The Hundred-Year Chair · back matter

Appendix: The Keel Pattern

Working appendix, 29 September 2026. These retained drawings and instructions describe the earlier Keel pattern. They have not yet been reconciled into the final, independently checked construction packet for this revision. The dated version, hardware details, drawings, and assembly instructions must agree before this appendix can be called a complete recipe. It does not describe the thousand-year armchair.

FPO · F4 practical reconciliation, informed by A5/C1. Resolve the older screw/glue instructions against later bracket and insert versions; check loads, fasteners, drawings, and assembly sequence. Ordinary sitting is not a structural certification. Do not use an unresolved instruction as a verified build specification.

The Keel pattern

What follows records the earlier panel version of the Keel chair. Its geometry uses two congruent triangles sharing a keel line. The retained drawings label their angles 40, 60, and 80 degrees, with corresponding sides of 219, 295, and 335 millimeters, and an offset of 70 millimeters along the keel. The exact-angle model and these rounded side lengths still need to be reconciled before publication as a build specification. The intended posture for this version is a seat at 440 millimeters with a 5 degree pan, a back raked 15 degrees, and a 100 degree seat-back angle. These numbers describe the selected geometry, not everything needed to make a chair.

The three drawings show the assembled chair, the keel layout, and the parts laid flat. They must be checked against the named build version before publication and accompanied by the complete joint, hardware, and assembly instructions. The keel is an important reference part, not the only part that asks for care.

The Keel Chair drawn in side elevation: the red keel raking down to the rear, the blue back, yellow seat, green front and black tie closing two dashed congruent triangles, with the two 80 degree apexes ringed and dimensioned. — Keel Chair Side Elevation. The assembled chair from the side, with both 80 degree apexes located: B where the seat meets the back, F where the tie meets the front, each dimensioned along both of its members from the keel kiss and located above the floor.

The keel drawn full length with its three fish-mouth notches, the two kiss lines dashed along it, and running dimensions to each station from a datum at the left, with the three joints repeated as enlarged details below. — Keel Layout. The three joint positions measured from one datum corner at the left, with the three fish mouths enlarged beneath and each pilot hole marked. A common reference avoids chaining one measurement to the next; it does not prevent marking or cutting errors.

Four parts drawn as labeled bars, one above another, their lengths to a single scale: the back 687 by 400, the seat 413 by 400, the front leg 388 by 35 with two of them called for, and the tie 295 by 400, each bar carrying its keel and apex crossings and its pilot holes. — Keel Chair Parts. A schematic: the four lengths share one scale so they compare at a glance, while the widths and thicknesses are given as figures. The dimensions govern, not the picture. Pilot holes are marked on every part.

Seven parts: two keels, three flat panels and two front legs.

Part	Qty	Stock	Blank	Triangle side
Keel	2	dense hardwood, 50 x 35	cut to the layout below	335, twice
Back	1	18 ply, 400 wide	687	219 (opposite 40 deg)
Seat	1	12 ply, 400 wide	413	295 (opposite 60 deg)
Front leg	2	18 ply, 35 wide	388	219 (opposite 40 deg)
Tie	1	12 ply, 400 wide	295	295, kiss to kiss

A whole chair takes about a tenth of a 2400 by 1200 sheet in each thickness, plus the two keel boards, salvaged if you have them. Run every part's length along the face grain and write the grain direction on the part. The only angled cuts are the two 80 degree apex cuts where seat meets back and tie meets front, ten degrees off square, a run of about 2.1 millimeters across the twelve millimeter thickness. Everything else is straight and square.

The keel provides a common reference for locating the other parts. Scribing them to fit does not remove the need for accurate cuts and holes or for checking the assembled chair. Measure from one physical corner a tape can hook, the end of the front-and-tie edge, where the bevel the seat beds on runs out. From that datum the three joint vertices sit at 70 (front), 335 (back) and 405 (tie), which are the pattern's own numbers: three stations struck from one end rather than measured in sequence. Each joint is a fish mouth with a right angle at its vertex, its two walls being the mating panel's own face and square end, and the vertex sits 25 millimeters in from the edge at every station. At 25 and 25 on a 50 board the two kiss lines land on the same line, so the two triangles share one line exactly. Strike the vertex, drill 1.5 millimeters through it, and saw both faces down to the hole; the drilled hole stops the cut and leaves a small fillet exactly where an inside corner wants one. Cut both keels from two boards stacked, then separate them. They are the same part, not a mirrored pair. Matching profiles help align the two sides; they do not by themselves guarantee a square assembly. Both ends of the keel come to an acute point, and both points are trimmed off parallel to the back, which is 60 degrees to the keel, leaving an end face of about 19 millimeters. The foot is cut flat to the floor and keeps about 47 millimeters of contact.

The Keel Chair from the rear quarter: the two hardwood keels running down the back faces of the panels to the floor, the tie closing the triangles low between them. — The structure from behind: two identical keels, the panels seated in their mouths, the tie closing both triangles. What the sitter never sees is the whole pattern.

The intended finish should be renewable: a finish that can be re-coated in place, without stripping, by whoever keeps the chair in fifty years. A wiping varnish or a hard wax-oil both qualify. Then sign it, and write the part dimensions on the underside of the seat in pencil, so the next rebuild can read its cut list off the chair itself, the way I read Rietveld's off his.

FPO · Verified assembly and fastener schedule for this named version. The old schedule and informal sit-and-wiggle pass criterion are preserved in the baseline, not offered here as a checked test or final instructions.

The finished appendix must include the instructions needed to build without a live website. Online templates and later variants should be labeled by version, with corrections distinguished from optional changes.

Notes

"219, 295, and 335": Author's retained Keel geometry. [VERIFY] Reconcile exact angles, rounded lengths, offset, stock dimensions, drawings, and the named build version before release as instructions.
"Seven parts": Author's retained parts list. [VERIFY] Check quantities, thicknesses, grain directions, dimensions, hardware, and material yield together against a dated construction packet; the list alone is not sufficient to build safely.
"a tenth of a 2400": [VERIFY] Recompute sheet usage for each thickness and layout, including kerf, defects, and grain orientation.
"run of about 2.1": Author's geometric calculation for a ten-degree cut across twelve millimeters. [VERIFY] Confirm applicability to the final named parts and mating faces.
"Strike the vertex": [VERIFY] Check the entire retained notch-cutting sequence, hole size, offsets, remaining sections, and foot contact against the final drawing and a practical safety review. These are provisional instructions, not certified fabrication guidance.
"hard wax-oil": [VERIFY] Specify actual finish products and manufacturers' maintenance instructions. Recoating without stripping depends on the product, existing coating, preparation, and condition.

A chapter of The Hundred-Year Chair, drafted and refined in public. The same text lives in the book; the interactive tools and the fully-sourced technical notes live here. home · the book · the technical notes · hundredyearchair.com