A video of the cardboard uke in action can be found on YouTube.
Step 1: Materials...
Several large shipping boxes made from corrugated cardboard. The tighter the corrugation the better.
Several sheets of non-corrugated composite cardboard like cereal boxes or the back of notepads
2 fully threaded bolts or a threaded rod
4 geared guitar or ukulele tuners with flanged bushings
1 set of soprano ukulele strings
12 1.5" long cotter pins
2 small hinges
1 bottle of wood glue
2 wood screws (1.5 - 2 inches)
Sharp hobby blade
Step 2: Templates...
Body A: Top (aka Soundboard)
Body B: Middle
Body C: Back
Neck A: Edge
Neck B: Middle
Step 3: Trace templates...
Body A: 1
Body B: 9
Body C: 1
Neck A: 6
Neck B: 7
1) The majority of the body pieces should be cut with the lines of the cardboard running along the length of the piece.
2) Mix in a few pieces of "Body B" cut in other directions to provide strength in all directions.
3) For the neck, cut the pieces in a variety of orientations, but avoid any with the lines running along the neck.
4) Avoid any areas of the cardboard that has dents or wrinkles.