The Flagman Table is made of a sign on a frame, which is a little bit cheap -- it avoids the challenge of using the sign structurally, and doesn't have the purity of concept that something made only from the sign would have. The Four Square Chair was based on a geometry of four squares, as the title suggests. Classical architecture, especially in plan, was derived, generally speaking, from a four-square grid: bilateral symmetry. Modern architecture was/is derived, generally speaking, from a nine-square grid, which allows for asymmetry.
A road sign 48" to a side breaks down neatly into a nine-square grid of 16" squares. Seat height for side chairs is usually in the 16"-17" range. I made a bunch of 1" to 12" scale models out of cereal box cardboard before I settled on a form that would turn into a chair without the need to add anything for bracing or stiffness -- purity of concept. I made a full-size mock-up out of cardboard to make sure of all the dimensions and folding sequence, then worked on the sign.
This bad boy is 100% recycled except for fasteners, and is virtually waste-free in its construction. Later in the instructable there is a picture of all the waste generated win the process, and it was only one dustpan full of aluminum shavings, which are recyclable.
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Step 1: Mock-Up
To hold the chair together, triangular fins are positioned such that adjoining squares will have overlapping fins, which can be through-bolted to hold it. For the model, use brads or stapels. This folding scheme is one of many possibilities using this general geometry and working method, so you may want to explore other designs.
Cut slits where appropriate, and perforate the seams that need to be folded. Then, fold squares seven, eight, and nine under squares four, five, and six. Pin seven to four, eight to five, and five to six. Fold 7/4 and 5/6 up ninety degrees from 8/5. Bend out the triangular fins from seven, eight, and nine, and they should overlap. Pin through them to secure the legs.
Flip the chair over and bend up the back and pin it by joining the fins from squares two and five.
Step 2: Signs!
Start by laying out your sixteen inch grid again, this time with masking tape. Mark out the triangular fins. The fins on the underside of the seat in the finished chair are cut from squares seven, eight, and nine. You can see how they are laid out in the pictures: those fins are 12" by 6" and are creased along the hypotenuse.
The fins that secure the back are 12" by 4" (attached to square 2) and 8" by 4"(attached to square 5), creased along the 12" and 8" sides.
The fin that holds the back of the legs together is made from squares three and seven and is 12" by 6", creased along the hypotenuse.
Along all the folds, strike a center line and, measuring from the centerline towards the corners, make a tick every 3/4". Drill out each tick with a 3/8" bit to make the perforations that will allow the sign to bend. This makes 3/8" diameter holes that are 3/8" apart.
Where cuts are necessary, use a jigsaw with a fresh metal blade. Aluminum is very strong, but rather ductile and soft. I dulled the drill bit considerably -- there are an awful lot of holes to drill.
Step 3: Fold
Next, fold squares seven, eight, and nine undeneath squares four, five, and six. Drill through and pin seven to four, eight to five, and nine to six with number ten by 3/4" long machine bolts. Bend 7/4 and 9/6 up ninety degrees. The fins protruding from these three panels will overlap. Drill through the overlap and bolt to hold the legs in place.
For the back, fold square one 180 degrees to match up with sqaure two. Bolt through. Bend 1/2 up ninety degrees to form the back. The fins attached to that piece should overlap the fins coming up from the seat, square number five.
Last, bend square six ninety degrees so that its fin overlaps with the fin coming off of panel seven, forming the back of the legs. Bolt through twice.
You might want to run over the seams with some eighty-grit sandpaper on a block or use a bastard file to take off any burrs and sharp edges.