Abstract:
To facilitate pre-plating of nail plated truss joints, a nail plate ( 10 ) has teeth ( 13 ) of increased length in a region of the plate for fixing plate to one member of a joint prior to assembly of the joint.

Description:
FIELD OF THE INVENTION 
     This invention relates to the manufacture of wooden structures such as roof and floor trusses, where structural members such as webs and chords are attached by means of metal connector plates, consisting of plates from which have been struck a pattern of projecting teeth which are driven into the members to effect the joint. The invention also relates to connector plates for use in the manufacture of such members. The invention is particularly applicable to the location and attachment of webs to chords in the manufacture of wooden roof trusses. 
     BACKGROUND ART 
     Various procedures are used in the assembly and fixing of trusses. In one approach. the chords are laid out and connected, then the webs are positioned and stapled to the chords to maintain their position while connector plates are applied successively to each side of each joint. The plates are driven home by pressing. The need for a stapling operation at each joint adds to the assembly time, as does the positioning of the underneath plate, for example by the use of a jig or frame device, or by temporarily locating the underneath plate by means of a harnmer. The latter technique has the further disadvantage that teeth may be bent, reducing the quality of the joint. 
     Attempts have been made to reduce the time involved in truss manufacture by attaching the connector plates to components of the truss prior to their assembly with the other components. For example, International patent application No. PCT/FI91/00104 describes an approach in which the plates for one side of the truss are pre-attached to the webs, while the plates for the other side of the truss are pre-attached to the chords. Such a method is of limited usefulness. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to provide an alternative approach, which enables the plates for both sides of the joint to be pre-attached to each end of a web, while still enabling the webs to be brought into position in the truss without difficulty, prior to pressing of the joint. 
     This is achieved by providing the nail plates with at least one, but preferably several, teeth of greater length than the remainder of the plate teeth, these longer teeth being located only in the region of the plate which is to be attached to one of the joint members, preferably the web. 
     In this way, plates can be attached to the-web ends by pressing the plates into position, the press driving only the longer teeth into the web. The opposed ends of the teeth of the portion of each plate which extends beyond the end of the web will thus still be separated by at least the thickness of the chord to which the web is to be attached, so the web can be brought into position for fixing to the chord without these teeth fouling the chord and thereby obstructing movement of the web. 
     Of course, while it is preferred to pre-attach the plates to the webs, they may instead be pre-attached in the same way to the chords at the correct joint positions and the webs then brought into position with their ends between the projecting opposed pre-fixed fixed plates. 
     It may be noted here that in U.S. Pat. No. 3,304,106 of Gerald M. McCormack there is described a nail plate which is divided into a region having short teeth and a region having longer teeth. In the McCormack patent, however, the short teeth have low withdrawal strength, so that the plate may be permanently fastened to the member by means of the longer teeth and removably fastened to the other member by the short teeth, in order that the truss may be disassembled for transport and later reassembled on site. Because the short teeth are incapable of forming a permanent joint, nail holes are also provided and the final joint is achieved by nailing through these holes. 
     A connector plate of the kind described by McCormack is distinguished from plates according to the present invention by the fact that the short teeth of McCormack are designed for low withdrawal resistance and are incapable of forming a permanent joint, whereas in the case of the present invention the short teeth are of conventional connector plate design, and consequently have conventional withdrawal resistance and are capable of forming a permanent joint. In other words, McCormack achieves the ability to disassemble the joint by having shorter than normal teeth over one half of the plate, whereas in the present invention the ability to pre-attach plates to one side of the joint is achieved by using in one half of the plate some teeth which are longer than normal. The conventional teeth employed in the plate are, ipso facto, capable of forming a satisfactory joint without additional means such as nailing. Such a joint will be referred to herein as a permanent joint. 
     The invention will be exemplified below in its application to roof trusses, but it is to be understood that it is applicable to other structural assemblies of wooden components, such as floor trusses. 
     The accompanying drawings illustrate, by way of example only, the application of the invention to the manufacture of roof trusses. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, 
     FIG. 1 is a plan view of a connector plate according to a first embodiment of the present invention; 
     FIG. 2 is a side elevation of the connector plate of FIG. 1; 
     FIG. 3 illustrates a connector plate pre-fixed to a web; 
     FIG. 4 illustrates a connector plate according to a second embodiment of the invention prefixed to a first member; 
     FIG. 5 illustrates the connector plate of FIG. 4 in a first stage of temporary fixing to a second member; 
     FIG. 6 illustrates a connector plate according to a third embodiment prefixed to a first member; 
     FIG. 7 illustrates the connector plate of FIG. 4 permanently joining the first and second members. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in FIGS. 1 and 2, the connector plate  10  is provided, in a conventional manner, with rows of teeth  11  struck out from the plate leaving apertures  12 . 
     The manner of formation and the pattern of these teeth may be of any suitable kind. 
     At four locations on the left hand portion of the plate (as viewed in FIGS.  1  and  2 ), a longer tooth  13  is formed by punching from a longer aperture  14 . In this way, as illustrated in FIG. 3, a pair of the plates  10  may be attached to an end of a web  15  by driving the longer teeth  13  into the web, but stopping short of the point where the shorter, conventional teeth  11  penetrate the web. 
     The web can then be introduced with a rotational movement into a truss so that the opposed free ends of the pre-attached plates embrace the chord  16 , shown in ghost outline in FIG. 3, and the joint subsequently formed by pressing the plates in any conventional manner. 
     The plate  10  illustrated in FIGS. 1 and 2 is provided with four long teeth  13 , one approximately at each corner of the region of the plate to be engaged with the web. This is but one example of a suitable pattern of location of the longer teeth. They may, for example, all be located at the rear of the plate, or towards the middle, or along one or both sides. The location of the longer teeth is entirely a matter of choice. Similarly, the number of longer teeth may be chosen to suit the convenience of the application to which the plate is to be put, and to enable efficient production of the plates. While it is possible to use only one longer tooth, a greater number is preferred to give stability to the pre-fixing of the plate. It is also preferred in the interests of stability that longer teeth are located both at the rear and the forward parts of the relevant region of the plate. 
     Connector plates according to the invention can be employed at joints between more than two members, for example where two or three webs are connected to a chord at the same location. 
     FIGS. 4 and 5 illustrate a further development of the invention, in which the second portion of the plate is provided with a number of teeth the length of which is intermediate that of the longer teeth provided for the pre-fixing of the first portion of the plate, and that of the conventional teeth  11 . 
     This plate enables the elimination of separate means, such as stapling, for the temporary fixing of the web  15  in its correct position in conjunction with the chord  16 , prior to the pressing of the joint. The plates  10  (only one of which is shown here) are pre-fixed to the web  15  by pressing them only by a distance which does not exceed the difference between the length of the teeth  13  and the teeth  17 . At this stage the teeth  11  will be proud of the surface of the web, and the teeth  17  will not obstruct the engagement of the web with the chord, as the chord enters the space between the opposed free ends of the plates. The plates can then be engaged with the chords by driving the intermediate teeth  17  into the chord, for example by means of a hammer blow, prior to the final pressing of the joint. 
     FIG. 6 illustrates a third, less preferred, embodiment in which the first region of the connector plate has only a single long tooth  13 . 
     FIG. 7 shows the arrangement after the final pressing operation, whereby the teeth  11 ,  13 ,  17  are driven into both the first and second members, so as to effect a permanent joint between the members. 
     It will be understood that the principles disclosed in this specification can be applied to connector plates and connector plate joints in wooden structures in many ways other than those given by way of example.