Abstract:
The present invention relates to an accessory for use with bar clamps, and more specifically, to a bar clamp attachment for extending a bar clamp to a plurality of working lengths. The bar clamp extension of the present invention generally comprises an extension bar and a coupler that releasably attaches the extension bar to a primary bar of a bar clamp.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to an accessory for use with bar clamps, and more specifically, to a bar clamp attachment for extending a bar clamp to a plurality of working lengths. 
     2. Background of the Prior Art 
     Bar clamps are well known to craftsmen for use in holding a work piece in a fixed position. Typically, a bar clamp is used to hold a workpiece comprising multiple objects together for gluing, welding, or other purposes where it is advantageous to temporarily retain the workpiece in a fixed position. When encountering a clamping task, a craftsman will assess the size of a workpiece and select a clamp suitable for its retention. In cases calling for a bar clamp application, a craftsman selects a clamp having an appropriate length to embrace the subject work piece. However, to accomplish a variety of clamping tasks in association with a variety of projects, a craftsman is required to have multiple clamps of varying lengths. 
     One example of a prior art bar clamp is disclosed in U.S. Pat. No. 4,926,722 issued to Sorensen et al. The Sorensen et al. bar clamp comprises a movable jaw, a bar, and a fixed jaw. A disadvantage of the clamps known in the art, such as the Sorensen et al. bar clamp, is the finite length of the clamping bar. For example, while a movable jaw provides a variety of clamping positions along the length of the clamping bar, the finite length of the clamping bar limits the range of clamping positions available for each clamp. The finite length of each bar clamp requires a craftsman to purchase multiple clamps of varying lengths to accommodate various workpieces in association with accomplishing a variety of clamping tasks. 
     Therefore, a longstanding need remains for improvements in bar clamping devices. Such improvements would provide a craftsman the capability of utilizing a movable jaw component and a fixed jaw component in conjunction with a variety of bar lengths to achieve a modifiable bar clamp of varying lengths. 
     SUMMARY OF THE INVENTION 
     An improved bar clamp extension attachment for extending the working length of a bar of a bar clamp to a plurality of working lengths is described comprising an extension bar that has transverse dimensions matching those of the bar of the bar clamp. The bar clamp extension of the present invention will extend the working length of a typical bar clamp that has a moveable jaw and a fixed jaw in slidable and fixed engagement, respectively, with the bar of the bar clamp. A plurality of projections or pins extend transversely from a first and second end of the extension bar. The pins engage a coupler at the first end for releasably joining the extension bar to the bar of the bar clamp at the end which held the fixed jaw, and engage the fixed jaw at the second end. In operation, the fixed jaw is removed from the bar of the bar clamp and attached to the second end of the extension bar. The first and second ends of the extension bar are interchangeable. 
     A coupler includes a receiving member that is generally U-shaped in transverse cross-section wherein the web section and leg sections are sized to closely accommodate the end portions of the bar of the bar clamp and the extension bar. The end portions of the bar and extension bar are placed in the receiving member with their pins aligned with corresponding recesses in the receiving member. The coupler or clamp also includes a cover plate with recesses that is placed over the bar and extension bar end portions with the recesses aligned with the pins at the end portions of the bar and extension bar. A central throughbore in the receiving member and cover plate receives a nut and bolt combination for securing the coupler to the end portions of the bar and extension bar. The extension bars pins are comprised of metal, or alternatively, are spring pins, roll pins, or dowels. 
     After the extension bar is connected to the bar clamp, the extended clamp functions in the same manner as the bar clamp prior to its modification. In operation, a workpiece is clamped between a movable jaw and a fixed jaw. Sqeezing a handle on the clamp advances the movable jaw along the bar until a desired pressure is applied to the workpiece. To open the clamp, a trigger is squeezed and the movable jaw is pulled and released from the workpiece. 
     These and other aspects of the present invention will become apparent to those skilled in the art upon reference to the following specification, drawings, and claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a prior art clamp comprising a movable jaw, a bar, and a fixed jaw. 
     FIG. 2 is a perspective view of a bar clamp extension attachment in accordance with the teachings of the present invention with the prior art clamp of FIG. 1 shown in phantom. 
     FIG. 3 is an exploded perspective view of the bar clamp extension attachment of FIG. 2 with the prior art clamp of FIG. 1 shown in phantom. 
     FIG. 4 is an enlarged perspective view of the cover plate and receiving member of the coupler. 
     FIG. 5 is an enlarged perspective view of the extension bar. 
     FIG. 6 is an enlarged top plan view of the extension bar and coupler. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in the drawings, and referring in particular to FIG. 2, numeral  10  designates the bar clamp extension assembly of the present invention. The assembly  10  generally comprises a coupler  12  that releasably attaches an extension bar  14  to a primary bar  20  of a pistol-grip bar clamp  16  (shown in phantom). 
     Referring now to FIG. 1, the pistol-grip bar clamp  16  includes a movable jaw  18  that is adjustable to a plurality of positions along primary bar  20 . A proximal end  22  and a distal end  24  define primary bar  20 . Typically, clamp  16  is configured with a fixed jaw  26  in secure engagement with the distal end  24  of primary bar  20 . Bar  20  includes a proximal pin  32  and a distal pin  34  (FIG.  3 ), both of which extend transversely from bar  20 . Distal pin  34  releasably engages fixed jaw  26 . Sqeezing handle  30  advances jaw  18  along bar  20 . In operation, a workpiece (not shown) is clamped between jaws  18 ,  26 , by advancing movable jaw  18  along bar  20  toward fixed jaw  26  until a desired pressure is applied to the workpiece. To open the clamp, trigger  28  is squeezed in the direction of proximal end  22  and jaw  18  is pulled in the direction of proximal end  22 . 
     As shown in FIG. 3, a proximal end  36  and a distal end  38  define extension bar  14 . Bar  14  further includes proximal pin  40  and distal pin  42  extending transversely from bar  14 . To attach extension bar  14  to clamp  16 , fixed jaw  26  is released from pin  34  and jaw  26  is slideably removed from end  24  of primary bar  20  and reattached to distal end  38  of extension bar  14 . Jaw  26  releasably engages pin  42  to retain its fixed position at the distal end of bar  14 . Also shown in FIG. 3, coupler  12  comprises a cover plate  46  and a receiving plate  44  having a cavity  48 . Plates  44 ,  46  each include a plurality of pin recesses  50 ,  50 ′ and a central bore  52 ,  52 ′. Pin recesses  50 ,  50 ′ are provided for receiving pins  34  and  40 . To attach the extension bar  14  to the clamp  16 , the distal end  24  of primary bar  20  is aligned within the cavity  48  and receptively engaged by plate  44  and pin  34  is thereby receptively engaged by recesses  50 . The depth of cavity  48  is consistent with the width of bar  20  such that cavity  48  snugly receives bar  20 . Pin recesses  50  of plate  44  receives pin  34  and fixes the position of plate  44  relative to bar  20 . Likewise, cavity  48  snuggly receives the proximal end  36  of extension bar  14  and recesses  50  receive pin  40 . Pin recesses  50  of plate  44  receives pin  40  and fixes the position of plate  44  relative to bar  14 . The cover plate  46  and its recesses  50 ′ and bore  52 ′ are aligned with receiving plate  44  and pins  34 ,  40 , such that central bores  52 ,  52 ′ are aligned for receiving a bolt  54  for securely engaging the sandwiched arrangement of plates  44 ,  46  about the junction of bars  20  and  14 . Bolt  54  is received by central bore  52 ,  52 ′ and is threadably engaged by nut  56  to secure the placement of plates  44 ,  46  in releasable engagement with bars  20 ,  14 . 
     To accomplish the desired clamping effect, a user would have a series of extension bars  14  of varying lengths at his disposal. A modified pistol-grip bar clamp incorporating the bar clamp extension  10  easily accommodates a large workpiece by selecting an extension bar  14  having a length suitable for clamping the subject workpiece. A small workpiece is accommodated in much the same manner. The bar clamp extension  10  provides a user with a variety of clamping solutions without the need for individual clamps of varying lengths. Rather, a user merely selects an extension bar of a length suitable to accommodate a workpiece and modifies the pistol-grip bar clamp accordingly. 
     In a preferred embodiment, coupler  12  is non-orientation dependent, meaning it works equally as well in connecting bars  14  and  20  when the position of the plates  44 ,  46  relative to the bars  14 ,  20  is rotated by 180° about an axis formed by the bolt path  58  as shown in FIG.  3 . Furthermore, the non-orientation dependent positions of receiving plate  44  and cover plate  46  can be reversed from the embodiment as shown in FIG.  3 . 
     Also in a preferred embodiment, extension bar  14  is constructed of ¼ inch by ¾ inch surface hardened steel. Pins  40 ,  42  are ¼ inch in diameter and ⅝ inch in length. Furthermore, pins  40 ,  42  are spring pins, or alternatively, roll pins, or alternatively dowels pressed into bar  14 . Plates  44 ,  46  are constructed of aluminum or steel and are machined to a configuration to receive and fit bar  14 . Bolt  54  is preferably  ¼ inch by  1 inch having 20 coarse thread per inch and is threadably received by plate  46 . Nut  56  is  ¼ inch in diameter having  20 coarse thread per inch. Alternatively, fasteners of other types well known in the art can be substituted for the nut/bolt fastener arrangement. For example, a hand knob having a female  ¼ inch in diameter threaded receiving member,  20 coarse thread per inch, could be substituted for nut  56 . 
     The foregoing description and drawings comprise illustrative embodiments of the present inventions. The foregoing embodiments and the methods described herein may vary based on the ability, experience, and preference of those skilled in the art. The foregoing description and drawings merely explain and illustrate the invention, and the invention is not limited thereto, except insofar as the claims are so limited. Those skilled in the art who have the disclosure before them will be able to make modifications and variations therein without departing from the scope of the invention.