# Drawer clearance must cover the calculated movement of every solid-wood part that closes the gap Hewn Shop Notes · https://hewn.build/shop-notes/the-drawer 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: "Drawer clearance must cover the calculated movement of every solid-wood part that closes the gap." Hewn Shop Notes, hewn.build/shop-notes/the-drawer. Drafted 2026-03-15; AI-drafted, not yet checked. --- A drawer binds in the humid season when the clearance left at assembly is smaller than the seasonal swelling of its solid-wood parts. The clearance has to cover the calculated movement of every solid-wood part that closes the gap, and fitting the drawer at the seasonal midpoint keeps it working through the year [1]. ## Clearance is a movement calculation A drawer fitted in the driest part of the year is fitted to the wrong season, and it binds when humidity rises. Solid-wood drawer parts expand across the grain when humidity rises. Where a solid-wood case part also moves into the same gap, the clearance is consumed from both sides at once. Drawer clearance is calculated, not estimated: for each solid-wood part that closes the gap, movement = width × species dimensional change coefficient × moisture content swing in percentage points, and the movements are added together [1]. A managed shop held at 30 to 50% relative humidity sees a seasonal moisture content swing of about 3.5 to 4% [2]. Worked example: a 10-inch flat-sawn white oak part through a 4% swing moves 10 × 0.00376 × 4 = about 0.15 inch [1]. Worked example: two 10-inch flat-sawn white oak parts closing the same gap through a 4% swing move about 0.30 inch together, and the clearance at assembly has to cover that total [1]. ## The drawer bottom A solid-wood drawer bottom is a panel, and it floats in its grooves. A solid-wood drawer bottom has its grain running side to side, perpendicular to the direction the drawer travels, so its seasonal movement runs front to back [3]. A solid-wood drawer bottom glued in at the back, or fitted snug in its groove on assembly day, has nowhere to go in the humid season. The bottom cups, splits the back, or pushes the drawer sides apart. A solid-wood drawer bottom is glued only at the front center. At the back, the bottom slides under a short back rail or is held by a single fastener through a slotted hole so it can travel [3]. A plywood drawer bottom does not need to float, because plywood is dimensionally stable. A plywood bottom can be glued and fastened on all four edges. ## Fitting season A drawer fitted in a shop at its driest slides well when first fitted. As humidity rises its parts swell and use up the clearance, so it binds in the humid season. The easy fit on fitting day hides the problem until then. A drawer fitted at the seasonal midpoint, in spring or fall when the shop is near its middle moisture content, is slightly loose in winter and slightly snug in summer. It works in both when its clearance covers the calculated movement. Whether a drawer fitted at a seasonal extreme still works in the other season depends on the clearance it was given. Fitted at the driest, it binds in the humid season if its clearance is smaller than the calculated swelling. Fitted at the most humid, it runs loose in the dry season by the amount its parts shrink. A drawer built for a different climate needs that climate's conditions as the design input. A humid basement and a dry upper-floor apartment are different design problems. ## Solid-wood runners A solid-wood drawer runner fixed to a solid-wood case side runs across the case side's grain. A runner glued along its full length makes a cross-grain joint that eventually fails. A solid-wood drawer runner is glued at the front, where it meets the face frame, and held at the rear by a single fastener through a slotted hole. The runner stays registered at the face frame and the case side moves freely behind it. A solid-wood runner uses the same principle as a breadboard end: one fixed point, with every other point free to move. A plywood case does not need slotted runners. Plywood is dimensionally stable, and runners can be glued along their full length. ## What drawer plans leave out Drawer plans often give a fixed clearance, such as 1/8 to 1/4 inch in total for wooden runners, written for another builder's wood, shop and climate [4]. A drawer plan often does not say whether its clearance is per side or total, whether the case sides are solid wood or plywood, or whether a solid drawer bottom has a float groove. Each of those answers changes the clearance calculation. ## Sources 1. USDA Forest Products Laboratory, *Wood Handbook* (FPL-GTR-282), Chapter 13, Equation 13-3 and Table 13-5, dimensional change coefficients (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, Drawer Construction and Fitting, entry DRW-B02, 2026-03-06, unreviewed. 4. Hewn heuristic seed data, Drawer Construction and Fitting, entry DRW-04, 2026-03-06, unreviewed.