I set myself the challenge of building a shelf from cardboard. Not a temporary, flimsy shelf but a permanent, rigid and functional shelf.
The cardboard I chose was from shoe boxes. It was thin corrugated cardboard with a thicker, nicer looking presentation side.
Step 1: Step 1
To make the brackets start by cutting 1.5” (40mm) wide strips. For maximum strength cut the stips so that the corrugations run along the length of the piece like the grain in a piece of wood. Glue (school glue) them together in an L shape. Be sure to alternate where the joints are so that no two joints are directly on top of each other. Make these L shapes the same thickness as a pencil. In this case it was three layers.
Trim a pencil and cut a notch into the bracket about a third of the brackets width. Cut these notches to fit the pencil as tight as possible. Add another layer of cardboard to each side to cover the notches. Once the glue dries, trim the brackets to 1” (25mm) thickness.
I know its a bit of a cheat using pencils as struts but i didn't have enough cardboard to make them. I'm confident 1” wide cardboard struts would work instead of pencils.
Step 2: Step 2
To make the top layout 5 or 6 layers of cardboard pieces and trim them to make sure none of the joints overlap. Alternate the direction of the corrugations for maximum strength. Use the biggest pieces possible and use the best pieces for the top layer. Glue and allow to dry.
Step 3: Step 3
Glue up a 1” (25mm) wide back brace as shown in the picture. Allow to dry thoroughly and trim all the pieces square. Notch the outer corners of the brackets to fit the back brace. Glue and screw the back brace to the brackets.