Abstract:
A rotary worktable positioning structure used in a miter saw is disclosed to include a first positioning unit controllable by biasing a handle to lock the worktable to the machine base or to unlock the worktable for free rotation, and a second positioning unit controllable by rotating a switching wheel to move a lock pin into one of a number of locating holes on the periphery of the machine base and to further lock the worktable in one of a number of predetermined cutting angles.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a miter saw and more particularly, to a rotary worktable positioning structure for miter saw for controlling the positioning of the worktable. 
         [0003]    2. Description of the Related Art 
         [0004]    To facilitate adjustment of the clamping angle of the workpiece for enabling the workpiece to be cut obliquely, a miter saw has the workpiece carrying worktable rotatably mounted on the machine base, and is provided with a positioning structure for locking the workpiece to said machine base. This positioning structure comprises a screw rod coupled to the worktable. The screw rod can be rotated forwards and stopped against the periphery of the machine base to lock the worktable. It is inconvenient to lock the worktable to the machine base by means of rotating the screw rod. Further, when stopping the screw rod against the periphery of the machine base, the periphery of the machine base may be damaged. Further, this design does not allow the user to lock the worktable to the machine base in a specific cutting angle (for example, 15-degrees or 30-degrees) rapidly. 
         [0005]    Therefore, it is desirable to provide a rotary worktable positioning structure for miter saw that eliminates the aforesaid drawbacks. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention has been accomplished under the circumstances in view. It is one object of the present invention to provide a rotary worktable positioning structure for miter saw, which is easy to operate and, which positively locks the worktable of the miter saw in the desired cutting angle position. 
         [0007]    To achieve this and other objects of the present invention, the rotary worktable positioning structure is used in a miter saw having a machine base and a worktable e rotatably supported on the machine base. The rotary worktable positioning structure comprises a first positioning unit and a second positioning unit. The first positioning unit comprises a handle and a locating block. The handle is pivotally connected to the front side of the worktable with a first pivot pin, and turnable relative to the worktable between a lowered position and a lifted position. The locating block is stopped against the periphery of the machine base when the handle is in the lowered position. When the handle is in the lifted position, the locating block is kept apart from the periphery of the machine base. The second positioning unit comprises a switch wheel, a lock pin, and a plurality of locating holes formed on and spaced around the periphery of the machine base. The switch wheel is coupled to the first pivot pin, and turnable about the first pivot pin between an inward position and an outward position. The lock pin is engaged into one locating hole of the machine base when the switch wheel is in the inward position. When the switch is in the outward position, the lock ping is kept apart from the locating holes of the machine base. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is an elevational view of a miter saw constructed according to the preferred embodiment of the present invention. 
           [0009]      FIG. 2  is an exploded view of the worktable and the machine base of the preferred embodiment of the present invention. 
           [0010]      FIG. 3  is an enlarged view of a part of  FIG. 2 . 
           [0011]      FIG. 4  is a sectional view of a part of the present invention, showing the handle of the first positioning unit in the lowered position. 
           [0012]      FIG. 5  is a sectional view of a part of the present invention, showing the position arrangement of the torsional spring of the first positioning unit. 
           [0013]      FIG. 6  is similar to  FIG. 4 , showing the handle of the first positioning unit moved to the lifted position. 
           [0014]      FIG. 7  is an enlarged scale of  FIG. 6  when viewed from another side. 
           [0015]      FIG. 8  is a sectional view of a part of the present invention, showing the non-work status of the first positioning unit and the second positioning unit. 
           [0016]      FIG. 9  is a sectional view of a part of the present invention, showing the pin of the second positioning unit moved to the switching point of the link. 
           [0017]      FIG. 10  is similar to  FIG. 9 , showing the front end of the lock pin stopped against the periphery of the machine base. 
           [0018]      FIG. 11  is similar to  FIG. 10 , showing the front end of the lock pin engaged into one conical locating hole of the machine base. 
           [0019]      FIG. 12  is a sectional view of a part of the present invention, showing the first positioning unit and the second positioning unit in the locking position. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    Referring to  FIGS. 1 and 2 , a miter saw  100  is shown comprising a machine base  10 , a worktable  20  rotatably mounted on the top side of the machine base  10 , a fence  30  affixed to the machine base  10  with a screw bolt  32 , a fixture  40  fastened to the worktable  20 , and a saw blade assembly  50  coupled to the rear side of the worktable  20  and carrying a circular saw blade (not shown). When lowering the circular saw blade, the track of the circular saw blade defines with the bearing face  34  of the fence  30  a predetermined contained angle. This contained angle is indicated subject to the pointer  22  at the worktable  20  and the graduations  12  on the surface of the machine base  10 . This contained angle is referred hereinafter as “cutting angle”. 
         [0021]    The rotary worktable positioning structure of the present invention is installed in the front side of the worktable  20 , comprising a first positioning unit  60  and a second positioning unit  70 . The first positioning unit  60  provides a stepless positioning effect, i.e., allowing the worktable  20  to be positioned in any non-particular cutting angle. The second positioning unit  70  provides a rapid positioning effect to have the worktable  20  be positioned in one of a number of predetermined cutting angles, for example, 15-degrees, 30-degrees, etc. The structure and operation of the first positioning unit  60  are described at first as follows: 
         [0022]    Referring to  FIGS. 3 and 4 , the worktable  20  has a forwardly protruding mounting frame  24 . The mounting frame  24  comprises two wing panels  241  arranged in parallel, and a transverse panel  242  connected between the wing panels  241 . Each wind panel  241  has a first through hole  243  and a second through holes  244  for the passing of a first pivot pin  26  and a second pivot pin  28  respectively. One wing panel  241  is processed to provide a threaded through hole  245 . The first positioning unit  60  comprises a handle  62 , a limiter formed of a screw bolt  63 , a follower member  64 , a locating block  66 , and a return spring, for example, torsional spring  68 . 
         [0023]    The handle  62  has two lugs  621  bilaterally disposed at the front side. Each lug  621  has a pivot hole  622  for the passing of the first pivot pin  26  so that the handle  62  is pivotally connected to the mounting frame  24  of the worktable  20  and turnable about the first pivot pin  26  between a lowered position P 1  (see  FIG. 4 ) and a lifted position P 2  (see  FIG. 6 ). Each lug  621  has a bottom cam  623  (see also  FIG. 7 ), a plurality of ribs  624  disposed at one lateral side, and an open space  625  defined between each two adjacent ribs  624  The screw bolt  63  is threaded into the threaded through hole  245  of the wing plate  241  and engaged into one open space  625  of the adjacent lug  621 . 
         [0024]    The follower member  64  comprises a first panel  641 , a second panel  642  connected to the first panel  641  at right angles to show with the first panel  641  a L-shaped configuration, a through hole  643  in the connection area between the first panel  641  and the second panel  642  for the passing of the second pivot pin  28 , an actuation portion  644  formed of the outer wall of the first panel  641  and stopped against the bottom cam  623  of the handle  62 , and a mounting hole  645  extending through the bottom side of the second panel  642  remote from the first panel  641  for the passing of the locating block  66 . The locating block  66  has an elastic member  69  at the front end, forming a working end. 
         [0025]    The torsional spring  68  is sleeved onto the second pivot pin  28  before insertion of the second pivot pin  28  through the second through holes  244 , as shown in  FIG. 5 . The torsional spring  68  has one end stopped against the bottom side of the worktable  20 , and the other end stopped against the outer surface of the second panel  642  of the follower member  64 . The torsional spring  68  imparts a pressure to the follower member  64 , forcing the outer surface  644  of the first panel  641  into contact with the bottom cam  623  of each lug  621  of the handle  62 . 
         [0026]    After understanding of the structural features of the first positioning unit  60 , the stepless positioning functioning of the first positioning unit  60  is outlined hereinafter. 
         [0027]    When in the state shown in  FIGS. 4 and 5 , the handle  62  is in the lowered position P 1 . At this time, the bottom cams  623  of the lugs  621  of the handle  62  are stopped against the outer surface  644  of the first panel  641  of the follower member  64 , forcing the elastic member  69  of the locating block  66  to stop against the periphery  14  of the machine base  10 , prohibiting the worktable  20  from rotation. At the same time, the follower member  64  compresses the torsional spring  68 . When wishing the adjust the cutting angle, lift the handle  62  to change the position of the bottom cams  623 , as shown in  FIGS. 6 and 7 . At this time, the torsional spring  68  releases the preserved energy to bias the follower member  64  and the handle  62  to the position where one rib  624  is stopped at the screw bolt  63 , and therefore the handle  62  is positioned in the lifted position P 2 . Thus, the elastic member  69  of the locating block  66  is kept apart from the periphery  14  of the machine base  10 , allowing the worktable  20  to be freely rotated to the desired cutting angle position. After adjustment of the worktable  20  to the desired cutting angle position, the handle  62  is biased in the reversed direction to force the elastic member  69  of the locating block  66  against the periphery  14  of the machine base  10 , thereby locking the worktable  20  again. 
         [0028]    The structure and operation of the second positioning unit  70  are described hereinafter. 
         [0029]    Referring to  FIG. 8  and  FIG. 3 , the second positioning unit  70  comprises a switch wheel  72 , a link  74 , a support  76 , a lock pin  78 , a spring member  79 , and conical locating holes  16  on the periphery of the machine base  10 . Each conical locating hole  16  represents one specific cutting angle. 
         [0030]    The switch wheel  72  is a hollow member set between the two lugs  621  of the handle  62 , having an axle hole  721  for the passing of the first pivot pin  26  so that the switch wheel  72  can be turned about the first pivot pin  26  between an inward position S 1  and an outward position S 2 . Further, a pin  73  is inserted through the switch wheel  72 , forming a driving member convenient for manipulation by a person&#39;s fingers. 
         [0031]    The mounting frame  24  of the worktable  20  has two lugs  246  forwardly protruded from the transverse panel  242 . The link  74  is a L-shaped plate member suspending between the two lugs  246 , having a through hole  741  in the turning angle thereof. A third pivot pin  75  is inserted through the two lugs  246  and the through hole  741 . The outer edge  742  of the upper part of the link  74  forms a driven portion that is kept in contact with the pin  73 . The link  74  further has a switching point  744  near the end edge  743  of the upper part, and an elongated slot  745  in the lower part. 
         [0032]    The support  76  is a substantially U-shaped frame member invertedly affixed to the bottom side of the transverse panel  242  of the mounting frame  24 , having two parallel side panels  761  and a hole  762  in each side panel  761  for the passing of the lock pin  78 . The lock pin  78  has its body mounted with a retainer ring  781 , and its rear end provided with a clamping notch  782 , which receives the bottom end of the lower part of the link  74 . A pin  783  is inserted through the rear end of the lock pin  78  and the elongated slot  745  of the link  74  to pivotally couple the link  74  and the lock pin  78  together. Further, the lock pin  78  has a front end terminating in a cone head  784  that works as an engagement end. 
         [0033]    The spring member  79  is sleeved onto the lock pin  78  and stopped with its one end against the retainer ring  781  and its opposite end against the inner surface of one side panel  761 . The spring member  79  imparts a biasing force to the outer edge  742  of the upper part of the link  74  into contact with the pin  73 . 
         [0034]    After understanding of the structural features of the second positioning unit  70 , the particular angle positioning functioning of the first positioning unit  60  is outlined hereinafter. 
         [0035]    When in the state shown in  FIG. 8 , the first positioning unit  60  and the second positioning unit  70  do no work relative to the worktable  20 , and therefore the worktable  20  is freely rotatable relative to the machine base  10 . When wishing to position the worktable  20  in a particular cutting angle, rotate the worktable  20  relative to the machine base  10  to the desired angle subject to the assistance of the pointer  22  and the graduations  12 . Thereafter, turn the switch wheel  72  in direction toward the inward position S 1 , as shown in  FIG. 9 . When the pin  73  moved over the switching point  744 , the spring force of the spring member  79  moves the lock pin  78  toward the machine base  10  to force the cone head  784  of the lock pin  78  against the periphery  14  of the machine base  10 , as shown in  FIG. 10 . At this time, adjust the worktable  20  to let the cone head  784  of the lock pin  78  be forced into the assigned conical locating hole  16  that represents the desired cutting angle position, as shown in  FIG. 11 , and therefore the worktable  20  is positioned in the desired cutting angle position. When wishing to release the worktable  20  from the constraint, reverse the switch wheel  72  in the direction toward the outward position S 2  to have the pin  73  moved over the switching point  744  again, keeping the lock pin  78  away from the conical locating holes  16 . At this time, the operator needs to lower the handle  62 , as shown in  FIG. 12 , providing a double-locking positioning effect. 
         [0036]    Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.