RE:

UPDATE:

I manually edit the gcode writing G1 E-10 / G1 E10 (retract 10 instead 20) and now it works like a charm.
Do somebody know where is this value configured? 
dependes on machine, filament, print settings? it's harcoded?

Thanks in advance!

RE: filament stuck only when tool changes

Thank you so much. I have just assembled my machine and am going crazy over exactly this problem.

I have scrutinized my assembly, swapped filaments, tubes and extruders and gotten no wiser other than it seemed to improve if I gave the filament some slack when the extruder was paused so that the filament roll did not have to turn during the load.

I am not by the printer right now, but I will check patch my generated Gcode (slicer 2.9.0) and if it is the same as yours see if I see the same improvement by patching it.

Since my printer is new this firmware version is the only one I have tried, but as you have found this in the Gcode, maybe file a bug report on Prusa slicer?

I think that if the error really is in either firmware or the slicer it is strange that it has not been more widely observed and got reported as a bug - so maybe this is not the correct fix, but a good workaround?

Another source could be that the speed of the load is so high that accellerating the filament roll from idle cause to high inertia force in the filament? (I am using full 1kg rolls and noticed some improvement when moving the filaments from the original holders to roll bearing holders.)

RE: filament stuck only when tool changes

 I have the same issue. When I have printed a multi color object with PLA, I had a filament stuck with nearly each toolchange (idepentandly from the tool). I checked the postion of the filament when the issue happens, it was still in the hotend, but the the feeder can't move it forward. But the printer was each time able to unload automatically the filament and finally he also loaded it eachtime without any problems.  I tested to reduce the print temperature of the PLA that reduces the problem a lot, but not completely. The interessting thing is with PETG I don't have that issue. So I think the problem is realted to the properties of PLA. I also thought about retraction speed and length but I didn't where I can set this stuff for the tool change.

It's a new printer and I tried already all the standard ideas for sovling such issues. So does anyone have further ideas? This mould make me happy. 🙂 Thanks.

RE: filament stuck only when tool changes

Posted by: @abegines

UPDATE:

I manually edit the gcode writing G1 E-10 / G1 E10 (retract 10 instead 20) and now it works like a charm.
Do somebody know where is this value configured? 
dependes on machine, filament, print settings? it's harcoded?

Thanks in advance!

Printer Settings -> Extruder # -> Retraction when tool is disabled -> Length

RE: filament stuck only when tool changes

Problem solved - and here's the reason!?

Being a newbie in the printing world (only been a printer owner for less than a month and made my first print ever a week ago) there is good reason to question what I write, but  am pretty sure I am not too far off and looking forward to comments.

Some prerequisites

• I have only printed PLA so far - so other materials may be less sensitive for this to occur
• Filament stuck error only occurred during the printing to the plate had been going on for a (sometimes short) period and only when the tool came out from park
• This discussion relates to XL multi-tool only

The workaround - and why I think it works

@azekia wrote above that reducing the filament retraction at tool change solved the problem for them, and the same turned happened in my case. I spent a lot of time looking through other potential issues, but I was not able to isolate any other action that had a significant and repeatable effect on the problem. While cleaning out the nozzle and making a cold pull "just in case" - I noticed that the filament at the entrance to the tool was rather "rugged" in one spot around the circumference and for a rather long section of the perimeter (more than 20mm).

• If the filament is only consumed by a small volume on each load the same section of the filament will be pass down and up through the tool feeder wheel multiple times
• A brittle filament such as PLA is more likely to get sharp impressions or even have minuscule chipping when fed by "sharp" teeth. At one point in my investigations the filament even broke in the upper part of the feeder.

I think that as the section of the filament get more and more rugged and chipped it finally jams when it has advanced deep enough to be fed into the extruder tube. Also, small chip-lets other debris in the feeder gear area may be caught in the grooves on the filament and dragged into the extruder with the filament

How to diagnose

If you think you are having the same problem, you can try the following using a print that suffers from the problem:

• Purge the filament to check for good flow, and if necessary do a cold pull or two to get out any debris
• If you have one extruder that works well in the print and one that does not and the materials and profiles in the splicer are the same remap these filaments in the print meny of the xLCD so that the colors/filaments swap roles in the print. See if the problem stays with the extruder or stays with the part of the model. (Skip this if you don't have a "good" filament/extruder that makes sense to swap with
• If the problem still happens do the following:
  • Clean the nozzles and feeder again
  • After the cold pull but before reconnecting the PTFE tube to the tool , cut away all filament that has markings, grooves from the feeder gear. Then mount the tube and purge to make sure there is good flow
  • Reprint the model - does it take more tool changes before the problem reappears than when you just reprinted the model without removing the worn front section of the filament? (I assume you have been reprinting without cutting of filament - at least I did so.) Then it may be reason to reduce or eliminate the "filament retraction of tool change"

My own comments

The filament retraction on tool change is a filament property. According to the Pruse Slicer documentation the default value is 10mm. The Pruse presets (eg Prusament PLA) set this to 20mm. This is in addition to the regular retraction made when pausing print. With a 0.4mm nozzle and a thickness of printing of 0.2mm, 1mm of filament feed corresponds do approx 30mm of print. To avoid any wear out the filament by repeated parking operations, more than 600mm (20mm parking retraction plus "normal" retraction movements) needs to be consumed at each tool unpark.

If your model prints significantly less 30× the parking retraction length on consequtive un-parkings, there is chance that reducing the parking retraction can help. Alternatively wipe towers or just an object can be placed on the side of the main object to consume filament could be used. Wipe towers are disabled in the default Prusa XL profile for Prusa Slicer, but I believe this can be circumvented by choosing the SOLVABLE variant - but I have not tested this.