Most woodworking projects are built with solid wood lumber. Therefore, woodworkers should become intimately familiar with this ubiquitous material.
• Hardwood vs. softwood: Most furniture-grade lumber, known as "cabinetwood," fits into the hardwood category.
• Buying lumber: Look for rough lumber without twists or checks.
• Kiln-dried vs. air-dried: Either way, furniture-grade lumber must be dried to a low moisture content.
Hardwood vs. softwood
Most furniture-grade lumber, or "cabinetwood," is classified as hardwood, save for some popular softwoods like pine. Scientifically speaking, a hardwood is porous, has broad leaves, and is a member of the botanical group angiosperms. Softwood is non-porous, and produced by coniferous trees in the botanical group gymnosperms, according to Bruce Hoadley's Understanding Wood. The terms don't refer to the actual hardness of a species, although softwoods are generally less dense than hardwoods.
Rough lumber for furniture making is most commonly sold in thicknesses of 1/4-inch increments, referred to by the total thickness in fractions. For example, 4/4 lumber (pronounced "four-quarter") is roughly 1 in. thick, and 8/4 lumber (pronounced "eight-quarter") is roughly 2 in. thick. Most lumber is dealers routinely carry lumber up to 12/4. Thicker stock is available, but price per board foot increases with thickness.
Rough lumber should be purchased oversize in thickness to account for material that will be lost during the milling process. If you buy lumber that is relatively straight and without warps or twists (be sure to inspect lumber for straightness before you buy it), you should expect to lose no less than 1/8 in. to the planer and jointer. Rough lumber should also be purchased oversize in length so that the if the ends check, they can be cut back.
Kiln-dried vs. air-dried
Most handmade furniture is produced with lumber that has been dried to a stable moisture content. Most woodworkers purchase kiln-dried lumber, which has been put through a controlled drying process, usually by a lumber mill equipped with a massive kiln.
Woodworkers with the means to dry their own lumber have a few other options for acquiring furniture-grade lumber. Rough cut greenwood can be dried in shop-made kilns, sometimes powered by the heat from a light bulb, or by air drying. Air drying involves stacking rough-cut lumber in a location where it can dry slowly over time. Rough boards must be stickered, or stacked with thin strips of wood separating the boards, so that air can circulate around all sides and allow even drying. Lumber that is not properly dried may distort or split during the milling process, or challenge the integrity of a furniture piece.