The Cardboard Marble Run
A two-hour build from the recycling bin: a tower of zig-zag tracks, a lot of failed test runs, and one very satisfying marble. This is our most-built project. No special tools, no perfect cuts required.
How it comes together
5 stages, photographed as we went. No perfect studio shots, just the real process.
Raid the recycling bin. You want three medium boxes with clean, unbent faces. Flatten them along the folds and cut away any taped or torn panels. Flat, stiff cardboard is what makes tracks roll smoothly.
Cut strips 6 cm wide and as long as your box allows. Score a line 1.5 cm from each edge and fold the sides up to make a U-channel. Each channel is one section of track, and you need six to eight of them.
Stand the largest box on its side; this is your tower. Hot-glue the track channels in a zig-zag down the face, each one tilted just enough that a marble keeps moving. Test the angle with a dry fit before gluing.
Send a marble down. It will fly off somewhere, and that is part of it. Add cardboard bumpers at every crash site and re-test until the marble survives the whole run three times in a row.
Now everyone gets a brush. Acrylics cover cardboard beautifully. Paint each track section a different color and let everything dry for an hour before the grand opening run.