It has a long piece of 1mm piano wire running through that acts as a spindle. It's a standard hinge design called a continuous hinge. I suppose I could have 3D-printed the spindle but it would have made the hinge huge and not very nice-looking.

They're prescription glasses. They're my regular glasses I wear every day. I made the frames but I can't print optical lenses, sadly. I wish I could because they cost a fortune and they're a real rip-off...

Thanks!

I just made one initial print but I didn't leave enough free play in the frame holder at the bottom of that case, so while it worked, it was kind of a pain to insert the frames into it. I widened the play from 0.4 to 1.5 mm and now there's zero usablility issue.

Another unexpected problem I discovered with that first print is that I couldn't tell the top shell from the bottom shell when the case was closed. I completely overlooked this and it turned out to be a massive PITA: 50% of the time, I would open the case upside down. Silly eh 🙂 It seems obvious in hindsight.

But I like the symmetry of it. So I added "engraved" text at the front edge to tell if the box is the right way up before opening, and put my name and a description of the particular correction in that case as a bonus.

The rest - stiffness, hinge, lid fit. magnet fit - came out okay the first time out. I'm getting really good at knowing the printer's tolerances in advance and leaving enough play for things that shouldn't assemble with an interference fit.

Halting the print to insert the magnets would be problematic: I print on the company's printer and it's a 5-hour print, so I start it before going home in the evening to avoid annoying everybody during work hours.

We're allowed to use the printer for personal prints. But the rule is, if someone arrives at the office and needs to print something for work, whatever private stuff is in the printer is removed to make way for work things. And of course, if the printer is running - or paused waiting for someone to attend to it - the print is cancelled.

So I'd have to arrive really early in the morning to make sure I get there before the most early birds but there are no buses at the wee hours of the morning. Therefore realistically, my long prints need to complete unattended and be ready to be chucked out in the morning if I'm not first to arrive at the office.

But I'm not worried about the magnets coming out: the fit is tight and I use really strong epoxy. I've yet to see anything assembled with that stuff come undone.