Here’s a rule I learned the hard way a few decades ago:

• If you type “rm”, take you hands off the keyboard and take one deliberate breath before continuing your command.
• If you then type “-r”, do it again.
• If you then type “-f” do it again.
• In all cases, re-read what you wrote before hitting ENTER.

The more I look at it, the more I think that is in fact TPU. And in fact I’ve read somewhere that most varieties of TPU are in fact impervious to acetone. The one roll I have here isn’t, but maybe this yellow piece is such a kind.

Interesting… I didn’t know purge filament existed. In fact, I wondered what would happen if I ever ran something that truly gummed up the nozzle, if I’d have to replace it entirely or something.

Resin is well within reach of the casual hobbyist now - we’re talking a couple hundred dollars to get an entry level machine, and a little extra coin for the materials/consumables. I have a (now old) Mars 3 that is ticking along beautifully

I am very tempted by a resin printer. However - and this is going to sound weird - I actually like the limitations of FDM.

And this is why: I’m a hacker at heart (in the old sense, not the nasty illegal stuff) and I like to push the envelope of what our Prusa Mk4 printer can do. I’ve printed stuff with that thing that I had no right to print by working the workarounds in the model, playing with layer sizes and controlling the path of the nozzle so it ends up printing features that are right at the limit of what it can do. Hell, even the hinges in those specs of mine are kind of pushing it.

And it’s fun! It provides hours of good fun trying this or that and finally getting the little printer to print something right.

A resin printer would make very good prints without anything to do, if that makes sense 🙂

Also I want to work with different materials. I’m actually looking into getting a Prusa XL with several heads to combine TPU for flexible, hollow parts and PLA for the supports inside the parts. That’s something a resin printer can’t do: resin printers print… well, resin.

And finally, I’m always kind of designing parts with a view to making it available to anybody who has any old printer at home for them to print and enjoy. That approach entails designing for the lowest comon denominator (to a reasonable degree), something a resin printer is not.

So you see, while I would like a resin printer, I feel it’s just not the right printer for me.

tweak and reprint the frame a bit to match the lenses. That’s not really the end of the world, but I don’t count on any opticians to understand that

Oh believe me, they understand perfectly.

Here’s the thing - and I’m not inventing this: my current optician is a friend and she told me this verbatim: an optician’s bread and butter is selling you frames, and the services around fitting the lenses on the frame and fitting the frame on you. Opticians make almost no money on the lenses - which they have made abroad in developing countries usually.

I don’t deny that there’s a lot of measuring prior to ordering lenses, counselling the customer, and then a lot of fiddling with the temples and the nose pads after the glasses are completed to make sure the glasses are comfortable and yada-yada. The services provided by opticians are definitely useful, particularly for young wearers and for people who change frames often.

But really, if you’re a lifelong glasses wearer, you’re reasonably handy and you settle on one frame geometry, those measurements never change and you just don’t need the services.

Me, the last time I needed an optician’s services was over 20 years ago when I made my first frames out of nickel silver. Since then, I’ve only made copies of those exact frames because I really like them - including those 3D-printed ones I drew a few weeks ago: they’re a bit different to account for the nature of the 3D-printing process, but the key measurements are the same.

So whenever I go to an optician to order new lenses - which you almost have to because you can’t order the lenses direct, even if you have all the measurements needed by the lens maker, the convo always goes something like this:

• Hello, I need a pair of lenses with these dimension (or for these frames), with this prescription. My pupillary distance is x, the vertical angle is y, the bevel is z all around and the optical axis is marked here. I don’t want you to mount the lenses on the frames and I don’t want you to fit me. How much and when?
• Well okay, the lenses are $something. But since you don’t buy frames from us, we’ll have to charge you an extra $something.

I kid you not, it’s extortion. They hate it when you can do their job yourself so they charge you for the privilege. And since you don’t have access to their suppliers (they look out for each other) you have to go through them.

That sounds like a great idea!

In fact, an even better idea would be to split the lens in the plane that contains the crest of the bevel (which isn’t at the center of the edge all around). That way, the widest point would be on the bed for both halves, totally eliminating any overhang.

I’ll try that tomorrow. Thanks for the idea!

Lol

Clearly that’s progress 🙂

Thanks for the offer! But actually I didn’t model that part for me but for others who need a model of a finished lens. I already have real lenses myself.

The thing is, I shared the design of my glasses for others who might want to print themselves the same glasses too, and there seems to be enough interest that some folks printed them and went to their opticians with it, only to be turned away because the frames are unusual - or they didn’t want to risk having lenses made using the lens template only to find out that the lenses are unusable in the final frames - and they didn’t want to risk filing a notch in the lenses either, which is something that’s not usually done to fit lenses to frames.

And I can understand the opticians too: if they agree to order lenses and they don’t fit the frame, the loss is on them and they don’t need the aggravation.

I wanted to provide a model of a lens that those folks could print out of PLA to convince the opticians that it’s not sketchy or far-fetched. If this parts needs a resin machine - which, I agree with you, it absolutely looks like it does if you really want a quality part - then it sort of defeats the point of self-sufficiency of my little project.

Well, I toyed with the printer’s temperature settings until I found a combination of nozzle temperature and bed temperature that finally made it spew out parts without making a disaster.

It seems to flow best at 260C, but then when it lands on the bed, it immediately shrinks as it cools and the part curls up and comes unstuck. I had to lower the temperature to 245C and raise the bed temperature to the maximum this printer does - 110C - for the part to stick enough to complete.

The nozzle clearly isn’t hot enough because some layers on the final parts look like they’re about to delaminate. But any hotter than that and the material curls up. And it doesn’t matter what bed plate I use: that stuff doesn’t seem to stick to anything properly.

I printed spectacles with that mystery filament. You can see how floppy it is here:

https://toobnix.org/w/qJJ1htb9eqmiHx7gSpq2RT

It looks like TPU alright, but the temperatures involved aren’t really typical of TPU. Also, acetone does nothing to it whatsoever.

The material also doesn’t like to be filed or sanded, and the best results for a nice finish without bits of material sticking out all over the place is to “polish” it by running a very sharp x-acto blade across the surface until all the junk is gone and the surface is shiny.

Weird filament. Kind of useless…

There should be no need to pile on. Any one of those things would have been disqualifying in times past. Clinton almost got impeached over a blowjob. But Trump and all the things he said and done over the past 9 years is somehow okay. The mind boggles.

A post in all caps isn’t doing the work you think it’s doing.

I had no illusion in 2016. In fact, I had no illusion back in 2002 when I left the US and gave up my citizenship after Dubya was elected and signed the USA Patriot Act into law after 9/11. America is hosed and has been officially on the path to idiocracy and fascism since then.

It’s just that a 3rd round of millions of Trump votes should confirm it without the shadow of a doubt to even the most wide-eyed believers in American exceptionalism. America today is the 1933 Germany of our time.

Even if Trump had lost, one fact remains: tens of millions of Americans voted for this guy three times in a row.

The first time, it’s conceivable that Americans made a mistake.

The second time, they knew Trump as actual President.

The third time, they knew Trump as a convicted felon, insurrectionist and overtly wannabe dictator, and they voted for him even harder.

At this point, MAGA isn’t a freak event, it’s the norm. Even if the dems had won, they’d have won the presidency of a MAGA country, and quite frankly, what’s the point… You can’t cure someone who wants to be sick.

It will be when the Trump voters discover that they will pay for the tariffs and not China.

I hate Elon Musk as much as the next guy - and all the more now that he has this massive conflict of interest working in his favor and at the American public’s expense.

But I will say this for the sake of exercizing critical thinking: everybody is happy to say AI hallucinates when what it says doesn’t suit their narrative, and call AI intelligent when it does.

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.

That’s kind of my problem: my correction is not simple. I can get near or far lenses with my correction for relatively cheap - like $100 a pair. But progressives are eye-wateringly expensive.

As for my frames, they’re both free and priceless to me because I make them myself. And just because they’re not off the shelf, they’re more rewarding to wear.

So having some understanding and control of that part of the process could have helped.

The only things you can rely on with regard to how the lenses are edged is:

• The bevel will be “bevelly” - meaning it’ll be a bevel of some kind, between 90 and 120 degrees, but no flatter than that. In other words, you can rely on having something to grip the lens with and that’s enough.

• The bevel follows the curvature of the frame. If you frame is flat, the bevel will be placed all around the edge of the lens flat too.

• As much as your correction will allow, the bevel will be placed as far forward as possible so the lens looks like it’s tangent with the front of the frame all around, and all the thickness will be hidden at the back of the frame. So if your frame is, say, 2mm in width, the root of the bevel will be placed 1mm from the front of the edge.

The other thing you can rely on is that the bevel will be slightly oversized so they can be snapped into the frame, and the amount of oversize will be a bit higher for plastic frames which are more flexible. And that’s where the danger lies: if your frames are designed to hold the frame without pressure like mine, you have to tell the optician so they pass the information to the lens cutter. Otherwise you will received lenses that are slightly too big.

But don’t sweat it too much: the great thing with 3D printing is, even if the lenses you received aren’t the right size, you can always print another frame with slightly revised dimensions.

And if you really don’t want to print another frame, don’t forget that you pay beaucoup bucks for those damn bits of plastic, so you can always copiously warn the optician that your frames are not made of the kinds of plastics plastic frames are usually made of, and then the onus will be on the lens maker to make the lenses right for your frames (remember that they will be sent your frames, so they’ll know rightaway if the lenses fit).

If the lenses aren’t right, it’s their problem and you can reject the lenses and tell them to try again. If you warn the optician in no uncertain terms that your frames are PLA, they or the lens maker can’t claim they didn’t know.

Just design the frames you want with the shape you want, with a 120-degree bevel, and ask your optician if it’s workable for the lens maker. They might tell you they’ll ask them - and you can leave them a test print too if they want to sent it to the lens maker too. There isn’t much more to this really.

I’ll definitely add cable temples to the list of things to try and see what works well.

Be aware that cable temples are a lot more finicky to adjust than regular curved temples. If they’re too short, even a little, they’ll dig into the skin behind your ears and you’ll hate them. Likewise, if the hook is too narrow, the tip will hurt you under your ear.

That’s a big reason why cable temples went out of favor in the 1920’s: they’re great when they’re well adjusted, but they quickly become nasty and uncomfortable when they aren’t - unlike maladjusted curved temples which can simply ride up the ear a little without too much drama.

With regular metal wire, you can bend the temples this and that way to make them fit. Not so much with PLA. You can shape it with heat but if you do it more than once, it becomes rough and unpleasant to wear - if the PLA doesn’t delaminate completely. So take the time to design the right length and shape directly in your model. It’s a bit long and tedious but once you know the right dimensions, you’ll love how natural they feel.

Also, don’t make the wire too thin or it will dig into your skin as well. And too thick will make the wire inflexible and difficult to put on. The wire profile that works best for me is this (for PLA):

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…

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.