Green Chair Parts: Using Moisture on Purpose

Wet wood is easy wood

Green woodworking takes advantage of what this course has been warning about. Freshly split wood is soft and easy to shave, bend, and shape. It also shrinks predictably. Chairmakers working in the post-and-rung and Windsor traditions turn both facts into joinery: they control which parts are dry and which are wet at assembly, so the drying locks the joints instead of loosening them.

Rive, don’t saw

Chair parts are split (riven) from logs with a froe and maul, then shaved on a shaving horse with a drawknife and spokeshave. Splitting follows the fibers, so a riven part has no runout, no cross grain, and no short grain to break. A riven green rung only an inch or so across dries in days to weeks indoors, not the months a board needs, and because its fibers are continuous it seasons with little distortion. White oak, hickory, and ash, which rive cleanly, are the traditional choices.

Riven parts also tell you their ring orientation: you can see on the end exactly where radial and tangential lie, which matters for the joint.

The moisture-difference joint

In a post-and-rung chair like the ladderbacks in Jennie Alexander’s Make a Chair from a Tree, the rungs’ tenons are dried hard, well below normal room moisture, often in a warm box or over a stove, while the posts that receive them are left at a higher moisture content ¹. The rungs are driven into holes bored in the still-moist posts. Then two things happen as the chair comes into equilibrium:

• The post shrinks around the tenon. Chairmakers orient the parts with the shrinkage directions in mind so the post’s larger tangential shrinkage closes on the tenon.
• The tenon swells slightly as it takes up moisture from the post and the room.

The result is a joint that tightens as it seasons, and often needs no glue. Peter Galbert’s Chairmaker’s Notebook uses the same principle for Windsor and stick-chair joints, with tenons dried dry before they go into wetter or equilibrium parts ².

Getting tenons drier than the room

Room air in a Wisconsin winter puts wood at around 5 to 7 percent; summer, 10 to 12 ³. Tenons for a moisture-difference joint need to be drier than they’ll ever be in service, so they always swell a little after assembly rather than shrink. Chairmakers do this in a simple hot box: an insulated box warmed by a light bulb or small heater, where tenons sit for a few days. Weighing a test tenon until its weight stops dropping tells you it’s there.

Because the dried tenon will swell back, it’s turned or shaved to fit the hole snugly after drying, and assembled promptly before it regains much moisture.

Bending green

Steam bending, used for chair backs and bent rungs, also works best on wet, straight-grained, air-dried or green wood. Kiln-dried wood generally bends less reliably than green or air-dried stock. After bending, parts are held on forms until they dry and set, which takes days to a couple of weeks for chair-sized parts.

Matching the wood to the joint

The principles from the rest of this course still apply:

• Use the shrinkage directions: tangential shrinkage is about twice radial, so the orientation of post and tenon decides how hard the drying clamps the joint.
• Know the target: assembled chairs end up at the equilibrium of the house, so design for the indoor range.
• Weigh test pieces to know where you are, instead of guessing.

What to take from this

Green chairmaking rives parts from straight-grained logs, shaves them green, and dries them quickly because they’re small. Tenons are dried below room moisture in a hot box and fit after drying; mortised posts are left wetter. As the chair seasons, the posts shrink onto the tenons and the tenons swell, locking the joints, so the drying does the work that glue would.