Under extrusion on flat surfaces but first layer is fine?

[btile]

Machine: X1C + AMS with Cool Plate (Machine has 1030 hrs and I have not replaced anything, just regular lubrication and cleaning)

Filament: BambuLab PLA Matte Ivory White (Opened a day ago, and I have a new desiccant in my AMS)

I’ve recently had a lot of trouble with under extrusion on the second layer for flat, larger areas. I’m printing a site model for a class, and I’m trying to conserve filament with a very thin bottom part of the model(one bottom layer and then a second layer for sidewalks and such)

The first layer has been going down fine with no gaps, but the next layers, specifically the second layer, has become a huge problem because I need it to be almost perfect, and it’s coming out all under-extruded. I’ve tried calibrating the flow and pressure advance numerous times, whether manually or trying the auto features. I’ve tried turning the flow all the way up to 1.032, which made little to no difference; I tried stock 0.98 and the auto-calibration, which set it at 0.97. I’ve tried slowing down the top layer to 80, and still, the same problem. I’ve tried other filaments, and again, the first layer goes down great, but the second layer does not.

I’ve retightened my belts, done self-calibration, tightened the hardware securing the hotend, and there are no kinks in the PTFE tubes. I regularly clean the build plate and apply a thin layer of gluestick. I checked the hotend and there still appears to be thermal grease on the thermister and heater, which was something I saw mentioned in another thread.

I’ve done at least ten cold pulls and gotten some junk and black debris, but this doesn’t explain why the first layer goes down perfectly and the second doesn’t. I would expect that the clog would affect the first layer as well.

I’m kind of scratching my head right now because it’s never been this bad before, and the problem only crept up recently. Immediately before this problem, I printed a decent amount with the white PLA+ from MicroCenter, my understanding is that it’s eSun PLA+ rebranded, so I don’t think I’ve been putting any garbage through the machine, and I really only print with PLA, no CF or anything abrasive. I have also updated my BambuStudio and X1C+AMS to the latest firmware versions, but this error didn’t seem to coincide with any of the recent updates.

Any help is great!

[EnoTheThracian]

Four items come to mind.

While you mentioned that you have done a lot of the right things, you did not mention that you dried your filament. New filament can be quite wet fresh out of the bed.

Did you use the hex key method when doing the cold pull? That was the only one that reliably worked for me to date.

Is your nozzle straight? It can get bent accidentally. But there should be a spare with your X1.

Is your extruder slipping? If it is grinding on the filament (visible on the filament end and can be felt if feeding filament manually) you’ll need to clean it. It’ll not resolve likely root causes (hex key cold pull for that), but it’ll prevent the problem from repeating.

Hope this helps and

[btile]

So I went in and cleaned my extruder. There was a little dirt, but everything was in good condition, and there was no excessive wear on any of the components. I did the hex cold pull, but I didn’t get any debris, so I ended up replacing the hotend itself. However, it was not bent. I figured maybe there was something wrong with the nozzle diameter or there was something inside that I wasn’t getting, but the bore still looks good. Looks identical to the new one. Additionally, the old hotend had a bunch of crud stuck to it for some reason. I don’t know why it was so sticky.

I reprinted several samples, and nearly all had the same problem.

I tried turning down the volumetric speed back to 21 because that’s what Bambu had it at previously, but the default is now 22. I tried bumping the flow up again. I tried stock 0.98, 1, and 1.01, and no difference. It is still under-extruding.

I also stopped the print, inspected the first layer, and noticed some under-extrusion, so I was wrong that it only affected the subsequent layers, but the first layer is by far the best. I did get an okay print at 1.02, but there was somehow over-extrusion and under-extrusion on this part in strange places.

Another thing I noticed was that the under-extruded areas were in the same spots every time, those being the larger open areas. I tried rotating the print to see if maybe it was because there was a dip in the bed that the auto leveling wasn’t getting, and maybe that dip happened to align with those larger open areas. However, this didn’t change anything, so it’s still just those large flat regions it’s struggling with.

My AMS is reading one humidity, and the filament has sat in the AMS for two days now, so I believe it should be pretty dry.

[EnoTheThracian]

Mhm, seeing that the 1st layer always has an issue at the same spot. How are you preparing the plate?
Soap & water for cleaning, the glue stick and spreading a thin fulm with a wet cloth? That works best in my experience.

[btile]

I normally wash with dish soap and a soft sponge and then reapply a thin layer of glue stick across the whole build plate, but I haven’t done the wet cloth spreading trick before. (Attached photo is cleaned, glue stick, and wet cloth wiped build plate). I did that for a few more prints, and the first layer came out better, but unfortunately, it didn’t resolve the under-extrusion on the next layers.

I went back and did a sanity check and printed out my test piece with some different filaments and… the problem mostly went away. I tried printing with my other Bambu Red Matte PLA, and the under extrusion was nearly gone with default settings. Still, somehow, on the same print, I have perfect extrusion in some areas and pretty bad under extrusion in others (see image). I don’t know how this happens.

So it’s something with the filament? Do you think I should try the filament drying in the printer, or should I just buy a separate filament drying box?

It’s odd that this could be the issue because the moisture sensor in my AMS was reading 1, and all the spools, including the good red one and the bad white ones, have been sitting in there together, closed up for days now. I would assume that the moisture would’ve moved between them and balanced out. Additionally, I’ve never had this problem before with any filament I’ve ever ordered from Bambu. I’m currently in the Chicago area, but usually, I’m in Virginia, so the climate is a bit different, but not as much as I think these prints would suggest.

[EnoTheThracian]

Drying is a bit of a must do for troubleshooting. While you wait for a dryer, you can use the printer. It has an option for a filament drying cycle. Filament Drying Recommendations | Bambu Lab Wiki

[bernd.kueppers80]

Hello Everybody …
I have the same issue and worked on it for a week now.

• I removed and cleaned extruder, Filament sensor and hotend
• i changed filament and a brand new hotend
  but unfortunately all the last prints failed. Either the first layer was already faulty, or it prints 100 layers perfectly and then suddenly no more material flows.
  I would be grateful for any help

[btile]

So I decided to buy a Nesco FD-75A food dehydrator because I was reading that it typically performs better per dollar than specialty “filament” dryers. I dried a Bambu PLA Matte Ivory white spool for 6.5 hours at ~55c, and the problem… worsened. This is some of the worst layer performance I’ve seen, and the first layer didn’t go down well at all. I tried cleaning the bed and reapplying glue stick again to ensure that wasn’t an issue, and the problem continued to be the same. I understand that BambuLab recommends a total of 8 hours, but the performance is so bad that I don’t think an hour and a half of more drying would have been the difference maker. Now I’m really confused

The support team recommended I measure the diameter to see if it is a consistent thickness, so I will try that next.