Patent Publication Number: US-6708966-B1

Title: Adjustable C-clamp

Description:
BACKGROUND 
     1. Field of the Invention 
     This relates to clamps generally, and more specifically to adjustable C-clamps. 
     2. Prior Art 
     It is well-known to have clamps generally in the form of a “C” formed by two arms depending from a back. Typically, a threaded rod passes through a matching threaded hole in the first arm and extends toward the second arm in such manner as an object can be secured between the second arm and the threaded rod. 
     A C-clamp is useful for securing objects of various sizes that fit between the threaded rod contact end and the second arm. Objects suitable for clamping by a given size C-clamp can range in size between a maximum when the threaded rod is effectively withdrawn away from the second arm and a minimum comparable to when the threaded rod is threaded through the hole toward the second arm essentially the full length of the threaded rod. For an object outside of this range, a C-clamp of a different size must be used. Commonly, a tool shop will have a wide range of C-clamps to accommodate objects of different sizes. Usually one will choose a C-clamp comparable in size to the object being clamped. 
     The primary object of the present invention is to have a C-clamp that is adjustable in effective width, extending the size range of objects that a single C-clamp can secure. 
     SUMMARY 
     This object is achieved in a typical C-clamp modified to include a two-member back with one member extending from the other to a selective position where it is releasably secured. In the preferred embodiment, a first member telescopes from a channel in a second member. Across the channel at its entry end is a pin. The channel web recedes from its entry end to provide a slot through which the first member enters under the pin. The pin blocks the channel at its top, so the first member enters the channel at an angle to the channel web and then rotates down onto the web and into engagement with the pin. 
     When the first member is rotated into contact with the channel web, the pin engages one of a plurality of grooves in the top of the first member to prevent the first member from moving in the channel. To later adjust the relative position of the first member in the channel, it is rotated away from the web and the pin. After the first member is repositioned, it is rotated back into contact with the web and the pin is received into a different one of the plurality of slots. 
     Significantly, when an object is clamped in the clamp, the object is forcibly pressed against an arm depending from the first member, which causes a rotational force on the first member. That is, the first member is urged up against the pin further locking the pin in the selective first member groove. The pin also becomes a fulcrum in a lever action that urges the first member portion in the channel hard against the channel web in a lever action causing increased frictional resistance to the first member sliding in the channel as well as maintaining the pin in the groove. 
     In an alternative embodiment, the pin moves in the second member out of engagement with the first member rather than the first member moving out of engagement with a stationary pin. In such case, the second member is typically a tube and the first member simply telescopes in and out of the tube. Typically, the pin passes through a transverse hole in the tube and into a selective one of a plurality of transverse holes in the first member aligned to receive the pin. The pin should be deemed only representative of many mechanisms known in the art that could releasably secure the back members together during use. Other configurations, such as a ratchet or a pawl in the second member engaging a rack on the first member are deemed equivalent to the pin. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a flange perspective view of the adjustable C-clamp shown holding an object of near maximum width, the back members fully telescoping to maximum extent. 
     FIG. 2 is a flange perspective view of the adjustable C-clamp of FIG. 1 shown holding an object of near minimum width, the back members fully telescoping to minimum extent. 
     FIG. 3 is a flange perspective view of the adjustable clamp shown with the telescoping members mutually counter rotated into adjustable position from a position with the back members maximally telescoping together. 
     FIG. 4 is a flange perspective view of the adjustable clamp of FIG. 3 shown with the telescoping members in counter rotated relative position with the telescoping members adjusted into position maximally telescoping apart. 
     FIG. 5 is a perspective view of the adjustable clamp showing the inner back member with a series of transverse grooves aligned for entry into the channel of the outer back member. The cross pin across the entry end of the channel at its top, sized to fit in one of said grooves, blocks entry of the inner member requiring it to enter rotated at an angle through the slot between the cross pin and the receded channel web. 
     FIG. 6 is a perspective view of the adjustable clamp showing the inner back member with a rack on the top of the inner member and a pawl disposed for engagement with the rack as it enters the second member comprising a tube. 
     FIG. 7 is a perspective view of the adjustable clamp with the outer member comprising a tube and the cross pin shown removable from the grooves of the inner member. 
     FIG. 8 is a perspective view of the adjustable clamp with the outer member comprising a tube with a hole through its sides and the cross pin shown insertable through those holes into a selective one of a plurality of holes in the inner member. 
     FIG. 9 is a perspective view of the adjustable clamp with the outer member comprising a tube, the inner member including a rack on its top, and a ratchet mechanism disposed to engage the rack as the inner member enters the tube. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The adjustable C-clamp  10  of the present invention comprises a back  12  and opposing first and second arms  14  and  16  depending from the back  12  to form a C-shaped frame. A threaded rod  18  moves through a matching threaded hole  20  in the first arm  14  directed toward the opposing second arm  16  adapted to clamp an object  100  by forcibly pressing the object between a contact end  22  of the threaded rod  18  and the second arm  16 . The threaded rod  18  thus tightens against the object  100  to secure it within the clamp  10 , typical of common C-clamps. (The threaded rod is only representative of any bar or other pushing member in adjustable and releasable engagement with the first arm where the bar is securable to the first arm at a preferred position. Any other form different from a threaded rod through a matching hole is deemed equivalent and included in this invention. For example, such a different form might be a rod secured in place by a cam urged to rotate on a pin against the rod.) 
     As stated, the clamp  10  becomes adjustable through a back first, or inner, member  24  telescoping from a back second, or outer, member  26 . The first arm  14  depends from the outer member  26  and the second arm  16  depends from the inner member  24 . The back inner member  24  releasably engages the back outer member  26  firmly and when thus engaged forms the frame back  12 . 
     The back outer member  26  comprises a U-shaped channel  28  defined by opposing flanges  30  separated by a web  32  on flange proximal ends  33 , the channel thus opening opposite the channel web  32 . The back inner member  24  then telescopes out of the channel  28  at a channel entry end  34 , sliding in the channel  28  between the opposing flanges  30  and resting on the channel web  32 . In the preferred embodiment, the back inner member  24  enters the channel  28  at its entry end  34  under a cross pin  36  that bridges between opposing flanges  30  at the channel entry end  34  on flange distal ends  37 , partially obstructing passage into the channel  28  at its top (opposite the web). To allow the inner member  24  to pass into the channel  28 , channel web  32  recedes from the entry end  34  longitudinally spacing the cross pin  36  from the channel web  32  defining therebetween a disengagement slot  38  that allows the back inner member  24  to enter the slot  38  at an acute angle from the back web  32 . When the back inner member  24  is located at a preferred position, it is rotated toward and into contact with the channel web  32  where a selective one of a plurality of grooves  40  in the back inner member top  42  engages the cross pin  36  to prevent the back inner member  24  to slide in the channel  28 . To adjust the relative position of the back members  24  and  26 , the back inner member  24  is again rotated into the disengagement slot  38  away from the channel web  32  to disengage the cross pin  36  from the grooves  40  of the back inner member  24 . The back inner member  24  then slides to a new preferred position and rotated back toward the web  32  to again engage the cross pin  36 . 
     In operation, when an object  100  is secured in the adjustable C-clamp  10 , the threaded rod  18  pushes the object  100  against the second arm  16 . That push causes a rotational force on the back inner member  24  that urges it against the cross pin  36  intermediate the back inner member  24  into firm engagement with the grooves  40 . The rotational force also presses a back inner member portion  44  within the channel  32  against the channel web  32  as the cross pin  36  becomes a fulcrum for rotation of the back inner member. The back inner member  24  is thus prevented from telescoping from the back outer member  26  during use both by the secure engagement of the cross pin  36  in the grooves  40  and by the force pressing the back members together. 
     In an alternate embodiment, the cross pin  36  is moveable instead of stationary in the flanges  30 . The cross pin  36  and grooves  40  of the back inner member  24  are disengaged by moving the pin  36  instead of rotating the back inner member  24 . In this embodiment, the disengagement slot  38  is not required and the back inner member  24  simply slides horizontally within the back outer member  26 , which then may be a tube  46  instead of a channel. The cross pin  36  likewise may be removable from the flanges  30  and reinserted through a transverse hole  48  in the tube  46  aligned with a selective one of a plurality of holes  50  in the back inner member  24 . 
     It is noted that the cross pin  36  is representative of several securing mechanisms known in the art that might be employed for engaging the back inner member  24  with the back outer member  26 . In alternative embodiments, one of those securing mechanisms may substitute for the cross pin  36  without detracting from the invention and is deemed included in this disclosure. In one such alternative, the grooves  40  on the inner member  24  may comprise a rack  52  and the cross pin  36  may comprise a removable pawl  54  engaging the rack  52 . Thus, the rack  52  slides under the pawl  54  to a preferred position and then held in that position during use. It is then released or withdrawn for adjustment of the back inner and outer members  24  and  26 . Likewise, a ratchet  56  is a similar mechanism to control relative movement of the back members that is deemed included in this disclosure. 
     Significantly, the securing mechanism is not required to sustain longitudinal force derived when the threaded rod  18  forcibly presses the object  100  between its contact end  22  and the second arm  16 . Rather, it is required only to hold the back inner member  24  in its longitudinal relation to the back outer member  26  while the back inner member  24  receives the rotational force generated by the bar against the second arm  16 . The rotational force then urges the back inner member  24  against the back outer member  26 . When the outer member  26  is a tube  46 , the rotational force urges the back inner member  24  up at the tube entry end  34 , which becomes an effective fulcrum at the entry end causing the portion of the back inner member in the tube to push down against the tube. This upward and downward force in the tube significantly prevents the back inner member from moving within the tube in concert with the securing mechanism. The mechanism therefore can be of less structural strength than if it alone had to sustain the pushing force of the bar.