JustMKollum
Posts: 9
Joined: Mon Oct 01, 2018 7:11 pm

Tips for preventing a warped glass bed?

Sat Sep 19, 2020 8:00 pm

Hello. I am wondering if anyone has tips or tricks to prevent a glass surface on a heated bed from warping?

The problem is, my warp is happening upwards, where the center is higher than the four corners.

Image

I drew a red curve to make the bend more apparent, as it's tricky to capture with a camera.

Image

I've looked at several Youtube videos, and many say to lay masking or painter's tape down, but that's usually for warps happening in the center of the heated platform that go downward, forming a pit. My bending is in the opposite direction.

Does removing the glass bed from the heating platform, with the print on it, to let it cool down cause the warping? Should I let the print cool down while staying on the heated platform? Would that make a difference? The prints will automatically separate from the glass once the glass itself has completely cooled. I thought it would do it faster if I remove the glass from the bed and let it sit on the dining room counter. I'm still an amateur as I've only been printing for 3 years.

This bending happened on my Anycubic Mega X, the same size as the Creality CR-10. But I owned a CR-10 for 2 years and this did not happen. Since day 1 of receiving my Anycubic Mega X, I had to perform at least 5 leveling tests, since the prints always came out inconsistent, especially on the 1st layer. Now the bending has become apparent.

I received my Mega X for my birthday a couple days ago via Amazon, so they're letting me do an exchange.

But it's guaranteed that this could happen on my newly exchanged version once I receive it. How can I prevent this kind of bending from happening?

Thank you.

- Justin

parallyze
Posts: 193
Joined: Fri Jun 05, 2015 4:18 am

Re: Tips for preventing a warped glass bed?

Sat Sep 19, 2020 10:19 pm

JustMKollum wrote:
Sat Sep 19, 2020 8:00 pm
Hello. I am wondering if anyone has tips or tricks to prevent a glass surface on a heated bed from warping?
I'm not sure there's really a way to avoid this completely starting from a certain size... there's a lot of variables like heat
distribution/thermal expansion which can contribute to this. The glass cooling down while not on the bed shouldn't do any harm.
(some people use cold spray to speed things up while the glass is still on the printer)
The problem is, my warp is happening upwards, where the center is higher than the four corners.
Is it a coated glass plate? If not, maybe just flipping it by 180° will give a somewhat "flatter" surface.
But it's guaranteed that this could happen on my newly exchanged version once I receive it. How can I prevent this kind of bending from happening?
It does help if the bed is heated very evenly. Cool corners/borders will lead to different expansion rates - also the positioning of
the clips can make a difference. Some people suggest using small clips to just fix the glass in it's x/y direction, not along z. But as far
as I can tell most of this is more a "long term" problem, nothing that should happen within a few days.

Sometimes it's just a flaky glass plate. What amount of distortion are we talking about, problems when using 0.3mm layer height
or 0.1mm? ^^

If that's a 4 point leveliing on the mega x you might want to read a bit about pros/cons of 3 vs. 4 points. 4 point levelling can "warp"
the bed quite easily. This can lead to massive variations between a cold and a heated bed (and when heating this can take 10-15 minutes
to reach it's final state).

zemlin
Posts: 334
Joined: Mon Feb 01, 2016 11:36 am

Re: Tips for preventing a warped glass bed?

Sun Sep 20, 2020 10:54 am

Make sure you're barking up the right tree.

Is the glass warped, or is the gantry sagging? On my old Makergear M2, the plate with the linear rail for the X axis would take on a little warp. Some said it was a reaction to the belt tension - I never confirmed the true cause. I removed the linear rail and put shims under it to flatten it out.

On my current printers - Raise3D N2/N2+, the gantry is supported by 8mm linear shafts. The length of the shafts and the weight of the print head result is an slight sag in the gantry. Many users make the same claim that you are - that the bed is high in the center. The reality is that the gantry is low in the center.

On my machine, I confirmed this by placing a 3/4" piece of MIC-6 aluminum on the print bed after upgrading the control board and adding a BL-Touch probe. The sag in the gantry resulted in a bed map that looks like this:
N2 Gantry Sag.JPG

parallyze
Posts: 193
Joined: Fri Jun 05, 2015 4:18 am

Re: Tips for preventing a warped glass bed?

Sun Sep 20, 2020 12:20 pm

zemlin wrote:
Sun Sep 20, 2020 10:54 am
Is the glass warped, or is the gantry sagging?
<snip>
Many users make the same claim that you are - that the bed is high in the center.
You're right. I know exactly that from one of my replicator clones. But on his printer the x axis is running on a 20x20 profile and not
using a (heavy) direct drive extruder. Sagging there would be quite worrying... ^^

Somehow I assumed he's been checking this using a metal straight edge ruler after he's been watching quite some videos regarding this,
thanks for pointing out other obvious points.

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