# A solid-wood panel is designed from its calculated seasonal movement Hewn Shop Notes · https://hewn.build/shop-notes/the-panel AI-drafted, not yet checked: Drafted by Chip, the writing system Hewn runs on Claude, from Hewn's craft corpus. Jonathan Salomons has not read this note yet, and no outside reader has checked it. Read it as a shop note: check a number before you cut to it. Cite as: "A solid-wood panel is designed from its calculated seasonal movement." Hewn Shop Notes, hewn.build/shop-notes/the-panel. Drafted 2026-03-15; AI-drafted, not yet checked. --- A solid-wood panel moves across its grain every season, so its design starts with a movement calculation for the environment it will live in, then a decision to float or fix the panel, then float clearance at least equal to the calculated movement [1][2]. ## Why panels are glued up Wide single boards are expensive, increasingly hard to find, and prone to cupping. Most solid-wood cabinet sides, tabletops and case backs are edge-glued from narrower boards. A properly prepared long-grain glue joint is stronger than the wood around it. The design question for a glued-up panel is not whether the joint holds but whether the panel has room to move. ## The movement calculation Seasonal panel movement = width × C × moisture content swing in percentage points, where C is the species' dimensional change coefficient per 1% moisture content: tangential for flat-sawn stock, radial for quartersawn stock [1]. White oak has a tangential dimensional change coefficient of 0.00376 and a radial coefficient of 0.00194 per 1% moisture content [1]. A managed shop held at 30 to 50% relative humidity sees a seasonal moisture content swing of about 3.5 to 4% [2]. An unmanaged home in the British Columbia interior is designed for a 6% seasonal moisture content swing as the safe default. Forced-air heating lowers winter humidity and widens the swing [2]. The service environment, not the shop, controls a panel's design, because the finished piece spends its working life where it is delivered [2]. Worked example: a 20-inch flat-sawn white oak cabinet side at a 4% shop swing moves 20 × 0.00376 × 4 = about 0.30 inch across the year [1]. Worked example: the same 20-inch flat-sawn white oak side at a 6% home swing moves 20 × 0.00376 × 6 = about 0.45 inch across the year [1]. Worked example: a 20-inch quartersawn white oak side at a 6% swing moves 20 × 0.00194 × 6 = about 0.23 inch, roughly half the flat-sawn figure [1]. Quartersawn panels also move more predictably board to board than flat-sawn panels, because the grain angle is consistent across every board. ## Alternating growth rings The standard glue-up instruction is to alternate the growth-ring orientation of adjacent boards, one cupped up and one cupped down, so cupping tendencies balance across the panel [3]. Alternating growth rings can produce a washboard grain pattern that shows under finish, especially on wide flat-sawn stock, and it works against grain and color matching across each glue line. Alternating growth rings suits painted work, shop furniture and workbench tops. On show surfaces, matching grain and color usually matters more, and cupping is controlled by drying and acclimating flat, straight-grained stock before glue-up. Edges should be glued up on the same day they are jointed, because a freshly jointed edge exposes wood that begins moving as soon as it is cut. ## Float or fix A floating panel sits unglued in a groove, moves freely, and leaves the case square. Frame-and-panel construction works because the panel never fights the frame. A fixed panel, glued into a dado or a rabbeted case, is sound in plywood, which is dimensionally stable, and in narrower solid-wood panels where the calculated movement stays small. A wide solid-wood panel glued into a dado will try to move against the case, and either the panel or the case fails. A 20-inch flat-sawn white oak side at a 6% swing tries to move about 0.45 inch [1]. ## Float clearance The float clearance for a floating panel is at least the calculated seasonal movement, rounded up to the nearest 1/8 inch [1]. Worked example: a 20-inch flat-sawn white oak panel delivered into a 6% swing moves about 0.45 inch, so its float clearance rounds up to 1/2 inch total, split equally on each side of the panel [1]. Float clearance runs perpendicular to the grain, because wood moves across the grain and not along it. In a cabinet side with vertical grain, the clearance runs horizontally. On a breadboard end, the center fastener is fixed and the slots run outward from center. Each side of center gets half the panel's total seasonal movement as its slot travel. ## Five questions before the first cut Every solid-wood panel wider than 6 inches gets a movement calculation at the plan stage [4]. The calculation answers five questions: 1. What species is the panel? 2. Is the stock flat-sawn or quartersawn? 3. Does the shop swing or the delivery swing control the design? 4. What is the calculated seasonal movement? 5. Is the panel fixed or floating, and if floating, is the clearance in the plan large enough? Panel failures from wood movement are set at the plan stage, when dimensions are scaled from a drawing without asking how the wood will move after delivery. ## Sources 1. USDA Forest Products Laboratory, *Wood Handbook* (FPL-GTR-282), Chapter 13, Equation 13-3 and Table 13-5, dimensional change coefficients; with the round-up-to-1/8-inch float convention recorded in the same entry (as listed in Hewn's notes, entries HEU-R735 and HEU-R739). 2. Hewn heuristic entry HEU-R736, moisture content swing by environment, 2026-03-15, Hewn internal, unreviewed. 3. Hewn heuristic seed data, S4S and Wood Movement, entry WM-04, 2026-03-04, unreviewed. 4. Hewn heuristic entry HEU-R734, governing rule for panels wider than 6 inches, 2026-03-15, Hewn internal, unreviewed.