A new person was coming in to share my office temporarily. I needed extra space on my desk, and I had a lot of cardboard. So I decided to build a shelf.
The main portion of the shelf was a 1.5″ thick “honeycomb” panel. It is 4′ long x 8″ wide. You can see the internal ribs in the picture. ->
The outer skin is simply folded into a box-like shape and overlapped in the back to provide extra strength and an easy-to-glue surface.
The front “Tube” in the shelf has no internal cross bracing along its length to allow for storage of dowels and rulers. Te entire thing was glued with Titebond 2.
The legs of the shelf are made of folded cardboard. The grain runs vertically, and the side walls are double thick. The leg vertical pieces are one continuous piece that starts in the back, folds around in front, goes back to form the rear wall, then out front and back again. The shelves are also double thick with the fold in front, so it looks nice. They are set in dadoes that penetrate the inside layer of the cardboard legs. The top and bottom pieces are just single sheets glued in place. The legs are 18″ tall, 6″ wide and 8″ deep. This results in a span of 3′.
Here you can see that I have it loaded with about 10lbs. My deflection testing from my cardboard boats shows that the shelf could support a lot more weight before it came crashing down.