On the bottom of my prints, there’s an area of underextrusion and I can’t figure out what’s causing it.
I first noticed it when I switched back to a textured PEI bed while trying to print ASA. It’s on 20x20mm squares, and it’s on the test print for setting up pressure advance… But only on the left-most object.
It’s the same even if I add 2 lines of skirt or not. (In addition to my KAMP Voron purge.)
It happens everywhere on the bed that I’ve tested. It happens to PLA, but it harder to see. For ASA, it’s very obvious. For PLA, it’s almost as smooth as the rest of the surface, but it’s there if you know what you’re looking for.
I’ve only been printing PLA for quite a while now, so I don’t know when this started.
I’ve got an LDO Voron 2.4 with Tap, KAMP, Revo hot end. I’ve calibrated pressure advanced and changed the value, and I’ve tried different z offsets with the textured bed, which doesn’t change it. (But does change how good the rest of the bottom surface looks.)
Anyone got any ideas?
It looks like it is happening in the same spot on your bed, and it looks almost like the filament is not extruded near the bed in that area.
It’s is possible for you to have a cool spot in that area? It sounds silly, but do you have a dent in that area?
Does this happen if you move the print away from where the defect is happening? Try moving it in your slicer.
If it still happens in the same spot on your print, try rotating it in your slicer and see if it appears in the same spot.
It’s happening in multiple spots on the bed. I’ve tried about 6 or 7 now, and 2 different sheets. (PEO for PLA, PEI for ASA).
Rotating the square 45 degrees puts a pattern on the corner instead. It’s always to the left. (To the right, when flipped upside down so I can see it.)
All seems to indicate something related to pressure advance, whereby the printer thinks it needs to extrude less because of some pressure buildup but it underestimates how much is really needed. Does it happen if you print slowly? E.g max 15 mm/s or less.
At 15mm/s, it looks like the underextrusion is about half the size.
If you’re slowing down significantly and seeing an improvement, I wonder if it’s an adhesion issue vs an extrusion issue. It is very weird that it’s so localized though. I almost wonder if the nozzle might be influencing things somehow. Is it clean? Get it up to temp and give it a wipe with a folded over paper towel.
I tried a never-used nozzle with no difference.
The bed hasn’t been cleaned in a while, but the parts that aren’t underextruded stick very hard. And it happens the same in every place on the bed (I’ve tried about 8 now, always with the same pattern) and 2 different beds.
I’m still thinking it’s a pressure issue, where it initially doesn’t have enough pressure for some reason. But I turned up the KAMP purge flow and it made no difference, and extruding 2 skirt lines made no difference that I could tell.
My next step is going to give the bed a good cleaning… And even try the other side that I’m pretty sure I’ve never used yet.
Interesting, that would confirm the pressure advance as the likely culprit (speed and acceleration are taken into account in the algo). Maybe your slicer has a bug related to this? If changing the value wildly does not improve or worsen it, then it might not be calculating what it’s supposed to. Can you try another slicer?
I’m printing ASA at 30/50mm/s right now, and I’ve halved the pressure advance value without any noticeable change. I agree with looks like pressure advance, though. I’ll try a really slow print soon and see if that matters.
Printing PLA at 120mm/s had it show very lightly, but it’s still there.
You said that you can place the part on different locations in your bed and get the same results? That’s interesting.
How clean is your PEI? Dish soap, a new sponge, and paper towel is a good cleaning method.
Have you done a basic tuning cycle? What’s your temp setup and extrusion multiplier?
I’ve tried it on a textured PEI (ASA) sheet in multiple spots, and a smooth PEO (PLA) sheet, same results. It’s always the same size and orientation, thought the PLA one was a lot harder to see.
The plate isn’t that clean, and I’ve used a lot of 3DLAC on it. I’ll likely try cleaning it again soon out of desperation, but I can’t see it being likely to change anything.
I’ve tuned basically everything, and changing my pressure advance value made no difference. 105 bed, 245 hot end for ASA. 60/220 for PLA.
What are your bed temps for PLA and ASA? Does it still happen if you preheat the bed? If you rotate the print, does the rough spot follow the rotation?
