Due to poor mechanical design, the spring hinge of my glasses broke twice. Once while still under warranty, and it got exchanged for free. Then once again now, but the warranty is over. Being self-darkening prescription glasses, they were not cheap. Gosh...
So I decided to repair them using 1mm thick steel string (*) to form a hinge and temple in one single piece.
This method may not apply to any glasses. It depends on how the hinge is made.
(*) that is used in RC models to transmit the force from servos to controls.
Step 1: Make a New Hinge
With pliers, make a loop with the steel string. You can use a small screwdriver to roll the string around.
The internal diameter must correspond to the original hinge screw.
Cut out the excess string, and hammer the loop flat.
Adjust the loop so that it turns smoothly into the hinge, with proper angular limitation. This is the only tricky part.
Assemble using the original hinge screw.