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I am building my CoreXY 3D printer with 350x350 mm heated bed at about 4 mm thickness. I just found out that borosilicate glass is unavailable at the local glazier. He offered tempered or ceramic glass instead. Which one should I go for? I read that both are a more expensive option to borosilicate glass, but I worry about the temperature stability, warping of the glass (in case of the tempered one), and parts (not) sticking to it. Any experience is appreciated.

PS. The ceramic glass of this size would cost me about 45 USD. The glazier did not tell me the price of the tempered option, but I reckon it will be around 30 USD, which is much more acceptable if it does the same job.

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    $\begingroup$ Side note, I've printed years on the bare aluminum plate with 3DLAC, that works well too! :-) Good question to probe for alternative sheets of glass! I know some people just use plain window, mirror or photo frame glass, that also works for a while. I'm curious to see the answers. $\endgroup$
    – 0scar
    Sep 6 at 10:12
  • $\begingroup$ Well, I will probably go with the tempered glass. But since my printer is still far from finished, I will not have results for quite some time and by then I will most likely have forgotten to post them here. I plan on having one side bare glass and a PEI sticker on the other side. If anyone can share their experience, it will be most appreciated since I have to tell the glazier what I want in just a few day at maximum. $\endgroup$
    – MStarha
    Sep 6 at 11:28
  • $\begingroup$ I'm no fan of PEI, since I print mostly PETG, the prints get fused with the bed. Even with 3DLAC difficult to remove. We cannot foresee when this question is answered, hopefully before you have to order. $\endgroup$
    – 0scar
    Sep 6 at 12:18
  • $\begingroup$ I print mostly PETG and ABS with at least a thin layer of gluestick (even a layer that was applied days before is good enough). This keeps PETG from sticking too well, and ABS sticking well enough to print models as large as 20x20 cm. Btw this is with Prusa i3 MK2.5 with Kores glue stick. $\endgroup$
    – MStarha
    Sep 6 at 12:42
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People choose borosilicate because of its thermal properties.

Between ceramic and tempered, I would suggest tempered glass, it's not good as borosilicate when comes to adapting to rapid temperatures but better than ceramic. The other option I would suggest will be "Aluminium", which is much better.

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  • $\begingroup$ Do you mean bare aluminium plate? Everywhere people say that prints do not stick to that. $\endgroup$
    – MStarha
    Sep 6 at 19:18
  • $\begingroup$ @MStarha You can print perfectly fine onto aluminum build plates, I've done that for years. From the first day I got my first printer I tore the tape, removed it to print directly onto the plate, never changed that for that printer. $\endgroup$
    – 0scar
    Sep 6 at 23:09
  • $\begingroup$ @0scar But you print mostly PLA, right? I almost never touch PLA because my prints are mechanical parts and PLA is too brittle and melts too soon for my liking. Though it is tougher than PETG or ABS. I worry that it would not stick well enough. Plus I do not want to hammer the print of the heated bed itself inside the printer. Or I would have to get another aluminium plate cut, which would cost me about the same as the tempered glass. Also I asked for help on reprap.org forum with interesting, but contradicting, answers. $\endgroup$
    – MStarha
    Sep 7 at 6:49
  • $\begingroup$ @MStarha I rarely print PLA nowadays (under 3 kg), I've printed 20+ kg of PETG/NGEN, mostly mechanical parts as well. You just need to add the correct bonding agent. 3DLAC has served me very well, used it on aluminum or glass. Getting the prints from the plate hasn't been an issue (until I used a PEI sheet... PETG fuses with PEI). $\endgroup$
    – 0scar
    Sep 7 at 7:05
  • $\begingroup$ Ok, thank you. Some people also report that PETG stuck to glass so much it took a piece of glass with it. $\endgroup$
    – MStarha
    Sep 7 at 7:09
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Mirror glass is commonly used. It's flat and cheap. There isn't really a sudden thermal shock to worry about, and if you're going to be printing at temperatures that need borosilicate glass, you might find the aluminium parts of the bed sagging. Remember to ask for the edges to be smoothed.

Thinner glass will transmit the heat better - but you might be able to get tempered glass as thin as 1/8" thick (~3.2 mm).


I print with PLA and use 3 mm mirror glass secured with a bulldog clip near-ish to each corner, and Elnett "Normal Strength" hairspray for adhesion (applied holding the glass over the bath to avoid it getting everywhere) - it's easy to clean off under running water. Demounting the parts cleanly is a simple matter of popping it in the fridge for half an hour if they don't come off with a slight nudge.

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  • $\begingroup$ I was thinking that mirror as a print bed looks quite cool, but the reflection seems a bit impractical to me. I also plan on putting PEI sticker on the other side, and that could be a problem. $\endgroup$
    – MStarha
    Sep 9 at 7:14
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The primary advantage of borosilicate isn't that it's resistant to thermal shock -- as someone already noted, there's not much in the way of rapid heating or cooling in FDM printing (yes, the filament is hot, but its mass is low enough the glass it touches won't pick up much heat). Rather, it's the low expansion. Common soda-lime glass (window glass, mirror glass) expands several times as much as borosilicate, which means it will also shrink several times as much when it cools back down.

If you're holding constant temp throughout the print, and give adequate preheat time, that won't matter, but if (for instance) you heat the bed 10 °C hotter for the first layer, then cool it, plain glass will shrink enough to potentially cause the print to come loose, while borosilicate won't.

Ceramic glass is like borosilicate only more so (akin to Corningware) -- but again, not worth paying for unless you expect to change your bed temperature during the print.

For any kind of glass, my own preference is to use glue stick. I apply a "squiggle" (a precise metric volume), use 91% isopropyl to spread it evenly over the build area, and my prints stay stuck, but pop right off when the glass cools a little.

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