{"$schema":"nativecad-dfm-pack/1","id":"furniture-construction","title":"Furniture construction & joinery — how a chair is actually built","sector":"furniture-construction","version":"2026-09-12","summary":"The construction vocabulary of furniture — rail, stretcher, splat, apron, shell, star base, cantilever, lamination, tenon, dowel, cord seat — each mapped to the ops that build it, plus standard member sections, joint-selection rules and worked recipes for ten chair construction types.","aliases":["joinery","woodworking joinery","furniture joinery","chair construction","furniture construction","chair frame","mortise and tenon","mortise-tenon","stretcher","splat","apron","crest rail","bentwood","bent lamination","bent plywood","moulded shell","shell chair","star base","cantilever chair","sled base","cord seat","danish cord","cane seat","turned leg","cabinetmaking","chair joint"],"crossSector":false,"size":"core","sources":[{"id":"joyce-furniture","title":"Ernest Joyce, The Technique of Furniture Making (rev. Alan Peters), 4th ed. — chair and table joinery proportions","note":"Standard cabinetmaking reference for rail, stretcher and leg sections and tenon proportions."},{"id":"hayward-joints","title":"Charles H. Hayward, Woodwork Joints — mortise-and-tenon, half-lap, bridle and dowel proportions","note":"Source of the one-third and two-thirds tenon rules."},{"id":"wood-handbook","title":"USDA Forest Products Laboratory, Wood Handbook FPL-GTR-190 (ch. 8 fastenings, ch. 10 adhesives, ch. 19 bent wood members)","url":"https://www.fpl.fs.usda.gov/documnts/fplgtr/fpl_gtr190.pdf","accessed":"2026-09-10"},{"id":"en-1728","title":"EN 1728:2012+AC:2013 Furniture — Seating — Test methods for the determination of strength and durability","accessed":"2026-09-10"},{"id":"en-1022","title":"EN 1022:2018 Furniture — Seating — Determination of stability","accessed":"2026-09-10"},{"id":"en-636","title":"EN 636:2012+A1:2015 Plywood — Specifications (veneer thickness and panel build-up)","accessed":"2026-09-10"},{"id":"en-10305-3","title":"EN 10305-3:2016 Steel tubes for precision applications — Welded cold-sized tubes (furniture tube sizes and wall thicknesses)","accessed":"2026-09-10"},{"id":"astm-d3574","title":"ASTM D3574-17 Standard Test Methods for Flexible Cellular Materials — Slab, Bonded and Molded Urethane Foams","accessed":"2026-09-10"},{"id":"pu-handbook","title":"Covestro (Bayer) Polyurethanes Handbook — cold-cure moulded flexible and self-skinning foam seat shells","accessed":"2026-09-10"},{"id":"iso-4762","title":"ISO 4762:2004 Hexagon socket head cap screws","accessed":"2026-09-10"},{"id":"din-7997","title":"DIN 7997 Countersunk head wood screws with cross recess","accessed":"2026-09-10"}],"entries":[{"id":"op-inventory-for-furniture","kind":"note","tier":1,"title":"Which ops build furniture today","summary":"Furniture is built today from cad_box, cad_cylinder, cad_extrude_profile, cad_revolve_profile, cad_sweep_profile, cad_tube_sweep, cad_loft_profiles, cad_boolean_subtract, cad_fillet_edges, cad_pattern_copies, cad_transform, cad_drill_hole and cad_hole_pattern.","applies":["chair","stool","table","cabinet"],"basis":"The tool surface this build ships, now including cad_joint (CADSF-1370) and cad_fastener (CADSF-1371); the recipes below predate them and remain valid manual alternatives.","tags":["glossary","ops","shipped"],"sources":[]},{"id":"planned-joinery-ops","kind":"note","tier":1,"title":"cad_joint and cad_fastener ship","summary":"A one-call mortise-and-tenon (cad_joint, CADSF-1370) and standard fastener (cad_fastener, CADSF-1371) now ship; cad_fastener_audit must return zero findings before a bolted assembly ships. The manual recipes below remain valid alternatives.","applies":["chair","stool","table"],"basis":"cad_joint and cad_fastener appear in this build's tools/list (CADSF-1370, CADSF-1371); the recipes below predate them and remain buildable manual alternatives.","tags":["glossary","shipped","joinery"],"sources":[]},{"id":"glossary-rail","kind":"feature","tier":1,"title":"Rail — the horizontal member between two legs","summary":"A rail is the horizontal member tying two legs at seat level (seat rail) or at the back (back rail); 20-30 mm thick and 50-80 mm deep. Build it with cad_box, or cad_extrude_profile for a shaped rail, and tenon it into the legs.","applies":["chair","stool","table"],"basis":"A rail carries the seat load in bending between the legs, so it is deep in the load direction and thin across it.","tags":["glossary","rail","frame"],"sources":["joyce-furniture"]},{"id":"glossary-stretcher","kind":"feature","tier":1,"title":"Stretcher — the low rail that triangulates the legs","summary":"A stretcher is a low horizontal member between legs, 20-25 mm square or round, whose job is to stop the leg frame racking. Build it with cad_box or cad_revolve_profile (turned) and tenon or dowel it into the legs.","applies":["chair","stool","table"],"basis":"A stretcher works in tension/compression against racking, not bending, so its section is small and square.","tags":["glossary","stretcher","frame"],"sources":["joyce-furniture"]},{"id":"glossary-apron","kind":"feature","tier":1,"title":"Apron — the skirt rail under a seat or table top","summary":"An apron is the rail immediately under a top or seat, set back 5-15 mm from the edge, 18-25 mm thick. Build it with cad_box and cad_transform; it is the member a top screws down onto.","applies":["table","chair","casegoods"],"basis":"The apron stiffens the top and hides the joint line; the setback reads as a shadow gap.","tags":["glossary","apron","frame"],"sources":["joyce-furniture"]},{"id":"glossary-splat","kind":"feature","tier":1,"title":"Splat — the shaped vertical board in a chair back","summary":"A splat is the single shaped board rising from the back seat rail into the crest rail, 8-16 mm thick. Build it with cad_extrude_profile on a curved outline, or cad_loft_profiles for a twisted splat, then tenon both ends.","applies":["chair"],"basis":"One wide board spans the back with fewer joints than a set of spindles.","tags":["glossary","splat","back"],"sources":["joyce-furniture"]},{"id":"glossary-shell","kind":"feature","tier":1,"title":"Shell — a one-piece seat-and-back surface","summary":"A shell is a single curved panel forming seat and back, 8-10 mm in moulded veneer or 25-40 mm in moulded foam. Build it with cad_sweep_profile (a thin rectangular section along the curved side profile) or cad_loft_profiles plus cad_shell / cad_thicken.","applies":["chair"],"basis":"A shell replaces a seat frame, a back frame and their joints with one moulded part.","tags":["glossary","shell","moulded"],"sources":["en-636"]},{"id":"glossary-star-base","kind":"feature","tier":1,"title":"Star base — the radial multi-arm foot of a swivel chair","summary":"A star base is a hub with 4-5 radial arms carrying glides or casters. Build one arm with cad_box or cad_sweep_profile and repeat it with cad_pattern_copies {type:'circular', count:5, totalAngle:6.2832}, then cad_boolean_union it to a cad_cylinder hub.","applies":["chair","office chair"],"basis":"Radial arms put the support polygon under a single central column.","tags":["glossary","base","swivel"],"sources":["en-1022"]},{"id":"glossary-lamination","kind":"feature","tier":1,"title":"Bent lamination — a curved member glued up from thin plies","summary":"A bent laminate is a curved solid member glued from 1.0-1.5 mm veneer plies over a form. Model the FINISHED member, not the plies: cad_sweep_profile with a rectangular section along the bend path, corner radii via path.fillets.","applies":["chair","stool"],"basis":"Thin plies bend elastically and the glue line holds the curve; the finished part is one solid in CAD.","tags":["glossary","lamination","bent"],"sources":["wood-handbook"]},{"id":"glossary-tenon","kind":"feature","tier":1,"title":"Tenon — the tongue formed on the entering member","summary":"A tenon is the reduced tongue on the end of a rail, one third of the rail thickness and two thirds of the receiving member's width long. Cut it today as a cad_box tenon cad_boolean_union'ed to the rail; cad_joint ships (CADSF-1370).","applies":["chair","table"],"basis":"One third of the stock leaves equal cheeks and a shoulder that resists racking.","tags":["glossary","tenon","joinery"],"sources":["hayward-joints"]},{"id":"glossary-mortise","kind":"feature","tier":1,"title":"Mortise — the socket cut in the receiving member","summary":"A mortise is the rectangular socket in a leg that receives a tenon, 0.2 mm larger than the tenon on each face for glue. Cut it today with cad_boolean_subtract of an oversize cad_box, or cad_drill_hole for a round mortise; cad_joint ships (CADSF-1370).","applies":["chair","table"],"basis":"A socket in the leg keeps the joint's glue area on long grain.","tags":["glossary","mortise","joinery"],"sources":["hayward-joints"]},{"id":"glossary-mount-plate","kind":"feature","tier":1,"title":"Mount plate — the metal plate between a shell and a frame","summary":"A mount plate is a 3-5 mm steel or aluminium plate brazed or welded to a tube frame, drilled 4 x M6, that the shell bolts down onto. Build it with cad_box + cad_hole_pattern and bolt through with cad_drill_hole; cad_fastener ships (CADSF-1371).","applies":["chair"],"basis":"A plate spreads a bolt load over a thin shell that a bolt head alone would crush.","tags":["glossary","plate","shell","frame"],"sources":["iso-4762"]},{"id":"section-leg-square-timber","kind":"dimension","tier":1,"title":"Chair/table leg section, solid hardwood (square)","summary":"A solid hardwood chair or table leg is 30-45 mm square, typically 36 mm; below 30 mm the mortises for the seat rails leave too little cheek, above 45 mm the leg reads as a table leg.","applies":["chair","stool","table"],"value":{"min":30,"max":45,"typical":36,"unit":"mm"},"basis":"Leg width must leave >= 2 x tenon-thickness of cheek each side of a 1/3-thickness rail mortise, at a seat height that puts the leg in bending.","sources":["joyce-furniture","wood-handbook"],"tags":["section","leg","timber"]},{"id":"section-stretcher","kind":"dimension","tier":1,"title":"Stretcher section (square or turned)","summary":"A stretcher between chair or stool legs is 20-25 mm square or round, typically 22 mm — big enough for a 7-8 mm tenon, small enough to stay out of the sitter's way.","applies":["chair","stool","table"],"value":{"min":20,"max":25,"typical":22,"unit":"mm"},"basis":"Sized by the tenon it must carry (1/3 of 22 mm = 7 mm) rather than by bending, because a stretcher works in tension and compression.","sources":["joyce-furniture","hayward-joints"],"tags":["section","stretcher"]},{"id":"section-tube-leg","kind":"dimension","tier":1,"title":"Light steel tube leg, outside diameter","summary":"A light chair tube leg or stretcher is 12-16 mm outside diameter, typically 14 mm, with a 1.0-1.5 mm wall — the section used for stacking-chair leg frames and understructures.","applies":["chair","stool"],"value":{"min":12,"max":16,"typical":14,"unit":"mm"},"basis":"EN 10305-3 precision welded tube is stocked in this range; below 12 mm the frame is not stiff enough to pass EN 1728 seat fatigue.","sources":["en-10305-3"],"tags":["section","tube","frame"]},{"id":"section-veneer-shell","kind":"dimension","tier":1,"title":"Moulded veneer (bent plywood) shell thickness","summary":"A moulded veneer seat/back shell finishes 8-10 mm, typically 9 mm: 7-9 plies of 1.0-1.5 mm veneer laid with alternating grain and pressed in one operation.","applies":["chair"],"value":{"min":8,"max":10,"typical":9,"unit":"mm"},"basis":"Thinner than 8 mm the shell flexes past its glue lines under EN 1728 seat load; thicker than 10 mm it will not take the compound curve without splitting.","sources":["en-636","wood-handbook"],"tags":["section","shell","veneer"]},{"id":"section-moulded-shell","kind":"dimension","tier":1,"title":"Moulded polyurethane foam shell thickness","summary":"A cold-cure moulded PU foam shell over a rigid substrate finishes 25-40 mm, typically 30 mm, measured normal to the substrate at the seat pan.","applies":["chair"],"value":{"min":25,"max":40,"typical":30,"unit":"mm"},"basis":"Below 25 mm the sitter feels the substrate; above 40 mm the shell loses the sharp moulded silhouette and the demould time climbs.","sources":["pu-handbook","astm-d3574"],"tags":["section","shell","foam"]},{"id":"joint-leg-rail-mortise-tenon","kind":"rule","tier":1,"title":"Leg to rail: mortise and tenon","summary":"A rail meeting a leg is ALWAYS a mortise-and-tenon: tenon 1/3 of the rail thickness, 2/3 of the leg width long, 0.2 mm clearance on the cheeks. Never butt-and-screw a seat rail to a leg.","applies":["chair","table","stool"],"basis":"The seat rail carries the racking moment; only a tenon puts long-grain glue area on both sides of that moment.","sources":["hayward-joints","joyce-furniture"],"tags":["joint-selection","tenon"],"value":{"typical":0.2,"unit":"mm","note":"cheek clearance per face"}},{"id":"joint-shell-to-frame-plate","kind":"rule","tier":1,"title":"Shell to frame: screws through a mount plate","summary":"A moulded shell NEVER bolts straight to a tube: braze or weld a 3-5 mm mount plate to the frame and bolt the shell to the plate, 4 x M6 on a 60-120 mm pattern with washers under the shell.","applies":["chair"],"basis":"A bolt head bearing on 9 mm of veneer crushes it; the plate spreads the load and gives the frame a flat datum.","sources":["iso-4762","en-1728"],"tags":["joint-selection","shell","frame"],"value":{"typical":6,"unit":"mm","note":"M6 through a 4 mm plate"}},{"id":"joint-bent-leg-to-seat-screws","kind":"rule","tier":1,"title":"Bent laminate leg to seat: screws, not a tenon","summary":"A bent laminate leg meets a seat panel on its flat glued end and is fixed with 2-4 wood screws up through the seat into the leg end grain, pilot 4.0-4.5 mm, 25-40 mm long. Do not tenon a laminate leg.","applies":["stool","chair"],"basis":"The leg's glue lines run along the leg, so a mortise across them would sever every ply; a screw up the leg axis loads them in shear.","sources":["din-7997","wood-handbook"],"tags":["joint-selection","screws","lamination"],"value":{"min":2,"max":4,"unit":"count","note":"screws per leg"}}]}