Build a Westport Plank Chair

The plan

The Westport chair is a few wide boards ¹:

• A, two sides: solid boards with a straight base, an angled front edge, and a top edge sloping down toward the back.
• B, the back: one wide board running up and back between the sides.
• C, two front legs carrying broad, flat arms.
• D, the seat, resting on the forward top edges of the sides.

Bunnell added a hinged foot-rest, cushions, and a compartment under the seat ¹; skip those for a first chair. Aim for about the Yale chair’s overall size, roughly 38 in. high, 40 in. wide, and 40 in. deep ².

Set the geometry on a mock-up

The patent doesn’t give angles, so you set them by sitting. Use the cardboard side from The Westport Plank Chair, or screw scraps together into a rough side frame, with a board for the seat and one for the back.

Starting points to test (a low lounge chair, not a dining chair):

• Seat front height: about 14 to 15 in.
• Seat tilt: about 10 to 15 degrees down toward the back.
• Back recline: about 25 to 35 degrees behind vertical.
• Arm height: so your forearms rest without lifting your shoulders.

Check the included angle between seat and back: 90 + back recline − seat tilt. Twelve degrees of tilt and 30 of recline give 90 + 30 − 12 = 108 degrees. If you slide forward, add seat tilt or reduce recline (see The Geometry of Sitting in the Chairs course).

Sit for ten minutes, adjust, and repeat. Then trace the final side outline onto hardboard as a pattern.

Parts

For 7/8-in. boards (adjust widths to your mock-up):

Wide parts from narrow boards

Few lumberyards sell clear 20-in. boards. Make the back and seat from two or three boards:

1. Edge-joint the boards so they meet without gaps (or leave 1/8-in. gaps in the seat for drainage).
2. Screw battens across the underside of the seat and the back of the back board, one near each end and one in the middle.
3. Drill slotted holes in the battens, except at the center screw, so the boards can swell and shrink across their width without splitting. Wood moves across the grain, hardly at all along it ³.

Assembly

1. Cut the sides from the pattern; clamp them together and plane the edges so they match.
2. Join the sides with the front rail and the seat battens, keeping them parallel and the chair square. Check the diagonals.
3. Fit the back between the sides at the angle from the mock-up, screwed through the sides into its battens.
4. Lay the seat on the forward top edges of the sides and screw it down through its battens.
5. Front legs outside the sides at the front, through-bolted with 3/8-in. galvanized carriage bolts.
6. Arms across the tops of the front legs and back to the back board, screwed down; round all edges and the front corners.

Use exterior screws (stainless or coated) and galvanized bolts; ordinary steel stains the wood black where it rusts. Pre-drill near every end.

Wood and finish

The Yale chair is hemlock ². Northern white cedar, white pine, and white oak work well. Cedar and white oak heartwood resist decay much better than pine sapwood ³. Leave it bare to weather gray, paint it, or oil it yearly. Keep the base off wet ground: the sides sit flat, so their bottom edges take water first. A pair of hardwood glides or a coat of pine tar on the bottom edges helps.

Try it

Build the mock-up this week, even before buying lumber. Sit in it reading for an hour. Write down the seat front height, tilt, and recline that you ended with; those three numbers are your chair.

What to take from this

Build the Westport chair from Bunnell’s parts: two diamond-outlined sides, one back, a seat on the sides’ forward edges, and front legs with broad arms, about 38 by 40 by 40 in. overall. Set seat tilt and back recline on a mock-up and check the included angle (90 + recline − tilt). Make wide parts from narrower boards with battens and slotted screw holes. Assemble with exterior screws and galvanized bolts, round the edges, and use hemlock, cedar, pine, or white oak.