Very strange problem printing with PLA after printing with PETG

Bambu Lab P1 Series Troubleshooting
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Having a really strange problem printing PLA with my P1S. Bear with me…this is a long one.

So last night I printed one of the Bambu filament spools in translucent PETG on my P1S. It printed well and there were no issues.

This morning, I took the PETG out of the AMS and put some Bambu basic green PLA back in. Started to print a card game box at 0.08mm layer height (which I used quite successfully 2 days before). Everything seemed fine, the “test strip” looked good, but the PLA just would not stick to the build plate (a Bambu Supertack).

I stopped the print, and tried again…same issue. Tried it again with some Bambu matte white PLA from a different slot in the AMS…this time, the filament just clumped up around the nozzle.

I cleaned that off, manually extruded some more filament, and it seemed to come out fine. Tried the print again…same thing.

Heated the nozzle up to 260 and extruded a bunch of filament manually. Tried printing a tiny little filament clip in the white…worked perfectly. Tried it in green…perfect. Tried the card box again in green…back to the filament not sticking to the plate.

Washed the plate with hot water and dish soap…no change. Switched to the textured PEI plate that came with the printer, and printed 4 filament clips…one in each colour of PLA that were in the AMS. All came out perfectly. Repeated it just to be sure…same thing, they were fine.

Switched back to the Supertack plate and again printed 4 filament clips…came out fine. Grabbed a simple little box and printed it in the white at 0.2mm: perfect. Printed it in Bambu basic yellow at 0.2mm: perfect. Tried the green at 0.2mm: perfect. Reduced to 0.12mm with the green: a little bit of stringing, but it printed. Wouldn’t call it perfect, but it printed. Moved down again to the 0.08mm: same issue, filament not sticking. Went back up to 0.2mm: now it clumped around the nozzle.

Cleaned that off, switched back to the white PLA and tried again at 0.2mm: clumped around the nozzle again.

At this point I’m stumped. I have no idea where to go from here. Any help or suggestions would be very much appreciated.

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I should note that the printer is only about a month old, as is the supertack build plate. The printer has a 0.4mm hardened steel nozzle in it.

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When I get nozzle troubles with sticking I tend to do the following.

Preliminary cold pull. Clean while hot with a brass brush. Polish the tip of the nozzle with a leather strop and jewelers paste. Reclean hot with brass brush again. Another coldpull to ensure no grit from the polishing is stuck inside. The double cleaning is so I don’t contaminate my strop with plastic.

You can also rub peanut oil on the cold nozzle, then heat it up to 232. As the heat cooks it, it polymerizes and forms a barrier that isn’t really PLA/PETG compatible. It’ll help reduce nozzle sticking for about a day of printing.

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Not really sure how to do a cold pull. I Googled it, and it looks simple enough, but I think I’ll try and brass brush first, and then maybe the peanut oil (both of which I had to order). I’ll let you know how that goes once I’m able to give it a try.

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Are you sure the AMS is spooling out the right filament?

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They’re all currently Bambu PLA (either matte or basic), and each one is a different colour. So I can definitely confirm it’s extruding what I ask it to.

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Are you letting the printer run the flow calibration? If so, does that look right? If not, run it. If it looks OK, flow isn’t the problem and you can forget about a cold pull.

The printer came with a 0.4mm needle for poking out the nozzle without taking it off. You could try that if the flow seems to be off, easier and less likely to damage the machine than a cold pull.

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Ran the flow calibration…this is what came out.

Now I’m very new to all of this, but I’m guessing this doesn’t look right. Besides the fact that it looks like the nozzle dragged some of the filament behind it.

IMG_3526
IMG_35261920×865 442 KB

I’ll try that needle in the morning and see what happens.

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It is not uncommon to have adhesion and flow issues when printing PLA after PETG. If there is any residue remaining on the plate, PLA will just slide off the plate untill thoroughly cleaned. That can take a few attempts.

Similarly, residue in the nozzle or (rarely) residue travelling from the extruder to the nozzle can quickly cause (recurrent) clogs.
So sometimes, it becomes neccessary to both clean the extruder gears and do a couple of hot hex wrench cold pulls (the “simple clog” method never worked for me).
Extruder Maintenance Guide: Cleaning and Lubrication - P1 series | Bambu Lab Wiki
Nozzle/Hotend Unclogging Procedure for X1/P1 | Bambu Lab Wiki

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I can see from how the label side on the right is “Peaking” like frosting, that you have a flow ratio issue. (not flow dynamic / pressure advance which is what that photo you posted.)

I typically advise flow ratio first, flow dynamic second. That said, a wild thought, are you cleaning with super hot water? Rinse off with cold afterwards. It could be your water heater is full of minerals and leaving behind a residue. Super hot water and dawn soap, with an extra rinse at the end of cold water. I go so far as blowing my plate off with a quick blast from a keyboard cleaning blower instead of using a towel since fabric softeners on towels can also inhibit adhesion.

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I had the same problem on both sides of the Supertack plate, and I only printed with the PETG on the one side, so it can’t be anything on the plate. But I will add cleaning the extrusion gears to my list of things to try later on today.

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Not sure how to fix flow ratio issues, but I’ll look into that.

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I did not get a supertack since there are a lot of mixed reports here in the forum. So unfortunately, I can not really advise on that.

I did however have quite a few clog instances when switching between PETG and PLA. It is rare, but it does happen, that there’s a need to clean both the extruder and do a couple of “hot hex wrench” cold pulls (link above) before trying again.

As for the critically important flow calibration, that can be found in the slicer. It looks like you did a Pressure Advance calibration from the picture above? Usually, you can run through the calibrations from top to bottom with flow calibration coming first. I am not very good at the manual calibration though. Got an X1 which uses the Lidar for that. Using pic magnification for flow calibration is said to be helpful though.

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It’s the other test in the calibration tab. Set your filament flow ratio to “1” in the filament edit window before you do.

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So just an update. Doesn’t appear to be a clog or nozzle problem, as I can print perfectly fine at all layer heights on the Textured PEI plate. The Supertack is just an instant no go. Not really sure why…I’ve cleaned it multiple times, and I don’t think it can be a problem with residue from the PETG, as the problem occurs on both sides of the build plate, and I only printed with PETG on one side.

Gonna try using some 99% isopropyl tomorrow and see if that makes any difference. Otherwise…well, I’m not sure where to go next. It almost seems like the SuperTack plate is a write-off, which seems like a rather sudden change to me since I had zero issues with it up until this point.

At any rate, thanks everyone for all the assistance. It was much appreciated.

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One final update, for those curious. The scrub with 99.9% isopropyl alcohol, followed by (yet another) scalding hot wash with Dawn seems to have worked for the SuperTack?

It’s early, only 1 single partial print so far…but the first layer seems to have stuck, so progress?

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Something else I somewhat noticed. The calibration the printer does, it calibrates at 65C, that warmth makes print plates thicker. Trouble is that supertak is run at about 45-55c on most prints? Not only does this mean that the z-gap is larger than it should be (not enough bed squish) it also means the filament is going to cool on contact way faster than normal so it wont have as much chance to adhere.

In the filament profile, you can increase the first layer bed temp by 5c or 10c to see if that helps. Be careful though, too high, and it’ll adhere so strong you’ll rip apart your models or take a chunk out of the plate to get one off.

Now with flow ratio calibration and flow rate calibration, you can’t really do this because it ignores your print profile, but another thing you can do when printing non-calibration is play with the initial layer height settings. So for a .4 nozzle with 0.2 height, you can try 0.15 first layer height, it’ll squish to the bed much more forcefully. Just be careful that you don’t get so close that you hear the extruder skipping (clicking) because you got it so close to the bed that the plastic actually can’t get out. I’d adjust this in 0.1 segments until you get enough squish.

Besides layer height and bed temp, there’s a third and final thing you can chance with advanced options enabled in studio. That’s initial layer flow rate. You can increase or decrease this number to solve issues like I’ve mentioned. A higher rate means that you’ll put out more plastic pressure, which means more adhesion at the risk of extruder stalling. If you print with a 0.2mm nozzle at some point and you are stalling, you can do the opposite, reduce the flow rate of the first layer, and that will stop stalling – might also have to increase bed temps in conjunction with this to get the ideal balance.

I actually had the opposite problem as yourself. When I was using a 0.2mm nozzle with a low-temp filament, I was too close to the bed and it was jamming my nozzle. Going to 0.13mm layer height instead of 0.1mm layer height gave my nozzle enough first-layer room not to croak.