Patent Abstract:
This invention describes a snap-lock interlocking joint which locks a pair of mating construction pieces together by the insertion of a specially shaped tongue into a corresponding groove (having a complimentary shape to the tongue). The invention works well with engineered wood composites such as medium density fiberboard and certain other plastic products, namely free foam cellular plastic. The pieces may be joined together in the complete absence of glue or nails. No clamping is required to provide a strong joint.

Full Description:
BACKGROUND OF THE INVENTION 
     This invention deals with a method of manufacturing permanent interlocking joints, where it is desired to snap together at least two construction pieces of a material resembling wood which can quickly be assembled to form a composite assembly. This assembly may or may not be incorporated into another assembly or it may be complete as joined. It is to make such an assembly which snap-locks together in the total absence of glue, or other adhesive material, or nails that this invention is directed. 
     It has been common practice to nail wooden pieces together to form an assembly. With the advent of the powered nailing devices it has even become less complicated to construct a wooden assembly. If the wooden article is to function as a piece of furniture or some other display device where appearance is of importance, the nail holes must be filled with a suitable substance before a finishing coat of varnish or some other protective coating is applied to the surface of the article. 
     A much slower but clearly an acceptable method of joining wooden construction pieces together is by using glue or an adhesive substance which is applied to the surfaces of the pieces to be joined. In this instance the mating surfaces which are to be joined are suitably prepared for the application of an adhesive material. After the adhesive has been applied to the mating surfaces it is standard practice to clamp the pieces undergoing the gluing process in a particular configuration. The process may require that the pieces undergoing the gluing operation be held in a suitable “jig” in order to ensure correct alignment of the pieces undergoing joining. 
     In any event the two surfaces which are to be joined together are either both coated with an adhesive material, or only one surface is coated. The two wooden pieces are then pressed or clamped together at the joining surfaces where the adhesive material has been previously applied until the adhesive material has set or cured. The clamping device may now be removed from the glued assembly. With this method of joining no nail holes are present to be filled before finishing the assembly. 
     In the woodworking and construction industries, methods of joining wooden or wooden composite members which snap-lock together in the absence of glue or nails have been sought without much success until this time. 
     SUMMARY OF THE INVENTION 
     This invention seeks to assemble two pieces of wood (or other suitable material) in a snap lock joint in the complete absence of glue or nails to form a permanent joined assembly. This is accomplished by providing a suitably prepared pair of construction members each having a joining surface which has been machined to a special profile. The profile provided on the members yields what appears to be a “tongue and groove” but it is not such a joint. 
     One of the members is provided with a “tongue” that is somewhat wedged shaped as it arises from the mitred surface on which it formed. The widest part of the tongue occurs at some distance above the mitred surface. 
     A mating piece of wood (or other similar material) will be supplied with a specially profiled groove which is the complimentary image of the tongue supplied in the first instance. The wood surrounding the groove must have sufficient elasticity to permit the groove to expand slightly during the insertion process so as to permit the insertion of the tongue into the groove. The groove then snaps shut and grasps the specially shaped tongue to form the completed assembly. The result is a finished assembly which snaps together and once the snapped together, remains together until pried apart. 
     
       
         
               
             
               
               
             
           
               
                   
               
               
                 PRIOR ART 
               
             
          
           
               
                 U.S. Patents 
                   
               
               
                   
               
               
                 7,131,242 
                 Nov. 7, 2006 
               
               
                 6,606,834 
                 Aug. 19, 2003 
               
               
                 6,421,970 
                 Jul. 23, 2002 
               
               
                 5,987,845 
                 Nov. 23, 1999 
               
               
                   
               
             
          
         
       
     
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the completed assembly. 
         FIG. 2  shows a joint of an assembly where the angles between the members being joined is much greater than 90 degrees. 
         FIG. 3  shows an assembled joint where the members being joined lie at an angle of slightly greater than 90 degrees. 
         FIG. 4  is a partial sectional perspective of a pair of assembly members about to be coupled. 
         FIG. 5  shows the members shown in  FIG. 4  now in an assembled configuration. 
         FIG. 6  is a plan view of a pair of wooden members coupled in an assembly. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIG. 1 , a finished assembly  10  is shown. This assembly comprises members  12 ,  14 ,  16 ,  18  assembled together by means of a specially shaped joint  20  which holds the entire assembly tight together in a stable manner in the absence of any adhesive. The joint  20  is produced in both components by a milling operation; it is most difficult to produce this profile with a router. For convenience, the shape of the joint described in this disclosure will be referred to as being frusto-cardioid shaped. This joint is produced by several machining operations and produces a stable joint. Other shapes for the interlocking parts of the joints are no doubt possible, however applicants have selected this shape for this application. 
     As shown in  FIGS. 2 and 3  the frusto-cardioid joint may be effectively used to connect members which are to form an angle greater than 90 degrees; for instance when assembling a polygonal assembly. It will be seen that members  22  and  24  are connected at a joint  26 . 
     The frusto-cardioid joint is probably best illustrated at  FIG. 4 . Here a pair of composite wooden members  40  and  42  are about to be snapped together in a joined relationship. Member  40  is provided with a female receiving groove  44  and member  42  is provided with a complimentary shaped projection  46 . The member  40  is provided with a pair of coplanar surfaces  48  and  50  which form the abutments on the base surface for the resulting joint between members  60  and  62 . 
     The groove  44  has a peculiar shape in that the widest dimension of groove  44  occurs at a line joining points  52  and  54  which is located at a distance “d” from the base surface  48 - 50 . 
     Member  42  is provided with a male projection  46  which has the surface contour to match that of groove  44  of the member  40 . Member  42  has two engaging coplanar surfaces  60  and  62  which will abut surfaces  48  and  50  when the joint between members  40 - 42  has been accomplished. 
     The widest portion of projection  46  occurs at a line passing through points  66 - 68  and this point occurs at a distance “d” from the coplanar surfaces  60  and  62  of member  42 . 
     To assemble the joint, the groove  44  of member  40  is mated with the projection  46  of member  42 . The projection  46  is forced into groove  44  by any suitable means, usually a mallet. The groove  44  springs open slightly and the projection  46  slides into groove  44  until the base surfaces  48 - 60  and  50 - 62  engage each other. At this time the widest part of projection  46  is now located at the widest part of groove  44 . 
     Because of this peculiar shape the curve, which is referred to as a frusto-cardioid, it is most difficult to produce this shape with a router. It is usually produced by at multi spindle machine usually referred to as a moulder. 
       FIG. 5  shows the joint of  FIG. 4  assembled. Here the members  40  and  42  have been snapped together to form a complete interlocking joint. 
     The opening in female groove  44  of member  40  must be sprung apart slightly to accept projection  46  of member  42 . As soon as the projection  46  enters the groove  44 , the elasticity of the material forming the groove  44  returns the groove  44  to its original profile and projecting strip  46  is grasped by groove  44 . 
     This joint is intended for materials such as engineered wood products or wood products which by their nature are not extrudable. Other products which may be successfully utilized are: high impact plastic materials such as PVC; cellular PVC and so on. The materials which have yielded the best interlocking joints to date are MDF composite wood products. These materials exhibit no grain preference and have enough elasticity to yield a stable joint when assembled. 
     Although some metals may be extruded to yield the frusto-cardioid joint, generally the modules of elasticity has been found to be too high to permit the insertion of the projection into the female groove. 
     In summary, this is truly a “green” invention. No glue or nails are required to make the joint between two mating pieces. If the completed assembly is being used as a temporary assembly, the whole assembly may be recycled at a later date without fear of contamination of the surrounding media with glue residue etc. 
     To a large extent the success of this invention resides in the elasticity of the material wherein the recess is formed. That is why the engineered composite wood products such as MDF and HDF composites perform so well. 
     Many modifications and other embodiments of the invention will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is understood that the invention is not to be limited to the specific embodiments disclosed, and that the modifications and embodiments are intended to be included within the scope of the dependent claims.

Technology Classification (CPC): 5