Materials and Techniques
The most basic woodworking task is simply joining one plank to another: two flat, smooth edges meet and are held together with glue and a little pressure. Any woodworking glue, used in such a tightly-fitted seam, will produce a bond that is stronger than the wood itself, thereby forming one wide board from many narrow ones. This technique is used to make panels such as those of tabletops, furniture cases and doors, as well as the panels within most frame-and-panel doors.
Thousands of years ago, some bright soul thought of stacking thin slices or veneers of wood together and gluing them into a single slab. Veneered lumber is still around, though we call it plywood nowadays, especially as it is commonly purchased from a lumber yard.
Though some people might disparage "plywood" furniture, it is usually because the piece in question is made of poor-quality plywood, and not because plywood itself is an inferior material. A well-made veneered panel is the equal of solid wood in look, feel, durability and usefulness; in fact, there are many situations where plywood is a better choice of material than solid wood.
First of all, a veneered panel or case of almost any size will stay dimensionally stable, which cannot be said for structures made of solid wood--especially if the panels are wide. Plywood is made up of layers of wood stacked perpendicular to one another; any one layer's tendancy to shrink or swell is counteracted by neighboring layers which shrink and swell in a perdicular direction. The panel as a whole retains the same dimensions, and it will continue to do so throughout the seasons.
This is not true of solid wood. Wood's natural tendency to cycle through changes in size, but only perpendicular to the grain, creates difficulties in building which plywood solves. Many times, going to the trouble to handmake a veneered panel will mean the piece will experience less cracking, distorting and separation over its lifetime.
It is also possible to make our own "plywood": commercially available veneers, or veneers sawn from larger planks of unique or rare wood, laminated onto plywood cores, can be used to create unique patterns and display the wood's beauty. A single board with a striking grain or pattern can be used to cover a huge surface area. In the final product, such a panel is usually indistinquishable from one made of solid wood.
Last but not least, the use of veneers allows for symmetrical or book-matched panel designs, since many pieces of identical veneer will be produced from a single plank.
Plywood or solid wood? Each has its advantage, though in practice, most furniture is a mix of veneered panels and solid wood, each with its own appropriate use and purpose.