Introduction: Load-bearing Cardboard Chair
Constructed from two sheets of double ply corrugated cardboard. No glue, no tape -- only cuts and folds. Holds the weight of one person and the seat flips open to reveal two storage compartments. Three vertical load-bearing elements are braced by the seat which folds around them. This one is a beauty.
As I no longer have the diagrams or drawings for this specific design, I use it here as a generic test case to show the process of designing your own chair -- the tough (and fun) work of creating your specific design is up to you!
Step 1: Purchase Two 60
The best way to hone your design will be to first sketch out ideas, and then sequentially make quarter-scale (25% of full size) and half-scale (50% of full size) models using single ply cardboard. Use single ply on the scaled mockups as it will be easier to fold. Use double ply on the final as it has to support your weight!
Step 2: Mark Your Fold and Cut Lines in Pencil
Once you have your design, and are assured that it will work from testing it at quarter- and half-scale, lay out your two 60" by 49" sheets of double ply cardboard and use a T-square or reliable right angle to draw your fold and cut lines in light pencil. Make sure to draw the lines on the 'inside' of the fold if you want them to remain hidden on the underside of the chair once it is constructed. Remember when drawing your cut lines that the double ply cardboard that will slot into the cuts has a thickness! You can mark the center line, and use that to cut what is in essence a rectangle whose width matches the thickness of the cardboard you are using. This will result in a snug fit when assembling and should not require any glue or tape.
You may want to mark your cuts as dashed lines and your folds as solid lines with your pencil, so if you take a break and come back to it later, you'll be able to differentiate them.
Step 3: Make Your Folds and Cuts
It's easier to have a helper for this part! You'll notice that the corrugation in the cardboard has a constant direction -- you want to fold with the corrugation rather than against it. Try both ways on a smaller, scrap piece of cardboard to experience the difference: in folding with the corrugation, you should get a smooth, straight line; in folding against it, not only will it be difficult to fold, but you may crack the cardboard, leaving you with an erratic dent rather than a straight line.
The best way to maintain a straight and clean fold is to have a friend hold a metal ruler (make sure it is long enough to run the full length of the fold) along the pencil line that you've drawn. Then gently raise one side of the cardboard until the ruler edge forces a clean fold.
Step 4: Assemble Peices
Almost there! This is the fun part. It is basically an IKEA kit at this point, except even better designed as it requires no screws, bolts, or connector pieces. With a friend, take the two sheets and fold the around each other as your design dictates. Depending on your design, there is probably a specific order that makes it easier to assemble. Be patient with this step, as you don't want to force any pieces or weaken the cardboard by introducing unwanted buckling or creases.
Now -- sit and enjoy!