What part of the MK4 Nextruder hates being enclosed?  

RE: What part of the MK4 Nextruder hates being enclosed?

Maybe different thermal expansion (plastics vs. steel) leads to either slippage (gear) or misalignment (idler)? Anyway I would check whether all screws in that area are tight.

Last week or so somebody posted an issue with disturbing "filament noses" on nextruder parts. I think it was on the idler parts. Can not find the post right now to provide the link.

RE: What part of the MK4 Nextruder hates being enclosed?

I was wondering about differing thermal properties. I'm going to reprint the parts of the extruder in ASA to see if maybe the PETG is just getting soft at those high temps. All the screws are tight right now but I haven't checked them when everything was at temp and failing--I'll give that a try soon when I run another long day of prints.

I've blown through a few hundred grams of filament with parts that failed after that eight hour window. For now I'm just going to print two parts a day and stop for the night. That's a bummer but it beats continuously wasting the expensive Prusament.

RE:

I’d be surprised if it was the plastic expansion - there are others doing long prints with Nextruders in enclosures at higher temperatures (45 degrees c) not having this issue - including on the XL: https://forum.prusa3d.com/forum/postid/680987/

Have you tried chatting to support - they may just send you a new one - or the key components rather than you rebuilding it. Not sure what happens to the warranty if you’ve rebuilt it yourself. Might be worth trying to resolve it with Prusa first.

Posted by: @justin-3

I was wondering about differing thermal properties. I'm going to reprint the parts of the extruder in ASA to see if maybe the PETG is just getting soft at those high temps. All the screws are tight right now but I haven't checked them when everything was at temp and failing--I'll give that a try soon when I run another long day of prints.

I've blown through a few hundred grams of filament with parts that failed after that eight hour window. For now I'm just going to print two parts a day and stop for the night. That's a bummer but it beats continuously wasting the expensive Prusament.

RE: What part of the MK4 Nextruder hates being enclosed?

Just wrapped up with support (and partial printer disassembly) and they are going to reach out to others to see if anyone has any ideas. Their initial idea was an overheating stepper but nothing in their database indicates a problem with my particular stepper (based on QR code).

Should hear back this week. The strangest part is that this is the second potentially stepper related issue on my kit. I also have some artifacts along the Y axis that were mostly resolved (but not eliminated) by switching to a toothed idler. It's almost as if these steppers don't like me or the stepper drivers are questionable.

RE: What part of the MK4 Nextruder hates being enclosed?

I’ve suffered this exact problem myself. At first, I thought it was just a duff roll of filament I’d gotten from Prusa with my mk4 upgrade, as other prints with different spools of filament seemed to work.

https://forum.prusa3d.com/forum/english-forum-original-prusa-i3-mk4-general-discussion-announcements-and-releases/weird-filament-issue/#post-671459

But I’ve started to encounter it again - and I’ve come to the same conclusion. It’s time dependant, and it happens when a longer print is running. Case in point my last print was approximately 8.5 hours long, but it stopped extruding in the last 30-40 mins of printing given the results (it was a large print covering most of the print bed, and the last good layer was the first top layer… I don’t think I’d seen it before the initial failures as I’ve been printing smaller items using the IS profiles to decrease the print times. This was the first IS print in a long time that breached the 8 hour time barrier.

My printer has been upgraded from a mk3s+ and is in a Prusa enclosure. I had re-calibrated the printer prior to starting the print - the full start the wizard and run through everything - so the extruder was re-calibrated at the same time.

RE: What part of the MK4 Nextruder hates being enclosed?

I have the same issue in my Mk4 Enclosure kit, I had 2-3 prints that the filament broke in the Nextruder, than all the other prints I made that where longer than 7-8h, the filament started to slip on the Nextruder gear. I tried different idler tension ajustement but nothing seems to work.

RE: What part of the MK4 Nextruder hates being enclosed?

Did you hear anything back from Prusa on this? 

Posted by: @justin-3

Just wrapped up with support (and partial printer disassembly) and they are going to reach out to others to see if anyone has any ideas. Their initial idea was an overheating stepper but nothing in their database indicates a problem with my particular stepper (based on QR code).

Should hear back this week. The strangest part is that this is the second potentially stepper related issue on my kit. I also have some artifacts along the Y axis that were mostly resolved (but not eliminated) by switching to a toothed idler. It's almost as if these steppers don't like me or the stepper drivers are questionable.

RE: What part of the MK4 Nextruder hates being enclosed?

I found the issue for my printer! I did 2 cold pull as per the Prusa instruction, than I use a needle the exact same size of my nuzzle (0,4mm needle for a 0,4mm nozzle) and my needle was 3inch (75mm) long to make shure that there is no clogs in the nozzle. I than remove the nozzle from the printer, turn it up side down and I gave gentle taps on a flat surface to make shure that there was no burned filament peaces stuck inside. After that reassemble and purge filament a couple times.

Also, in the instruction, they are telling you that the iddler tensionner screws need to be flush with the plastic part, but it is way to tight for my printer. The end of my screws are about 2-3mm inside de end of the hole, and since than I have no more clicking and everything works perfectly! When the filament is not charged in the extruder you will find that the iddler door is way to loose, but when you charge the filament it is perfect.

RE: What part of the MK4 Nextruder hates being enclosed?

Posted by: @greatoldone-2

Did you hear anything back from Prusa on this? 

I did not. This is the third time I had a more advanced issue that required Prusa support "get back to me" and none of the three ever have. But I digress.

There is a thread about this on Reddit but the long story short is that it was my idler. It seems the idler had warped and was no longer applying tension. In the attached photo, notice the extruder on the left has essentially no gap between the idler and Nextruder body. On the right, I reprinted the pieces in ABS and notice how there is a couple threads worth of gap.

This explains why applying more and more tension to the screws didn't work--the idler was allready pulled tight against the Nextruder body and simply couldn't get any tighter.

I think it also explains why the delay in the failure. It was only after numerous hours of a hot enclosure near a hot stepper that the idler would start to deform. Come back the next day when everything has cooled and you sort of get a reset on the clock where the idler start out stiff then slowly deforms as the hours pass by.

After installing the new idler, I noticed how I had completely forgotten that the idler does take a little force to close. With my deformed idler the lever would practically fall into place without effort.

I hope this helps. I've been printing for over a month now with this change and haven't had a single failure since replacing the idler parts.

RE:

I have the same problem between the screw and the hotend heatsink (load cell) there must be a gap otherwise the tensioning roller has no tension... Attention I have to unscrew and clean the gearbox afterwards because there are filament residues and install it according to the instructions...

Print the parts in abs or asa is working great

RE:

Another confirmation here that the idler appears to be the issue. I reprinted the idler arm pieces, the ‘nut’ and the latch pieces all in ABS. Kicked off a long 10 hour print and it worked flawlessly.

I’ll keep an eye on it, as that was just one print. But thanks @justin-3 for the investigation and the fix.

RE: What part of the MK4 Nextruder hates being enclosed?

Thanks for posting this and pointing out the problem. I have a similar issue with a new Mk4 in the Prusa Enclosure. Yesterday my colleague started a print (not a large one, about 3 hrs with 0.1 mm layer height) which seemed totally fine at the beginning. After a while the filament (Prusament PLA Galaxy Black) wasn't extruded anymore. Regardless, the printer "printed" until the end without detecting an error. I don't think that the ambient temperature in the enclosure was far above 40°C but can't be sure about that since I wasn't there.

I could remove the filament but wasn't able to load it again. The idler didn't grab it, I just got scraping noises and the filament didn't move. I carefully tried to tighten and loosen the tensioner screws without effect. I will try again with a completely cooled down printer. If it works again it is very probable that I'm experiencing the same problem as you.

RE: What part of the MK4 Nextruder hates being enclosed?

I don't think that the ambient temperature in the enclosure was far above 40°C...

That was roughly the ambient temperate I was able to achieve in my old enclosure when I started having the problem. The issue isn't just the ambient temperature, it's the temperature of printer components. The Nextruder is one giant heat sink for the stepper. Since its goal is to remove heat, it itself heats up. That heat is easily transferred to the plastic idler pieces and bring about the issue.

A cooled down printed seemed to help me a bunch, right until it didn't. Not sure if the parts were cooling and returning to their original shape (doubt it) or if just being cool meant they weren't able to deform until they warmed back up again.

Hope you can reprint the idler pieces in ASA/ABS and get better results!

RE: What part of the MK4 Nextruder hates being enclosed?

It's working again. I had to do some loosen-tighten-cycles with the idler screws but at last the idler grabbed the filament and everything is fine. The part that originally triggered the problem was printed without any issues.

Heat definitely causes problems. Don't get me wrong, I'm not surprised about that but I did think that I wouldn't run into them so fast with a Prusa Printer in a Prusa Enclosure in an air vented room with about 20°C room temperature. Of course, I can't be absolutely sure that this is the reason.

I will install a ventilation system on the enclosure. We'll see if the problem occurs again. Reprinting the idler with ABS seems like a good idea.

RE:

I experienced the same failure mode: mid-print, in particular with tough-to-print filaments or when the enclosure got hot, the Nextruder stopped extruding altogether, and I continually developed clogs.  I couldn't finish any print that went on for more than, say, 20 minutes.  PETG, PLA, ASA... you name it.  What's worse is that the filament extruded as if it was an extremely wet noodle, but it truly wasn't.  Absolutely disgusting to go through a 7-hour print and discover that the extruder had decided to give up halfway (though, fortunately, due to my smart enclosure, I could watch and stop the print whenever that happened and I'm in the office).

I found the solution in much the same way as others did — extruder gear tension by way of a superior idler.  What I found out is that my idler lever had ever so slightly deformed after printing high temperature filaments for dozens of hours, meaning it couldn't actually add any pressure to the extruder gear anymore.  No adjustment of the idler catch tensioner springs made a difference.

Here's where the modified idler lever came to the rescue!  I printed that lever in PLA (continually pushing the filament using my hand, to avoid extrusion failures with the shitty deformed lever my printed had — all 19 minutes of it).  Then I swapped the lever following the Nextruder assembly instructions, and adjusted the tensioner screws on the idler nut (in my case I unscrewed them about a turn and a half each, making the idler nut tug a bit harder on the lever).  Finally, with a lever that allowed me to print without problems, I printed the final lever in ASA, knowing that future high temperatures will not deform that one... and replaced the lever once more, tossing the temporary "tide-me-over" lever into the trash when I was done.  I did not need to print a different idler nut!

Here is the new, modified lever — printed in white Made for Prusa ASA — sitting in my MK4's Nextruder.

With this setup, everything printed flawlessly.  Under the current screw adjustment, there is about 0.6-0.77 mm gap between the nut and the housing where the PTFE tube screws, which wasn't there before.

I have had other types of failure induced by heat.  The plastic (PETG?) clamps that hold the Y (bed) belt have deformed to the point that they now no longer properly grip the ends of the belt, and at some point even one of the screws that hold the far end of the clip just... came off altogether!  The result of this was horrible quality and the printer failing bed calibration self-test.  This was a royal pain in the anus to fix, because my printer is in an enclosure, so removing the printer from it to do maintenance on the bottom is excruciatingly hard.  To get around this issue, I had to jam paper in between the belt teeth and the clip's teeth grip, which didn't work, then I jammed paper directly in the screw hole that makes the clip expand and grip the belt when tightened down.  I think my next upgrade will be to print the superior Y belt tensioner (once I have found a way to remake the belt clips such that they won't deform).

RE:

Update: my replacement idler crapped out.

I noticed because I began experiencing the exact same phenomenon once again -- mid-print failed extrusion coupled with what appears to be a clogged extruder nozzle (but isn't — I can force push the filament into the extruder while purging, and it purges).

So what happened?

One of the halves of the idler was totally bent almost straight (it's supposed to have a curve on its "back").  The part that was bent had "repositioned" the idler bearings to be almost 30% skewed from their true position (parallel to both halves).  Needless to say, the extruder gear basically just kept shaving filament crumbs rather than pushing the filament into the nozzle.

Upon closer inspection, I realized that the totally destroyed half of the idler was printed in PLA, whereas the other was printed in ABS.  I had mistakenly mated one of the halves of the PLA trial (easier to print with a failing printer, as told above) with the other half of the final ABS one (printed using the temporary PLA idler I used to bootstrap me out of the hole I dug myself into).

Worse still, I had trashed all other idler halves I had (the originals and the PLA ones, or rather what I thought were the PLA ones).

I went dumpster-diving into my trash and, at the very bottom of the trash can, I found the other half of the ABS idler!  I put it together with the installed, correct, unbent half that was on the printer, replacing the bent-out-of-whack PLA idler half.

The printer is printing fine again.

Edit: if you look closely at the photo I posted above, it's very much clear that I fucked up the assembly of the replacement idler — there are two tones of white in that idler!

RE: What part of the MK4 Nextruder hates being enclosed?

I consider the improvements to the Nextruder for the MMU3 of the idler and mainplate with an added grease seal, to be nextruder 1.1.  

The Idler  has added back-bone to avoid bending.  The idler and main plate are made with heat resistance material.  They are purchased, the print process takes a special machine.     The main plate added a groove for an o-ring grease seal.  

In heated enclosures over time the PETG idler bends.   

I had idler and mainplate made out of ASA before I put on the MMU3.  I  liked the main plate mod that that a bar to entrap flexible filaments better.  I wish the MMU3 version had that.