Abstract:
A joint connects one end of a tube to the side of a hollow member. It employs a pair of wedge elements that have sloping sides. A threaded fastener passes freely through a proximal wedge and then is threaded through a distal wedge. The fastener first passes through a hole in the side of the member and the wedges are inserted into the end of the tube. Tightening the fastener draws the wedges toward the member and causes the wedges to cooperate with one another to grip the inner surfaces of the tube to create a strong joint stable in many directions. Joints shown for tubes with various shapes.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to methods and apparatus for rigidly connecting one tubular member to the side of another tubular member, and more particularly to such connections that employ an internal wedging plug. 
     DESCRIPTION OF THE PRIOR ART 
     When framing members for diverse structures such as bookshelves, carts, screen rooms, and the like were made of wood, they employed solid members that required certain joining means. With the substitution of metal and plastic materials, hollow members could replace the solid wood with improved function and savings in cost and weight. However, they required the use of different connecting methods. Welding has been preferred for joining one hollow member to the side of another hollow member. However that method has serious limitations. The two members must be made of compatible materials. The heating may weaken the walls at the joint. The strength of the joint is limited to the wall thickness at this weakened area. As a consequence, failures generally occur at the joint. The designer will often select a greater wall thickness for the tubing than is required for structural strength to ensure a secure joint. This leads to increased weight and cost. One of the applicants has used a novel wedge type internal plug connector for joining one square tube to the side of another square tube, as shown in the prior art drawing FIGS. 2-5. The joint was difficult to align unless it was constructed to engage less of the structure. It also had poor lateral stability. 
     SUMMARY OF THE INVENTION 
     The instant invention comprises a wedge plug tubing connector for a joint that facilitates alignment, engages more of the structure, and provides more stability in all directions. It employs a distal wedge element and a proximal wedge element that cooperate with one another when a fastener draws them together. Specially shaped fastener channels keep the wedges aligned. Specially shaped wedge surfaces enable the wedges to engage more of the connecting tube to enhance stability in all directions. 
     These and other objects, features, and advantages of the invention will become more apparent when the detailed description is studied in conjunction with the drawings in which like elements are designated by like reference characters in the various drawing figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a welded connection of the prior art. 
     FIG. 2 is a vertical section of a wedge connection of the prior art. 
     FIG. 3 is a top view of the connection of FIG. 2 with tube ready for joining. 
     FIG. 4 is a perspective view of the two wedges of FIG.  2 . 
     FIG. 5 is an end view of the wedges of FIG.  2 . 
     FIG. 6 is a top view of a joint with a connector of the invention with the side member partially cut away. 
     FIG. 7 is a side view of the joint of FIG. 6 with the tube and side member in phantom. 
     FIG. 8 is an end view of the proximal wedge of FIG.  6 . 
     FIG. 9 is an end view of the distal wedge of FIG.  6 . 
     FIG. 10 is a sectional view taken on line  10 — 10  of FIG.  8 . 
     FIG. 11 is a sectional view taken on line  11 — 11  of FIG.  8 . 
     FIG. 12 is an exploded view, partially cut away, of another embodiment of the invention. 
     FIG. 13 is a perspective view of another embodiment of the invention. 
     FIG. 14 is a sectional view taken on line  14 — 14  of FIG.  13 . 
     FIG. 15 is an end view of the joint of FIG.  13 . 
     FIG. 16 is an end view of the joint of FIG. 13 before the wedge is tightened. 
     FIG. 17 is an end view of the distal wedge of FIG.  13 . 
     FIG. 18 is an end view of the proximal wedge of FIG.  13 . 
     FIG. 19 is a perspective view of another embodiment of the invention with a cylindrical hollow member to which a cylindrical tube is joined. 
     FIG. 20 is a perspective view of a washer for use with the joint of FIG.  19 . 
     FIG. 21 is an end view of another embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Many constructions use hollow members, or tubes, for framework and the like because of their rigidity, light weight and low cost. It is common practice in the art, as shown in FIG. 1, to join one tube  10 ″ at right angles to the side of a hollow member  4 ″ by welding the parts together at the seam  100 . It is difficult to produce a cosmetic joint, and the metal subjected to the heat may lose some of its strength. One must often use thicker walls than is required by the balance of the structure to compensate for this weakness. This method is even less useful with non-metallic tubes such as PVC pipe. These generally use bulky molded sleeve connections. 
     Many of these objections have been overcome by a wedge plug connection invention of one of the applicants, as shown in FIGS. 2-5 that constitutes prior art. Referring now to FIGS. 2-5, a square tube  10 ′ with a long axis  11 ′ has a first end  14 ′ that is joined to the side of square hollow member  4 ′. A fastener  1 ′ has a threaded shaft  2 ′ and an enlarged head  3 ′ with a hex socket. An aperture  7 ′ in first wall  6 ′ is large enough to pass the head  3 ′, and aperture  9 ′ in second wall  8 ′ is just large enough to pass the shaft. A washer  33 ′ supports the head. A pair of cooperating wedge elements, a proximal element  16 ′ and a distal element  25 ′, are mounted on the fastener outside of member  4 ′ to fit into the end of tube  10 ′, as shown in FIG.  3 . The shaft  2 ′ passes freely through channel  20 ′ in the proximal element and threadedly engages the threaded channel  28 ′ in the distal element  25 ′. When the tube  10 ′ is fitted over the wedges and the fastener is rotated by a wrench through aperture  7 ′, the distal wedge is pulled toward member  4 ′. The sloping faces  19 ′ and  29 ′ of the proximal and distal wedges cooperate to force the proximal wedge element downward relative to the distal wedge element until the upper face  27 ′ of the distal element is tightly applied to the upper inner wall surface of the tube, the lower face  18 ′ of the proximal element is tightly applied to the lower inner wall surface of the tube, and the edge  14 ′ of the tube is tightly applied the outer surface of the member side wall. In order for the proximal wedge to move relative to the distal wedge, its channel  20 ′ must be larger than the channel  28 ′ in the distal wedge, as shown in FIG. 5, where the moved relative position  28 ″ of the threaded channel is shown in phantom. The wedges were both cut from square section bar. A problem with this connector related to the large channel required in the proximal element. As shown in FIG. 3, the two wedge elements often are not aligned as they are to be inserted into the tube. For this reason it was necessary to fabricate the elements from a square bar considerably smaller than the inner dimensions of the tube so that even misaligned elements would fit into the tube. As a consequence, the full upper and lower surfaces of the tube were not used in the connection, leaving it weaker. Furthermore, there was little lateral strength to the joint, because the sides of the tube were not engaged. 
     New and improved joint connectors and methods for joining are provided by the instant invention that utilize more of the internal surface if the tube, eliminate misalignment of the elements, and provide enhanced lateral strength. Referring now first to FIGS. 6-11, a rectangular cross section tube  10  with a long axis  11  is joined at cut first end  14  to elongate rectangular cross section hollow member  4  having long axis  5  employing a wedge plug connector and method of the invention. 
     Fastener  1  has an enlarged hex socket head  3  and a threaded shaft  2 . Member  4  has a first wall  6  with a first aperture  7  large enough to pass the head  3  and an opposed, second wall  8  with a second aperture  9  large enough to pass shaft  2 . The joint is formed by first passing the fastener through the first wall aperture  7  and the shaft through second wall aperture  9 . A washer  33  may further support the head, especially useful when member  4  is of soft thin wall material. A proximal wedge element A and a distal wedge element B are mounted on the shaft and fit inside end  14  of tube  10 . They may be cut from bar stock having a cross section closely matching the internal dimensions of tube  10 . 
     Element B has a first face  26 , a second face  27 , and a planar sloping face  29  substantially joining the other two faces, with the exception of a small portion  25  cut off to prevent that element from touching member  4 . A threaded channel  28  passes through the element parallel to face  27 . 
     Element A has a first face  17 , a second face  18 , and a planar sloping face  19  substantially joining the other two faces. First face  17  is configured planar to closely engage the joining surface  15  on second wall  8  to which it will be drawn up by rotation of the fastener. A non-threaded channel  20  passes through the element parallel to face  18 . This channel has an unusual shape to enable the wedge to move up and down on the fastener shaft, but to restrict lateral movement, which was found to be such a problem with the prior art. The channel  20  has an upper wall  21  and an opposed, lower wall  22  that conform substantially to the outer surface of the shaft  2 . These walls are spaced apart by a distance sufficiently great to enable the wedge to move freely on the shaft between a first position when the wedges are together for insertion into the tube and a second position when the wedges are spread apart enough to tightly engage the upper and lower inner walls of the tube. This distance is greater than the diameter of the shaft shown in phantom in FIG.  8 . The width of the channel in the direction transverse to this spaced-apart distance is no greater than the shaft diameter. This ensures that the two elements will remain aligned on the fastener. 
     Referring now to FIG. 12, an embodiment of the invention is shown for joining three tubes  10  having rectangular cross sectional inner surfaces to a single hollow member  4 . Apertures  7  in a first wall  6  are large enough to pass the heads of fasteners (not shown). Apertures  9  in second wall  8  allow passage of the shafts of the fasteners. Because it is difficult to position multiple washers in a long hollow member, a long strip of metal  34 , preferably steel, is provided with appropriately punched holes  35  to provide the equivalent of multiple washers that is more easily positioned. At the same time, the steel strip provides further strength to the structure. 
     FIGS. 13-18 show another embodiment of the invention for joining a cylindrical tube  36  to the rectangular hollow member  4 . The proximal wedge element A′ and distal wedge element B′ are cut from elongate extruded bars having the cross sections shown in FIGS. 18 and 17 respectively. Distal wedge channel  28 ″ is then threaded. Proximal channel  20 ″ is configured as shown for proximal wedge element A. The bar stocks from which these elements are cut, as exemplified by FIG. 17 for element B′, have a first cylindrical surface  37  with a radius closely corresponding to the radius of the inner surface of the tube and a second cylindrical surface  38  of a lesser radius. Surface  37  does not extend to the diameter to enable the wedges to fit into the tube before the fastener is tightened, as shown in FIG. 16, and to tightly grip almost the entire inner surface of the tube as shown in FIG. 15 when the fastener is tightened. This provides great lateral as well as vertical strength to the joint. Channel  28 ″ is not at the center of the cylindrical surface  37 . An eccentric channel ensures that the element cannot spin in the tube when the fastener is tightened. 
     Referring now to FIGS. 19 and 20, another embodiment is shown in which a cylindrical tube  39  is joined to a cylindrical hollow member  40 . The end  41  of tube  39  is cut to match the wall of member  40 , and a special washer  42  is provided to match the inner wall surface of member  40 . 
     Referring now to FIG. 21, other embodiment of the invention for joining together two substantially rectangular tubes that ensures greater strength in all directions is shown. The view is an end view from the distal end of the wedge  52  before the fastener  48  is tightened. Tube  44  is to be joined to the side of vertical member  47 . Tube  44  has a rectangular outer surface  49 , and the inner surface has two parallel, opposed flat faces  50  joined by sloping sides  51 , which extend away from the flat faces at an angle of greater than ninety degrees. The distal end of distal wedge element  52  is seen. It has two parallel, opposed flat faces  54  joined by sloping sides  53 . The sloping sides are shorter than those of the tube inner surface as shown. The other dimensions of the inner surface correspond closely to those of the two wedges. This enables the two wedges to be inserted into the tube before tightening the fastener, and to have one of the wedges firmly engage the upper half of the tube and the other wedge engage the other half of the tube when the fastener is tightened. Only the length  55  on the tube inner surface is not engaged by the wedges. As shown by the phantom lines  56 , the outer surface of the tube may be extruded with uniform walls if desired. 
     A distinct advantage of the invention is the ability to disconnect the joint by simply unscrewing the fastener. 
     The invention disclosed above has a number of particular features, which should preferably be employed in combination, although each is useful separately without departure from the scope of the invention. While I have shown and described the preferred embodiments of my invention, it will be understood that the invention may be embodied otherwise than as herein specifically illustrated or described, and that certain changes in form and arrangement of parts and the specific manner of practicing the invention may be made within the underlying idea or principles of the invention.