Based on my previous implementation of Hex box. Follow my rule that joining mechanism should be integrated to the box structure.(rather than using a separate joint part)
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This time, a "sliding" joint was employed so that the surface area for taking the tensional force increase. This would make the box more durable.
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In additional, sliding mechanism also make the adding and removal of box easier.
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Moreover, you can joining two or more boxes, like what I do in the photo, to make the structure more resist to falling.
. Updated on 04-Oct-2015:
Added a Wall-Hang part. Not tested yet, but should work. .
Updated on 10-Aug-2014:
Some feed back saying that they want a flat surface. So I just add one.

For a fast but barely useable box, print with 0.4mm nozzle, 2.5mm layer height.