Randomly cut filament mid print then resume print

Bambu Lab P1 Series Troubleshooting
1

During mid print, about layer 8-12 maybe just finished that layer, it just moved to the chute then moved to the cutting area, cut filament then AMS rolled back the roll. Right after that, AMS started feed the same roll again. The printer purged very little (probably because of the same color) then it continued printing like nothing happened and finish the print. At that layer, there is nothing special, just perimeter walls and honeycomb infill, the previous and the next layer is the same as this layer. When the filament cutting happened, I notice there is no tension at the AMS port from the filament roll, just the right slack of filament. So I can rule out that there was no filament tangle on the spool. The print success anyhow but it triggered somewhat anxiety for something random will happen again.

The print is just single piece, about 5mm height, rectangle shape 300x400mm. Project file started fresh from empty with custom PETG profile and slow print profile for the PETG i am using. Then add one single STL file with one single object then slice and print. Printing using AMS, filament cheap no-brand PETG, only single color, no support.

This incident happened about 3 hours ago right after I rolled back from new fw update 01.07.00.00 down to 01.06.01.02

I had filament tangle on the spool multiple times before and it pretty much jammed the spool tight. I don’t think this incident is about mild tangle and it fixed the tangle by roll back the spool and feed in again.

Did you guys have this “problem” before?

I suspect it could be a SD card problem, but not really sure. Since the incident, I printed 3 more times but it hasn’t happened again.

Sorry, I didn’t take any picture or video for that mater. I didn’t have the phone with me while it happened.

Back of the story:

It happened once before but I didn’t give much thought about it. Early this morning I got massive spagetti, right after I updated to 01.07.00.00.

When I load the 3mf project in Bambu Studio to check if anything wrong with the profile, the filament changed from custom PETG profile to Generic PETG profile and the PA value (device tab) change to default 0.020 instead of custom PA profile of 0.040. The custom PA profile disappeared from dropdown box, but still there in the Flow dynamics Calibration Result window. The original 3mf project was from Makerworld, with PLA profile and massive different settings for each object in the same plate. I changed the setting back my custom PETG profile of course and print speed setting as well. I haven’t updated BambuStudio but just updated newest firmware on P1S last night before starting the print and turn off computer for bed time.

The Generic PETG profile was too fast and too much cooling for the PETG I’m using and caused layer delamination, unlike PETG - as we know - has the best layer adhesion compare to ABS/PLA if print correctly.

It’s just weird that fw update on the device could affect the settings on Bambu Studio. I am embedded software eng and also PC app programmer, I wrote PC app that connect to STM32 via BLE for my current work, but still I couldn’t speculate how this happens with the mess up of print profile and settings. Thus I didn’t want to investigate this problem, just moved on and rolled back the previous firmware 01.06.01.02 and pretent it never happened. Then it startled me with the random filament cutting during mid print, hence this topic.

It happened twice that I know of, maybe happened more before but I didn’t be there to notice.

The moral of the story: Don’t update firmware unless neccessary. Don’t trust print profile from Makerworld unless you have the very same filament and printer as the designer of that 3mf print profile.

2

Any update or solution to this? I just ran into this mid print at layer 5 but I am using the full xy area of an X1C so I have the cutter bar blocked. Or is really annoying since it errors out the printer.

1 Like
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After that incident, I had a few more times it cut filament mid print, AMS rolled the spool back then fed the spool to the printer again. There was one print that it did that 2 times, then finally it spat out the error message “The AMS assist motor is overloaded” and “pause” the print waiting me to solve the non-existing filament tangle which I just had to press “continue, I already solve the problem”. At this point, I blamed this on the AMS assist motor or current sense circuitry on the AMS motherboard.

I had enough of this, so I moved the spool to standalone sunlu s1 dryer and print without AMS. After finished 2 spools no incident, realized there was a bit of resistance when I manually load different spool of PETG to the printer. The brand name of this PETG is XVICO, bought from warehouse clearance.

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FYI, that tube is spare part come with the printer.

It couldn’t be the inlet caught the bumpy surface of the filament since I had small PTFE tube to smooth the inside of quickfit connector as well

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I still don’t know the culprit but my speculation now is the matte bumpy surface of the filament, unlike typical PETG filament which is smooth and shiny. This bumpy surface could cause more friction than smooth surface.

Compare to the old kingroon PETG spool I still have

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Zoom in

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It’s still unsure that filament was the problem but highly is. It could be the extension AMS cable I made (about 60cm long) contributes a bit of voltage drop and the assist motor loses a bit of power due to less voltage. It could be the friction from lengthy PTFE tube from the AMS. But the problem hasn’t showed up until I use this XVICO PETG.

Well, I still have 25 spools of this XVICO brand to grind before I can move on.

I have no idea how this plays out for you, using AMS but cutter bar blocked? How does it cut and change filament then?

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So my issue was then same as yours, except filament was wedged in between itself and causing the ams to thing there was a jam, hence trying to cut and retract.

I modified the ending gcode to add a pause after all printing is done before it attempts to cut filament and retract. That way I can just cancel the print at 99.9 percent done, remove the blocker and unload the filament as I please. No color changing, but can use AMS with one color and full build volume.