Blocking and Bracing
Furniture can last for decades or even centuries if constructed properly. Wooden furniture such as chairs and tables can withstand considerable strain if stress points are designed correctly. Blocking and bracing is a way of reinforcing the stress points of furniture, and is an indicator of quality construction.
Some of the least complicated forms of bracing involve stretchers between front and back legs, and side legs. Stretchers are simply crossbars that connect and strengthen the legs of furniture. They are often decorative, and elaborately carved or turned, and thus provide both stability and ornamentation. However, not all styles are suited for stretchers, and it is often the secondary, or hidden blocks and bracers of a piece that provide the most stability.
Sideways pressure exerts stress at the joints between the legs and rails of chairs and tables. Good mortise and tenon, or glued dowel joints are best able to cope with the everyday movement of these types of furniture, but to hold the frame rigid a corner block must be used. A corner block is a triangular shaped piece of wood that is joined to both the side rails and leg of a table or chair, usually by screws and dowel joints. Another way to strengthen the joints is by using steel braces or metal corner plates. A metal corner plate fits into grooves cut in the rails, and is attached by screws. A metal bolt is inserted through a hole in the center of the plate, and goes into the leg. The screw is then tightened with a wing nut, which pulls the legs and rail tight and holds the frame rigid.
No matter how carefully wood is selected for fine furniture, some amount of shrinkage is inevitable, even in kiln-dried wood. The smallest gap in a tabletop can ruin the appearance of an otherwise fine piece of furniture. One way to prevent gaps is by the use of shrinkage plates, which are metal plates or braces that form a right angle. One side is screwed into the rail and the other side, with slots at right angles, is placed under the tabletop. A screw is inserted through the tabletop into the slot in the plate that runs across the grain. This prevents the top from separating from the rail when natural shrinkage occurs.
Cabinets and bookcases also require bracing and blocking to prevent stress on the joints. Cabinets should be braced with either corner plates, a rigid back, or vertical pillars. Shelf support rails also add to the stability of casework.
- Back -