Dual extruder feed problems

[CCVirginia]

Community,
I have just had a chance to install and start using the dual extruder, at this point I am just using one extruder. We are trying to print out some larger robot models for my son (6-12 hrs) and have repeated problems with it just stopping feeding, sometimes hours in.
I tried adjusting the extruder tension multiple ways and times based on the advice on this forum. At first I was using PETG, which I know is a bit fussy about this. I then switched to ABS and had the same problem. I then switched to the other extruder (0.5mm head), same problem.
I am starting to think that over a long print the temp may change and alter the tension or flow in some way.
Very frustrated and running out of time . Any ideas?
Thanks!

[Jules]

Couple of ideas:

The mechanical one is, if you are stripping the filament, you might not have the tension set correctly yet.

You need to adjust the tension any time you switch to a different kind of filament. (Like from PETG to ABS or back again.) On both nozzles, if you are using them both. If it's still stripping when you switch to a larger bore nozzle, then the problem is the tension. (Or you are trying to shove it through before it melts, and after several successful hours, that's not as likely.)

Did you retract the filaments and look at the bite marks to see if you had them correct before you started the long prints? (I've run many 8 to 10 hour PETG prints without any issues, but you do need to make sure the bite marks are at no more than 15% depth, or you can strip it out very easily.) You really have to run the filament drive tension tests when you set up the machine for the dual, for both nozzles.

The "How To" is here:
viewtopic.php?f=3&t=2694

Also, slowing it down a little bit helps - give it time to melt the filament and make sure you're not trying to push it through too quickly.

Unfortunately the other possibility relates to software limitations....if you upgraded to Windows 10, i understand there is an intermittent communications issue for that OS when you try to print over USB.

Try printing from the SD card if you have checked the tensions out on the drives and they are good, and you're not feeding full speed.

[CCVirginia]

Jules,
Yup - adjusted the tension per your posts first thing. These are all materials I have used before (in fact, same spools). Right now I am trying it with PLA (Not ideal) after taking the hot end apart for a full cleaning. No windows 10. Still seems like these extruders are much more picky than the single.
Thanks!

[Jules]

Jules,
Yup - adjusted the tension per your posts first thing. These are all materials I have used before (in fact, same spools). Right now I am trying it with PLA (Not ideal) after taking the hot end apart for a full cleaning. No windows 10. Still seems like these extruders are much more picky than the single.
Thanks!

It took a few tries for me to get the tensions set with the dual at first. (Practically no tension on the dual - maybe it's the shape of the drives.)

One other thing that i ran into, (although if you got it to print, it probably isn't what's causing your problem), but i didn't have the filament holes lined up correctly the first time i set up the dual. The filaments were dragging a little when they spanned the gap before they went into the hotends. It came from not having the motors pushed forward enough in the plastic plate step of the assembly. It was causing a slight kink in the filament.

Maybe something like that? Or maybe your filament diameter swung up?

I can't think of anything else that might be causing it.

[Tim]

Any ideas?

Too many variables changing? If you have never printed this particular model before, the problem may not be the dual extruder at all. If you're printing with PETg or ABS, watch for pieces that warp either due to popping off the bed in one corner, or just on top due to a thin overhang. Either situation can cause the top layer to push up against the nozzle enough to block the flow, and if the flow is blocked for long enough, that can cause a jam.

Not that it necessarily has to do with this problem, but in general, when printing only one material using the dual extruder, keep the unused nozzle pushed up as far as it can go (about 1 to 2mm), as that prevents additional problems caused by having the unused nozzle hitting the print. Again, if the print pops off the bed at a corner, warps upward at a thin spot, that's a point where the 2nd nozzle can run into it.

[CCVirginia]

The model I was printing, and failed multiple times, used a 0.25 layer. Trying to get something printed I stripped and cleaned both nozzles, set it to 0.20 and was carful about the tension.
While stripping it down I also found that the right extruder nozzle was offset from the hot end by about 1mm, so I loosened the motor mound and got it lined-up.
I was able to get several successful prints out.
Then, I had another big print and set it back to 0.25. Again it failed in the same way. I have been able to print 0.25 and 0.3 previously and these don't seem like challenging models.
I cleaned everything AGAIN and printed it at 0.20 (for 17 hrs!), This time it works. So, the larger layer is the culprit.
Note that on my first try I had even slowed it down, so it would not be pushing to much plastic.
So it seems to me that somehow the geometry of the dual extruders is not as effective as the single and the tension setting is more "picky".

[CCVirginia]

Thought I would do a "public service" update on this. After some hiatus, printing things again. Have made 2 changes:
1) Ball bearing filament spool holders so that it would feed more smoothly.
2) Replaced hot-end/extruder fan connector (see below)

I have not had any more of these feed problems - even with long prints (like 36 hrs). Note I did not have this problem prior to the dual extruder (which replaces the harness).
After breaking a fan blade by sticking a tool in it I replaced it with a "temporary" fan. I noticed it was intermittent - may go off if wiggled. I thought it was the temporary fan connector but replaced it with a proper MG fan, it still happened. Tracked it down to the wire being broken just aft of the connector on the harness, inside of the insulation. MG sent me a new connector (thanks), that is now installed and no longer intermittent. My guess is that on long prints and only when no one was looking, the fan may have cut out for a bit and the hot end got well, hot. This could cause the filament to get soft and not feed. So, if you suspect problems - wiggle your wires!

Or, it was is ball-bearing spool holders. But why would this have changed on installing the dual extruder?