Figure 18.—Showing the construction of seven-ply plywood. The grain of each layer is at right angles to that of the adjacent ply.
Briefly, we can say that the logs must be transported, studied carefully in order to determine just how to secure the most beautiful effects from the wood, usually soaked or conditioned to soften the fiber, and sliced or sawed into sheets of veneer, which are afterward dried carefully. This is a work for specialists, and is usually done at established veneer mills. At the furniture factory the sheets must again be carefully studied, matched, clipped, taped, glued, and built under a pressure of 200 to 300 pounds into the finished plyboards.
A single tree may yield 500 board feet of lumber or the same number of surface feet 1 inch thick. Cut into thin face veneers this same tree would yield 10,000 square feet or 20 times as much in terms of surface area.[14]
ADVANTAGES OF PLYWOOD
Technically, plywood is the product resulting from three or more layers of veneers joined with glue, and usually laid with the grain of adjoining plies at right angles. Almost always an odd number of plies are used to secure balanced construction. The outside plies are called faces, or face and back. The center ply is called the core, and intervening plies, laid at right angles to the others, are called cross bands. Plywood is a device for combining lightness and great strength with freedom from the tendency to warp and split.
Modern engineering, chemistry, and machinery have brought the production of plywood to a point of perfection where it is as strong, weight for weight, as steel. It is wood engineered for beauty, strength, and economical application. Its peculiar excellence, as contrasted with solid wood, results from equalizing the normal internal stresses of the wood by running alternate layers in different directions. In standard five-ply construction, widely used for good furniture, the two outer and the middle ply, or core, have the grain running in the same direction, while the second and fourth plies, or cross bands, have the grain running at right angles to that of the others. Plywood was produced by the Chinese thousands of years ago, and is found in the furniture of the ancient Egyptians. Yet it has taken modern ingenuity plus engineering and chemical skill to develop a product capable of meeting the large scale but exacting requirements of today—a product now used on land, in the air, and on the seas. Plywood was not produced by machinery, and in commercial quantities, until about 50 years ago, when plywood factories were started in Russia. Ninety percent of all wood furniture manufactured today is of veneer and plywood construction. It is used in the interest of economy, strength, flatness, and beauty, not only in cabinet and furniture making but also in residence and office building, coach-building and various engineering industries, including aviation. Plywood offers maximum strength in all directions combined with minimum weight.
BOTH SOLID AND VENEER AVAILABLE IN WOOD FURNITURE
Some persons adamantly insist that to be truly good quality, furniture must be solid, built wholly of one wood. While many experts insist that this view is untenable, those who insist upon it should, of course, buy solid pieces. To do so will frequently involve denying themselves the full beauty of the fine graining which normally can be had only in veneer. The salesman and the industry should jointly educate the customer that good veneer is not only with us to stay, but is used in some of the best furniture made anywhere in the world and that good American veneer has lasting qualities in addition to its value in bringing to the average home graining and finish that can never be obtained in furniture made from solid wood.