How would you like an incredibly strong, cool, and cheap building material for making lightweight tables, chairs, shelves, or anything else you can think of. Reusing cardboard to make furniture has always been a good idea, but the results I've seem have been either incredibly complex, or shoddy looking.
By laminating sheets of cardboard together into a large block and cutting this up with a table, or circular saw, you can create cardboard lumber of any dimensions you want: 2x4s, 2x8s, 4x4s. If you alternate the grain of the corrugations you can create plywood. If you glue your lumber together end-to-end you can create strong honeycomb-like boards.
You will only need three things to create cardboard lumber:
1) A Saw
2) Lots of cardboard
3) Glue... lots of glue
Step 1: Types of Saws
Table Saw: The best saw you could possibly use to do this is a table saw. You can adjust a table saw's fence to help you cut perfectly uniform lumber out of your cardboard block. This allows you to easily mass-produce cardboard lumber. Because of a table saws fence, you should be able to cut lumber twice as thick as the max height of your blade by cutting once, and then flipping your cardboard block over and cutting through entirely.
Circular Saw: If you're really good at cutting straight lines and have no other option then I guess you could give it a try.
Hand Saw: Possible, but too labor intensive for me.
Band Saw: If your band saw is as powerful as a circular saw than go for it, this could open interesting options.
Chain Saw: Messy...
No Saw: Unfortunately for people without access to saws, this instructable is not for you. I know it looks cool and all, but it's just not gonna work out.