IU 
 
 k, JM1 OF WSTRY, UBBARY 
 
 TECHNICAL NOTE number 172 
 
 FOREST PRODUCTS LABORATORY - U. S. FOREST SERVICE MADISON. WISCONSIN 
 
 HOW TO OBTAIN RIGIDITY IN CRATE CONSTRUCTION 
 
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 One of the features of a good crate is rigidity 
 or ability to resist weaving and skewing during trans- 
 portation. No method of joining the corner members of 
 a crate, not even the 3-way corner construction, is 
 sufficient alone to give rigidity to a crate. Some 
 kind of bracing across the faces is usually necessary. 
 
 Figure 1 shows a kind of bracing found in many 
 crates which are sent to the U. S Forest Products Labo- 
 ratory, Madison, Wisconsin, for testing. Partly because 
 of the amount of material used, this construction ap- 
 pears to be very strong. Laboratory tests h^y^&howrr] 
 however, that crates so braced are weak in the diagonal 
 direction of the faces, and are' therefore apt to weave 
 and skew during transportation.' m 
 
 FIG. 1 
 
 FIG. 2 
 
 FIG. 3 
 
 Diagonal braces on six sides as shown in Figure 
 2 have been found to give a crate maximum rigidity for 
 a minimum amount of lumber. Crates so braced withstood 
 with considerably less distortion twice as great a 
 diagonal compressive force in actual tests as crates 
 braced as shown in Figure i. 
 
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 A combination of diagonal and parallel slat "brac- 
 ing, as shown in Figure 3, makes the crate more rigid 
 than parallel bracing alone but not so rigid in all di- 
 rections as cross bracing on the six sides. It maybe 
 found an advantageous construction in packing contents 
 which need protection on the sides and are rigid enough 
 themselves to withstand stresses in the direction in 
 which the crate is weak. 
 
 Solid sheathing on all the faces does not make 
 a crate so rigid as diagonal bracing, except perhaps 
 sheathing which is made of wide boards with tighter 
 joints than can usually be obtained. The crate with 
 ordinary sheathing might withstand as great a load, 
 but the distortion caused by that load would be greater 
 than in a crate with diagonal braces, and would ordi- 
 narily be great enough to allow damage to the contents.