3DPrinting @lemmy.world ExtremeDullard @lemmy.sdf.org 1 mo. ago

My personal benchy: this one really tests a printer's capabilities

In the process of refining the design for my 3D printed glasses (yes, I'm still at it 🙂) and trying to streamline the lens ordering process a bit, because some folks have told me their optician, or their optician's lens supplier, didn't really want to mess with "unusual" things like this, I decided to draw and print a fake ophthalmic lens. You know, not optical-quality - or even see-through - but something that looks and feels like a lens, that can be mounted in my frames, to show an optician hands-on how it works and that it's not weird or delicate to work on.

I figured it would be a quick print in clear PLA, that would require only a bit of cleanup and mount right into the frames, complete with the bevel and the notch and everything. How wrong I was...

This part is almost impossible to print right:

It's modeled after a real bispherical lens with an offset optical axis. I mean it's optically incorrect, but it has everything a real lens would have: uneven edge thickness, one convex and one concave side.

You just can't set it flat on the bed in the slicer: none of it sits flat. The slicer has trouble generating support around the edge on the concave side that it interprets half of as overhang, and even if the beginning of the support doesn't get ripped off by the head and the print completes, the surfaces will be absolutely awful.
If you print it vertical - which frankly is the least bad option - then the bottom of the lens, under the support, will be a complete mess. The bevel won't even be visible. It takes quite some time to create supports that won't mess up the bottom of the lens too much
If you print it in clear PLA with only perimeters, it'll be transparent enough to see the spots were the perimeters are started at the next layer. And depending on your wall generation strategy, the spots where the printer tries to fill the voids will show up as round "halos" inside the lens.

The lens' thickness varies everywhere, so the slicer tries its best to fill each layer, but it's slightly different at every layer. At any rate, it reveals the slicer's idiosyncracies in tool path stragegy right away.
The bevel all around the lens is only 0.5mm high. If the printer is dialed in, the bevel will show as an actual 120-degree bevel near the front face of the lens, particular where the bevel is normal to the layer, about half-way up the lens if you print it vertically. If not, it will look like a barely-raised blob.

I've tried this print on 3 different printer and I just can't get a decent print. All I can do is play with the settings in the slicer until it comes out not too terrible.

So, that part is a bit frustrating for my original purpose, but it turns out to be a great part to test a printer and/or the slicer software! If you want to try it too, it's here:

https://github.com/Giraut/3D-printed_eyeglasses/raw/refs/heads/main/lens_example.3mf

19 comments

A part like this is begging to be done on a resin machine. You can't beat them for the kind of shapes and tolerances you're working with here.

I'd give it a go on my FDM machine, but I have .8 nozzles loaded right now - no hope haha.

I'd be happy to turn a few of these out in resin if you don't have a machine, would only ask for the freight cost.
- 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.
  
  Sounds like the eventual end. Will be learning how to take raw circler optical lenses. As the optical centres do. And build the tools for folks to shape them at home.
  
  Such a project would be a huge advantage to many 3rd world environments. And would likely be about embedding quality glass cutting blades etc into 3d printed frames/mechanisms. Likely from PA. With the ability to embed metal rods and gears where stability, strength is needed.
  
  You're welcome - glad to see you have it really sussed out. Finding something that works for you and knowing it won't just up and disappear off the market (as many fashion frames do) is excellent.
  
  Can see the optician side as well - they have an established process and deviating from that is unwanted faff. However, they are perfectly capable of ordering a lens to a customer given spec. A short 'if this doesn't work then lol you suck' disclaimer is all it would take to make the sale.
  
  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.
  
  Safety/PPE/ventilation is the main downside compared to FDM. It's a stinky job but you can't fault the results for presentable and functional parts. These things can print stuff like screw threads and other teensy features perfectly.
  
  Offer always stands if you ever want something to demo and can't get anyone more local to help :)
  
  The other point here is that if the lenses a user gets don't quite match the frame you could always just 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. The concept of a user being able to so easily self manufacture a set of frames is probably completely alien to them.
What about printing it in two halves the each have a flat bottom? Since the optical quality doesn’t matter, the line down the middle of the lens won’t matter.
- 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!
- Was going to make the same recommendation!
"Would you like an after dinner mint? It's only wafer thin."
- hhhhhhhwoffer thin
Wait wait wait. You’ve got a goal to 3D optical lenses? Nice!

I’d probably start with a resin 3D printer though. It’s seems the precision would be beneficial for an optical lenses?

I don’t know about any clear resins though. I don’t have a resin printer. It’s a very PPE oriented printing process, that didn’t suit when I tried it.
I should try this on my XL. I have big dumb 0.6 nozzles right now so it'd look like garbo, but I could print it in PLA with PETG supports. Being able to have almost no space between the support and primary material would probably make many alternative orientations possible.
You could try leaning it over on a slant, like 60 degrees so it's not in aggressive overhang territory, and then design in a custom support that can be cut off after. Since it doesn't need to be optically anything the marks from the support cutaway don't matter.

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