Abstract:
A clamping device having a C shaped frame and anvils which cannot rotate while applying a clamping force is disclosed. One anvil is affixed to the C shaped frame while the second anvil is mounted to a drive tube which telescopes within a guide tube fixed to the frame. The conformal shapes of the guide and drive tubes prevent rotation as compressive force is applied to a work piece placed between the two anvils.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to clamping devices wherein the work piece is held between two adjustable anvils. Specifically, the invention comprises a “C clamp” having two adjustable anvils that maintain a fixed, non-rotating relationship as the work piece is clamped between them. 
     2. Description of the Related Art 
     C clamps are commonly used hand tools used to hold or immobilize a work piece between two adjustable anvil surfaces. Please refer to  FIG. 1  (prior art). In C clamps of the prior art, one anvil  104  is rigidly attached to the C shaped frame  102 , and the movable anvil  106  is mounted on a screw device  110  which rotates via handle  112  to direct the movable anvil  106  surface toward the fixed anvil  104 . The movable anvil  106  is typically mounted on a ball joint  108  which allows the anvil  106  to stop rotating after contact with the work piece is engaged, theoretically allowing compression of the work piece without transferring a rotational torque. However, in actual usage, the friction generated by the increased clamping pressure causes the ball joint to freeze up, imparting torque to the work piece. This often causes the clamp to “walk” off the work piece and limits the amount of compression force that can be applied. 
     What is needed is an improved clamping device wherein both anvil surfaces remain fixed, maintaining a non rotating relationship as the work piece is clamped between them. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a clamping device including a C shaped frame, the C shaped frame terminating in a first end surface and a second end surface, the first end surface being oriented approximately 90 degrees from the second end surface; a fixed anvil, the fixed anvil attached to the first end surface of the C shaped frame; a guide tube having a rectangular shape, the guide tube having a first open end, a second open end, an inner surface and an outer surface, the outer surface of the guide tube attached to the second end surface of the C shaped frame; a drive tube having a rectangular shape, a first open end, a second open end, and an outer surface, the outer surface of the drive tube conformal in shape with the inner surface of the guide tube, the drive tube residing within the guide tube, a portion of the drive tube extending through the first open end of the guide tube, the outer surface of the drive tube in contact with the inner surface of the guide tube in at least two opposing locations. The invention also provides a movable anvil attached to and enclosing the first open end of the drive tube; a threaded collar attached to and enclosing the second open end of the drive tube, the threaded collar having a threaded bore; a screw device having a threaded portion extending through and engaging the threaded bore of the threaded collar; a retaining collar, attached to and enclosing the second open end of the guide tube, the retaining collar operative to hold a position of said screw device fixed relative to said guide tube while allowing free rotation of said threaded portion of said screw device within said threaded bore of said threaded collar. 
     It is another object of the present invention to provide a clamping device including a C shaped frame, the C shaped frame terminating in a first end surface and a second end surface, the first end surface being oriented approximately 90 degrees from the second end surface; a fixed anvil, the fixed anvil attached to the first end surface of the C shaped frame; a guide tube having a hexagonal shape, the guide tube having a first open end, a second open end, an inner surface and an outer surface, the outer surface of the guide tube attached to the second end surface of the C shaped frame; a drive tube having a hexagonal shape, a first open end, a second open end, and an outer surface, the outer surface of the drive tube conformal in shape with the inner surface of the guide tube, the drive tube residing within the guide tube, a portion of the drive tube extending through the first open end of the guide tube, the outer surface of the drive tube in contact with the inner surface of the guide tube in at least two opposing locations. The invention also provides a movable anvil attached to and enclosing the first open end of the drive tube; a threaded collar attached to and enclosing the second open end of the drive tube, the threaded collar having a threaded bore; a screw device having a threaded portion extending through and engaging the threaded bore of the threaded collar; a retaining collar, attached to and enclosing the second open end of the guide tube, the retaining collar operative to hold a position of said screw device fixed relative to said guide tube while allowing free rotation of said threaded portion of said screw device within said threaded bore of said threaded collar. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be better understood when consideration is given to the following detailed description thereof Such description makes reference to the annexed drawings, wherein: 
         FIG. 1  (Prior Art) is a side view of a C clamp of the prior art. 
         FIG. 2  is a cross section view of a clamping device in accordance with embodiments of the present invention; 
         FIG. 3   a  is a side view of a clamping device in accordance with a first embodiment of the present invention; 
         FIG. 3   b  is a partial cross section view through section B-B of  FIG. 2 , in accordance with the first embodiment of the present invention; 
         FIG. 3   c  is a partial cross section view though section A-A of  FIG. 2 , in accordance with the first embodiment of the present invention; 
         FIG. 3   d  is a side view of the component parts of the clamping device of  FIGS. 3   a - c,  in accordance with the first embodiment of the present invention; 
         FIG. 4   a  is a side view of a clamping device in accordance with a second embodiment of the present invention; 
         FIG. 4   b  is a partial cross section view through section B-B of  FIG. 2 , in accordance with the second embodiment of the present invention; 
         FIG. 4   c  is a partial cross section view though section A-A of  FIG. 2 , in accordance with the second embodiment of the present invention; 
         FIG. 4   d  is a side view of the component parts of the clamping device of  FIGS. 4   a - c,  in accordance with the second embodiment of the present invention; 
         FIG. 5   a  is a side view of a clamping device in accordance with a third embodiment of the present invention; 
         FIG. 5   b  is a partial cross section view through section B-B of  FIG. 2 , in accordance with the third embodiment of the present invention; 
         FIG. 5   c  is a partial cross section view though section A-A of  FIG. 2 , in accordance with the third embodiment of the present invention; and 
         FIG. 5   d  is a side view of the component parts of the clamping device of  FIGS. 5   a - c,  in accordance with the third embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  (Prior Art) is a side view  100  of a C clamp of the prior art. Details have been covered in the Background section of this disclosure above. 
       FIG. 2  is a cross section view  200  of a clamping device in accordance with embodiments of the present invention. The present invention includes an outer guide tube  210  attached to C shaped frame  202 . A fixed anvil  204  is attached to frame  202 . A movable anvil  206  and threaded collar  214  are attached to drive tube  208 . Drive screw device  216  engages threaded collar  214  and is held in place by retaining collar  218  attached to outer guide tube  210 . Anvil  206  is moved relative to anvil  204  by the rotation of screw device  216  via handle  212 . Rotation of anvil  206  relative to anvil  204  is prevented by the shape and conformal contact of guide tube  210  with drive tube  208 . The drive tube  208  “telescopes” out of guide tube  210  as torque is applied to handle  212 . As a work piece (not shown) is clamped between fixed anvil  204  and movable anvil  206 , no rotational torque is applied to the work piece, allowing the maximum amount of clamping force to be applied without having the clamp “walk off” the work piece. Please see the embodiments disclosed below. 
     The outer guide tube and fixed anvil  204  are attached to frame  202  preferably by welding, but other process well known to those skilled in the art, such as glues, screws or rivets (not shown) may also be employed. Alternatively, anvil  204  may be an integral part of frame  202  (as opposed to two attached parts) via a casting or machining. Movable anvil  206  and threaded collar  214  are attached to drive tube  208  preferably by welding, but the other techniques mentioned above may also be applied. Further, either the anvil  206  or the threaded collar may be integrally cast (or machined from bar stock) as part of drive tube  208 . Retaining collar  218  is attached to outer guide tube preferably by welding. 
       FIG. 3   a  is a side view  300  of a clamping device in accordance with a first embodiment of the present invention. In this embodiment drive tube  302 , guide tube  304  and retaining collar  306  have a square shape. The conformal fitment of the drive tube  302  within guide tube  304  prevent rotation of anvil  206  as anvil  206  is moved toward anvil  204 . FIG.  3   b  is a partial cross section view  301  through section B-B of  FIG. 2 . Retaining collar  306  is composed of two parts  306   a  and  306   b , to allow assembly of screw device  216  within the guide tube  304  and drive tube  302 . Retaining collar  306 , while fixed to guide tube  304 , allows free rotation of screw device  216 .  FIG. 3   c  is a partial cross section view  303  though section A-A of  FIG. 2 . In this view, the relationships of the guide tube  304 , drive tube  302 , and drive screw device  216  are shown. A portion of threaded collar  308  is also visible.  FIG. 3   d  is a side view  305  of the component parts of the clamping device of  FIGS. 3   a - c . Screw device  216  has a threaded portion  216   a  that engages threaded collar  308 , threaded collar  308  being affixed to drive tube  302  at joint (surface)  312 . Threads may be “left hand” or “right hand”, depending on the desired direction of rotation. For example, a left hand thread would be desirable to produce a clamping action of the anvils with a clockwise rotation of handle  212 , as viewed from the bottom of the clamp. Screw device  216  is fabricated to provide a recessed bearing surface  216   b  that allows free rotation of device  216 , while also holding the screw device  216  in position within guide tube  304  via engagement with retaining collar  306 . Retaining collar  306  ( 306   a  and  306   b ) are affixed to guide tube  304  at joint (surface)  310 . 
       FIG. 4   a  is a side view  400  of a clamping device in accordance with a second embodiment of the present invention. In this embodiment drive tube  402 , guide tube  404  and retaining collar  406  have a circular shape. Rotation of the drive tube  402  within guide tube  404  is prevented by a pin  416 , inserted through the wall of guide tube  404 , through a slot  414  fabricated within guide tube  402 . Typically, pin  416  is affixed to guide tube  404  in such a manner as to prevent loosening during operation. Pin  416 , while preventing rotation of the drive tube  402  relative to guide tube  404 , allows unrestricted extension and contraction of the drive tube within the guide tube.  FIG. 4   b  is a partial cross section view  401  through section B-B of  FIG. 2 . Retaining collar  406  is composed of two parts  406   a  and  406   b , to allow assembly of screw device  216  within the guide tube  404  and drive tube  402 . Retaining collar  406  is also fabricated in such a manner as to allow free rotation of screw device  216  within the retaining collar  406 .  FIG. 4   c  is a partial cross section view  403  though section A-A of  FIG. 2 .  FIG. 4   d  is a side view  405  of the component parts of the clamping device of  FIGS. 4   a - c.  Screw device  216  has a threaded portion  216   a  that engages threaded collar  408 , threaded collar  408  being affixed to drive tube  402  at joint (surface)  412 . Threads may be “left hand” or “right hand”, depending on the desired direction of rotation. Screw device  216  is fabricated to provide a recessed bearing surface  216   b  that allows free rotation of device  216 , while also holding the screw device  216  in position within guide tube  404  via engagement with retaining collar  406 . Retaining collar  406  ( 406   a  and  406   b ) are affixed to guide tube  404  at joint (surface)  410 . 
       FIG. 5   a  is a side view  500  of a clamping device in accordance with a third embodiment of the present invention. In this embodiment drive tube  502 , guide tube  504  and retaining collar  506  have a hexagonal shape. The conformal fitment of the drive tube  502  within guide tube  504  prevent rotation of anvil  206  as anvil  206  is moved toward anvil  204 .  FIG. 5   b  is a partial cross section view  501  through section B-B of  FIG. 2 . Retaining collar  506  is composed of two parts  506   a  and  506   b , to allow assembly of screw device  216  within the guide tube  304  and drive tube  302 . Retaining collar  506 , while fixed to guide tube  504 , allows free rotation of screw device  216 .  FIG. 5   c  is a partial cross section view  503  though section A-A of  FIG. 2 .  FIG. 5   d  is a side view  505  of the component parts of the clamping device of  FIGS. 5   a - c . Screw device  216  has a threaded portion  216   a  that engages threaded collar  508 , threaded collar  508  being affixed to drive tube  502  at joint (surface)  512 . Threads may be “left hand” or “right hand”, depending on the desired direction of rotation. Screw device  216  is fabricated to provide a recessed bearing surface  216   b  that allows free rotation of device  216 , while also holding the screw device  216  in position within guide tube  504  via engagement with retaining collar  506 . Retaining collar  506  ( 506   a  and  506   b ) are affixed to guide tube  504  at joint (surface)  510 . 
     The present invention is not limited by the previous embodiments heretofore described. Rather, the scope of the present invention is to be defined by these descriptions taken together with the attached claims and their equivalents.