Filament Change Mid print  

RE: Filament Change Mid print

Yes!  This started happening to me upon flashing the new 5.1.0-beta firmware and updating Prusaslicer to 2.7.0-rc1.  It keeps ejecting the filament. I've been troubleshooting for hours and can't fix it.

RE: Filament Change Mid print

Sniper, just had a conversation with Tomas on live chat and got instructions to recalibrate the filament sensor, and if that fails to clear the filament manually per these instructions:

https://help.prusa3d.com/article/filament-sensor-mk4-mk3-9_465702

RE: Filament Change Mid print

I might be able to offer a different perspective on the problem.

I never had the unexpected filament changes so far. I've been using the 5.0.0 firmware since it came out in combination with PrusaSlicer 2.6.1.

Yesterday, I did my very first print with a color change in it, which went well. When I printed an entirely different model today, the issue suddenly appeared, i.e. the printer requested a filament change without any reason to do so. The interesting bit is that this filament change happened at the exact layer in which the change in the model I printed yesterday happened.

To me, this looks as if there is a problem where the layer change command stays "stuck" after a print and will be executed even when you print something else. I could imagine ways to implement that function that would be prone to this kind of bug - but my C skills are sadly lacking, so I can't verify this by reading the firmware source.

I assume that resetting the printer to system defaults might clear the stuck command, but I can't check that right now because my print is currently running and will be for some time...

RE: Filament Change Mid print

Hi, I find this really unlikely, the printer reads a text file. If there is no pause for a filament change, it does not do so. It does not plan pauses ahead, so they might not get cleared. But ou might have reused you prusaslicer session and forgotten bout the filament change being there. It is really easy to miss

RE: Filament Change Mid print

I am quite sure that this is not the case as the print that got interrupted was a print of a gcode File I had sliced before my first multicolor print. I am not an expert though, so I have attached the gcode and the source 3MF to this post. I had a look through the gcode, and the only M601 I could find there was in a comment, so there was absolutely, definitely no color change in the code that was printed.

So, even if my root cause hypothesis might be wrong, there is still the question why the printer should ask me for a filament change if none are in the gcode. It might be mere coincidence that this happened at the same height as it did with that previous print, but to me (I am a software developer, actually) it's the kind of coincidence that smells like a problem.

RE: Filament Change Mid print

Another observation that may or may not be helpful:

I just printed another model, but this time I didn't send the gcode via PrusaLink, but used by Beagle Camera instead. No weird filament changes happened that way, which may either indicate that the problem is intermittent or that it only happens when using PrusaLink as the controller. I will report if anything else comes up.

RE: Filament Change Mid print

Update. Ive had this happen a couple times now. And yes as i have printed dozens of models already. I have a feeling that its a bug in the firmware. I turned off the filament sensors and then no issues. 

I know that it reads a text file for printing and see no filament changes in gcode which validates my thought of it being either a sensor problem or a bug. 

Past times this has happened i would recalibrate the sensor and it would go away for a couple prints but ultimately come back. 

RE: Filament Change Mid print

yup, sounds like fs problems. You can always try contacting support. Tell them you have repeated fs failures and what you already tried.

RE: Filament Change Mid print

I have been wrestling with this for a week now, and I think it's physical just like chat support suggested it was -- the Hall sensor in the filament seems to be sensing falsely that the filament has run out.  Although the warning calls it a "filament change" and  not a "no filament" alert.   Opening up the extruder and blowing with compressed air seems to help, but this is still happening for me.

RE: Filament Change Mid print

I've fixed my filament changing midpoint problem.  User @kaaaaaaaaaaaaal helpfully posted this photo in the User Mods section that helped me figure out where to find the extruder filament sensor.  

Open up the extruder gear box cover, carefully pull out the gears with the brass part (watch out for the flat washer that will come out with it), and then remove the final plastic insert.  The filament sensor is right under that.  Pull it out with small needle nose pliers, be careful not to lose the tiny spring, and use compressed air to blow out the filament chunk that is blocking the magnet Hall sensor.  When I did this, the tiny spring was attracted to the docking magnet on the extruder and I couldn't find it anywhere.  I swapped it for the spare spring that came with the printer, and finally found the original spring when I was re-docking the extruder.

RE: Filament Change Mid print

This is really helpful; I'm having the same issue. Were there instructions you followed (and can provide a link to) to get to the extruder filament sensor?

RE: Filament Change Mid print

@geoff There is just one main gear box cover on the side of the extruder head.  You have to disassemble it a bit (take out the gears) to get to the inside where the magnet and spring are.