FFCP Dual Extruding huge jamming issue. Advice requested..

[huntleybill]

I have been trying to print the traffic cone with dual extrusion and am having issues with the left extruder. I am using black PLA. The process will start fine but when it gets to about 10%, the extruder jams. It doesn’t jam at the nozzle but at the top of the barrel. I then have to remove the nozzle and PTFE tube, take out the stepper motor and extruder block, let the heater cool down, then snap out the jammed piece. I then reassemble everything, load the filament, and extrude some material to make sure it is ok. It extrudes during the loading process quite well. I then restart the print and at about 10%, it stops extruding again. This only happens to the left extruder. The right extruder does not have any issues.

I have tried the following variations but none of these fixed the problem.

• Made sure filament feed roll is not binding.
• Checked and re-checked that the bed is leveled and the extruder is not too close to the glass.
• Raised the temp to 225
• Lowered the temp to 200
• Slowed the speed to about 40%

I tried slicing the model using ReplicatorG, Flashprint, and S3D. Didn’t make any difference.

Curious thing is when I use ONLY the left extruder to print a model (single extrusion), it prints the whole model with no jamming. Using the same filament with the same settings.(last picture of tugboat).

In the attached pictures I am attempting to show you where the filament is jammed. You may have to zoom in. Not sure if these are helpful or not.
How do I prevent this from happening???
Thank you for your time.

20161028_171039 (800x800).jpg20161028_171118 (800x800).jpg20161029_115759 (800x800).jpg

[wirlybird]

Sounds like heat creep. Heat moves up the barrel and softens the filament. Make sure both extruder fans are running.
Could be printing to fast. Trying to extrude to much filament, over extrusion.

[huntleybill]

Thanks Wirlybird. Both fans are running. If it was over extruding, why would printing as a single extruder with the same filament and the same temps work just fine with no jamming? This only happens when I dual extrude.

[curious aardvark]

what temps do the control panel show when it jams ?
Could be the left extruder isn't holding it's temp.

[huntleybill]

The temps remain constant in the display. I did a feed rate calibration as per the sailfish manual and found that I have to adjust the extrusion multiplier to .95 to get the 20mm block level. Is 0.05% enough to cause the issue? If so, why does the extruder print fine when I'm doing single extruder models? That just doesn't make sense to me.

But then, that is why I talk to you guys!

[wirlybird]

My guess is that the right extruder is causing excessive heat on the left but it is really odd. Your picture really looks like heat creep. Google heat creep with PLA and see what you can find.

[curious aardvark]

Can't see how the right extruder could effect the left.
But with dual extrusion it;s possible the gcode is getting mixed up somewhere.

I just use makerware desktop for dual extrusion. simplify3d just doesn't have good enough wipe walls.

But it's not an issue I've ever had.

[wirlybird]

It is odd. I am just guessing that the additional temp from the right extruder is bleeding over through the mounting block. Maybe the left is running hotter than displayed and it doesn't take much for heat creep to set in.