Iris Box

Inspired by http://www.thingiverse.com/thing:4244 this is a box that opens when you twist the outer rings in opposite directions. See this video by Labmat: http://www.flickr.com/photos/matthewlaberge/5101233486/

Edit I: Design has been modified to increase the clearance between moving parts. I've also centered and oriented the parts in better positions for printing.

Edit II: Design files posted. DXF, STEP and the original CATpart for those with access to Catia. Thanks to everyone for you