I found a small length of filament in the parts bin. I don't know what it is, and nobody else here does, or remembers ordering it. I'm pretty sure it's a sample that was sent by Prusa when we ordered the printer, and it's probably not a special material.

It's feels "gummy" and a lot softer than PLA, but not really rubbery either. And I tried printing something with it at 230C as if it was PLA and it's clearly not hot enough: it's able to flow out of the nozzle but it barely sticks to the bed.

Any idea what it could be?

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

Interesting account of what happens before amputation in the case of frostbite, why surgeons wait as long as possible to amputate and how they try to salvage as much limb as possible.

I made this custom case for my 3D printed spectacles:

It holds the glasses by the edge of the frames, so the lenses are suspended above the bottom of the case without touching anything and no padding material is necessary to prevent scratching.

And being specially sized for those glasses, the case is no larger than it needs to be.

Did I mention that I love 3D printing? 🙂

I love FreeCAD (I use the daily build, 1.1.0dev), but there are two limitations with it that are driving me crazy. Maybe someone can tell me what I'm doing wrong:

• How can I select hidden features? By that I mean, features that are stacked on top of each other or hidden behind another feature. For example, 2 lines sharing the same space in a sketch, or like in the assembly in the attached image, something inside the box.

  In SolidWorks, you can hold Shift (IIRC - I haven't used it in 15 years) and it cycles through the elements that occupy the same space where you click, I can't believe there isn't a similar feature in FreeCAD because it's so essential. But I can't find it for the life of me.

• In an assembly (new 1.x default assembly workbench), is there a way to manually "grab" parts that aren't fully constrained and move them with the mouse?

  Again, in SolidWorks, this is trivially easy to do. I used to use that all the time to quickly see if my parts moved as they should. It's really hard to get a feel for whether the design is correct when nothing readily moves in FreeCAD.

  Not to mention, very often, the constraint resolver doesn't quite understand what I want and I'd like to manually locate the parts close to where they ought to be to "help" the resolver, if that makes sense.

  Can you do that in the new assembly workbench? That too seems so essential I can't believe it's missing.

You might recall last month that I posted about my 3D-printed spectacles.

Enough people asked me for the files and for details on how to order lenses and mount them into the frames that I figured I'd release everything with instructions - and also redesign the hinges a bit so the temples fold more compact, something I meant to do for some time.

You might find this little tool useful:

3D-printed holes gauge block

This is a block with a series of vertical and horizontal holes from ⌀1 mm to ⌀3.6 mm (nominal) in 0.1-mm increments. I print this block with any new printer / new material at the layer thickness and speed I use most often and keep the blocks as references.

Then, when I want to print a part with a hole in it that will end up printed at the final diameter without any rework (or very close, but usually it ends up exactly right) I use the gauge block I printed with the printer and the material I intend to print the part out of to find out which nominal diameter hole I need to use in the model for the hole.

For instance, the block in the photo was printed on a Prusa Mk4 with PLA at 0.2 mm layer thickness. If I want a ⌀0.8-mm vertical hole with no interference in my final part in PLA out of that printer, I'll need to model a ⌀1.2-mm hole. I know that because the shank of a 0.8-mm drillbit will slide freely in the vertical hole marked ⌀1.2 in the block.

Or if I want a hole that I can screw an M3 screw into without having to run a tap through it, the block tells me I would have to use a ⌀3.2-mm hole to fit a ⌀3-mm pin in freely, and I back off 0.4 mm to get a hole in which the screw thread will engage well but reasonably lightly, or 0.5 mm for a tighter engagement (but with a bit more risk with horizontal holes near an edge, because the layers might separate) so I know I'll have to model a ⌀2.8 or ⌀2.7 hole in the model.

I use those gauge blocks all the time. They save me a lot of time on parts that I print often because I never have to ream or thread the holes: they come out the printer just right and ready to use.

This is the worst possible setup to print living hinges: PLA isn't terribly flexible, and here the flexible bits have to be printed vertically, which really isn't ideal to withstand cracking.

Yet when the application isn't heavy-duty like in this clamp-on connector, even PLA printed "against the grain" works well too: this connector can spread its hooks linearly 3 mm apart and the living hinges don't crack or weaken even after many cycles.

I'm generally left-learning and I enjoy the usual left-leaning comedians - you know, TDS, Colbert, Kimmel and the likes.

But I also pride myself on being open-minded and listening to all sides, and I don't know any good right-leaning comedians. And ya know, if it's funny, I'll laugh at anything said by anyone.

So please make suggestions! Whose jokes and commentaries are worth listening to?

And in case it wasn't clear, this is NOT flamebait: I'm genuinely looking for good comedy material from comedians on the side of the political spectrum I'm not on, for my own education.

So I'm on the market for a 4G or 5G mobile hotspot with a build-in VPN client I can carry around in my backpack and connect my cellphone to. I've looked far and wide, and really the only manufacturer that seems to make what I want is GL.iNet.

The two battery-powered models they offer that interest me are the Mudi v2 and the Puli: they only do 4G and I wish they did 5G too, but I can live with that. Other than that, they really tick all the boxes for me.

From what I could read, the GL.iNet company also seems very open and very responsive. That's a plus too.

But I have one giant problem that prevents me from whipping out the credit card: GL.iNet is a Chinese company, and those products are sensitive applications. I know I can flash OpenWRT separately on those devices to ensure they're not doing stuff behind my back, but I don't really want to do that because I'd lose the GL.iNet plugins and custom UI. Not to mention, I have no free time for that. I'm looking for a ready-made solution if possible with this one.

Anybody knows if GL.iNet can be trusted?

Also, has anybody ordered from Europe using their EU store? They say they ship direct from Europe but they give no details.

And finally, what do you think of those two mobile VPN routers if you own one. Do they work well? I read somewhere that they can be buggy with certain VPN providers. Do they work in Europe? I assume they do since they sell EU plugs but maybe there are caveats.