Rule 13 of 31 · Chapter III — Read the Wood

Account for wood movement in joinery

Why this rule exists

A tabletop can swell and shrink a good fraction of an inch across its width with the seasons, while its length barely budges. Screw it down tight across the grain or glue a wide panel into a rigid frame and something has to give: the wood cracks, or the joint tears loose. Wood movement isn't a flaw to defeat, it's a fact to design around. Respect it and your pieces survive the dry winters and the humid summers alike.

In practice

Let wide parts expand and contract freely across their width. Fasten tabletops with slotted clips, buttons, or oversized screw holes that let the top slide as it moves. Float raised panels in their frame grooves, glued only at the center so they expand evenly toward the edges, never glued all the way around. Run grain in the same direction where parts join, and avoid gluing long-grain hard against cross-grain over any real width, since that combination is what splits.

When it doesn't apply

Small parts, narrow rails, and plywood move so little you can treat them as stable and glue or screw freely. Movement matters in proportion to width and to how much the humidity swings. In a climate-controlled space that stays steady year-round, you can be a bit more relaxed, though designing for movement never hurts.