CALCULATING BOARD FEET
Ordering lumber by the board foot
The “board foot’’ is a unit of measurement used to calculate the volume of a given amount of stock. It is commonly used with hardwood lumber. As shown in the illustration at right, the standard board foot is equivalent to a piece that is 1 inch thick, 12 inches wide, and 12 inches long. To calculate the number of board feet in a piece of wood, multiply its three dimensions together. Then, divide the result by 144 if the dimensions are in inches, or by 12 if just one dimension is in feet.
The formula for a standard board:
Г x 12і x 12* = 144 = 1 (or 1-х 12ex Г* 12 = 1)
So, if you had a 6-foot-long plank that is 1 inch thick and 4 inches wide, you would calculate the board feet as follows: Гх4,х6| = 12 = 2 (or 2 board feet). Other examples are shown in the illustration. Remember that board feet are calculated on the basis of the nominal rather than actual dimensions of the stock; consequently, the board feet contained in a 2-by-4 that actually measures T^-by-3/a inches would be calculated using the larger dimensions.
J hile a chair can be made from virtually any species of wood, there are advantages to choosing strong, dense hardwoods. Such woods will resist the stress and abuse that chairs must typically endure. A chair need not necessarily be built from a single species, however, particularly if it will be painted or if the visual effect of contrasting woods is not too jarring.
Your local lumberyard is an obvious source of wood, and often the most convenient. But selection may be limited to construction woods such as pine, spruce, and other softwoods. Although you may find the occasional cache of hardwood, more often than not you will have to venture farther afield, consulting the
Yellow Pages or woodworking magazines to find lumber dealers who specialize in some of the less common hardwoods used for fine furniture. You will usually pay more, but the quality of the wood will be higher too.
There are other less costly options for finding the wood you need. A lumber mill may sell you boards at a reasonable price, but most often the wood will need to be seasoned and surfaced, which means that you must have access to a jointer and a thickness planer. Salvaged wood is relatively inexpensive and, because it often comes from old-growth timber, it can be visually and structurally superior to recently harvested lumber. And if you can fell your own trees or
obtain some recently felled stock, green wood is ideal for some chairs.
Regardless of your chosen supply, define your needs carefully before ordering your wood. When calculating how much lumber you need, make a detailed cutting list of the finished pieces of lumber needed for a particular chair (page 27 for frame chairs; page 53 for slab-ami – stick chairs).
Use the formula shown below to determine how many board feet you may need, and add 20 to 40 per cent (depending on the grade) to account for inevitable waste and defects in the wood. Because some chairs feature many curved parts, the degree of waste can run 50 percent or higher. The tips that follow
will help you buy what you need at a reasonable cost.
• Species: Ask for a specific wood species, rather than a broad family’ name. For example, order hard maple, not simply maple. To be sure you get what you want, learn the botanical name of the wood you want and ask for it.
• Quantity: When ordering wood, specify whether you want the stock in board feet or lineal feet. A lineal foot is merely an expression of a board’s length, regardless of its width or thickness. The board foot is a specific volume of wood; it is usually necessary for ordering hardwoods, which are often available in random widths only. See page 16 for information about calculating board feet.
• Size: Wood is also sold in nominal rather than finished sizes, so you need to make allowances for the difference when ordering surfaced lumber. A 2- by-4 is actually V/: inches-by-31/: inches. The thickness of hardwoods is often expressed as a fraction in quarters of an inch. A 1‘/’-inch-thick hardwood board, for example, is often expressed as 6/4. The nominal and real dimensions of unsurfaced, green boards are the same.
• Surfacing: Surfacing refers to how the stock is prepared at the mill before it comes to the lumberyard. Softwood lumber is usually surfaced on both faces; hardwood is often sold rough. If you have a planer and jointer, buying
Light woods such as hickory, white ash, and white oak riven from green wood are flexible yet strong
Any hardwood can be used, although softwoods such as poplar and pine allow leg and spindle tenons to be deeply seated and the seat to be scooped out with a minimum of effort
rough lumber and surfacing it yourself will prove less expensive.
• Seasoning: Lumber is sold either kiln dried (KD), air dried (AD), or green. Kiln-dried wood is generally the most stable. It has a moisture content (MC) of 8 percent, whereas air-dried lumber has a MC of 12 to 20 percent.
• Grade: Within the higher hardwood grades, the primary difference between the various grades is appearance rather than strength. Considering the difference in price, it is best to reserve the best stock for the visible parts of your projects, using less expensive, lower-grade wood for hidden components. Consult you lumber dealer for a chart of the different grades available.