Abstract:
A clamping apparatus includes a clamp arm that is pivotable between a raised position and a lowered position, and a clamp spindle assembly that is adjustably positionable along the length of the arm. A magnet in the clamp spindle assembly magnetically engages the clamp arm with sufficient magnetic force to maintain the spindle assembly in a selected position as the clamp arm is moved between its raised and lowered positions, while allowing the position of the clamp spindle assembly to be manually adjusted.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     Not Applicable 
     
    
     FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not Applicable 
     
    
     BACKGROUND OF THE INVENTION  
       [0003]     This invention relates to clamping devices for holding a workpiece during assembly or manufacture. More specifically, it relates to an adjustable clamp having a locking clamp spindle that is adjustably positionable in a clamping arm, wherein the spindle can be maintained in a desired position in the arm by means of a permanent magnet fixed to the spindle.  
         [0004]     Clamps for holding workpieces typically include a clamping spindle that is installed in a pivotable clamp arm and that is adjustably positionable along the length of the clamp arm. The spindle is held in a desired position by means of spindle locking nuts or similar fasteners. To adjust the position of the spindle on the clamp arm, the nuts or fasteners are loosened, and the spindle is re-positioned. Movement of the clamp arm between its raised and lowered positions while the nuts or fasteners are loose can result in the spindle shifting from its desired position. Thus, adjustment of the spindle position to accommodate workpieces of differing shapes and thicknesses requires constant attention to assure that there is no shifting of the spindle when the clamp arm is moved before the spindle locking nuts are tightened. Even with the exercise of such caution, some inadvertent shifting frequently occurs, with resultant inconsistency of results.  
         [0005]     It would therefore be an advantage over the prior art to provide a clamp spindle positioning mechanism that allows the adjustment of the spindle position on the clamp arm, while maintaining a set position as the clamp arm is rotated between its raised and lowered positions.  
       SUMMARY OF THE INVENTION  
       [0006]     Broadly, the present invention is a clamping apparatus, of the type having a clamp arm that is pivotable between a raised position and a lowered position, and a clamp spindle assembly that is adjustably positionable along the length of the arm, wherein the improvement comprises a magnet in the clamp spindle assembly that magnetically engages the clamp arm with sufficient magnetic force to maintain the spindle assembly in a selected position as the clamp arm is moved between its raised and lowered positions, while allowing the position of the clamp spindle assembly to be manually adjusted.  
         [0007]     More specifically, the spindle assembly includes a threaded spindle that is threaded through a non-magnetic metal (preferably aluminum) block. Attached to the bottom end of the spindle is a clamp foot, and attached to the top end of the spindle is an actuation knob or handle for loosening or tightening the clamp foot against a workpiece as the knob or handle is turned, thereby threading the spindle into or out of the block, depending on the rotational direction. A permanent magnet is installed in a recess in the side wall of the block. The clamping arm comprises a hollow tube of magnetizable metal (e.g., steel), preferable of rectangular cross section, with an open first end and a second end that is pivotably attached to a clamping bracket for movement between the raised and lowered positions. The arm includes a longitudinal slot in each of its top and bottom walls. The interior of the arm defines a channel that is dimensioned to receive the block of the clamping assembly, and the longitudinal slots are dimensioned to allow the spindle to pass through both slots when the block is installed in the arm channel.  
         [0008]     The block is installed in the arm channel through the open arm end, and then the spindle is threaded into the block through the slot in the top wall of the clamp arm. When the bottom end of the spindle emerges through the slot in the bottom wall of the arm, the clamp foot is threaded onto the spindle. The magnet in the block is situated so that its is closely proximate one of the side walls of the arm, whereby the magnetic field established between the magnet and the arm maintains the block (and thus the spindle threaded through it) in any selected position, even while the clamp arm is rotated between its raised and lowered positions. If a new position of the spindle is desired, it can be moved manually within the arm channel without the need to loosen any nuts or fasteners.  
         [0009]     It will be appreciated that the clamping apparatus of the present invention provides a much simpler means for adjusting the spindle position, without the need for locking nuts or fasteners, whereby the chances for spindle shifting or slippage during arm movement are substantially reduced if not eliminated. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is an exploded perspective view of a clamp arm and spindle assembly of the type used in the improved clamping apparatus in accordance with the present invention;  
         [0011]      FIG. 2  is a cross-sectional view taken along line  2 - 2  of  FIG. 1 ; and  
         [0012]      FIG. 3  is a perspective view, partially in phantom, of an improved clamp in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]     Referring now to the drawings,  FIGS. 1 and 2  illustrate a clamp arm  10  and a clamp spindle assembly  40 , of the type used in an improved clamping apparatus  100  ( FIG. 3 ) in accordance with the present invention. The arm  10  comprises a hollow tube of a magnetizable (i.e., ferrous) metal (preferably a suitable structural steel) having an open first or clamping end  12  and second or pivoting end  14  that may be closed or open. The arm is preferably rectangular in cross-section, with a top wall  16 , a bottom wall  18 , and side walls  20  that define a rectangular interior channel  22 . A first longitudinal slot  24  is formed in the top wall  16 , and a second longitudinal slot  26 , in registry with the first slot  24 , is formed in the bottom wall  18 . The arm  10  may also be provided with a locking pin aperture  28  in one of the side walls  20 , and a registered pair of pivot pin apertures  30  in the side walls  20 , near the second end  14  of the arm  10 .  
         [0014]     The clamp spindle assembly  40  is mounted for longitudinal movement in the clamp arm  10 . The clamp spindle assembly  40  comprises a spindle block  42  having a threaded bore or passage  44  through its vertical dimension, and a spindle  46  threaded through the bore  44 . The block  42  is preferably made of a machinable metal, such as aluminum, or it may be made of any suitable metallic or non-metallic material. The spindle  46 , comprising a threaded rod that is threaded through the threaded bore  44 , has an upper end that protrudes through the top of the block  42 , and on which is threaded a handle or knob  48 . A lower end of the spindle  46  protrudes through the bottom of the block  44 , and a clamp foot  50  is threaded onto the lower end of the spindle  46 . The diameter of the spindle  46  is slightly smaller than the widths of the slots  24 ,  26  in the arm  10 , so that the spindle  46  can be slidably received in the slots  24 ,  26 , as described below.  
         [0015]     The block  42  has a recess in one side in which a permanent magnet  52  is fixed (as by a suitable adhesive). The magnet  52  is preferably made of an Nd—Fe alloy, such as NdFeB, but any suitable magnetic alloy may be used. The surface of the magnet  52  is preferably flush with the adjacent surface of the block  42 . The block  42  is dimensioned so that it slidably fits in the channel  22  of the arm  10 , with the exterior surfaces of the block  42  advantageously being in a slidable frictional fit against the interior wall surfaces of the channel  22 . Thus, the external dimensions of the block  42  are preferably just slightly smaller than the internal dimensions of the channel  22 .  
         [0016]     The spindle assembly  40  may be installed in the arm  10  as follows: The block  42  is inserted into the channel  22  through the open end  12 . The block  42  is oriented so that the magnet  52  is adjacent one of the side walls  20  of the arm  10 , and the threaded passage  44  is aligned with the slots  24 ,  26 . The spindle  46  is threaded into the threaded passage  44  through the upper slot  24 , preferable after the knob  48  has been threaded onto the upper end of the spindle  46 . The spindle  46  is threaded through the block  42  until the lower end of the spindle  46  emerges through the bottom of the block  42  and the lower slot  26 , after which the clamp foot  50  may be threaded onto the lower end of the spindle  46 .  
         [0017]      FIG. 3  shows the clamping apparatus  100  with the clamp arm  10  attached. Specifically, the second end  14  of the clamp arm  10  is pivotably attached to a clamp bracket  102  by means of a pivot pin  104  inserted through registering pivot pin journal holes (not shown) in opposite sides of the bracket  102 , and through the pivot pinjoumal apertures  30  in the arm  10  which are alignable with the journal holes in the bracket  102 . The arm  10  thus may be pivoted between a raised position and a lowered position, the latter being shown in  FIG. 3 . The arm  10  may be locked into its lowered position by means of a conventional spring-loaded locking pin (not shown), which engages the locking pin aperture  28  in the arm  10  through a registering aperture in one side of the bracket  102 . The locking pin may be disengaged from the locking pin aperture  28  by means of a locking pin knob  106 .  
         [0018]     In use, the longitudinal position of the spindle assembly  40  in the arm  10  is adjusted by manually moving the spindle assembly  40  longitudinally to a selected position between the ends of the slots  24 ,  26 . Once a longitudinal position is selected, the magnetic force created between the magnet  52  and the adjacent side wall  20  of the arm  10  will maintain the spindle assembly  40  in that selected position until the spindle assembly  40  is manually moved to another position, even if the clamp arm  10  is pivoted between its lowered and raised positions.  
         [0019]     Although a preferred embodiment of the invention has been described above, it will be appreciated that a number of variations and modifications may suggest themselves to those skilled in the pertinent arts. For example, the configuration and location of the magnet  52  described herein are exemplary only. Also, it may be advantageous, in certain applications, to have a pair of magnets, one on each side of the block  42 , rather than the single magnet shown in the drawings. Indeed, more than one magnet may be provided on each side of the block. These and other variations and modifications that may suggest themselves should be considered to be within the spirit and scope of the invention, as defined in the claims that follow.