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?
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.
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.
At 15mm/s, it looks like the underextrusion is about half the size.
https://imgur.com/a/F0sXBvJ
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 used an older Cura that I already had installed (instead of Orca 2 that I’ve been using) and the underextrusion pattern is different, but still there.
I turned pressure advance to 0 in both Orca and Klipper, and saw no difference. :(
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.
I’ve cleaned the bed and not applied 3DLAC, and it hasn’t helped.
That’s disappointing. I’m sorry to say, but I’m out of ideas. Maybe try the Voron design forums since they have more active users?
Yeah, it’s pretty weird. I appreciate the help, though!
I’ll probably post over there soon. I’m a little burnt out by it at the moment.
I completely understand that. I’m fighting my own battles with getting a consistently perfect first layer. I’ve been fiddling away for a while now and for whatever reason my last print had extrusion stop about 2/3 way through. Heated the nozzle up this morning, told klipper to extrude, and it extruder perfectly happily. No console errors from the print and klipper thinks it completed successfully.
When I’ve had something like that (or just underextrusion randomly part way through a print) I’ve decided it was a clog and did a “cold pull” on the filament to fix it and it seemed to work. It can be insidious because it sometimes clog and sometimes doesn’t.
Though, I’ve also had people suggest it was “heat creep” where the heat gets too far upwards and melts the filament too early.
I’m planning on swapping nozzles soon, might as well do a pull or three just to be sure. I wonder how that will work on my Rapido though… it seems to melt all the filament in it and it all just oozes out by the time it gets cold. 9 times out of 10 I can flip the latch on the CW2 open and just pull the filament out of the reverse boden cold.
Whatever happened happened, I’m much more bothered by my inability to get a consistent first layer. Each new thing I try also sets me back some while I tune. The joys of tinkering with your printer and wanting to get it just so. It’s already miles better than my old i3 clone ever was but the possibility of near perfection is too enticing.