The lumber used to make furniture-quality projects differs in several ways from the dimensional lumber used in building construction. It's drier (less than 9 percent moisture content), has fewer defects (the number depends on the grade), and costs more. The first step to becoming a savvy lumber shopper is to learn the difference between softwoods and hardwoods.
Commonly available lumber made from softwood species is cut from coniferous evergreen trees, which do not drop their needles each year.
Of the many types of softwoods, the following are easiest to find:
Softwoods are both lighter and softer than hardwoods, making them easier to work with.
Redwood and western red cedar lumber are sold a bit differently from other softwoods. They're graded both by appearance and by the amount of decay-resistant heartwood the boards contain—the more, the better. Clear all-heart is the most costly; construction common, the least.
Softwood boards 1 inch thick—the type you'd use for bookcases and shelves—are sold in 2-inch-width increments, such as 1x2, 1x4, and so on up to 1x12. Home centers usually group softwood boards by width and length.
You won't want to use boards that display any major defects, especially ones that are warped. To check a board for warp, lay it on the floor and see if it lies flat. Also check for knots. Reject boards with loose ones—they'll have a visible dark line around them and will work loose and eventually drop out. Tight knots, on the other hand, are structurally sound but must be coated with a sealer before painting so they don't weep sap and discolor the paint.
Produced by broad-leafed, deciduous trees that—in the world's temperate zone—lose their leaves each year, hardwoods are often used for cabinets and furniture because of their beauty, stability, strength, machining predictability, and resistance to abuse.
Here are some woodworking favorites:
Hardwood trees are not as abundant as softwood trees in North America, so their lumber is more valuable. That's also why hardwood logs are sawed to minimize waste, resulting in boards of varying quality. Because of that, hardwood boards are assigned grades. The higher, costlier grades yield more defect-free (clear) material.
There's also a major difference in the way hardwoods are sold. You buy them by the board foot. That's a volume measurement of thickness, width, and length that equals 144 cubic inches. A board measuring 1x12x12 inches equals one board foot. You seldom have to do those calculations because most retail hardwood outlets, including home centers, have already done so before pricing their boards. Board footage is usually rounded up or down to the nearest one-half board foot.
Woodworkers usually refer to hardwood board thickness in 1/4-inch increments. A 1-inch-thick board is 4/4 (four-quarter); a 1-1/4-inch-thick one, 5/4 (five-quarter); a 2-inch one, 8/4; and so on.
Hardwoods (and the best softwood grades) are also kiln-dried at a controlled temperature to reduce their moisture content to 6 to 9 percent, the ideal range for interior projects. Kiln-dried lumber won't readily reabsorb moisture when properly coated with a finish. That means it will remain stable in use and will be less likely to swell, shrink, crack, or warp over time.
Lumber can have a number of defects that buyers should look out for. Cups, bows, crooks, and twists refer to warped boards that are no longer straight and level.
Knots, on the other hand, can be okay. It just depends on the type of knot. Avoid boards with loose knots. Loose knots often fall out as the wood dries, leaving a hole. Tight knots are acceptable but need sealing.
Both softwood and hardwood come in different grades. Here's what each means:
First and seconds (FAS): Best grade. Boards yield 83 1/3 percent clear wood.
Selects: One side FAS, other side No. 1 common. Same yield as FAS on one side.
No. 1 common: Economical. Boards yield 66 2/3 percent clear cuttings on one side.
C select and better: Minor imperfections.
D select: A few sound defects.
3rd clear: Well-placed knots allow for clear cuttings.
No. 1 shop: More knots and fewer clear cuts than 3rd clear.
No 2, No 3 common: Utility shelving grades. No. 2 has fewer and smaller knots.