view of the base of the miter saw shown in  FIG. 1 ; 
           [0013]      FIG. 6  is a cross-section of a portion of the base, table and the first preferred embodiment of the locking assembly shown in cross-section taken generally through the center of the threaded rod of the locking assembly; 
           [0014]      FIG. 7  is a perspective view of the back of the threaded jaw portion of the first preferred embodiment of the locking assembly; 
           [0015]      FIG. 8  is another perspective view of the threaded jaw portion of the first preferred embodiment of the locking assembly; 
           [0016]      FIG. 9  is a perspective view of the non-threaded jaw component of the first preferred embodiment of the locking assembly; 
           [0017]      FIG. 10  is another perspective view of the non-threaded jaw component of the first preferred embodiment of the locking assembly; 
           [0018]      FIG. 11  is a perspective view of a retention plate of the first preferred embodiment of the locking assembly; 
           [0019]      FIG. 12  is a cross-section of a second preferred embodiment of a locking assembly shown in its locked position; 
           [0020]      FIG. 13  is a cross-section of the second embodiment of a locking assembly shown in its unlocked position; and 
           [0021]      FIG. 14  is a perspective view of a portion of the mechanism shown in  FIGS. 12 and 13 . 
           [0022]      FIG. 15  is a perspective view of a portion of a third preferred embodiment of a locking assembly; 
           [0023]      FIGS. 16 and 17  are perspective views of one of the locking jaws of the third embodiment shown in  FIG. 15 ; and 
           [0024]      FIG. 18  is a side view, partially in section of a fourth preferred embodiment of a locking assembly. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    Broadly stated, the present invention is directed to several preferred embodiments of a locking assembly for a power miter saw of the type which has a base and a table that is rotatably mounted on the base about a center pivot axis. The locking assembly embodiments comprise floating, parallel clamping mechanisms which are preferably provided on the rotatable table, that interact with a base to lock the table in a particular miter angle, with the locking assembly experiencing none of the undesirable characteristics or problems that have been previously described. By having two clamping surfaces that interact with a cooperative structure on the base, the floating, parallel clamping mechanism which has two clamping surfaces, isolate the locking forces to the clamp itself. Stated in other words, there are virtually no forces that are transferred to the pivot axis of the interconnection between the table and the base, which eliminates any out of plane movement when the locking assembly is engaged. Bending of the table is also eliminated, because the forces are concentrated over a very short span. 
         [0026]    Turning now to the drawings, and particularly  FIG. 1 , a miter saw, indicated generally at  10 , has a base  12  with a generally circular portion on which a rotatable table  14  is attached. A miter arm control assembly, indicated generally at  16 , is either integrally formed with the rotatable table  14  or is attached to it and is provided for adjusting the horizontal angular position of the table  14  for setting the miter angle for cutting a work piece that would be placed on the table  14 . 
         [0027]    A saw blade and motor assembly, indicated generally at  18 , is operatively connected to the table  14  by a linear guide mechanism, indicated generally at  20 . The saw blade and motor assembly  18  has an electric motor  22  that is operatively connected through a gear mechanism that drives a saw blade  26 , the gear mechanism not being shown but located within a housing portion  24 . The blade and motor assembly  18  is pivotable about a horizontal shaft  28 . A handle  30  is provided for use by an operator to bring the blade and motor assembly  18  from a rest position shown in  FIG. 1  where it is elevated relative to the table to a lowered cutting position if a work piece is placed on the table  14 . 
         [0028]    The miter arm control assembly  16  has a slot  32  that extends to the table  14  and enables the blade  26  to be lowered to a position below the top surface of the table  14  so that the blade can cut completely through the work piece during a cutting operation. The linear guide mechanism  20  has a pivot head  34  to which the shaft  28  is mounted and the pivot head  34  is connected to a pair of rods  36  that are slidable in a support frame  38  to provide a sliding action that extends the capacity of the saw. The combination of the support frame  38  pivoting about the table, and the table  14  pivoting about the base  12 , gives the saw a compound cutting action. The support frame  38  has a bottom portion  40  that is attached to and is pivotable around a bevel pivot shaft (not shown) that is supported by a rear portion of the table  14 . 
         [0029]    From the foregoing it should be understood that the support frame  38  which carries the linear guide mechanism  20  as well as the blade and motor assembly  18  will pivot around the bevel pivot shaft for the purpose of orienting the blade  26  at the appropriate bevel angle for making bevel cuts on a work piece that may be placed on the table  14 . The saw shown in  FIG. 1  is in a neutral position where vertical cuts are made, assuming that the table  14  is in a horizontal position. 
         [0030]    During operation, an operator places a work piece on the table  14 , brings the handle  30  down into cutting position after activating the motor  22  and makes a chop cut on the work piece. However, if a sliding cut operation is needed for increased capacity, the operator will typically use the handle  30  to pull the blade and motor assembly forwardly to some forward position where the work piece will be engaged, activated the motor and bring the handle down into a cutting position, and then push the handle  30  toward the work piece to cut it. 
         [0031]    With regard to the first preferred embodiment of the locking assembly, it is generally shown in  FIGS. 2-11 , which illustrates the embodiment principally being attached to the table  14 , that interacts with the base  12  shown in  FIG. 5 . The base has a generally semi-circularly shaped portion  50 , which is substantially similar in size to the table  14 , which is attached to the base portion and is rotatable about a center axis that is inserted into a center aperture  52 , which receives a bolt structure (not shown), which fits within the aperture  52 , as well as within a recess  54  in the bottom of the table  14  (see  FIG. 2 ). The base  12  has an annular recess  56  that extends from a left end  58  to a right end  60 , with the annular recess having a substantially constant width, and a depth of approximately ½ inch, thereby defining an inner locking surface  62  and an outer locking surface  64 , against which the locking assembly may contact to provide locking engagement of the table  14  relative to the base  12 . The base  12  also has several through openings  66 . They are provided to enable saw dust and cuttings to be expelled from the recess, and thereby not to interfere with the operation of the locking assembly. It is of course understood that the inner and outer locking surfaces  62  and  64  are concentric with the aperture  52  that defines the center pivot axis of the table  14  relative to the base  12 . 
         [0032]    The locking assembly is indicated generally at  70 , and is shown in  FIGS. 2-3  in connection with the table  14 , which is particularly configured to receive components of the assembly  70 . Turning initially to  FIGS. 2 and 3 , the assembly  70  has a threaded jaw, indicated generally at  72 , and an unthreaded jaw, indicated generally at  74 , which fit within a chamber  76 , having side walls  78  that are formed as a part of the table  14  that is preferably a metal casting. The chamber  76  is generally box-shaped, and has a front opening  80 , through which a threaded rod, indicated generally at  82 , may pass for engaging the threaded jaw  72 . The side walls  78  have a flat top  84  with apertures  86  in enlarged end portions thereof. A cover plate  88  is attached to the side walls  78  by screws  90  that are inserted into the apertures  86 . 
         [0033]    The rod  82  is connected to a rotatable knob  92  that enables a user to engage and disengage the locking assembly for locking the table  14  in the desired position. The rod  82  has a threaded inner end portion  94  that is configured to engage a threaded aperture  96  of the threaded jaw  72 . The threaded end portion  94  may not be threaded beyond that which is needed to cause the threaded jaw  72  to move through its movable range, and therefore, it may be smooth, i.e., unthreaded at  98 . The smooth, unthreaded portion  98  may be in contact with the inside surface of an aperture  100 , located in a bushing  102 , that is secured to the table  14  by screws  104 , that engage apertures  106 . The bushing  102  thereby provides lateral support to the rotatable rod  82 . 
         [0034]    The general operation of the locking assembly shown in  FIGS. 2 and 3 , is that the rotation in the clockwise direction will cause the rod  82  to translate through the threaded aperture  96  of the threaded jaw  72  causing the end  108  to contact surface  146  (see  FIG. 9 ) of unthreaded jaw  74 . The threaded jaw  72  has a contact surface  110  that is designed to contact the outer locking surface  64  of the annular recess  56 , and the unthreaded jaw  74  has a contact surface  112  that is positioned to abut the inner locking surface  62  of the base  12 . Further turning of the rod will cause unthreaded jaw  74  to move to the right until surface  112  of the unthreaded jaw makes contact with locking surface  62  of the base  12 . Further rotation of the rod  82  will cause the threaded jaw  72  to move to the left as viewed in  FIG. 3  until the locking surface  110  of threaded jaw  72  makes contact with locking surface  64  of base  12 . Further rotation of the rod  82  will cause the surfaces  110  and  112  to separate from one another into locking engagement with the inner and outer locking surfaces  62  and  64 . 
         [0035]    In this regard, the contact surfaces  110  and  112  are curved so that they have the same curvature as the locking surfaces  62  and  64 . Thus, the surface  110  has a convex curvature corresponding to the curvature of the locking surface  64 , and the contact surface  112  is concave to conform to the shape of the contact surface  62 . As will be hereinafter explained, the threaded jaw  72  nests within a portion of the jaw  74 , so that it is slidable relative thereto, and both jaws  72 ,  74  float within the annular recess  56  when they are not engaged. 
         [0036]    Thus, the rod  82  is capable of axial movement, in addition to its rotation movement, so that the contact surfaces of the jaws tend to have equalized forces when they are moved into an engaged or locking position, as shown in  FIG. 6 . A spring  114  is provided, and it has a diameter slightly larger than the rod end  94 , which fits inside of the spring. One end thereof also fits around a cylindrical boss  116 , and the opposite end around another cylindrical boss  118 , on the threaded jaw  72 . Since the bushing  102  is stationary, the spring tends to push the threaded jaw  72  away from the bushing  102 , which biases the threaded jaw  72  away from the outer locking surface  64  of the annular recess  56 . 
         [0037]    Similarly, a spring  120  is interposed between a wall  122  and an annular recess  124  in the right end of the unthreaded jaw  74 , as best shown in  FIG. 6 . This tends to bias the jaw  74  to the left, as shown in  FIGS. 3 and 6 , and disengage the contact surface  112  from the inner locking surface  62  of the annular recess  56 . Thus, when the threaded rod  82  is backed off, i.e., it is moved in the counter-clock-wise direction, the jaws  72  and  74  will be urged to maintain contact with one another, but will disengage the contact surfaces from the annular recess  56 . 
         [0038]    The jaws  72  and  74  are preferably made of steel, and the curved contact surfaces  110  and  112  are provided to conform to the shape of the annular recess  56 , so that when the locking assembly is engaged to lock the table  14  to the base, the jaws will not deform the table, which is preferably an aluminum casting. 
         [0039]    Since the jaws  72  and  74  slide within the table  76 , a flat, steel wear plate  126  is provided to minimize wear that would otherwise be experienced by the table  14 . Referring to  FIG. 4 , the bottom surface of the chamber  76  is provided with a plurality or raised ribs  128 , as well as a raised square portion  130  that defines a stop for the jaw  72 . The wear plate  126  has a cut-out portion  131  so that it can rest on the raised ribs  128 . 
         [0040]    As is best shown in  FIGS. 3 ,  7  and  8 , the threaded jaw  72  has a lower base portion  132  from which a transverse upper portion  134  extends and which has the contact surface  110 . The jaw  72  has side walls  136  that extend from the base portion upwardly to the upper portion and define the width of the jaw. The base portion  132  is formed with a pair of opposite horizontal shelves  138  as well as outwardly extending plane portions  140 . The jaw  72  also has a pair of reinforcing ribs  142  for strengthening the upper portion  134 . 
         [0041]    Referring to  FIGS. 3 ,  9  and  10 , the unthreaded jaw  74  is shown and has a base portion  142  with an upper portion  144  that has the contact surface  112  in the outer face thereof. The annular recess  124  is provided in the contact surface  112  for receiving the spring  120 . The interior vertical face  146  presents a surface for contact by the end  108  of the rod  82 . The outer side walls  148  define the width of the jaw  74  and a central opening located between interior walls  150  has a width that is slightly larger than the raised square  130  in the bottom of the chamber  76 . A lower shelf  152  is provided on each side of the opening and an upper shelf  154  is provided immediately adjacent to the shelf  152 . The upper shelf  154  has a curved end portion  156  that has the cooperative shape to the flange  140  of the threaded jaw  72 . As previously mentioned, the two jaws  72  and  74  nest together with one another and are also slidable with one another. The threaded rod  82  has an axis that extends through the aperture  100  of the bushing  102 , the spring, the aperture  96  of the jaw  72 , and the annular recess  124  in the jaw  74 . Thus, the force is applied along this axis through these various components. 
         [0042]    The top flange  140  of the jaw  72  slides on the upper shelf  154  of the jaw  74  and the shelves  138  of the jaw  72  slides on the lower shelf  152  of the jaw  74 . The top flange  140  transfers the load from shelf  154  of the unthreaded jaw  74  to the threaded rod  82  rather than the cover plate  88  when the locking assembly is tightened to lock the table  14 . Also, the end surface  108  of the threaded rod  82  contacts the lower part of the interior face  146  of the upper portion  144  and thereby minimizes the tipping moment that may be produced. 
         [0043]    The cover plate  88  has a generally square shaped, larger cutout  158  that has a width corresponding to the distance between the side wall  148  and a narrower cutout  160  that is only slightly larger than the width between side walls  136  of the jaw  72 . The cover plate  88  is provided to retain the jaws within the chamber, particularly during shipment of the miter saw. 
         [0044]    A second preferred embodiment for locking the table to the base is shown in  FIGS. 12-14 , with this embodiment including a scissors mechanism, indicated generally at  170 , and shown in perspective in  FIG. 14  in diagrammatic form. The scissors mechanism  170  has a first clamp jaw  172  and a second clamp jaw  174  that are pivotally attached to one another by a pivot shaft  176 . The top end of the clamp jaw  172  has a threaded nut  178  that is pivotally mounted on shaft  180  to an upper end  182  of the clamp jaw  172 . Similarly, the second clamp jaw  174  has a pivotable nut  184  that is connected to an upper end  186  of the clamp jaw  174  by a shaft  188 . Both of the nuts  178  and  184  engage threads on the locking rod  82  and the threads of the rod that engage the threads of the nut  184  are opposite to the threads on the rod portion that engages the nut  178 . Thus, because of the opposite threads, rotation of the locking rod  82  in one direction will cause the nuts to move away from one another and in the opposite direction move toward one another. When the upper part ends  182  and  186  of the respective jaws  172  and  174  move toward one another, lower ends  190  and  192  move away from one another. These ends also have a respective clamp pads  194  and  196  that are respectively pivotally connected to lower ends  190  and  192  by shafts  198  and  200 . 
         [0045]    The scissor mechanism  170  is carried by the shaft  82 , which as shown in  FIGS. 12 and 13  is slidably mounted in transverse downward extensions  202  and  204  of the table  14 . This enables the rod  82  to move in its axial direction so that the lower part of the scissors mechanism can adjust itself to equalize the forces applied to left and right vertical walls  206  and  208  of a clamp pocket  210  formed in the base  12 . The axial position of the rod  82  is also centered by the presence of compression springs  212  and  214  that bear against one of the nuts  178  and  184  and the adjacent extension  202  and  204 . 
         [0046]    As shown in  FIG. 13 , the pads  194  and  196  are not engaged with the vertical walls of the pocket  210  whereas in  FIG. 12 , they are in a locking position. It should be also understood that the outer faces  216  and  218  of the pads are preferably curved to conform with the curvature of the pocket so that the major surface of the outer faces will be in contact with the associated vertical wall. In this regard, it should be understood that the pocket  210  is concentric with the axis of the table  14  as was the case for the first embodiment as shown in  FIG. 5 . 
         [0047]    A third preferred embodiment of the present invention is shown in  FIGS. 15 ,  16  and  17  wherein a threaded jaw  72 ′ is shown to be substantially similar in its overall configuration except for the presence of opposed cam slots  220  which cooperate with a rod  82 ′ which has at least one and preferably a pair of radially oriented pins  222  that engage the cam slots  220 . Preferably, through the course of an approximate quarter turn, the rod  82 ′ moves the threaded jaw  72  in the axial direction of the rod  82 ′ between its locked and unlocked position. The amount of axial travel through the rotation of a quarter turn is a function of the angle of the slots  220  as is known to those of ordinary skill in the art. The angle can be determined to provide the correct amount of axial movement of the jaws  72 ′ and  74 ′ relative to one another to achieve the desired locking action. As with the first preferred embodiment shown in  FIGS. 1-11 , there is no appreciable force applied to the table in a radial direction when the table is locked to the base by the locking mechanism. 
         [0048]    Yet a fourth preferred embodiment is shown in  FIG. 18  wherein a cam  224  is mounted to a rotatable shaft  226  that is preferably mounted to a connecting portion (not shown) that is a part of the jaw  72 ″. The rotation of the shaft  226  and the cam  224  will cause the cam to contact surface  228  of the jaw  74 ″ and cause the two jaws  72 ″ and  74 ″ to move away from each other so that their respective contact surfaces  230  and  232  will engage vertical surfaces  234  and  236  of a clamp pocket  238  and lock the table  14  to the base  12 . 
         [0049]    While various embodiments of the present invention have been shown and described, it should be understood that other modifications, substitutions and alternatives are apparent to one of ordinary skill in the art. Such modifications, substitutions and alternatives can be made without departing from the spirit and scope of the invention, which should be determined from the appended claims. 
         [0050]    Various features of the invention are set forth in the following claims.