Arcol 4.0 hotend jams ..

I am using this one with PLA

[ifeelbeta.de]

After some printing, usually longer time, it manages to squeeze some 2-3 mm hot PLA upwards, making a "blob" that jams (makes it very hard to push down new/more PLA.) - until I unload , clip off that end, reload, and continue.
What may be the problem ?
- I do have a fan blowing on the cooling fin and the hotend. - and my fill settings is currently too lean - so it's not that it's too packed to extrude..

Back flow usually means the bore o the insulator is too big for the filament diameter. Have you got undersized filament?

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[www.hydraraptor.blogspot.com]

Hi, Thanks for helping.

This is a photo of the "problem" - during "normal operation" if unloaded, there's no wider section at the bottom.
One side of the end have a clear "notch" mostly on one side.
My filament is close to 3.0mm, some sections are 2.9x or so.

What should I do to correct this problem ?


Out of pure desperation, I ordered a new hotend, even assembled, just to avod me making any mistake.:

1x Hot End Packs - Wooden Mounting Pieces - Wade for $6.00 each
1x Hot End Packs - Hot End - Fully Assembled (upgrade option with purchase of hotend pack) for $24.99 each
1x Hot End Packs - HotEnd Pack (.50mm Nozzle) for $75.00 each

At least, I hope it's a good choice.

Edited 1 time(s). Last edit at 01/27/2012 04:29AM by Andke.

Either the bore is too big, the cold end is too hot, or it is too short.

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[www.hydraraptor.blogspot.com]

Regarding "too hot"
Just to be sure - I purchased a professional dual channel thermometer (looks like a multimeter) - not that it's far from the IR one I used before.

While shielding only the probe end rrom the fan blowing on it , I adjusted the nozzle to be 185 degreesC (that is "198" for the printer)

I tried to lower the temperature before, but I guess back flow can be caused by too low temperature as well (hard to squeeze colder PLA through the nozzle?)

Edited 1 time(s). Last edit at 01/27/2012 07:06AM by Andke.

I don't think too cold would cause back-flow but it might stop the extruder. It is always much easier for the filament to flow backwards than through the tiny nozzle. The thing that stops it is it freezing as it reaches the cold end of the insulator.

If I blow a fan on by extruder it seizes unless I have good insulation over all of the hot end and nozzle. I haven't used a fan since moving to a heated bed. It makes the parts pop off and I don't want the hassle of insulating the extruder.

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[www.hydraraptor.blogspot.com]

do you know any faster method of reproducing backflow than printing for an hour (I am using low extrusion speeds, 6-8mm/s) ?

I tried to extrude by manually turning the gear while "blocking" the nozzle with a piece of cardboard to simulate too rich feed - no jam after 5cm of extrusion, no increased resistance on the gear.
I also tried to let the hotend be idle for several minutes, hoping for more filament to melt, and a start should jam it up then , no success.

ok, fanless printing with lower temp will be my next test then.

Thanks for the help.
After diverting airflow from the fan to *only* the cooling fins, the problem is gone. - no more jams.