Tool change failure with PLA, MK3S+MMU2S, filament tip issue?
 
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Tool change failure with PLA, MK3S+MMU2S, filament tip issue?  

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jprintmk3smmu2s
(@jprintmk3smmu2s)
Active Member
Tool change failure with PLA, MK3S+MMU2S, filament tip issue?

The MK3S prints fine by itself, and any of the 5 filaments solo from the MMU2s print fine. The first time it loads any of the filaments in a multi-color print it works, I cut them at a slight angle, but the second load of the same filament fails consistently. I watch the sensors screen, and see the filament make it to the extruder bondtech gears, move the idler door and trigger the IR sensor, but as it is backing out it goes too far, the door closes, and the IR triggers off. The tips often look stringy, but occasionally they look like they should have worked fine, albeit with a larger head. I tried default prusa slicer 2.0 settings with prusament pla and generic pla settings. I tried using the pretty pla v1.2 settings, playing with cooling moves and speeds and temps, but PLA always fails. Oddly enough I managed to get 6 or 7 tool changes with PETG working in testing.

I assume my issue is filament tips at this point, any suggestions?

Tips:

Posted : 03/07/2019 4:15 pm
jprintmk3smmu2s
(@jprintmk3smmu2s)
Active Member
Topic starter answered:
RE: Tool change failure with PLA, MK3S+MMU2S, filament tip issue?

So, I think I figured out the issue, and want to share it for others who may run into this.  As you can see above, I had these fat stubby filament ends and lots of load failures.  I decided to break down the extruder and do a ptfe tube replacement.  I went to my bags of extra parts for spares, and upon comparing the MK3S extruder ptfe tube (I assembled from MK3S kit) I was surprised to find that the spare parts bags ptfe tubes internal diameters were different!

First I tried to manually push the bad tips through the ptfe tube, and they either had extreme friction or outright could not be forced through by hand.  I guess the gear system was strong enough to yank them out, but not to push them back through.  So I got out my digital micrometer and found the removed PTFE tube was much larger than the parts kits tubes.  Surprisingly , the parts kits tubes were labeled 1.85mm, but I measured them to be about 1.70mm.  The MMU2S kit spare parts ptfe tubes were also 1.70mm.

My guess is I got a hot end in my MK3S kit that was really a MK3 hot end, because it uses a slightly larger internal diameter ptfe tube.  I bet a lot of people with filament reload issues have the same problem.

Anyway, swapped tubes, and had 10x filament changes with success, yay, so cautiously optimistic.

Build instructions do no say to replace extruder ptfe tube for MK3S -> MMU2S (but *do* for MK3 -> MMU2S)
https://manual.prusa3d.com/c/Original_Prusa_i3_MK3S_to_MMU2S

parts bags with wrong data for ptfe tube internal diameters
https://imgur.com/RtjrlJn

ptfe hot end hole size (you can measure pixel distances to get approximate if you care)
https://imgur.com/OegNnt1

at least I had no power failures!
https://imgur.com/WPwjLnj

 

 

This post was modified 3 years ago 3 times by jprintmk3smmu2s
Posted : 04/07/2019 5:24 pm
jprintmk3smmu2s
(@jprintmk3smmu2s)
Active Member
Topic starter answered:
RE: Tool change failure with PLA, MK3S+MMU2S, filament tip issue?

n.b.  I know the ptfe tubes can't be 1.70mm and have filament that is 1.75mm pass.  It's not easy to measure accurately. ><  My pre-built mk3s hot end was closer to 2.0 internal diameter hot end ptfe tube, which I guess some MK3's shipped with.

Posted : 04/07/2019 5:52 pm
ntdesign
(@ntdesign)
Estimable Member
RE: Tool change failure with PLA, MK3S+MMU2S, filament tip issue?

Could be I have the same problem (hotend PTFE from MK2.5s upgrade bag). I tried everything else and the symptoms never really changed. Also: Terrible grinding sound when it tries to rip the filament from the hotend.

How did your solution hold up? It wasn't exactly clear to me which diameter PTFE you finally used? Real 1.85mm ID?

Thanks for your effort, I kinda avoided taking apart the hotend tbh, because the printer works fine in single mode... 

Posted : 16/07/2019 6:27 pm
Nikolai
(@nikolai)
Noble Member
RE: Tool change failure with PLA, MK3S+MMU2S, filament tip issue?

During the MK3+MMU2 to MK3s+MMU2s upgrade I also realized the small tube diameter. It's hard to measure but I think it should be 1.85

Often linked posts:
Going small with MMU2
Real Multi Material
My prints on Instagram

Posted : 16/07/2019 6:37 pm
jprintmk3smmu2s
(@jprintmk3smmu2s)
Active Member
Topic starter answered:
RE: Tool change failure with PLA, MK3S+MMU2S, filament tip issue?

After I replaced the extruder ptfe tube with one that measured smaller internal diameter (I swear it was 1.70mm when it met resistance, but could be stretched to 1.85mm) I went on to print a 100+ tool change 2 filament PETG test object without any issues.  So that was absolutely my biggest issue.

As for changing the PTFE tube itself, it's actually much easier than you'd think.  You can loosen a few key bolts on the hot end assembly and slide the hot end out of the enclosure without completely separating it. 

Posted : 16/07/2019 7:01 pm
ntdesign
(@ntdesign)
Estimable Member
RE: Tool change failure with PLA, MK3S+MMU2S, filament tip issue?

OK thanks guys. Since this is somewhat contradictory I'll just go ahead and try. I went through my spares and all my replacements were the same in terms of my filament end not fitting through them when pushed by hand. I have PTFE with slightly wider ID around, will cut and chamfer a piece and see where that gets me.

This is what you get when you follow the manual by the letter. As such, no easy feat for a person of (very) male persuasion. I remember well sitting there and considering just shortening the top end of my well-run-in tube instead of putting in the new one 😣 

Posted : 17/07/2019 11:04 am
ntdesign
(@ntdesign)
Estimable Member
RE: Tool change failure with PLA, MK3S+MMU2S, filament tip issue?

Little update: I swapped in a wider diameter tube (1.9 officially but couldn't measure, my sub-optimal tip went through cleanly). This made things much worse. Now I can actually see&hear the extruder motor skipping. I guess the filament is still soft enough when it gets pulled out, so you need a bit narrower ID to allow it to expand. I'll go through my remaining spares tomorrow to see if one of them fixes it. If that fails I'll try some 1.7 ID capricorn.

Posted : 17/07/2019 5:31 pm
ntdesign
(@ntdesign)
Estimable Member
RE: Tool change failure with PLA, MK3S+MMU2S, filament tip issue?

OK, for those who have the same problem: I replaced the tube in the hotend now with Capricorn XS (1.9mm ID, blue, intransparent). The tube was cut and chamfered with this tool: https://www.thingiverse.com/thing:3121653

Top end was tapered with a cheap chinese reamer tool. That seems to have done it. 100+ tool changes so far, not a single error or 2nd loading attempt. No struggling or noises anymore during unload. As far as I can see the tips, they still seem to have a little ridge but it looks very symmetrical. If the print completes I'll post a pic here.

Only software changes: Dropped PLA temps to 205 (also for first layers), speed on unload 120mm/sec, 3 cooling moves. I had used those in all previous attempts without success.

This post was modified 3 years ago 3 times by ntdesign
Posted : 27/07/2019 12:10 pm
CybrSage liked
ntdesign
(@ntdesign)
Estimable Member
RE: Tool change failure with PLA, MK3S+MMU2S, filament tip issue?

OK, here it is. Needless to say I'm flushed with euphoria.
10 hour print, 176 tool changes, Fillamentum Pearl Ruby Red & old Prusa black (i.e. not Prusament). Will see how long the Capricorn XT will hold up, but it is very quick to replace, so not too worried. I quickly pulled it out to check the lower end, no deformation by the heat or filament. Sorry for the terrible photo, but believe me there is no stringing.

Posted : 28/07/2019 1:41 pm
cermi3
(@cermi3)
New Member
RE: Tool change failure with PLA, MK3S+MMU2S, filament tip issue?

@nils-t Is this PTFE tube you ended up using a 1.9 or 1.7 ID? 

Posted : 30/01/2020 4:28 am
ntdesign
(@ntdesign)
Estimable Member
RE: Tool change failure with PLA, MK3S+MMU2S, filament tip issue?

XT 1.9 ID. I had to replace it once, but probably the Prusa-supplied one wouldn't have lasted longer.

Posted : 30/01/2020 8:03 am
Primermecos
(@primermecos)
Eminent Member
RE: Tool change failure with PLA, MK3S+MMU2S, filament tip issue?

I had the same problem like @jprintmk3smmu2s with my MMU2S printing multicolor PLA but was printing fine with PETG. Testet many PLA filament brands, chimneys for the ir-sensor and so on. Nothing helped until I changed the PTFE tube in the extruder. It seems the tube get a bigger inner and outer diameter after time. I measured the inner diameter 2+mm and the outer diameter 4,10mm...the tube in the spare bag is 1,85mm/4mm...now my printer works fine.

Posted : 05/02/2020 7:13 pm
wldthng842
(@wldthng842)
New Member
RE: Tool change failure with PLA, MK3S+MMU2S, filament tip issue?

I ran into this issue, support had me loosen the idler screw on the hotend and tighten the screws on the MMU2.  So far it's pushing the filament through successfully now.  FYI

Posted : 29/12/2021 3:39 am
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