My first design, a small die in a larger die box with a working snap-fit hinge. Both dice are usable - even with one inside the other - but no guarantees about randomness.
Made to print with PLA in high resolution on e.g. a Replicator 2.
Created in Autodesks interesting (and free for now) Inventor Fusion.
This is a pretty small thing considering the working hinge - it probably has to be printed at 0.1 mm resolution (this is what I did) - or be scaled up a bit.
Update: Uploaded a slightly smaller inner die to make the die box close completely.