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Glass is really bad at transferring heat. Therefore using it with heated bed seems to be a strange solution since it will not be transferring heat from bed to the print.

However every article I see says it is actually good solution for printing.

The reason I am concerned is that I have pretty large bed (500x500 mm) which is pretty hard to keep flat. And in this case glass would be a good top surface that will keep bed rather flat. But same time I am concerned that it will kill the benefit of heated bed (PCB style) and will require higher bed temperature to get glass surface to equal temperature.

muru
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Alexey Kamenskiy
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  • similar but not duplicate: https://3dprinting.stackexchange.com/questions/11309/removeable-glass-bed-vs-removeable-springsteel-beds – Trish Jun 18 '20 at 09:29
  • Actually for an electrically insulating material glass a decent thermal conductor. Compare it to plastic and rubber. – Perry Webb Sep 30 '20 at 18:28
  • @PerryWebb not sure where you get that information. You can check the link in my post to a comparison of material thermal conductivity. It is rather bad thermal conductor and the reason why it is used as an insulator in construction industry (glass wool). – Alexey Kamenskiy Oct 01 '20 at 03:00
  • If you compare glass to metals, it is a poor thermal conductor. In general good electrical conductors are good thermal conductors, and good electrical insulators are poor thermal conductors. However, compared to other electrical insulators, glass isn't too bad of a thermal conductor. Often, fine particles of glass are added to plastic in plastic encapsulated electronic components to promote thermal conductivity. – Perry Webb Oct 01 '20 at 08:51

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I suggest to look at a similar question, but just the glass question here:

  • Glass is a very smooth surface
  • Glass shrinks when cooling to a degree it pops the print free on itself
  • Glass is virtually impossible to scratch with metal scrapers
  • Glass stays fairly flat under heating
  • Refurbishing of the bed isn't needed but for applying your adhesion solution (Woodglue, Gluestick, Hairspray, 3DLac, ABS-Slurry... pretty much ANY glue can work
  • Glass is one of the few surfaces upon which almost all materials can be printed without risking ruining your print surface on removal
    • PETG is one of the few that demands some sort of extra adhesion material with glass, most others don't need anything.
    • POM and some other materials love to rip PEI apart
    • I had a huge PLA-print stick so well to a BuildTak that I had to cut the sheet off the bed to get it off

The problems are fairly evident on the other hand:

  • Glass is brittle and shatters on impact or thermal stress.
  • Good glass can become rather expensive if you want a super flat sheet in non-standard sizing and a specific type.
  • Large glass sheets need a very even heater to prevent thermal stress.

Borosilicate?

Borosilicate glass ("labware" glass) is more resistant to thermal stress but also does not pop free from the print the same way as normal glass does. It is also more sturdy but MUCH more expensive. It also comes with its own problems:

Some people have experienced spalling in combination with PETG, as it created a perfect airtight seal, making an adhesive as a separation layer mandatory. This behavior was also reported for normal glass, which is why an adhesive material is strongly suggested for this material.

Trish
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    Maybe you could add hinting to borosilicate glass, more expensive, but very capable of handling thermal stress. This effectively removes the third bullet from your cons list ;-) – 0scar Jun 18 '20 at 10:40
  • @0scar implemented - though also note that Borosilicate is comparatively really expensive. – Trish Jun 18 '20 at 13:11
  • Pane glass is cheaper than aluminum, and practically ubiquitous. – user77232 Jun 18 '20 at 13:22
  • @user77232 depends on the size and quality of the glass and the special shape... – Trish Jun 18 '20 at 13:38
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    Also, glass being a good insulator, it will keep warm with less effort and even the heat out across the pane. – SnakeDoc Jun 18 '20 at 18:21
  • @FarO I've printed kilometers of 2.85 mm PETG on glass beds, that works excellent, so I don't understand why not to use it, glass works very well for PETG according to my experience (but I do use 3DLAC for adhesion, is that where you are hinting at?), what doesn't work well is PEI, PETG almost fuses to it... – 0scar Jun 19 '20 at 07:51
  • @0scar I refer to PETG adhering too much to plain clean glass, search online "petg chipping glass" and you'll find videos and webpages. Of course if you use any agent in between or you keep the first layer severely underextruded to reduce adhesion you are fine. I also plan to use borosilicate glass in my next printer. – FarO Jun 19 '20 at 09:11
  • @FarO Thanks for the update, as I'm lazy sometimes I don't put an agent under every print, I have never had spalling glass sheets, so I guess this is related to cheap glass only, not borosilicate glass as I have never had to deal with it? – 0scar Jun 19 '20 at 09:14
  • @0scar also I just read that the issue is particularly pronounced in borosilicate. Normal glass may be better. I will surely find a way to leave dirt on it, to reduce adhesion. Glass cleaner with vinegar, or water with salt, ... – FarO Jun 19 '20 at 09:19