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Comment by greeneggs | Hacker News Reader

Do you know what kinds of results are possible with a standard consumer 3D printer? (A PLA printer?) The page says, "Any layer lines in the print end up transferring through to the glass, which makes polishing a lot more difficult," but does "a lot more difficult" mean impossible?

(I have an Ender 3 printer, and a microwave, so it looks like I can possibly get started for <$100. But both because of price and turnaround time, I am not very interested in using online resin printing services.)

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Yes, your surface finish is limited by your print quality - but smoothing surfaces post-print goes a long way. "a lot more difficult" doesn't mean impossible at all, but you will have to remove more material to flatten the surface before you can start polishing. Coldworking (cutting and polishing glass) is a field in of itself, and requires some non-trivial equipment to do efficiently, so I would recommend designing your initial pieces to avoid much coldworking. Don't expect an optically clear surface anywhere the glass touched the mold - the default for investment cast surfaces is matte, and clear surfaces either need to be polished with abrasives or HF+H2SO4, or were the top of an open-face casting.

Unfortunately, most kiln-casters prefer very high lead glass (40%+), because it flows very well and doesn't devitrify easily. This, however, makes coldworking an environmentally-dicy proposition, as it generates lots of micron-scale lead dust.

A microwave may suffice to fuse small glass jewelry (...kinda, the annealing will be pretty horrid...), but isn't going to cut it for casting. Stuff at the scale presented in the article would require firing times of at least 12 hours, with much better temperature control than a microwave can provide.

I've got no practical experience with 3D printing, but surely dremel + grinding/sanding bits = no more layer lines?

Yep, sanding is an option. I've also seen people fill the valleys with some sort of goop filler and then start sanding from there, just to get it a little closer to smooth. But I can't say if introducing different materials like that might interfere with casting. They were doing it to paint over.

Another approach is vapor smoothing - you can use acetone vapor to smooth ABS prints. Acetone won't do anything to PLA though.

I've heard of other chemicals being available for smoothing PLA, but they're nastier than acetone and I don't know anyone who's actually tried them.

Wax is a very good material for modifying/smoothing prints pre-casting, and doesn't mess with the casting process. UV-cure resin is also a good choice, as you can set it fully, sand it down, and apply a gel-coat for a shiny finish.

ABS is a very bad material for casting if you're planning on burning it out, but vapor smoothed parts do make very nice plaster molds if you can remove them. Chloroform works very well for PLA, but it is much much nastier.

You should be able to use acetone. See the solubility table [0] for PLA. It takes longer, but it works.

[0]: https://onlinelibrary.wiley.com/doi/pdf/10.1002/app.38833

Acetone really don't work well for PLA. You need tetrahydrofuran to smooth PLA in the same way that acetone smooths ABS.

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