Inexpensive and disassemblable structural units
SUMMARY OF THE INVENTION 
     Devices commonly known as slot and tab or mortice and tenion or by other equivalent names are utilized in a novel system to produce opposing and interlocking force vectors which result in three-dimensional rigidity without usage of any permanent jointures, thereby being of useful service to a mobile society of disassembling easily to a least-volume solid package. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of horizontal panels utilized in the present invention; 
     FIG. 2 is a plan view of longitudinal vertical panels adapted to engage two of the horizontal panels of FIG. 1 for the uppermost and lowermost tiers of the present invention; 
     FIG. 3 is a plan view of longitudinal vertical panels adapted to engage two of the horizontal panels of FIG. 1 for the intermediate tiers of the present invention; 
     FIG. 4 is a plan view of transverse vertical panels adapted to engage the panels of FIGS. 1 and 2 in the present invention; and 
     FIG. 5 is a plan view of transverse vertical panels adapted to engage the panels of FIGS. 1 and 3 in the present invention. 
    
    
     DESCRIPTION OF THE INVENTION 
     The teachings of this invention permit the erection of strong structural units that are rigid in all dimensions, without usage of any permanent joining, for a variety of applications. The avoidance of permanent joints permits easy reduction of the unit to a least volume solid package when the purpose of the unit has been completed or the unit is to be moved to a new location. The design system is believed to differ substantially from earlier, cosmetically similar, usage of the slot-tab devices in such widely varying applications as barns and paper dolls. The system requires use of sheet materials having multi-directional strengths, such as plywood, fiberboard and hardboard, to resist the multi-directional forces imposed. The location of the temporary slot-tab joints in the system is critical to the uniform distribution of loading forces, whereupon the unit strength approximates the strength of the material used. Tensile and shear stresses are involved in local areas, but the system design goal is to translate these stresses into predominately compressive functions. 
     System usage is visualized over a range from modular buildings to small boxes, but primary usage is expected to occur in nonmotive furniture cabinetry such as storage shelving, bookcases, tables, doll houses and cabinets. A bookcase is shown in the drawings as a typical unit example. It is noted that system rigidity increases directly with load increases, due to the stress distribution design, within the strength of material. 
     Drawing FIG. 1 represents the parts pattern for the components lying in a horizontal plane or the shelves of the bookcase. The number of parts required is the number of shelf spaces desired plus one. FIG. 2 represents the vertical back of the top and bottom shelf spaces, having total tabs on one long edge and half-tabs on the other to interlock with a matching structure within the appropriate slots of FIG. 1. The number of parts required is two. FIG. 3 represents the vertical backs of the intermediate shelf spaces, having interlocking half-tabs on both long edges and requiring number of parts equal to the number of shelf spaces less two. FIG. 4 represents the vertical shelf ends and middle supports for the top and bottom shelf spaces with tabs analogous to those of FIG. 2 and requiring six parts. FIG. 5 represents the vertical shelf ends and middle supports for the intermediate shelf spaces, has the interlocking half-tabs on both top and bottom edges analogous to FIG. 3 and requires a number of parts equal to the number of shelf spaces times three and less six. 
     In the assembly sequence, one part from the pattern of FIG. 1 is placed on the floor. The side tabs of three parts from FIG. 4 are inserted into the matching slots of one part from FIG. 2 with the full-tabs down and these full-tabs inserted into the slots of the first part placed on the floor. A second part from the pattern of FIG. 1 is then placed over the upper exposed half-tabs of the assembled parts. The process is repeated for the intermediate shelves using parts from FIGS. 3 and 5 in the same manner and with half-tabs interlocking in the slots. The case is completed by finishing with the remaining set of parts from FIGS. 2 and 4 with the full-tabs up and the remaining part from FIG. 1 placed over them to form the top and lock the assembly into a three-dimensionally rigid unit ready for use. The reverse procedure disassembles the case, resulting in a solid stack of material approximating the total volume of the component parts for storage or moving. 
     System design criteria requires, firstly, that the edge slots be placed a distance from the edge normally equal to the thickness dimension of the material. Interior slots are, secondly, normally so placed as to divide the remaining space in the number of segments required by a calculation of the strength of the material and the design load. The tab insertion length is, thirdly, normally equal to the material thickness dimension to accomplish the criterion of containment. The tab width is, fourthly, a maximum function of four times the material thickness dimension. The tab width is, fifthly, a minimum function of twice the material thickness dimension. The tab-slot spacing is, sixthly, a minimum of two per linear edge of tab or slot device to derive alignment and of a number two or greater calculated from the strength of material and design load in vectors of containment and support. The satisfaction of said system design criteria comprises and describes the subject invention system.