First print attempt: filament is about to extrude...then disappears back to the MMU2S!
 

[Solved] First print attempt: filament is about to extrude...then disappears back to the MMU2S!  

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John L
(@john-l)
Eminent Member

I initially had issues with the IR sensor in the chimney not being aligned (so got melted filament pooling onto the plate). I fixed that, but now, as it's just about do Z calibration...the filament retracts all the way past the MMU2S.

It usually tries to do it a few times, before lighting the specific filament light red. I tried a filament from a different tube...same issue.

When I look close, it looks like it's started to melt the filament, and then when it withdrew, it was long and pointy. Ramming it back in a few times seemed to blunt it, before the printer gives up. Any ideas what to look at ? 

I really wish it was able to send more debugging information to something like Octoprint, about what's going wrong.

While I'm at it, setting up the 'buffer', made me think - for the first time - "This is really poorly designed". Once I get the printer up & running, I'm going to finish printing the bits for the MMU2S lack enclosure. I might try work out a better buffer that's not such a pain in the ass to hookup, and change filament on.

Posted : 16/02/2021 11:26 pm
John L
(@john-l)
Eminent Member

Huh. I kept reading through other posts. I also fell afoul of the PTFE-tubes-held-in-too-tightly. Pretty much every one of them going into the buffer was deformed by the 12mm screws holding them in. I took them out, paired them down 1.5cm or so, and gently reamed them out. Discovered any filament that made it to the extruder was badly damaged - as people describe, the gears pulled big bites out of it. It was catching a lot in the PTFE tubes. I might reduce the tension on the MMU2S...even where the filament wasn't deformed from the gears, it still had treadmarks in it. 

Also; it seems if I plug in the RPi3 that I had feeding off the main PSU, the Einsy resets. I'd not have thought just having the MMU2S connected, not actually doing much, would cause power issues...

This post was modified 2 months ago by John L
Posted : 17/02/2021 12:01 am
stewartr
(@stewartr)
Eminent Member

I have a summary of simple modifications to help with the PTFE tubes being held too tightly here:

https://forum.prusaprinters.org/forum/original-prusa-i3-mmu2s-mmu2-assembly-and-first-prints-troubleshooting/first-layer-calibration-mmu2s-constantly-loads-and-unloads-the-filament-to-the-nozzle/

As a bonus it makes dismantling easier, as well as feeding filament through the buffer.

As for you problem with retraction (three times?) that's usually down the the filament sensor. I know you've just adjusted it, but... Try watching the screen's sensor info as you push a string of filament in and out a few times. Possibly whilst applying a bit of force to the chimney to see if that has any effect on the readings.

Posted : 18/02/2021 7:02 pm
R3vela710n
(@r3vela710n)
New Member

@john-l-2

Hi there,

It sounds like you would benefit greatly from this modified part. I no longer have any issues at all after I printed and installed it.

https://www.thingiverse.com/thing:3233579

 

good luck

Posted : 22/02/2021 2:47 pm
John L
(@john-l)
Eminent Member

I have to say, I'm genuinely confused at how ... unfinished the MMU2S is, as a product. 

  • If you have never handled PTFE before, it's so easy to over tighten everything. This really should be stressed in manuals more. I ended up trimming and reaming out all of mine.
  • The hooks for the buffer confuse me. It's so easy to place them slightly wrong, and then when the plate moves back 100%, it'll hit off the hooks, and you lose calibration. Actually, now that I think of it, I cannot work out how to place it ... well. It catches on some screw or something.
  • Not having visual cues for FINDA/filament load indication is just annoying. It would literally add $1 to the price to get some more LEDs in the kit. (this FINDA LED was great and should really be a base feature. As should this one.
  • The official explanations of how to calibrate the chimney are really weak. Or else something changed a few times, because it took me ages to make that go.
  • Anything to do with one of the five extruders should have numbers etched onto them. Just embossed, so I can highlight them with a magic marker.

Once I get it printing again, I'll definitely try some of these mods! Thanks.

I'm really glad there is a community around it. Otherwise, I'd have sent it back....I suppose Prusa's support for the community, is why I bought the thing 🙂

 

Posted : 28/02/2021 12:24 am
John L
(@john-l)
Eminent Member

Update: the buffer catching the print plate exposed that bearings weren't quite tight enough. Belts are all good now.

Last odd problem....I sliced a replacement fan shroud (last one got melted goo all over it). In the slicer, I said "print that with filament 5". However, it tried to start with filament 4, and then the MMU2S threw a problem. I had no idea what the problem was, so hit the middle button (any idea why these buttons don't have names that might indicate what they do ?). It cleared the issue, and then it started again...pausing to ask if the filament was loaded, unloaded, or the wrong colour. When I indicated 'wrong colour', it paused for ten seconds, then asked me the same question again. Not sure it was trying to do anything differently.

Any idea what that might be ?

Posted : 28/02/2021 2:51 pm
John L
(@john-l)
Eminent Member

Ah. I saw this in the Octoprint UI:

Not queuing T4, that tool doesn't exist according to the printer profile or was reported as invalid by the firmware. Make sure your printer profile is set up correctly.

Posted : 28/02/2021 2:53 pm
John L
(@john-l)
Eminent Member

I'm pretty emotional right now. I managed to get it to print a few test pieces. Small problems with some little .. hairs .. coming off PETG, but...mostly good.

 

Then I noticed that there was a nut loose, holding the z-axis trapezoidal nut. So I disassembled, fixed it, put it back together, and did a full calibration wizard just in case. Now the X/y axes aren't square, according to the wizard...but it still passed.

However, I can no longer get it to print a first layer calibration...it's back to load/unload of the MMU. The filament is going in, I think there is no alignment issue....but when I disconnect the PTFE tube...it's really hard to force another filament in through the extruder. Should it be so difficult?

Can filaments that don't retract cleanly (so seem a little thicker) damage gears alignment when they are rammed in a few times ? 

Posted : 01/03/2021 11:15 pm
Robin
(@robin)
Estimable Member
Posted by: @john-l-2

Update: the buffer catching the print plate exposed that bearings weren't quite tight enough. Belts are all good now.

Last odd problem....I sliced a replacement fan shroud (last one got melted goo all over it). In the slicer, I said "print that with filament 5". However, it tried to start with filament 4, and then the MMU2S threw a problem. I had no idea what the problem was, so hit the middle button (any idea why these buttons don't have names that might indicate what they do ?). It cleared the issue, and then it started again...pausing to ask if the filament was loaded, unloaded, or the wrong colour. When I indicated 'wrong colour', it paused for ten seconds, then asked me the same question again. Not sure it was trying to do anything differently.

Any idea what that might be ?

Just use MMU-Single-Mode in PrusaSlicer. When the print starts the printer will ask which filament to use, load it and start printing. Note, that -as far as I know- right now there is no way to select the filament via Octoprint, because the respective plugin now longer works with the current version. You can start a single-mode print via Octoprint but you have to select the filament at the printer's interface.

If at first you don't succeed, skydiving is not for you....
Posted : 05/03/2021 4:26 pm
John L liked
EJTH
 EJTH
(@ejth)
Eminent Member

@john-l-2

Unless the gears are turning it SHOULD be nearly impossible to force filament through your extruder. I had problems with the MMU2 to begin with, where it would feed filament down the ptfe tube, but it would never catch the bondtech gears. The solution for me, was to unscrew the ptfe tube during my first filament load, then insert the filament first into the extruder and then reseat the ptfe tube holder screw thing. Now my MMU loads filament perfectly!

Posted : 10/03/2021 1:21 pm
John L liked
John L
(@john-l)
Eminent Member

Update: tried many of these hints, including the 'proper screw-in-ptfe connectors' and now I've used a whole roll of PETG without a single issue. I think I'm good. Thanks!

Posted : 11/03/2021 8:34 pm
3dJ
 3dJ
(@3dj)
Active Member

@john-l

Good to hear that the MMU PTFE holder fixed your problem. I used that holder right from the start, and I must say that my MMU works really well without issues. As for Octoprint: This plugin OctoPrint-Mmu2filamentselect does work with the current version of Octoprint and allows you to select which filament to load from the Octoprint interface.

Posted : 12/03/2021 7:47 am
Robin liked
Robin
(@robin)
Estimable Member
Posted by: @3dj

This plugin OctoPrint-Mmu2filamentselect does work with the current version of Octoprint and allows you to select which filament to load from the Octoprint interface.

Outstanding! Thanks for the link 3dj!!

If at first you don't succeed, skydiving is not for you....
Posted : 12/03/2021 8:29 am
John L
(@john-l)
Eminent Member

Ahahaha, I spoke too soon. Now that the enclosure is done...I moved the printer to a different part of the room. The filament jammed in the MMU2S (I think when it tried to move sideways) and now I can't get it out. Doing an 'unload filament' after resetting the MMU didn't work either. I suppose it's time to disassemble it all again 🙂

 

Posted : 12/03/2021 2:29 pm
EJTH
 EJTH
(@ejth)
Eminent Member

Damn thats a shame... I think you need to completely redo your MMU2s filament profiles when you have it sitting in an enclosure, because of the different temperature... Is the filament stuck?

It makes me kind of sad to see so many people struggle with the MMU, I think its potentially a great product, but it is some hardware, software and firmware revisions away from being perfect. 

Can you provide a picture of how it is stuck? Is it stuck in the extruder? Or is it stuck in the PINDA or PTFE tube?

 

I think a big problem with the MMU2s is that when operating it from the printer, it doesn't have any knowledge of your filament profiles, so when you unload from the printer, filament with edge cases will string and blob.

This post was modified 1 month ago 2 times by EJTH
Posted : 12/03/2021 3:05 pm
John L
(@john-l)
Eminent Member

It's stuck in the MMU...I can't pull it out the back. I disconnected the PTFE tube, and still couldn't pull it out...it's definitely going through the gears, as the PINDA in the MMU has detected it. but it's not left the MMUs.

Posted : 12/03/2021 4:20 pm
EJTH
 EJTH
(@ejth)
Eminent Member

@john-l

That sounds strange, so its stuck in the FINDA assembly or in between? Maybe it has been lodged in there by debree or a blob on the filament end. have you tried removing the two screws holding the PTFE connector and inspecting inside the FINDA assembly? Is it caught half way up the PTFE tube between the extruder and MMU unit? Or is it just inside the FINDA?

Posted : 12/03/2021 6:00 pm
John L
(@john-l)
Eminent Member

There was definitely no blob on it - it was cut sharp, with a snips, before it went in. 

I tried winding the screw manually, so that it went from the second PFTE tube, to the first. I could see the filament stretched, from the 2nd tube, to the PINDA. I snipped it off, at the PTFE tube, then pulled out the remnant with a pliers. Looks good now. Must have somehow ... not gone through the PINDA properly ? Got bent, perhaps...

Posted : 12/03/2021 10:25 pm
EJTH
 EJTH
(@ejth)
Eminent Member

@john-l

What filament are you using? Have you checked its diameter with a caliper?

This post was modified 1 month ago by EJTH
Posted : 12/03/2021 11:43 pm
John L
(@john-l)
Eminent Member

Prusa orange PETG. I don't think it was a filament problem. I think it was me, not being able to work out how to use the buttons on the MMU to select the proper filament, and possibly pushing it through a little too much, before it started moving around, looking for a filament.

 

Posted : 13/03/2021 11:05 am
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