Warping on MK3.9 with large prints  

have you tried enabling a draft shield?

Cheerio,

RE: Warping on MK3.9 with large prints

Thanks for the advice. I've tried to print with a draft shield, but that did not solve my issue.

I did some tests with a calibrated IR-thermometer and found out that my heatbed has some issues. For example if I set the heatbed to 85°C it actually has only about~75°C and less than 70°C on the left side of the heatbed. So my suspicion is that the low temperature on the heatbed causes the warping. I did some tests and if I set the heatbed to 100°C large prints only show minimal warping on one side.

I've already contacted Prusa support via mail and I'm now waiting for their response.

Regards Daniel

RE:

Sharp edges tend to lift quicker than round things, one thing you can do instead of adding a brim is to add some "dog ears" to the sharp corners by adding a cylinder in prusa slicer and set the height to one or two layers and place it where the sharp corner is.
then after the print is done remove it.

One thing about the heat bed, note that when you do the upgrade the heat bed termistor got two sides and they are not equal.
One side is thinner and the other looks like there is a layer of capton tape on it.
But if you got this wrong i suspect the temperature would be higher and not lower as in your case
See the picture at: https://help.prusa3d.com/guide/1c-parts-preparation_534120#534294

if I set the heatbed to 85°C it actually has only about~75°C and less than 70°C on the left side of the heatbed.

Are you printing in a draft?  Even a gentle air movement may cause uneven cooling.

Cheerio,

RE: Warping on MK3.9 with large prints

I guess I'm not the only one then.
Just finished my Mk3.9 upgrade and after some small prints decided to put it to work.
Both PLA and PETG prints are lifting on the right side, with both smooth and textured sheets.
My printer currently sits in an enclosure (due to this problem) with the front and top open to avoid heat buildup. My enclosure temp is around 24.3°
On the left side I have around 71.5°, on the right side around 70.6°

As soon as I start a print and the part cooling fan kicks in I drop around 10° on the right side.
I have made a number of tests over the last few days always with the same result

Conclusion: The parts cooling fan is also cooling the bed on the right side. My current print is about 5cm tall at the moment and now the temp is equal on both the left and right sides. But a bit too late as the right side has already lifted.

When I look at my old Mk3S+ hotend assembly the cooling is ducted both from the left and right side at the nozzle

RE: Warping on MK3.9 with large prints

I think your issue is a little bit different from mine. My issue was that both sides of only large prints lifted, after printing a couple of layers.

After lot's of troubleshooting together with Prusa support they sent me a new heated bed and with the new heated bed, the issue is gone.

Troubleshooting Warping Woes: Seeking Solutions for Large Prints on MK3.9

Greetings,

In the journey of upgrading my trusty MK3s to the advanced MK3.9, I find myself encountering a peculiar challenge. Everything appears to be in perfect harmony, except when I embark on the realm of large prints. As soon as I delve into projects that consume 80% or more of the print bed, an unwelcome guest arrives – warping along the sides of my prints.Determined to address this anomaly, I've experimented with an array of filaments, including Prusament PETG/PLA, Filamentworld, and Creality PLA. Additionally, I've tested the waters with both powder-coated and PEI steel sheets, yet the specter of warping persists. The software at play is Prusa Slicer version 2.7.1, with all settings adhering to their default values.In my quest for a remedy, I've tinkered with the heat bed temperature, elevating it 3-5°C above the default slicer settings during the crucial 2nd or 3rd layer. Even slowing down the print speed to 80% was attempted, but alas, the warping remains unaffected.Now, I turn to you, the experienced community, seeking a fresh perspective. What other avenues can I explore to unravel this perplexing issue? Your insights and suggestions are invaluable as I strive to conquer the challenge of warping in the realm of large prints.Thank you for being part of this troubleshooting journey.

Best regards."

RE: Warping on MK3.9 with large prints

Posted by: @doddster55

I guess I'm not the only one then.
Just finished my Mk3.9 upgrade and after some small prints decided to put it to work.
Both PLA and PETG prints are lifting on the right side, with both smooth and textured sheets.
My printer currently sits in an enclosure (due to this problem) with the front and top open to avoid heat buildup. My enclosure temp is around 24.3°
On the left side I have around 71.5°, on the right side around 70.6°

As soon as I start a print and the part cooling fan kicks in I drop around 10° on the right side.
I have made a number of tests over the last few days always with the same result

Conclusion: The parts cooling fan is also cooling the bed on the right side. My current print is about 5cm tall at the moment and now the temp is equal on both the left and right sides. But a bit too late as the right side has already lifted.

When I look at my old Mk3S+ hotend assembly the cooling is ducted both from the left and right side at the nozzle

Interesting, the part about the temperature on the bed being different on left and right side matches what i have observed.
I have used an ir thermometer to check bed temp at different spots and back left side is almost always hotter, sometimes even a bit over the set temperature but right side may be 5-10 degrees lower.

But i have so far not had any warping, but i print mostly PETG and some PLA

RE: Warping on MK3.9 with large prints

That's basically what I print with.
Steel sheet is cleaned with IPA, textured sheet has very little use on it, but I get lifting on the right side if it's a full width print.
What temps are you using for PLA?
Do you use a glue stick?

RE: Warping on MK3.9 with large prints

Satin sheet, no glue stick, standard temp from default profiles in prusa slicer (prusament petg & pla profiles).

With my old mk3s and those profiles i always had to increase the temp by 5-10 degrees on the nozzle but with my mk3.9 and the new profiles, the temp appears to be a bit higher that on the old printer and more closely matches what i used, so no need to change it.

Only time i used glue stick was petg on smooth steel sheet but i don't print petg on the smoot sheet, actually i almost never use it now with the textured and satin sheet.
But i only rarely use the full width also i cant use every last millimeter of the print width because i have the silver PSU and some of the plastic on it steals a few millimeters on the right side.