I have a pair of Clic reading glasses that I need to adjust. I have a larger than average head, and the plastic loop at the back is a bit too snug behind my ears. I like the glasses, and their magnetic latch at the bridge of the nose, but after a while it hurts to wear 'em.
I want to warm up the plastic just enough to bend it a bit. How hot is that? My wife is wary of using our Instant-Pot for the job, though its temp control seems ideal for the job.
Clic makes an extra-large version with extra slip joint at the back and longer temples. I had a pair, but they kept slipping out of adjustment. They eventually fell apart entirely.
It was easier than I expected to find what plastic they’re made from: They’re pure polycarbonate. And I’m finding online that polycarbonate becomes workable at around 180-190 C (which is probably hotter than your Instant-Pot can get, since it’s much hotter than boiling water). Your oven can get that hot, but then you’ve got the problem of only heating up the parts you want heated: Heating the lenses that much would probably distort them unacceptably.
You know, a LOT of optical shops will adjust your glasses in that manner for you, often at no charge, using equipment designed to warm the plastic to proper temperature without causing damage…?
I don’t think a hairdryer will work. They typically top out at about 140 degrees F, but the glass transition temperature of polycarbonate is 147 degrees C, or about 300 degrees F. You’d want to be above the glass transition temperature.
Another important point: prescription glasses with plastic frames typically have metal cores in the temples. If they’re made with a polymer other than polycarbonate, you heat the frames and then bend the temples. The metal core takes a set and holds its shape as the polymer cools. By heating the thermoplastic polymer, you prevent it from cracking as you bend the frames.
Since there is no metal core in these temples and since polycarbonate has a fairly high glass transition temperature, these readers may not be adjustable in the way most prescription frames are.
Regarding the lens distortion Chronos mentioned, the lenses are probably polycarbonate as well; they may or may not get distorted in the oven. To be safe, you might consider heating a pot full of cooking oil to 310 degrees F in your oven, dipping the temples in the oil and then bending them.
You might consider this, but I wouldn’t. Dipping plastic frames in a pot of hot oil sounds messy at best and like an invitation to your local hospital’s burn unit at worst. They’re cheap readers, right? Maybe just find a different pair that fits you better. Anyway, that’s my take on it.
Last time I had this done at the opticians (several years ago), he used a small pot with a strong heater at the bottom, then filled with a couple inches of sand. He embedded the parts of the frame that he was adjusting into the hot sand for a short time, then took them out and bent them. Sometimes he repeated this, making only a small bend each time.
Seems like a small pot filled with hot sand would be safer to work with than hot oil. And the optician had a large pan of cold water real close by – I’d certainly do that, too.