Filament twists during print  

RE: Filament twists during print

ok.  Whooo. I thought I was the only one.  

ive not iced this since day one.  I’m on alpha firmware now and still there. 

I was going to contact support but I want to get some video and photo done and I’m lazy 

RE: Filament twists during print

Thank you very much for your reply! So now I learned I'm not the only one (just as you did 😀)

Prusa support couldn't help me. I was told not to worry and that the Nextruder will continue pulling the filament no matter if it was twisted or not. 

Still – when the filament gets twisted too much it will break eventually. I tested this with a piece of filament and twisting it between my hands. So in order to don't have my prints fail I will  monitor it and twist in back as soon as needed. I also thought of pre-twisting it in the opposite direction before longer prints so it can untwist in the process before twisting again. With this method you'd gain about 6 hours before it looks critical.

I still wonder what could cause that issue. The only cause I can think of is the machining of the gears of the nextruder but that's nothing I could do about anything.

RE: Filament twists during print

Just out of interest - is this on an assembled or a kit MK4?

RE:

I see this issue on mine as well. And it is a big issue that we should worry about. Why? I use dual-colour filament. The one that makes the print one colour on one side and another colour on the other side. I've printed the cali dragon, so a small print, and half of the dragon is in wrong colour, meaning the filament twisted itself during printing. My MK3S+ never did anything like that. The prints with this filament look bad on a MK4 because of that. I love this printer and the quality and silence, but will Prusa pay me for the expensive dual-colour spools I bought and can't use now? 😛

To be clear, my filament doesn't twist nearly as much as yours. I just notice it because dual-colour filament shows the twisting instantly.

It's a kit.

RE: Filament twists during print

I can no longer edit the post, but just got an idea. Would appreciate if a mod merged the posts.

Could the tension screws being tightened unevenly cause the bearings to be slightly shifted to one side? And cause twisting due to uneven pressure? Or is it impossible? I'm not familiar with 2-screw design, so I have no clue.

RE: Filament twists during print

Mine is an MK4 fully assembled.

I will be contacting them tomorrow.  This is having and effect on my printer and prints.  

I’ve had a couple of times it get twisted to the point where it hits hard on the mount for the filament holder.    The printer even if at the start of the print while it checks axis’s, if the filament twist hits the mount it will stop and start over.  

RE: Filament twists during print

@iftibashir Mine is a kit

@shushuda I started playing around with the screws. When it twisted, they were perfectly at the same length (as instructed) but I recognized that the idler lever wasn't perfectly parallel to the Nextruder, so I fastened one of them about 1–2 mm more than the other. Since I didn't print anything for longer than 1.5 hrs without a change of filament so at this point of time I can't tell if this makes a difference. I'm just wondering why PRUSA didn't recognize this on their machines – I guess their prints should take longer because they fill the whole beds with parts.

RE: Filament twists during print

Hmm, maybe. I'm not sure if my idler is twisted, but I unloaded the filament for the night, reloaded it today and so far I see no twisting. Maybe I've inserted it wrong before? Strange.

Posted by: @textorumengineering

@iftibashir Mine is a kit

@shushuda I started playing around with the screws. When it twisted, they were perfectly at the same length (as instructed) but I recognized that the idler lever wasn't perfectly parallel to the Nextruder, so I fastened one of them about 1–2 mm more than the other. Since I didn't print anything for longer than 1.5 hrs without a change of filament so at this point of time I can't tell if this makes a difference. I'm just wondering why PRUSA didn't recognize this on their machines – I guess their prints should take longer because they fill the whole beds with parts.

RE: Filament twists during print

Any joy with a fix for this - I’m starting to see some signs of this also…..

RE: Filament twists during print

More discussion here - https://forum.prusa3d.com/forum/english-forum-original-prusa-i3-mk4-assembly-and-first-prints-troubleshooting/nextruder-twists-the-filament-as-it-feeds/

Adjusting the screws worked pretty well for me, but since the screws are now uneven I plan to replace the extruder plastic parts with ones I've printed which are higher quality than what Prusa supplied.

RE: Filament twists during print

As I mentioned above I have the idler wheel screws now fastened unevenly just by eyeballing getting the wheel straight – that seems to kind of work. It's hard to fine tune because it's trial and error with the result only after hours of printing time.

I still get a slight twist though but not as much as before.

RE:

Like my predecessor, I had problems with filament twisting. Tightening and loosening the bolts did not have an effect. Finally, I printed parts idler-lever-A-R2.stl, idler-lever-B-R2.stl, idler-nut-R2.stl and 2x idler-swivel-R2.stl. Print settings: layer 0.15QUALITY, 20% infill. After replacing these new parts, the filament stopped twisting. Do not forget to calibrate the gearbox after assembling new parts!

RE:

@miroslav-h4

Glad that you could solve your issue. What material did you use for the parts?

RE: Filament twists during print

Black PETG.

RE:

The idler-nut-R2 and 2x idler-swivel-R2 parts together with the 5.5 mm spacer must not be assembled too loosely. This assembly not only pulls the pulleys to the gear, but also holds the idler assembly so that it cannot move sideways. If the idler assembly is adjacent to the gear a little obliquely, I think this is one of the causes of filament twisting. The fact that the 5.5 mm spacer will not rotate completely freely does not matter so much, in my opinion. After all, this work is not manipulated so often.

RE: Filament twists during print

I had this issue with the MK4, and now with the MK4s (new kit build each time). I may try your suggestion of tightening the screws up!

Posted by: @miroslav-h4

The idler-nut-R2 and 2x idler-swivel-R2 parts together with the 5.5 mm spacer must not be assembled too loosely. This assembly not only pulls the pulleys to the gear, but also holds the idler assembly so that it cannot move sideways. If the idler assembly is adjacent to the gear a little obliquely, I think this is one of the causes of filament twisting. The fact that the 5.5 mm spacer will not rotate completely freely does not matter so much, in my opinion. After all, this work is not manipulated so often.

RE: Filament twists during print

Ok, I have started seeing this now.  I built the lack(?) enclosure myself (from an online video with parts) and only set up the spool on the far left (lazy to do more).  I have only started to notice this on taller and wide prints.  as the filament gets twisted it has more tension when going through the grommeted hole.  When this happens the print starts to squeak as it is pulled through.  When this tension is high enough the print stops noting a crash detection.

I have been using this set up for over a year now, and the only change I have made is installing a diamondback nozzle last Feb.  I have printed several things that went over night, but these just recently started happening as I was printing a figure stand that is almost the complete width of the bed, and about 9cm tall.  After the reported crash, I examined the top layer and it was fine, no oozes our blobs, it was actually clean.  So I said resume, and it continued to print fine.

As of late, while printing these, I am listening to the printer, and as it starts to squeak, I pull some excess filament through the hole (which shows the rotation as it twists inside the enclosure) and things are fine.

Its just harder to deal with this as the print gets taller.  I'm not the kind of person to fiddle with things that are working (as I tend to make things worse unless I really know what I am doing).

Pesonaly, I am going to trying printing a loop guide that will more center the filament as well as give it a bit of loop breathing room, but worried that will add more tension to the already tense print line...