Wood moves across the grain, never along it — design every joint with this in mind

A 12-inch wide board can expand or contract 1/4 inch across the grain with seasonal humidity changes. Along the grain: essentially zero movement. Tabletops attached rigidly to aprons will crack. Breadboard ends without allowance slots will split. Always use slots, elongated holes, or figure-8 fasteners for cross-grain attachments. This single principle prevents the most common furniture failures.