The chief purpose in overlaying wood, first practiced by the ancients and later by artisans of the 18th and 19th centuries, is to produce a surface of beauty over a less aesthetic surface. Modern hardwood plywood is a mixture of the aesthetic and the functional. A distinct characteristic of hardwood plywood is its ability to be used to create beautiful decorative effects and at the same time, be very useful – wall panels and furniture exemplify this characteristic. The inherent property of veneer cutting is such that full-size sheets of valued woods (i.e. Mahogany, Cherry, Walnut) can be obtained, whereas producing such sheets by other methods would be either impossible or too costly.
Advantages Of Plywood
Plywood has many structural advantages. Wood is stronger along the grain than it is across the grain. By alternating the direction of the grain 90 degrees with each successive wood layer or ply, the strength properties are equalized. Pound for pound, plywood has been proven to be stronger than steel.
A property of wood familiar to all is the ease with which it splits along the grain. An example of this is the method of cutting firewood with an axe or hatchet; also, nearly everyone has seen wood split from nailing.
Crossing layers of wood, as in plywood construction, reduces this tendency so that splitting is not a problem.
The cross-layering concept of plywood creates a more stable product. With changes in moisture content of the wood from its wet (green) condition to a completely dry state, it is possible for some woods to change dimension upto 12% or more across the grain while the dimensional change along the grain is only 1%. In plywood, this across-the grain dimensional change is greatly neutralized so that the maximum potential dimensional change of plywood in any of the two dimensions (across the grain and with the grain) is rarely over 1% to 2%.
Plywood manufacturing achieves a more complete utilization of the log than does lumber manufacturing. This is particularly true when comparing the yield of rotary cut veneer with lumber. No sawdust results from either rotary cutting or slicing, which are the two usual methods of cutting veneer.
Plywood manufacturing makes for a more efficient utilization of species. Valuable woods can be used as face veneers, and less valuable woods can be used as cores and inner plies. Low-grade veneers can be placed in the panel as inner plies without affecting the appearance of the face veneer and without materially affecting the strength of the panel.