Table 2.-Comparison of Strength of Three-, Five-, Seven-, and Nine-Ply Yellow Birch Plywood, All Plies of Same Thickness in Any One Panel 1 Specific gravity based on oven-dry weight and volume at test. 2 Parallel and perpendicular refer to direction of grain of faces relative to direction of application of force. Table 3-Strength of Various Species of Three-Ply Panels [Data by U. S. Forest Products Laboratory] NOTE. All plies in any one panel were of the same thickness and of the same species-grain of successive plies at right angles. In most cases 8 thicknesses of plywood, ranging from 330 to 36inch were tested. terial would be expected to modify the values appreciably in some cases. NOTE. In some of the species listed above the tests are rather limited in number. Since there is considerable variation in the strength of wood, further tests on additional ma 1 Parallel and perpendicular refer to the direction of the grain of the faces relative to the direction of the application of the force. 2 The relative splitting resistance of the various panels tested depends largely on the holding strength of glue. 3 Probably black cherry. 4 Probably eastern cottonwood. 5 Coast region. 6 Probably white fir. 7 Probably black gum. 8 Probably evergreen magnolia. Probably Khaya sp. 10 Probably tanguile. GLOSSARY [Some of the more common terms used in the plywood and veneer industry] Back. The veneer sheet on the underside of a plywood panel, corresponding in thickness, frequently in wood, to the face veneer on the upper, or exposed surface. Burl. A type of figure produced by cutting through burls, which are wartlike protuberances on trees. They contain the dark pith centers of a large number of undeveloped buds. Checks. Small hair-line splits which generally occur only in finely figured crotches and burls, caused chiefly by strain produced in the seasoning. Core. The center stock of a plywood panel. Counter Fronts.-Lumber core plywood, usually twelve feet wide, the face grain of which runs vertically with the short dimension. Cross-Banding. The veneer sheet between the core and the face veneer. Its grain runs at right angles to the grain of the core. Crotchwood.-Highly figured veneer produced from that portion of a tree where two limbs unite. Face Veneer. The veneer sheet on the upper side of a plywood panel. Its grain runs parallel to the grain of the core and crosswise to the grain of the cross-banding in five-ply construction. Figure.-Figure is the pattern formed by peculiar or abnormal arrangement of the elements within the tree; by reflected light caused by that arrangement, or by the exposure of the medullary rays. Flat Grain.-Refers to the grain produced in approximately tangential or plain cut veneers. Flitch. (a) A hewn or sawed log or a section of a log made ready for cutting into veneers by shaping up the edges, etc.; (b) after cutting, a complete bundle of thin sheets laid together in sequence as they were sliced or sawn. Grain. A rather loose term applied to the alignment and arrangement of cells and other elements of wood as it occurs in the living tree. Grain Character.—The pattern produced by cutting through growth rings and exposing the layers of springwood (porous) and summerwood (dense) and of prominent vessels, thus producing a varying pattern. Half-Round.-A method of cutting veneer to bring out certain grain character, accomplished in a manner similar to rotary cutting except that the piece being cut is mounted, off center, on a "stay log," a device that permits the cutting of the log on a wider sweep. Hardwoods.-General term used to designate the lumber produced from broadleafed, or deciduous, trees in opposition to the so-called softwoods (those produced by evergreen or coniferous trees). Heartwood. The inner, matured portion of the tree, darker in color. Knots.-Cross section of a branch or limb whose grain usually runs at right angles to that of the piece in which it occurs. Knots, Pin. A knot less than one-fourth inch in diameter which obviously shows a distinct central portion, as distinguished from swirls. Lumber Core Construction.-Plywood with core consisting of narrow edge-glued strips of lumber. Ply. A term that designates the number of layers or laminations of a plywood panel as, three-ply, five-ply, seven-ply, etc. Quarters.—Quartered or striped wood refers to sheets where quartered grain predominates with little or no heart grain. Quarters are produced by removing the center (or heart grain) from the sheets, or by cutting quartered flitches. Rotary Cut.-A manner of cutting veneer by which the entire log is mounted centrally in a lathe and turned against a broad cutting knife which is set into the log at a slight angle. Sapwood. The outer living portion of the wood in a tree. Sliced. A manner of cutting veneer by which logs or sawn flitches are held securely in a slicing machine and passed across a large knife which shears off the veneer in sheets. Stumpwood. Obtained from the base or stump of a tree. Figured stumpwood occurs where the wood fiber is crinkled into wavy ripple marks during the process of growth. Swirls. (a) The small spots developed by irregular grain adjacent to a pin knot, usually where the black center of the pin knot itself does not show, also described as a swirl or cat eye. These usually are but a fraction of an inch in diameter. (b) Irregular grain, usually surrounding knots or crotches. Small sheets with swirl figure are produced for overlays and small matched panels. Veneer Construction.-Plywood made entirely of veneers. о |