I need a chair for my workshop. I could buy one, but I'd rather make one. Since I've got a whole pile of 24" square pieces of 1/2" thick plywood, I figured that was a good place to start.
Plywood Chair, rear view
This particular design was inspired by a chair I saw somewhere, though I don't recall where. That chair was made of thick "boards" made of layers of used cardboard glued together. There were also tables and shelves displayed, all made from cardboard. Cardboard apparently worked, as I saw people sitting in the cardboard chairs, but I did notice they were all very skinny people. I'm not sure cardboard could deal with the gravitational effects of my big fat ass.
Plan for Seat
Plan for Side (2 required)
Plan for Back
Each piece is cut from a 24" square sheet of 1/2" plywood. You could use thicker wood if you wanted - I used 1/2" because I had a whole stack of it. I think I've dimensioned the correct side of every slot in the above plans, so can enlarge the slots to accommodate thicker plywood - just do it on the non-dimensioned slide of the slot and you should be fine. I think. Don't sue me if I'm wrong.
To assemble the chair, slide the seat into the sides (tab A into slot B and all that), stopping 1" before they bottom. Slide the back into the sides until it bottoms, then slide the seat back the last inch. The seat tab must engage the back slot, not only to lock the chair together, but also to give the seat a little more support. If the chair insists on coming apart, drill a hole in the tab and insert a pin through it.
If you're interested, the sides diverge at an angle of 10°, and the seat and back are tipped back at an angle of 5°. It should stand 36" tall, 24" wide, and 33" deep (front to back).
Turns out that 1/2" plywood is plenty strong enough to support me. It is important to make the notches wide enough and perfectly straight, or they'll bind when you try to put it together. I may trim a few inches off the front edge of the seat, but other than that, it's surprisingly comfortable.
It sure won't win any beauty contests, but when I'm sitting in it, I can't see it!
(Art and craft side table)