Patent Publication Number: US-6658778-B2

Title: Picture frame joint and method of assembling same

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application Serial No. 60/318,583, filed Sep. 11, 2001 and is a continuation-in-part of Ser. No. 10/054,050, filed Jan. 22, 2002. 
    
    
     BACKGROUND OF INVENTION 
     The present invention relates generally to hardware use for picture frames. More specifically, the present invention relates to the hardware used to connect various picture frame components together, such as “channel” or “profile” picture frame components. 
     In the industry, these known picture frame components are typically manufactured of aluminum but may be of other materials, such as molded plastic. Typically, these frames include a total of four members with ends mitered at 45 degrees so that they may neatly mate with one another to form the frame. There is a need in the art to secure the mitered ends together to maintain the frame in its desired shape. 
     Also in the industry, wood frames are also employed. These frames must be nailed, glued or stapled together. However, with metal frames, such as the above “channel” frames made of aluminum with a channel therein, some type of joint connector must be employed to secured the ends to each other. Known picture frame joints in the prior art typically include an L-shaped plate with two short threaded fasteners through female threaded apertures on each of the two legs of the L-shaped plate. The bottom of the screw members communicate with a thrust plate which is, essentially, the same size and dimension of the main plate but does not have any threaded apertures. These two members are mated together and inserted into the frame to form a “set screw” configuration. As the screws are threaded through the female apertures, the bottom of the screws emanate further below the main member to cause the main member and the thrust plate to be urged further away from each other. Since these two members are residing within a channel in the aluminum frame, the joint is secured therein in clamping fashion. Of course, a second frame member is provided 90 degrees to the one provided to, in turn, form the desired square or rectangular configuration. This prior art construction requires the formation of the threaded bores as well as the tapping of the screws for shipping. However, it is common for these screw members to back out of their respective bores during transit requiring replacement and further handling for installation. 
     In view of the foregoing, there is a demand for a picture frame joint to be very easy and inexpensive to mass produce. There is a further need for a picture frame joint to be simple and easy to install and remove. There is a demand for a picture frame joint that has few parts that cannot be lost during transit of the picture frame when in an assembled or partially assembled form. There is also a demand for a picture frame joint that does not use expensive tapped holes or other threaded parts. 
     SUMMARY OF INVENTION 
     The present invention preserves the advantages of prior art picture frame joints and related hardware. In addition, it provides new advantages not found in currently available joint constructions and overcomes many disadvantages of such currently available devices and assemblies. 
     The invention is generally directed to a novel structural joint that has particular application in the connection of picture frame members together. More specifically, the present invention is well-suited for connection of picture frame members together that are of the channel type which are either extruded, machined or molded with an elongated channel running longitudinally therethrough. 
     The picture frame joint of the present invention includes a base plate slidably residing in a channel of a first picture frame member and includes a ramped surface. A wedge plate slidably resides between the base plate and a top bearing surface of the frame and includes its own ramped surface where the ramped surface of the wedge plate is arranged in an opposite direction to the ramped surface of the base plate. The wedge plate is moved toward the base plate to cause the ramp of the base plate to bear on the ramp of the wedge plate to urge the base plate apart from the wedge plate creating a friction fit within the channel of the picture frame member thus securing the base plate relative to the frame. A second wedge plate is also provided for engagement with a second ramp on the base plate to further secure a second picture frame member to the first picture frame member, such as at a ninety degree angle relative thereto. 
     It is therefore an object of the present invention to provide a picture frame joint that replaces the well known picture frame joint of the “set screw” type. A further object of the present invention is to provide a picture frame joint that is inexpensive and easy to manufacture in high volume. Another object of the invention is to provide a picture frame joint construction that does not use expensive tapped holes and threaded set screws. A further object of the present invention is to provide a picture frame joint that is not susceptible to lost parts during transit of the frame when in an assembled or partially assembled form. Yet another object of the present invention is to provide a picture frame joint that requires less handling to reduce the labor associated with installing picture frames joints and assembling picture frames. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     The novel features which are characteristic of the present invention are set forth in the appended claims. However, the invention&#39;s preferred embodiments, together with further objects and attendant advantages, will be best understood by reference to the following detailed description taken in connection with the accompanying drawings in which: 
     FIG. 1 is a top exploded perspective view of the picture frame joint of the present invention; 
     FIG. 2 is a bottom exploded perspective view of the picture frame joint of FIG. 1; 
     FIG. 3 is an end view of a picture frame member which is partially broken away for illustration purposes; 
     FIG. 4 is a perspective view of the picture frame joint of the present invention installed into the picture frame member of FIG. 3; 
     FIG. 5 is a cross sectional view through the line  5 — 5  of FIG. 4 showing communication of the stepped surface of the base plate with the ramped stepped surface of the wedge member; 
     FIG. 6 is a perspective view showing insertion of the installation tool into the base plate for locking of the picture frame joint to the picture frame member; 
     FIG. 7 is a perspective view showing the installation tool in the process of locking the picture frame joint to the picture frame member; 
     FIG. 8A is a cross-sectional view of the base plate and wedge member when the picture frame joint is in an unlocked condition as shown in FIGS. 4 and 6; 
     FIG. 8B is a cross-sectional view of the base plate and wedge member when the picture frame joint is in a locked condition as shown in FIG. 7; 
     FIG. 9 is a perspective view of the installation tool used in accordance with the present invention; 
     FIG. 10 is a perspective view of an alternative embodiment of the picture frame joint of the present invention in a stamped, unfinished condition; 
     FIG. 11 is a perspective view of the alternative embodiment of the picture frame joint of the present invention in finished condition in preparation for installation into a picture frame; 
     FIG. 12 is a front elevational view of the picture frame joint of FIG. 11; 
     FIG. 13 is a top view of the picture frame joint of FIG. 11 after receiving the impact of an anvil during the installation process; and 
     FIG. 14 is a side elevational view of the picture frame joint of FIG.  13 . 
    
    
     DETAILED DESCRIPTION 
     Referring first to FIGS. 1 and 2, top and bottom perspective views of the picture frame joint  10  of the present invention is shown to include a base plate  12  and a wedge plate  14  slidably connected thereto. The base plate  12  includes base ramps  16   a  and  16   b  emanating upwardly from the top surface  18  of the base plate  12  where base ramps  16   a  and  16   b  decrease in height running toward the free ends  12   a  and  12   b  of the base plate  12  as shown in FIGS. 1 and 2. The wedge plate  14  includes a wedge ramp  20  on its bottom surface  22  that increases in height running from right to left as shown in FIG.  2 . The wedge ramp  20  is positioned to run in an direction opposite to the direction of base ramp  16   a  on the top surface  18  of the base plate  12 . As will be discussed in detail below, the wedge ramp  20  and the base ramps  16   a  and  16   b  engage in complementary fashion to secure members  24  and  26 , as in FIGS. 4 and 7, of a picture frame assembly together. 
     To connect two picture frame parts  24  and  26  together, a single picture frame joint  10  of the present invention is employed. For example, it is desirable to connect two picture frame members  24  and  26  together at a ninety degree angle relative to one another to form a corner of a picture frame. The corners are typically mitered at a complementary 45 degree angle to form a neat corner. As shown in the figures, the base plate  12  is preferably formed in an L-shape with two base ramps  16   a  and  16   b  provided at opposing ends thereof. In should be understood that a first base ramp  16   a  engages with one separate wedge ramp  20  to connect the joint to a first picture frame member  24  and a second base ramp  16   b  on the base plate  12  engages with a second separate wedge ramp (not shown) to connect the joint  10  to a second picture frame member  26  thereby effectively mating the first picture frame member  24  to the second picture frame member  26 . 
     The use of an L-shaped base plate  12  is one of many configurations that can be employed in accordance with the present invention and is preferred because it is well-suited to connect two picture frame members  24  and  26  together at a ninety degree angle relative to one another. In an alternative embodiment, which is not shown, the base plate  12  may be linear in configuration with a pair of base ramps  16   a  and  16   b  at opposing ends thereof. For ease and simplicity of illustration and discussion, the connection of the picture frame joint  10  will be described below in detail for the connection of one side of the picture frame joint  10  of the present invention to one channel type picture frame member  24 . The connection of a second picture frame member  26  is identical to the connection of the first picture frame member  24  to the first side of the picture frame joint  10 . 
     As best seen in FIG. 5, the wedge plate  14  is positioned so that the wedge ramp  20  loosely communicates with the corresponding base ramp  16   a  emanating upwardly from the top surface  18  of the base plate  12 . To complete the joint, a second wedge plate (not shown) is also placed above the second base ramp  16   b  on the base plate  12 . 
     In FIGS. 1 and 2, the wedge plate  14  further includes a pair of guide tabs  28  which emanate downwardly from front edge  30  and rear edge  32 . Also, a notches  34  are formed in the front edge  36  and rear edge  38  of the base plate  12 . When the wedge plate  14  is placed into communication with the corresponding ramp  16   a  on the base plate  12  the guide tabs  28  of the wedge plate  14  slidably reside within their corresponding notches  34  in the base plate  12 . As a result, sliding travel of the wedge plate  14  along the length of the base plate  12  is limited to the length of the notches  34 . As will be explained in detail below, leverage apertures  40   a ,  40   b ,  40   c  and  40   d  are provided through the base plate  12  on opposing sides of each of the ramps  16   a  and  16   b  on the top surface  18  of the base plate  12 . 
     Turning now to FIG. 3, an end view of a typical picture frame member  24  of the “channel” type is shown to include a longitudinally running channel  42  defined by a floor  44  with opposing upstanding walls  46  with lips  48  extending inwardly from the respective free ends of the upstanding walls  46 . Extending downwardly from the floor is an elongated flange member  50  for embracing a picture and other associated materials (not shown), such as glass and cardboard for the construction of an entire picture frame. Further details of the construction of this picture frame member  24  need not be discussed as they are well known in the art. 
     In accordance with the present invention, the picture frame joint  10  is employed to connect two picture frame members  24  and  26 , such as of the type shown in FIG. 3, together to form a complete picture frame assembly. Referring to FIGS. 4-7 the installation of the picture frame joint  10  of the present invention is installed to a channel type picture frame member  24 . First, as shown in FIG. 4, the wedge plate  14  is loosed mated to one leg of the L-shaped base plate  12  so that the guide tabs  28  of the wedge member  14  slidably reside within the notches  34  in the base plate  12 . FIG. 5 illustrates the loose communication of the base plate  12  with the wedge plate  14  prior to insertion of one leg of the base plate  12  into the channel  42  of the picture frame member  24 . 
     The coupled base plate  12  and wedge plate  14  are then inserted into the channel  42  of the picture frame member  24  via an open free end  52  of the picture frame member  24 . In the preferred embodiment, the free end  52  of the picture frame member  24  is mitered at a 45 degree angle which is typical in channel type picture frame assemblies. In the condition show in FIG. 4, the base plate  12  may easily slide within the channel  42  of the picture frame member  24  with wedge plate  12  loosely secured thereto via the guide tabs  28  and notches  34  of the base plate  12 . The floor  44  and inwardly turned lips  48  of the picture frame member  24  are a distance apart from one another that is larger than the overall stack height A of the base plate  12  and wedge plate  14  together, as shown in FIG.  8 A. However, the distance between the floor  44  and the lips  48  is not large enough to allow for the guide tabs  28  of the wedge plate  14  to ride out of their respective notches  34  to permit free sliding of the wedge member  14  within the channel  42 . Therefore, once the wedge plate  14  is mated with the base plate  12  and inserted into the channel  42  of the picture frame member  24 , it cannot be separated from the base plate  12  and subsequently lost. 
     Once the position of the coupled base plate  12  and wedge plate  14  within the channel  42  are adjusted as desired, they may be secured in place. In accordance with the present invention, the wedge plate  14  is moved so that the ramp  20  of the wedge plate  14  communicates with the ramp  16   a  of the base plate  12  so to increase the stack height of the base plate  12  and wedge plate  14  to frictionally secure the picture frame joint  10  between the floor  44  and lips  48  of the picture frame member  24 . To assist in movement of the wedge plate  14 , the tool  54  of FIG. 9 is employed. The tool  54  includes an elongated shaft  56  with an outer wall  58  that serves as a bearing surface. An eccentric pin  60  extends from the bottom free end  62  of the elongated shaft  56 . A handle  64  is provided on the top free end  66  to facilitate rotation of the elongated shaft  56 . 
     Referring to FIG. 6, the pin  60  of the tool  54  is inserted into the aperture  40   d  that is closest to the wedge plate  14 . Due to the eccentricity of the pin  60 , the installation tool  54  must be oriented accordingly to allow the pin  60  to be fully inserted into the aperture  40   d  because the wedge plate and its bearing surface  68   a  is proximal thereto. As shown in FIG. 7, the tool  54  is rotated about the longitudinal axis through the eccentric pin  60  to cause the outer wall  58  of the elongated shaft  56  to bear onto the bearing surface  68   a  of the wedge plate  14  to urge it to the right. The movement of the wedge plate  14  to the right causes the ramp  20  of the wedge plate  14  to climb up the ramp  16   b  of the base plate  12  in ratcheting fashion to provide a greater overall stack height B, as shown in FIG. 8B which is greater than the stack height A shown in FIG.  8 A. Such ratcheting is facilitated by the use of complementary steps  70  on both the ramps  16   a  and  16   b  on the base plate  12  and the ramp  20  on the wedge plate  14 . 
     The increase of the stack height from A to B occurs within the confines of the picture frame member  24 , namely between its floor  44  and inwardly turned lips  48 . Therefore, such increase in stack height causes the top surface  72  of the wedge plate  14  to bear against the lips  48  of the picture frame member  24  and the bottom surface  74  of the base plate  12  against the floor  44  of the picture frame member  24 . Essentially, the picture frame joint  10  of the present invention provides a unique expanding internal clamp that is ideally suited for connecting to a channel type picture frame member  24  and securing one picture frame member  24  to another picture frame member  26 . 
     Once the picture frame joint  10  is secured to the picture frame member  24 , a second picture frame member  26 , shown in broken lines in FIG. 7, may now be connected to the free end of the L-shaped base plate  12  to form the second half of the ninety degree picture frame structure. The second picture frame member  26  also includes a mitered 45 angle free end to mate cleanly with the 45 degree angle free end of the first picture frame member  24 . The second picture frame member  26  is secured and locked to the base plate  12  in identical fashion as the first picture frame member  24  by use of a second wedge plate (not shown) to engage with the second ramp  16   a  on the top surface  18  of the base plate  12 . With both sides of the base plate  12  connected to a picture frame member  24  and  26  respectively, the corner of the picture frame structure is fully assembled. A total of four picture frame joints  10  and four picture frame members are employed to construct a completed picture frame assembly. 
     To unlock the picture frame joint  10  from the picture frame members  24  and  26 , the pin  60  of the installation tool  54  is inserted into the aperture  40   c  which is closest to the wedge plate  14  and, namely, its bearing surface  68   b . Since the wedge plate  14  was shifted to the right for locking, the closest aperture is now the aperture  40   c  immediately to the right of the ramp  16   b . The tool  54  is rotated with the pin  60  in the aperture  40   c  to cause the outer wall  58  of the elongated shaft  56  to bear against the bearing surface  68   b  on the wedge plate  14  to urge the wedge plate  14  to the left out of frictional engagement with the lips  48  of the picture frame member  24  and into an unlocked condition. When unlocked, the wedge plate  14  still remains loosely mated with the base plate  12  due to the continued positioning of the guide tabs  28  within the notches  34  of the base plate  12 , as in FIG.  4 . Loss of the wedge plate  14  is thereby avoided during unlocking of the picture frame joint  10 . The picture frame members may now be separated to facilitate changing of the picture or glass (not shown) residing therein. 
     The picture frame joint  10  of the present invention may be manufactured in many different ways and of different materials. Preferably, the picture frame joint  10  is manufactured of steel for ease of manufacture and durability and may be anodized or otherwise chemically treated, if desired. Both the wedge plate  14  and base plate  12  are preferably die cut and stamped out of steel without the need for expensive thread tapping and custom set screws as required in prior art joint connectors for picture frames. Further, the picture frame joint  10  may be molded from other materials, such as plastic, to suit the application at hand. 
     Moreover, the construction of the picture frame joint itself  10  may be modified and still be within the scope of the present invention. For example, the ramps  16   a  and  16   b  on the base plate  12  preferably decrease in height running toward the respective free ends of the base plate  12 . However, reversing of the direction of the ramps  16   a  and  16   b , and the positioning of the wedge plates  14  thereon, is contemplated by the invention. While steps  70  are preferred to provide additional friction to the ramp  20  of the wedge plate and the ramps  16   a  and  16   b  base plate, other structures may be employed to add such friction. For example, the steps  70  on the surfaces of the ramps  16   a ,  16   b  and  20  may be replaced with a roughened surface or grit coating to provided the preferred friction interface. It is also possible that the steps  70  or additional friction structure be eliminated entirely and still be within the scope of the present invention. 
     As stated above, the picture frame joint of the present invention may be construction in many different ways. In the preferred embodiment of the present invention, the wedge plate and the base plate are separated from each other. The guide tabs of the wedge plate ride within their respective notches to permit the free sliding of the wedge member within channel  42 . This ensures that steps  70  on the wedge plate  14  are aligned with the complementary and corresponding steps on the base plate. However, it is possible for the guide tabs to eject out of their corresponding notches which can result in the wedge plate being separated from the base plate. Since the wedge plate and base plate are separate members, it is required that they be manually held together for installation, namely, during insertion into the channel of the picture frame. As a result, it is possible for the wedge plate to be misaligned with the base plate causing an unsatisfactory installation. 
     The use of apertures  40   a-d  and the tool  54  with eccentric pin  60  are preferably employed in accordance with the present invention. However, other structures may be employed as long as they facilitate the engagement and disengagement the wedge plate  14  to and from the base plate. 
     As shown in FIGS. 10-14, an picture frame joint  100  of the alternative embodiment is shown where the wedge plates  102   a  and  102   b  and base plate  104  are permanently connected to one another. This structure obviates the need for guides tabs  28  on wedge member  14  and notches  34  in the base member  12  shown in the preferred embodiment of FIG.  1 . The connected wedge plate  102   a  to one end of the base plate  104  and wedge plate  102   b  to the other end of the base plate  104  in the embodiment of FIGS. 10-14 ensures that the mating contact surfaces or ramps  106   a  and  106   b  of the wedge plates  102   a  and  102   b  are precisely aligned with the corresponding and respective ramps  108   a  and  108   b  during installation. For ease of illustration, FIGS. 10-14 are shown apart from a picture frame. It should be understood that this alternative embodiment is installed into the channel of a picture frame in the same general fashion as the preferred embodiment  10  as shown, for example, in FIGS. 4,  6  and  7 . 
     Referring specifically to FIG. 10, a perspective view the picture frame joint  100  of the alternative embodiment is shown in its stamped but unfinished condition. The picture frame joint  100  of FIG. 10 is formed into a unitary member by progressive tooling with the desired apertures and stepped structures. In similar fashion to the preferred embodiment  10  of the present invention, a preferably L-shaped base plate  104  is provided with free ends  110   a  and  110   b . Two wedge plates  102   a  and  102   b  are respectively connected to the free ends  110   a  and  110   b  of the base plate  104 . The wedge plates  102   a  and  102   b  each include a ramp  106   a  and  106   b , which is preferably stepped, for mating with a corresponding ramp  108   a  and  108   b  structure on the base plate  104  which is also preferably stepped. The communication of two stepped surfaces (for example, ramps  106   b  and  108   b ) is shown in FIG.  14 . It is also possible to employ a ridged or roughened surface on ramps  106   a ,  106   b ,  108   a  and  108   b  instead of stepped surface. 
     The wedge plates  102   a  and  102   b  are connected to respective ends  110   a  and  110   b  of the base plate  104 . A pair of connectors  112   a  and  112   b  are preferably employed to connect each of the wedge plates  102   a  and  102   b  to their respective free ends  110   a  and  110   b  of the base plate  104 . As will be discussed in detail below, the connectors  112   a  and  112   b  are folded to create hinges between the wedge plates  102   a ,  102   b  and the base plate  104 . It should be noted that while a pair of connectors  112   a ,  112   b  are preferred, a single connector (not shown) or more than two connectors may be used to form hinges depending on the size and configuration of the picture frame connector at hand. Any type of connector can be used as long as the wedge plates  102   a  and  102   b  are connected to the base plate  104 . 
     Turning now to FIGS. 11 and 12, the picture frame joint  100  of the alternative embodiment, in a finished condition ready for installation, is shown. FIG. 11 shows a perspective view of the finished picture frame joint  100  while FIG. 12 shows a front elevational view. The wedge members  102   a  and  102   b , as seen in FIG. 10, are folded over so that the respective ramped stepped surfaces  106   a ,  106   b  and  108   a ,  108   b  are in alignment with each other. In this initial condition, the surfaces  106   a ,  106   b  and  108   a ,  108   b  are not in communication with each other. As a result, the overall initial thickness of the picture frame joint, shown as A, is similar to the initial thickness A shown in FIG. 8A for the preferred embodiment  10  of the present invention. 
     In similar fashion to the preferred embodiment, in the alternative embodiment  100 , the ends  110   a  and  110   b  of the base plate  104 , with a wedge plate  102   a  and  102   b  positioned thereon, is inserted into the channel  42  of a picture frame  24  in similar fashion to the positioning of the preferred embodiment  10  shown in FIG.  4 . The thickness A is less than the height of the channel  42  to permit an end of the base plate  104  with a wedge plate  102   a ,  102   b  thereon to easily slide therein. 
     With a end of the base plate  104  positioned within the channel  42  of the picture frame  24 , as seen in FIG. 3, the picture frame joint  100  can be secured in place. In similar fashion to locking of the picture frame joint  10  of the preferred embodiment of the present invention, as shown in FIG. 6, the picture frame joint  100  of the alternative embodiment is secure in place by forming an internal clamp within the channel  42  of the picture frame  24 . More specifically, as shown in FIG. 13, the wedge member, for example, wedge member  102   b  is urged in a direction so that the stepped surface  106   b  of the wedge member  102   b  engages with the stepped surface  108   b  of the base plate  104  thereby increasing the thickness of the joint to thickness B which is shown in FIG.  14 . Wedge plate  102   a  is installed in the same fashion. 
     A wedge plate  102   a ,  102   b  can be urged or slid over the base plate  104  in a number of different ways. For example, as shown in FIG. 13, an powered anvil  114  may be used to forcibly impact an edge portion  116   a  of the wedge plate  102   b  to urge the wedge plate  102   b  in the desired direction. It is possible to provide two powered anvils to simultaneously and automatically contact surfaces  116   a  and  116  to respectively urge both the two wedge plates  102   a  and  102   b  connected to opposing ends  110   a  and  110   b  of the base plate  104  to form a complete picture frame joint in a single operation. Alternatively, the eccentric tool  54  of FIG. 9 may be employed to manually urge a wedge member  102   a  and  102   b  in the desired direction by cam action via engagement of the pin  60  of with the apertures  118  in the base plate. The appropriate aperture is employed, as discussed above, to urge a wedge plate  102   a ,  102   b  in the desired direction. 
     In contrast to the preferred embodiment  10  of the picture frame joint of the present invention, the alternative embodiment  100  of the picture frame joint includes a flexible hinge created by connectors  112   a  and  112   b  that connects the wedge members  102   a ,  102   b  to the base member  104 . As a wedge member  102   a ,  102   b  is urged in a direction, the connectors  112   a ,  112   b  hingedly flex to permit movement as desired. The connectors  112   a ,  112   b , as is the remainder of the picture frame joint, preferably made of metallic material, such as steel and are preferably integrally made from the same stamping as the wedge members  102   a ,  102   b  and base plate  104 . The thickness and dimensions of the connectors  112   a ,  112   b  is selected to permit them to give and flex during movement of the wedges  102   a ,  102   b  due to the forces of the anvil  114  or tool  54  yet is still enough to maintain the wedge plates  102   a ,  102   b  in place prior to installation as in FIG. 11 or after full installation within a channel  42  of a picture frame  24 . 
     Further, the picture frame joint  100  of FIGS. 10-14 has a further advantage of being of a profile that enables the overall assembly  100  to be much lighter than prior art assemblies. A reduced, ribbed profile enables the overall thicknesses A and B to stay the same while reducing the overall amount of material employed. The reduces weight profile is shown, for example, in FIG.  12 . As a result, the total weight of the assembly  100  is reduced thereby reducing shipping costs of the picture frame joint. The assembly is, particularly, much lighter in weight than known prior art corner joints that employ mating plates with screws and tapped apertures. Also, as with the picture frame joint  10  of the preferred embodiment of the present invention, the picture frame joint  100  of the alternative embodiment is preferably made of metal, such as steel, but could be made of other material. 
     It would be appreciated by those skilled in the art that various changes and modifications can be made to the illustrated embodiments without departing from the spirit of the present invention. All such modifications and changes are intended to be covered by the appended claims.