Woodworker's Journal 1993-17-4, страница 21

Buying Lumber: Bored Feet?

When buying lumber it's helpful to understand a bit of the lingo of wood measurement, grading, surface preparation and seasoning. Staff at good lumberyards, wholesalers and sawmills ought to be able to explain this stuff without making you feel like an idiot. If, however, you don't want to take the chance, here's a simplified, but serviceable introduction.

Board feet: Most places sell lumber by the board foot, a rather simple concept, but arcane enough to separate woodworking initiates from the sawdust-free populace. (A measure of the unworthiness of Home Improvement Centers is their tendency to sell boards by the square foot.)

A board foot (bd. ft.) is 1 ft. square by 1 in. thick. A board 2 ft. long. 6 in. wide and 1 in. thick contains 1 bd. ft.; so does a board 1 ft. long, 6 in. wide and 2 in. thick To find the board-foot measure of a board, plug its measurements into the following formula;

thickness (in.) x width (in.) x length (in.)

144

Thickness: Another peculiarity of the lumber trade is the nomenclature used for thickness. One-inch boards are called "four quarter"'(4/4); boards 1V? in. thick are "six quarter" (6/4); those 2 in. thick are "eight quarter" (8/4) and so on. (I notice that Paxton's catalog has done away with this quaint custom, though their salesmen still talk the talk.) The logic is obvious, but you have to keep on your toes. These numbers always refer to the board's rough-sawn thickness; even though subsequent planing can reduce a 1 in. board to Va in. thick (see "surface preparation"), it is still sold as "4/4" stock. And—remember this—board-foot measures are always calculated using the rough-sawn thickness.

Length and width: Hardwood lumber is often sold "random length and width" with all boards complying with specified limits. Assume, for example, you're buying random length and width cherry guaranteed to be at least 6 in. wide and 8 ft long. The boards you receive might all be 6 in. wide and 10 ft. long, or they might contain widths between 6 in. and, say, 15 in. and come in a range of lengths over 8 ft. If specific lengths and widths are important to your project, you can specify them in your order, though it will probably cost you a bit more.

Grading: This is truly arcane information and quite

unnecessary if you can pick the boards out yourself. However, some familiarity with the system is useful if you're buying boards sight unseen, say from a distant supplier. The standards, set by the National Hardwood Lumber Association, identify a range of grades that differ, basically, in the number of detects allowed on the board's faces.

Many suppliers lump together the top two grades into a single category, "firsts and seconds" (FAS). If you're buying small quantities or need wide, blemish-free surfaces, stick with FAS. Either ot the next two grades, "Selects" or "No. 1 Common" can be a good deal for projects requiring narrower finished pieces or if you're willing to glue up wide pieces from several narrow ones. You can save money on lower grades if your protects, or temperament, will allow for more detects. (For a good discussion of lumber grading, see Bruce Hoadley's book Understanding Wood, published in 1980 by the Taunton Press, Newtown. CT 06470.)

Surface preparation: Most local lumberyards sell boards that have been surfaced on the two wide faces, This S2S ("surfaced two sides") stock is easier for you to evaluate than rough-sawn boards because defects and blemishes are readily apparent. Planing the edges in addition to the faces produces S4S boards ("surfaced four sides") of uniform width as well as thickness.

Wholesalers generally offer rough-sawn lumber (though they'll surface faces and edges for an additional charge) and I prefer it that way. Pushing a board through a planer cleans its faces, but it rarely flattens it. Flattening and thicknessing your own roughsawn boards with a handplane or machines (after cutting them to the lengths and widths required for your project) allows you to get the greatest thickness out of the material and. most importantly, ensures the flat parts necessary for quality work.

Seasoning: With the exception of lumber bought directly from a sawmill, the lumber you buy will almost certainly be seasoned, either in a dry kiln or the open air. If you buy from a reputable supplier, you can count on most of it being properly dried.

If you buy from a sawmill, it's prudent to stack and air dry the boards, even if the mill has done so already. Regardless of who seasons the wood, remember that it placed in a moist environment seasoned wood will absorb water vapor and swell: to avoid problems, stack wood in your warm, dry shop for at least a week or two before beginning a project.

July/August I <W3

21