Upholstery Frame

In modern furniture-making, the upholstery frame gives structural support and determines the basic shape of any piece of upholstered furniture. If a frame is unstable, an upholstered piece will not be durable, no matter how fine or costly its design, padding, cushioning, or cover. Quality frames are generally made of solid wood, but plywood, engineered wood products, a variety of polymers and metals are also used.

Hardwood frames are usually constructed from kiln-dried mixed hardwoods. White ash is a superior frame making wood. White oak, red oak, and American elm are good, and hard maple and birch are acceptable. Softwoods make poor frames.

Kiln drying reduces the moisture content of the lumber, a process which inhibits checking, splitting, and strengthens the finished product.

Engineered wood products may not look strong, but can be stronger than hardwood because the layers add to the strength. They are sometimes used at critical stress areas when maximum strength is needed.

Wooden frame joints are often double doweled, which means that round wooden pegs are fitted into holes in two adjacent frame sections and glued. Epoxy coated staples and gang nails are also commonly used. The gang nail is a metal plate with saw teeth, which immobilizes the joint when it is pressed into the wood with a hydraulic press. Major joints need the additional support of corner blocks, which should be glued and screwed into place.

Since lumber costs increase rapidly with increasing board thickness, some manufacturers may hold down frame coasts by skimping at the precise point where ample strength is most important. The engineering principle involved is that strength varies directly with rail width and with the cube of thickness. If we assume that a certain 1î x 1î beam will sustain a load of 100 pounds, then a beam 1î thick and 2î wide will sustain 200 pounds. An old rule of thumb suggests that rails of 3î or more in width should be 1 1/8thî thick, while rails less than 3î wide should exceed 11/8thî in thickness.

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