# A breadboard end is glued only at the center tenon and slotted everywhere else Hewn Shop Notes · https://hewn.build/shop-notes/the-breadboard-end 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 breadboard end is glued only at the center tenon and slotted everywhere else." Hewn Shop Notes, hewn.build/shop-notes/the-breadboard-end. Drafted 2026-03-15; AI-drafted, not yet checked. --- A breadboard end is attached with several mortise-and-tenon joints. Only the center joint is glued and pinned. The outer tenons are left unglued in mortises elongated by half the panel's calculated seasonal movement on each side of center, plus a small margin, and any outer pins pass through slots, not round holes [1][2]. ## What a breadboard end is for A breadboard end caps the end grain of a panel. End grain looks unfinished, takes up and releases moisture unevenly, and seasons at a different rate than face grain. A breadboard end runs perpendicular to the panel's grain, which puts its length in exactly the direction the panel moves each season. A rigidly attached breadboard end stops the panel from moving, and the panel then cracks, usually along a glue line or straight through its face. Worked example: a 20-inch flat-sawn white oak top at a 4% seasonal moisture content swing moves 20 × 0.00376 × 4 = about 0.30 inch across its width each year [1]. ## One point fixed, everything else floats The center mortise-and-tenon joint of a breadboard end is glued and pinned through a round hole. The center joint is the anchor, and the panel expands and contracts equally toward both edges from that centerline [2]. The outer tenons of a breadboard end are not glued. Each outer tenon fits its mortise snugly, with firm hand pressure and full shoulder contact, but the mortise is elongated in the direction the panel moves [2]. An outer joint on a breadboard end that is pinned at all is pinned through a slot, so the tenon can slide with the panel. Each outer mortise is elongated by half the panel's total seasonal movement on each side of center, plus a small margin [2]. The total slot length for an outer pin is twice the travel on each side of center plus the pin or screw diameter [2]. Worked example: the 20-inch white oak top at a 4% swing moves about 0.30 inch, so each outer mortise needs about 0.15 inch of travel on each side of center, plus margin [1][2]. A breadboard end on a piece delivered to an unmanaged home is sized for the home's moisture swing, not the shop's. A 6% swing is the safe default for an unmanaged home in the British Columbia interior, where forced-air heat dries winter air [3]. Worked example: the same 20-inch white oak top at a 6% swing moves 20 × 0.00376 × 6 = about 0.45 inch, so each outer mortise needs about 0.23 inch of travel on each side of center, plus margin [1]. ## Diagnosing breadboard failures A cracked panel under a breadboard end means the outer joints were fixed, either glued or pinned through round holes. The panel hit the restraint and broke along a weaker path. Fixed outer joints are the most common breadboard failure. A breadboard end split along its length means the panel was fixed at several points, and the seasonal movement force went into the breadboard itself. A breadboard end standing slightly proud of the panel edge in winter is correct behaviour. The panel contracts toward its center, and the breadboard ends sit a little beyond the panel's edges. Surfacing the breadboard flush at a middle-humidity point of the year keeps the seasonal variation small on a well-proportioned joint. A breadboard end cupping across its width means the stock was not well seasoned or the breadboard is too wide. Riftsawn stock resists cupping in a breadboard end. ## What plans leave out Plans for breadboard ends usually give overall dimensions and a section of the mortise and tenon. Plans usually do not say which mortise is fixed, how much elongation to add for the species and climate, or how the outer pin holes are shaped. The breadboard end procedure in five steps: calculate the panel's total seasonal movement for its width, species and service environment; glue and pin the center joint; elongate the outer mortises by half the total movement plus margin on each side of center; leave the outer joints unglued; slot every outer pin. ## 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 deep-research note DR#34, Breadboard End Construction, as summarised in heuristic entries HEU-R354, HEU-R355 and HEU-R740, Hewn internal, unreviewed. 3. Hewn heuristic entry HEU-R736, moisture content swing by environment, 2026-03-15, Hewn internal, unreviewed.