Indescribable artifact on shallow overhangs, something like an ulcer

[AdvMoose]

Hello everyone! We’ve been having a very complicated issue with BOTH of our printers recently that I honestly can’t put into words. It only started recently, and was never an issue before that. I’ve attached a few images below. The artifact is hard to see in some of them, but the best description that I can give is that it looks like a slightly recessed “ulcer”, with what looks like overextruded layers inside. It’s not on every overhang, in fact it’s only on overhangs that are between a certain minimum and maximum. Too much overhang and it prints fine, too little and it prints fine. Importantly, this issue also only arises at lower layer heights. I haven’t tested exactly where it starts, but I know that it happens at least at 0.16mm, and not at 0.20mm. So far we’ve tried the following fixes with absolutely no effect:

• Drying the filament
• Trying different filament
• Trying a different printer
• Trying multiple different models
• Trying multiple different settings
• Testing with a brand new nozzle
• Cleaning and lubricating all axis
• Tightening all belts
• Tightening all screws
• Tramming the bed
• Re-calibrated basically everything
• Factory reset the printer

Suspicions we have that we have not been able to test yet include:

• The fan being messed up. We sometimes get warnings about it, but it always resolves itself, and we haven’t wanted to replace it only to find out that it’s not a problem.
• We have not messed with the cooling settings of the prints yet.
• We have not messed with the extruder gears yet.

If anyone has any other ideas or could confirm that any of these might be the cause, please let us know. We’re currently behind on two commercial orders because of this, so it’s a little time sensitive. Thank you in advance!

[mugglesmuggle]

The fact that it affects both your printers is suggestive of a slicer problem. Please try an earlier bambu slicer such as this one to rule out any recent changes. Just unpack this zip and run the exe directly.

https://github.com/bambulab/BambuStudio/releases/download/V02.00.03.54/Bambu_Studio_win-v02.00.03.54-20250424182834.zip

Other than that, I’d look at the fans first.

If you look at the speed or temperature (or line type) views do you notice anything in common with the problem areas? The layer height effect could be suggesting something not causing the extrusion to be regular at lower flows, but unless there was a correlation with flow in the speed views that seems less likely.

How often do you replace your extruder gears?

[AdvMoose]

Thank you @mugglesmuggle. I ended up slowing the print waaaaay down for overhangs and increasing the fan to be at 100% for overhangs. I also changed it to print the outer walls first.

I ordered fans and gears, too. We have only cleaned the gears once, and the machine has over 1,000 hours on. When the gears get here, I’ll clean them and relpace them if they seem worn. One of the fans gets an error every nowand then, so i will have the fans on hand when it does it again.

Again, thank you for your help!