Getting a MMU2 to print without reloading filaments  

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Chris
(@chris-17)
Active Member

Had a 3MKs working fine, wanted multiMaterial unit. Trying to get a reliable print before putting into Ikea enclosure.

I am using a coated copper .4mm tip from 3-D, and only printing in PETG

Nightmare, I think it's the tips. Really confused over the PETG filament settings, I have looked at all of the videos I can find. I am only using prusament PETG filaments. some people say to change the cooling stages, some the temperature, and one in this section hints at the drag of the filaments causing the issue, which may be right if you look at the grey filament 3.

Any suggestions would be helpful...

 

Posted : 08/11/2020 7:28 pm
Robin
(@robin)
Trusted Member

Hi Chri,

I am also new to this (got my MMU2 assembled 2 weeks ago and my first perfect multicolor print done yesterday) and had similar problems. I am also using prusament PETG with the unmodified settings in slicer. In my case it turned out to be (as you also suspect) to much drag in the system, making the extruder losing steps, resulting in similar faulty prints (strings and holes).
My troubleshooting process was: 

1) Get rid of all PTFE tubes between filament-spool and MMU. I fed the filament directly into the MMU -> prints where perfect.
2) Added the buffer, did not connect the tubes to MMU -> prints still perfect
3) reattached the tubes to MMU -> problems as before.

What I did:

1) adjusted all screws on the buffer to minimize drag (basically loosen everything quite a bit)
2) printed and installed this adapter on the MMU https://www.thingiverse.com/thing:3233579

after that, everything worked like a charm. I printed my first flawless multicolor lizard with 168 tool changes and no load-failure and no holes and strings.

Posted : 11/11/2020 9:43 am
Chris liked
Chris
(@chris-17)
Active Member

@robin-glave

Many Thanks, that's encouraging.  I'm printing in one colour, amazing how reliable and quick... pleasue to use.

 

Printing

https://www.thingiverse.com/thing:4484578

MMU2S-Buffer-M10x1-PTFE_Extension Remix for IKEA LackV2 Enclosure

and

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

Prusa MMU2 PTFE Holder M10 Passthrough Adapter

 

in fact reprinting 2nd link with 100% infill, because I split the one with 20% infill tightening the PC4-M10 Male Straight Pneumatic PTFE Tube Push In Quick Fitting Connectors..... It's not very big....

No idea why prusa aren't supplying these in the kit, I got 20 for £8.99

 

 

Posted : 11/11/2020 6:44 pm
Chris
(@chris-17)
Active Member

Prusa came back and pointed me

"You are correct about the cooling stages and temperatures. PETG works a lot better with the MMU if printed at a slightly lower temperature and if used with lots of cooling moves (and longer cooling moves)
 
 
interesting that the defaults for Prusement PETG in single mode (platter printer "Original Prusa i3 MK3S MMU2S Single" gives cooling moves as 4, whilst when you use ""Original Prusa i3 MK3S MMU2S" it says 1....
 
Posted : 12/11/2020 1:25 pm
Chris
(@chris-17)
Active Member

1st sucessful print, hurrah.... I'll send photo up of the filaments, still some stringing I think. I've changed all of the defaults for the PETG, and dropped temperature to 220. And used the PTFE Tube Push In Quick Fitting Connectors adapters, everything in a straight line....

This post was modified 3 months ago by Chris
Posted : 13/11/2020 11:35 am
Chris
(@chris-17)
Active Member

Ok so tips still not good, but maybe thinner

Posted : 13/11/2020 4:56 pm
Robin
(@robin)
Trusted Member

@chri-23

congrats! Looks a bit sheep though...

Posted : 14/11/2020 8:51 am
Chris
(@chris-17)
Active Member

This is more an art than a science 🙁

Brought some 2.5mm ID PTFE tubing, replaced the 150mm and 535mm tubes to the buffer.

Certainly no friction now, but causes the reels of filament to unwind... Didn't seem to make any difference to the stringing. I didn't change the internal short ones in the selector.

 

I have enabled the cutter, but this only comes into play if it fails to load the filament, and that doesn't help if the filament gets stuck in the 360mm selector to hot-end tube....

 

I may go back to 2mm ID all round.....

 

 

 

Posted : 25/11/2020 5:56 pm
Robin
(@robin)
Trusted Member

Did you check the tube in your hot end, the one below the gears in the extruder? It seems that some stock MK3 come with a 2mm ID, the ones in the MMU2 extruder spare bag are 1,85 mm ID. The link and some description is in the comments of the extruder disassembly, I can’t find it right now...

Posted : 25/11/2020 8:28 pm
Robin
(@robin)
Trusted Member

Found it! 
-quote-

VERY IMPORTANT!  Before moving on, follow the instructions for replacing the hot end PTFE tube with the spares provided in the MMU2S kit.  It is very easy, but essential.  Instructions here:  https://help.prusa3d.com/en/guide/how-to-replace-ptfe-tube-on-the-mk3s-mk2-5s-mmu2s_21664/ Reason: The MK3S printer hot end uses a PTFE tube with 2mm ID.  The MMU2S requires the hot end to have a 1.85mm ID.  The 2mm hot end tube creates large filament tips that get stuck in the long stretches of MMU2S tubing. The 1.85mm hot end tube makes the tips perfectly shaped for the MMU2S tubing.Please trust me.  It is worth your time to replace this tube before moving on.

-end quote-

Posted : 25/11/2020 8:32 pm
Chris liked
Chris
(@chris-17)
Active Member

Yep had changed it, but the mk3S I built had a 1.85mm hot end tube anyway... But good advice...

I must admit the unwinding of the reels is bad news :-(, I think sometimes the buffer doesn't do its job. Almost need something to stop the cable being pushed back onto the reel...

 I'll see how it is when I've put it into LACK enclosure.. and report back...

 

Posted : 26/11/2020 2:16 pm
stephen.h14
(@stephen-h14)
Estimable Member
Posted by: @chris-17

Yep had changed it, but the mk3S I built had a 1.85mm hot end tube anyway... But good advice...

I must admit the unwinding of the reels is bad news :-(, I think sometimes the buffer doesn't do its job. Almost need something to stop the cable being pushed back onto the reel...

 I'll see how it is when I've put it into LACK enclosure.. and report back...

 

I had that problem also. To fix it, I set up a five color print that changed colors fairly quickly and as each filament was being withdrawn I slowly tightened the screw for the PTFE tube on the spool side of the buffer just until the filament stopped returning to the spool and collected in the buffer. I needed to tweak it a little farther for some filaments, I assumed those were on the smaller side of the 1.75mm diameter and needed more tension on the screw. I left the screws on the MMU side of the buffer as loose as possible without the PTFE tubes working loose during a print.

Posted : 27/11/2020 10:55 pm
Chris liked
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