I've only tried PLA at the moment. I'll try nylon tomorrow for the heck of it.

I don't think I'll have to reprint them very often because I'm usually careful with my glasses. Also - something I learned when I made my first round frames out of silver nickel - my lenses are as close to my eyes as possible: it lets small light lenses provide a gigantic field of vision. But another nice effect is that it makes glasses much less prone to damage: if your head hits something - be it a pillow in bed or the road if you fall off your bicycle for instance - small, high-set glasses usually take a hit last after your head makes contact. I usually sleep with my glasses on and nothing ever happens to them.

ABS would be a better option.

The hinges on the rims are split in the middle, so the rims can open up. They're held closed by the temple part of the hinges that wraps around them, and everything is helds together by the hinge pins. Aside from the lenses, the hinge pins are the only thing that aren't printed.

They are not perfectly round. They're slightly elliptical - 38 mm / 40 mm diameters. I know that because they were mounted on a silver-nickel frame I made myself some 20 years ago with those dimensions, so I didn't have to measure them.

I did have to make a couple of prints and take out a few tenths here and there to get a tight fit around the lenses because my 3D-printed grooves and the ones in my metal frames don't have the same geometry. But it was only minor adjustments.

Haha no, I still need an eye test, and I need to have the lenses made. But I can print any frames I want provided they match the shape of the lenses and respect my pupillary distance - which is baked into the lenses too.