How to get glass flat.

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Hello all!

I have had a lot of cr-10's and with that, lots of bowed glass. I bought 6 pieces of regular glass from my glass maker and yet again, they are all slightly bowed. So I had 2 questions.

How do I test which one is the flattest? (Preferably this could be fast)

Anyone reccomend a good place to get a replacement for cheap?

Second big question.
What is your favorite printer surface? I have tried pei, lokbuild, and ultrabase.


If you want very flat glass then go with a mirror. But like others said try the other side. If you get frustrated check out the EZABL system as it can compensate for bowed glass. I run a company called TH3D and its our auto bed leveling product for the CR-10 and other machines.

As for favorite surface I use the TH3D EZMat on all my machines. We just got back from MRRF and we sold a lot of them. We got a lot of feedback on the surfaces from the CR-10 community and at MRRF. Let me know if you have any questions.

From what I understand there are two sides to the Chinese glass. One is flat, while the other is almost flat. So, this is what I did: I identified the side which was the flattest by testing the sides and marking one side as bad. Next, with the good side up you need to use it in a North South East, and West kind of way. So if the edge closest to the left is on the left then you should mark that so this side will be on the left forever. Get scientific on that peice of glass and be consistant, never lose track of which end is which and THEN and only then will you have a set up that you will no longer have to adjust constantly.
In some glass manufacturing there is a process that a roller presses down on the glass so it smashes against a flat surface, the side with the roller is the lump side, you need the other side.
And as a side note I shimmed my glass with two or three sheets of aluminum foil squares right in the middle , it is hard to tell how much of the problem was the aluminum bed or the actual glass.

Don't assume they are all bad. That seems unlikely, doesn't it: That everything you get from the glass shop is bad? Glass will deflect. Odds are the aluminum bed is bowed and you're clipping the glass corners to the bed, right? So you're forcing the glass to bow to match the shape of the bed curve. You need to shim between the bed and the glass to fill the gaps but keep the glass flat - plenty of videos on doing that.

Actually they are.......

Second of all, the glass is really hard to bow due to the thickness. I actually got mirrors today and it was perfect.

I use ultrabase on my cr10s and am having very good luck with it. In the past with my older printers I always used mirrors as they have to leave the factory optically perfect, meaning, they have to be flat. Mirrors are easily cut as well.
One trick that I have seen used with good success is using tape, paper, etc. under the glass the help the heated bed become level. There are several videos on youtube that you can hunt down to see how they do it.
On my mirror surfaces to help the print grip I used PVA stick glue. It's cheap and easily available at many stores.
Good luck!!

yeah i just brought some IKEA mirror tiles
300x300 pack of 4 for $15
testing at the moment but so far so good.

Paid $11 for 6. Loving them.

heh, we must be from different countries.
I'll visit soon human :P

I use Cheap Mirror Glass, its always flat enough. For 30x30cm Printbed there are Mirrors called "LOTS" at Ikea, they do it well.

I prefer to print directly on mirror, especially petg. Clean the mirror only with warm water and soap. Drying it with some paper-towels and then never ever touch the surface again. See https://www.youtube.com/watch?v=Kj4Xz3DwGSQ

Sometimes i use a Mirror with some Lokbuild apllied on it, with pla i do not need to heat the bed.

To check flatness: Put a steel-ruler standing on the surface and check against some light. You will see the light come through under the ruler, if its not flat. Just like this: https://www.youtube.com/watch?v=xUX2LSzOr3o