Summary

This is just a proof of concept for creating a simple hinge that is fully printable - the pin itself is made from filament.

Instructions

1 Print inner part
2 Print outer part
3 Cut a 50mm length of 3mm filament
4 Assemble using the filament as the hinge pin

You might need to straighten out the pin first. You can use a single long pin for both hinges, or individual smaller pins for each hinge, which will look better.
Optionally you can thermo-weld (a simple soldering iron you no longer need will do) the ends of the pin to keep it stuck between the hinges, as it might come loose at some point (thanks to JDCUBED for reminding me).

Simple Hinge Design