Cryptex!

Very cool idea (not mine it was posted as a competition idea by Everythingmechanical http://blog.makezine.com/archive/2010/04/makerbot_giveaway.html)

Seemed easy enough to make a simple one so here it is.

2 part inner tube 2 part outer tube and a tumbler (you need 5 to complete assembly)

I've included the SKP file for those interested.

I'm still very new to 3d modeling and sketchup (learned a lot this past couple of weeks tho) so my images are still pretty ordinary.

If I get the chance I'll come back and do an exploded image to show assembly a little bit more clearly.

I assumed that glue could be used to attach the end caps to the inner and outer tubes but it would not take much to put in a small hold and use a screw (allowing the tumblers to be changed if wanted ( or taken apart of the combination is forgotten)

obvious improvements would be to alter the tumbler design so the actual value for each tumbler could be changed, etc.

I can see a few ways this might be done but none I'm terribly happy with right now.

UPDATE:
Plate 5 v1.1
This is a modified tumbler with many pick groves to make it harder to use machine tolerance issues to determine the combination.

Plate 5 v1.2
This is a modified tumbler in 2 parts enabling the tumbler to be "re-configured" to change the values.