The Four Square Chair is a made from 2" strips of 3/4", furniture-grade birch plywood; pine dowels; cast aluminum; and pool noodles. I call it the Four Square Chair because of a mathematical game I played with the design: the four planes described by the front legs, back legs, seat, and back are all squares, sixteen inches to a side. These are the four squares. There are sixteen pieces of plywood in the frame; four squared is sixteen. These are the other four squares. The angle of the front legs, back legs, and seat back off the vertical are all the same, adding another level of symmetry to the design.
Each tubular cushion is a foam pool noodle, wrapped in black cotton, with a dowel running through the center. The plywood has been drilled to accommodate the dowels and hold the cushions in place. Each piece of plywood is a 1/2" from its twin, making the total breadth of each plywood assembly 2"; since the strips are 2" across as well, each of the eight plywood sides is two inches square in cross-section -- another set of squares.
The joints are cast aluminum, made using the lost styrofoam process. I know most people don't have access to a foundry, and getting custom work cast is expensive. However, the joints could just as easily be made out of wood, hopefully something that provides a nice contrast to the plywood.
This particular project doesn't hew too close to my "readymade" ethos, in that it is not made totally from recycled junk, and I spent some money on it. That being said, the plywood was leftover from another project, the pool noodles were leftover from a party, the fabric came from a thrift store, and the aluminum is recycled. Making a chair out of relatively small pieces means that you can usually make it with scrap.
All photographs by Alfonso Elia.
Step 1: Drawings
After many drafts, trying to get the proportions and angles right while still staying within my sixteen-inch rule, I came up with these drawings. I made the joint drawings full-size, the photocopied them, spray-mounted them to rigid styrofoam insulation, and cut out the shapes with a bandsaw. I made them slightly big because the casting process isn't super-accurate and I left a margin to machine down later. As in my other posts, you can print these drawings, then measure one of the pieces of plywood in the side view drawing. Since you know that has to be sixteen inches, divide it out to get a scale. As for the joints, the "legs" or parts with the holes in them, are two and half inches long by two inches.
Step 2: On to the Foundry . . .
With my styrofoam machined to satisfaction, it gets placed in a snap flask, which is a molding box for sand-casting bronze or aluminum. Then I shoveled in foundry sand, which is a mixture of very fine sand and clay particles. Dampened, it holds its shape, which is important.
Much tamping commences, with the handle of the shovel. It's amazing how much sand you can cram in that little box. The fourth picture shows post-tamping, with the snap flask flipped over. Now another piece is added, and the bottom half of the mold is built the same way.
In the fifth picture, we are adding vent holes, so when the hot metal evaporates the styrofoam, there is a place for the gases to escape, as well as a path for the bronze to flow.
The sixth picture shows the crucible a-glowing at about 2,200 degrees.
The last step is pouring, as Andy and Jim handle the yoke and crucible, and Caboeiria stands by to smother any blow outs or spills.
After about an hour, you can break out the mold and retrieve your piece.
Step 3: Machining the Aluminum
This step sucks. It's really tedious and time-consuming, but essential for a fresh product. I estimate I spent the better part of 30 hours just on these joints, and I still could have gone to finer and finer grits to get a mirror polish. That said, I could have cast them thinner, and, in retrospect, saved myself a lot of time.
The first picture shows the joints fresh from the mold, still coated with some sand. I machined the joints down on a band saw first, to remove the bulk of the material. Then I built a jig to hold them steady and used a 1/4 sheet orbital sander to grind them down with really coarse paper. I think I used floor refinishing sandpaper at sixty grit first, then worked up to 150 or so to smooth them out. The bench sander comes in handy here as well, but keep some water handy because the aluminum gets real hot, real quick. Always wear gloves and a dust mask when machining aluminum, or else those little bits of metal are ending up in your lungs.
After the dimensions were satisfactory, I drilled 3/4" and 1/2" holes on a drill press. Aluminum is pretty soft, so this part went mercifully quick.
The second picture shows all the raw materials laid out. After cutting my sixteen pieces of wood to width and length, I paired them up with masking tape and drilled holes in them on the drill press. I kept each pair together, so I knew whatever small inaccuracies visited upon each piece would at least have a symmetrical partner. This is also a good time to slap a couple coats of polyurethane on the wood, because certain sides of it will be pretty inaccessible as assembly gets going.
Step 4: Assembly
I neglected to take pictures of the cushion-assembly process. Get twelve dowels, cut them down to a little more than 20 inches long, maybe a half on each end. They should slide right into the hole in the center of the pool noodles. Cut the noodles to 16 inches. I then took the thrift-store fabric and wrapped each one, securing the seam with a couple dabs of hot glue. To finish the ends, just tuck the fabric into the holes with a butter knife, pushing it down so it gets trapped between the dowel and the noodle. Center the cushion (it should slide freely) on the dowel.
The assembly is pretty straightforward. Coat the ends of the cushions with heavy adhesive (I used Liquid Nails), line up all the holes, push the pieces onto the dowels, more glue, clamp, and wait. Wipe up all excess glue with mineral spirits and a lint-free rag. Sand and paint the dowels with two coats of polyurethane. For each side, keep your original "pairs" together, the ones that were taped together. It is crucially important here that everything line up just so.
The first picture shows one cushion set drying under pressure. Make sure the cushion is 16 inches wide and the cushions are all in the same plane, i.e. the sides aren't twisted relative to one another.
Cut some half-inch dowel pieces to about 2-1/4", 2-1/2", to give a margin to sand down later, and insert them in the two smaller end holes.
Step 5: Joints
To attach the joints to the wood, I used a urethane-based glue (Gorilla Glue, but there are many brands) because it is good at interfacing two different materials, wood and metal. It requires water to work, so dampen the wood and the metal with a wet rag. Spread the glue on both faces and in the holes and push on. Urethane glue expands while curing, so don't spread the glue too close to the edges, and clean it up while still wet with mineral spirits. The dried glue can be taken off later with a razor blade, but it's messier.
Put on the outside piece of wood with Liquid Nails. Cut some little blocks of material 1/2" thick to act as spaces along the length of the piece. Without spacers, once you clamped it, the middle will have a tendency to bow inwards. Clean the dowels as best you can by working a rag soaked in mineral spirits into the half-inch gap.
Step 6: Come Together
Once you've made the seat entirely, i.e. with all four joints and pieces of wood in place, you can match it with the back. Leave the outside pieces off the back for now, so it should just be cushions and two pieces of plywood, one on each side. Put the glue on the back joint attached to the seat, and fit on the back, then fit on the outside pieces to the back. Might want some assistance here to wrestle everything into the right angles and so forth. Let all the glue in this process set up for 24 hours before handling.
Starting to look like a chair, I daresay.
Step 7: Legs!
This part is pretty easy after messing with all those cushions. Make two more 3/4" dowels that are 20", and one 1/2" dowel that is 25-1/2". Drill a half-inch hole in the dead center of the 3/4" dowels. These will be the leg braces.
Assemble the legs with their feet and intermediate pegs, glue, and let set up. Leave pegs out of the 3/4" holes in the feet.
Slather on the glue, and put the sets of legs in with their brace, one at a time. Once one set is one, fit in the longitudinal brace into the 1/2" holes in the centers of 3/4" dowels, and put on the other set of legs. Clamp.
Step 8: Finish Up
Once dry and stable, clean up all the excess glue with a razor blade. Wrap the cushions in newsprint and tape, and give the whole thing a thorough sanding. The main purpose of this last finishing is to get all the dowels perfect flush with the face of the plywood. You can fill little gaps with Liquid Nails and a putty knife, let cure, and sand down. I then put on three more coats of hand-rubbed polyurethane, including working the rag down into the gap between the pieces and hitting all the dowels. Once dry, sand with 330 grit or higher, then wipe clean with mineral spirits and hand-buff with a lint-free cloth and some furniture wax.
Sit down and take a break.
I wrote this Instructable while sitting in the Four Square Chair. I would recommend it for an office or dining-type situation. It is quite comfortable, but it is also rather upright for relaxing. Should be pretty indestructible -- aluminum and plywood are incredibly strong.
If you want to save yourself the trouble, the one and only Four Square Chair currently in existence is for sale here: http://www.etsy.com/view_listing.php?listing_id=10798264