How a log is sawn profoundly influences a board's appearance and stability. Plain-sawn lumber, the most common cut, produces a cathedral grain pattern but tends to cup more as humidity changes. Quartersawn lumber is cut so growth rings are nearly perpendicular to the face, which is more stable and reveals distinctive ray flecks. Rift-sawn lumber is cut at an angle for stability and a consistent, linear grain appearance. Beyond solid lumber, engineered wood products offer stability that solid boards cannot. Plywood consists of thin layers, or plies, glued with alternating grain directions, producing a strong, dimensionally stable panel graded A through D based on face quality. Medium-Density Fiberboard (MDF) is made from fine compressed fibers, giving a uniform and smooth surface that does not tolerate moisture well. Particleboard is a lower-cost board of coarse wood particles, and melamine is a coated particleboard common in budget furniture. Veneer is a thin sheet of high-quality wood, typically 1/40 to 1/16 inch thick, applied to a substrate so that fine species can decorate stable cores.
Lumber itself comes in several forms. Rough lumber is wood as it leaves the mill, with irregular surfaces that must be flattened and dimensioned before use. S2S lumber has been surfaced on two sides and is flat but not yet squared along its edges, while S4S lumber has been surfaced on all four sides and is ready to use. Standard lumber sizes follow a nominal naming system: a "2x4" is actually about 1.5 by 3.5 inches once planed. Lumber is bought and sold by the board foot, calculated as thickness multiplied by width multiplied by length in inches, then divided by 144.
Preparing rough lumber for a project follows a sequence called four-square milling. The first step is jointing, where a power jointer flattens one face and one edge. Next, the planer, or thicknesser, makes the opposite face parallel at a consistent thickness. Then the jointed edge is used to straighten the second face and edge, and finally the ends are cut square. This ordered process guarantees flat, straight, and square stock ready for joinery.