AMERICAN HARDWOOD PLYWOOD

Hardwood plywood is the cabinetmaker's mainstay, the furniture designer's standby, the decorator's ally, and the architect's and builder's prop. Hardwood plywood is as much a part of modern life as is the bed in which you sleep and the table or desk at which you sit. Yet, numerous as are the everyday applications of this product, few persons beyond those directly engaged in its production and utilization are even aware of its presence, much less of its importance in the business and family life of the Nation.

Only through the utilization of plywood can the radio cabinets gracing practically every home in the county be economically produced. Wherever wide surfaces, either flat or curved, are used on fine furniture, plywood yields excellent results without sacrifice of durability or beauty. This holds true for the top of the small but exquisitely inlaid occasional table or of the large, pretentious dining table. The unusual and beautiful wood figures characterizing bedstead design could not be produced were it not for this application of hardwood plywood. Drawer fronts, also the sides and tops of dressers and commodes, are usually of plywood. To the furniture industry, hardwood plywood is indispensable. The paneled walls used so effectively in office buildings, hotel lobbies, and other public places are generally of hardwood plywood, as are the cabinets, counters, and showcases in our modern stores.

The extensive use of plywood is based on the three major factors of permanence, practicability, and economy of fabrication, as well as on the factors of space and weight saving.

The permanence of plywood is af first importance. By its construction, plywood overcomes the natural tendency of wood to swell and shrink across the grain. Plywood, properly manufactured, can be relied upon to render maximum service and dependability.

The practicability of plywood is evidenced by its widespread application. The facility with which panels can be worked, their ability to reveal the beauty of face veneers of unusual grain, their availability in almost unlimited sizes, and their high structural strength, account in large part for their popular use.

The utilization of wood through the medium of veneer and plywood manufacture has long been recognized, inasmuch as it allows for close economy in fabrication. Fine figured woods have, since time immemorial, appealed to the aesthetic sense of mankind. In the form of lumber, the supply of the more valued hardwoods would be greatly reduced and perhaps not available in sufficient quantities to satisfy the demand a condition which would raise their cost to a place beyond the limits of general usage. 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 more in terms of surface area. To illustrate, among some trees of fancy-figured wood, one tree can produce sufficient face veneer to panel 20 average rooms, whereas a single room would be its limitation if cut into solid lumber.

Panels faced with veneer from a single tree are harmonious in design and coloring. Thus, it is possible to carry out an architectural scheme or permit a designer's vision to take form in symmetrical or matched figures.

The fabrication of hardwood plywood is no new art. It has been practiced through a hundred generations by the master craftsmen of civilization. The ancient Egyptians believed in a life after death similar to man's earthly existence. In anticipation of human requirements in the new life, household goods and necessities of daily life were grouped about the sarcophagus. Many of the wood articles found by excavators are of plywood construction.1 Hepplewhite, Sheraton, and other renowned furniture craftsmen of the eighteenth century availed themselves of the wonderful opportunities veneered panels offered in the fine decorative handicraft for which they are noted.

However, as with all other medieval crafts, modern engineering and scientific achievements have so improved the technique of plywood manufacture that, despite the remarkable skill of the masters, twentieth-century hardwood plywood compares with their product much as the modern ocean liner compares with the Roman Galley.

Scientists have applied their intelligence to fathom the intricacies of wood structure. Engineers have devised precision machinery with which to take advantage of the knowledge that science has revealed. Chemists, notably during the past 20 years, have devoted their efforts to the perfection of modern adhesives. Their combined efforts have enabled modern hardwood-plywood mills to make a product of greatly improved quality. As a result, hardwood plywood now enters new fields to an extent scarcely anticipated a few years ago, especially where material combining strength and lightness with an attractive appearance and permanence is desired. The increasing use of hardwood plywood in marine and airplane construction, and even in truck trailers, is evidence of such trends.

WHAT IS HARDWOOD PLYWOOD?

Hardwood plywood is wood engineered for beauty, strength, and economical application. Technically, plywood is the product resulting from three or more layers of veneer 2 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. A technical distinction is usually made between

1 Veneer and Plywood, Knight and Wulpi. Ronald Press Co., New York, 1927.

2 Veneer is a thin sheet of wood manufactured by three basic methods: Rotary-cut veneer.-Veneer cut in a continuous strip by rotating a log against the edge of a knife in a lathe. Sawed veneer.-Veneer produced by sawing. Sliced veneer.-Veneer that is sliced off by moving a log, bolt, or flitch against a large knife. (Wood Handbook, Forest Products laboratory, Madison, Wis., 1935.)

230704°-40- 2

plywood, as such, and laminated wood. Through such balanced construction of plywood panels, full advantage is taken of the outstanding strength properties of wood. Plywood offers maximum strength in all directions, combined with minimum weight.

It becomes readily apparent that the word "plywood," in its broader sense or usage, may refer to various types of assembly or construction. For example, the essential features of plywood may apply to cores of veneer, lumber, or various combinations of veneer and lumber. The total thickness might be less than one-sixteenth of an inch, or more than 3 inches. The different plies may vary as to number, thickness, and kinds of wood, and the shape of the members may also vary. The purpose for which the resulting plywood is to be used and the qualities desired for this use govern the selection of the type of construction.

4

Hardwood plywood is not only decorative but, is relied on to give strength to the structure of which it is a component part. To the consumer, plywood offers many desirable and advantageous properties. First, plywood that is properly designed and is manufactured with balanced construction has very slight tendency to expand or contract and thus stays in place satisfactorily. Also, the approximate equalization of strength properties along the length and width of the panel results in greater resistance to checking and splitting. As a result of such balancing, a plywood panel might be described as being equally strong in all directions. This characteristic results in a high degree of rigidity in large structural sheets.

Another property of plywood is its great resistance to splitting by nails, screws, or other types of fastenings. Fastenings may be made very close to the edges without damage. Furthermore, in this connection, plywood has very satisfactory nail-holding ability. The power of plywood to resist splitting is also demonstrated by ability to withstand a sudden impact of force. For example, the sudden pushing of a table against a plywood panel would not result in a crack or split unless the force were sufficient to actually puncture the panel.

As previously indicated, hardwood plywood is produced in numerous types of assembly by varying the number of plies, their individual thickness, and the woods utilized, the variations being dictated by the mechanical requirements of the installation. Typical hardwood plywood is usually of three or five plies. The five-ply is built up from a center ply (the core) set between two sheets of cross-banding and two sheets of face veneer.

Core and cross-banding provide a structurally strong foundation for the face, veneers. Face veneers are primarily selected for their beauty, sometimes from the rarest and most unusual woods. Depending upon their thickness and properties, the veneers play an impor

3 Laminated wood is defined as a piece of wood built up of plies or laminations that have been joined either with glue or with mechanical fastenings. The term is most frequently applied where the plies are too thick to be classified as veneer and when the grain of all plies is parallel. (Wood Handbook, Forest Products Laboratory, Madison, Wis., p. 6.)

4 Balanced construction refers to matching of plies so that for each ply on one side of the central core there is a similar and parallel ply on the opposite side. Matching of plies involves a consideration of (1) thickness, (2) kind of wood with particular reference to shrinkage and density, (3) moisture content at the time of gluing, and (4) angle or relative direction of the grain.

tant part in the stability of the panel. Generally, however, this condition is governed by the core structure. Standard face veneers in fine hardwoods are generally cut one twenty-eighth inch thick. Engineers, furniture designers, architects-all those who direct the use of hardwood plywood-take cognizance of the advantageous properties of this modern product in building lighter weight but stronger jobs.

Figure 3.-Five-ply panel, showing the lumber core (center) with grain running longitudinally, the two pieces of cross-banding with grain running at right angles, and the two face veneers with grain paralleling that of the core.

Hardwood plywood is truly a splendid example of man's ability to improve on nature in the production of a vehicle for permanent craftsmanship in wood. Without resorting to plywood construction, many of the most beautiful woods which the world's forests produce could not be utilized commercially. Crotch, burl, and stump wood, in particular, have a marked natural tendency to crack and split, owing to the irregularity of their grain. Applied in the form of thin face veneers on plywood panels, such tendencies are minimized and the outstanding beauty of these woods is realized to the utmost.

AMERICAN AND FOREIGN HARDWOODS USED

The United States is rich in its resources of native hardwoods, many of which have become world-famous because of their outstanding useful properties. In color, figure, texture, hardness, and workability, American hardwoods cover such a wide range as to meet almost any demand of modern manufacture or construction.

In speaking of hardwoods it must be noted that the term "hardwood" does not necessarily mean that the wood is "hard" in the dictionary sense of the word. Woods from deciduous (broad-leaved) trees are considered hardwoods by the industry, and all coniferous (needle-leaved) trees are classed as softwoods. Thus, poplar and basswood are hardwoods, yet they actually are soft; and longleaf pine is a softwood, although it actually is hard.