Intro: Cardboard Cantilever Chair 2.0
In late 2008, the first Cardboard Cantilever Chair came into the world, wrapped in paper-mache and held together with five threaded rods: www.instructables.com/id/Cardboard_Cantilever_Chair/
However, this chair has a number of notable failures. First, the paper-mache surface, while nice-looking, smooth to the touch, and durable, was a huge amount of work. In the same vein, an attempt was made to save labor by constructing the chair out of strips cut on a table saw; however, those time savings were negated by the need to miter every strip to fit into the cantilever profile. To tie the layers together in the absence of big clamps, threaded rods shoot through the whole chair in five places, which in many ways defeats the purpose of making a cardboard chair in the first place -- what's the point if you're just going to throw a couple of big pieces of steel in the middle of the thing? Last, the form is clumsy, with five-inch wide strips for strength making a big, bulky, and extremely heavy chair.
The goals for Cardboard Cantilever 2.0 were to address all of these weaknesses: made only from glue and cardboard, no paper mache or steel fasteners; cutting the strips without miters to save time; cutting the strips to length after lamination, also to save time; and attenuating the cardboard strips' width so as to make the chair visually lighter and more delicate.
In addition, I wanted to explore the idea of making multiple copies of the same chair as precisely as practically possible. To make multiple copies, the cost had to be kept to a minimum. To that end, the steel was eliminated, but also using commercial glue was out due to the volume needed. Instead, this chair was made with wheat paste, keeping the glue cost to an estimated two to three dollars per chair. The other issue with multiple copies was finding a way to make the lamination process more refined so the layers lined up better and were clamped under even pressure while the glue dried for maximum strength.
The finished photos below give a good idea of how this one stacks up next to Cardboard Cantilever 1.0, as well as scans of drawings I made to develop the form and the clamping jig. For an explanation of the ergonomics and physics of the cantilever form, refer to the link to the first Instructable.
Step 1: The Jig
To make the layers as consistent as possible throughout the lamination process, I built a clamping jig to align and hold the cardboard under compression as the glue dried. If I were to do it over, I would use thicker plywood (at least 3/4"), as this plywood warped under the considerable pressure exerted by the threaded rods and wing nuts. However, keeping tot he spirit of the project, all this wood was salvaged -- the plywood from a job site, and the dimensional pieces from pallets and other scraps.
To start, draw out the profile of the chair on a piece of plywood. The pieces I used were a little under three feet square. You can print the drawings from the first step to replicate this exactly, but you could also design your own. If designing your own, keep in mind a few things: the length of the piece that rests on the ground needs to be as long or longer than the total chair to keep it from tipping back excessively; the leg, or vertical piece, should be as short as possible for comfort; and the seat needs to also be short to keep it from acting as too much of a lever.
Once the chair is plotted out, screw 2 x 4s to the back of each piece of plywood as shown as bracing. Add this bracing even if you use thicker plywood, to keep the jig from wracking.
Next, draw a circle for a peg at each intersection of the chair. Tape over the wood with packing tape to seal it from spilled glue; you could also varnish it, but the tape is quicker and cheaper. Drill out the marks you made for the pegs, which will register the cardboard into alignment. I made mine from hickory pegs donated by my landlady; you could use dowels, bolts, pipe, whatever. Since my plywood was so thin, I had to add little scraps to the backside of the bottom piece of the jig as shown so the pegs sat down into something. If you use thicker plywood, these pieces could be eliminated. It is important that the pegs be secure, because they will take some abuse and you want them to be accurate for layer after layer. I glued and screwed them in their sockets.
In each corner, put an 18" x 1/2" diameter threaded rod to work as the clamping element. Lay the top plate onto the bottom plate so that it is held up by the pegs and rods; reach in and scribe each peg's placement onto the top plate. Drill out those holes at least an 1/8" too big so you have some play in aligning the plates later. Test that it all fits together.
Step 2: A Word on Cardboard
I got all my cardboard out of dumpster. I would recommend you do the same. Look for big pieces, preferably double-corrugated, as this will save a lot of time as the layers are built up. Avoid dumpster-diving after rain or snow, and make sure pieces are relatively clean, dry, and unstained. It is fine if they have creases or wrinkles.
Remove all the tape and staples and cut the boxes into flat pieces. Cut them into strips 3-3/4" wide on the table saw, cutting half of them with the grain and half of them against the grain of the corrugations. When laminating, the grain will alternate, except in the legs, which will always be oriented with the grain of the cardboard running vertically for strength.
Cut the strips to length, about 22". Recycle all scraps.
The only pieces that must be mitered for strength are the leg pieces. Cut as shown, matching the angle of the slope of the seat piece, whatever that may be in your design. You can cut the strips to length by stacking them several high, setting an angle on a miter saw, and slicing through a bunch at once to save work.
Step 3: Wheat Pastin'
I got my wheat paste recipe from this excellent Instructable: www.instructables.com/id/Wheatpaste/
In a nutshell, bring some water to a boil, then add white flour in a proportion of one part flour to four parts water. Whisk in thoroughly, cook for a few minutes, take off the heat, add a little sugar, and whisk it smooth again. Some boogers and clumps are fine.
Step 4: Lamination
Lay out your jig and piles of cardboard. Use a paintbrush to apply glue to both sides of each piece except the first and last layer, as you want a clean side in contact with the jig so it doesn't stick.
Build up the layers, alternating the way the cardboard lays at each joint so the pieces overlap the previous layer. Also, alternate the grain of the cardboard of each layer for strength. All the leg layers need to be vertically-oriented grain; I also made a section where all the pieces were out of vertically-oriented cardboard to add some tearing strength in the middle of the finished chair. Where the cardboard is too long, just let it run wild and trim it later, after the glue has dried.
When you run out of glue or reach the top of your pegs, put the top plate on the jig and crank down the threaded rods with washers and wing nuts until glue squeezes out from in between the layers. I aimed for about four inches at a time, which makes a chair in four to five meta-layers. Let the glue dry overnight.
In the time-lapse video, you'll see me trim the miters into the legs, then lay up one layer.
Step 5: Finishing Up
To put the meta-layers together, trim them down and stack 'em up with a generous bit of wheat paste and some white glue for good measure between. Weight it down heavily. I added mitered strips to the outsides for a finished appearance.
After a day or two of drying, take off the weight and trim to desired dimensions with a circular saw.
Sit down and kick it.