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jflund

Retraction Problems

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I just got my Ultimaker 2 and it initially worked great. I printed 5 or 6 item without problems. I then upgraded the printer firmware and since the retraction seems to be working incorrectly.

When I print something with several different high areas separated by low areas (the latest is printing the ribs on a T-Rex skeleton with the ribs pointing up. I get massive stringing between the ribs, so much that they are essentially one solid part.

I have determined that the problem seems to be that when one rib is printed and the head is ready to move to the adjacent rib, the Ultimaker 2 pauses the print head, performs the retraction, but then advances the filament forward BEFORE moving to the next rib. Because of this, it essentially prints the space between parts. It seems this has to be a bug. Is there utility in retracting AND advancing before a move?

I have tried with combing enabled and disabled and the same think happens.

Even stranger, it appears that when the print gets to the top-most layers where each layer is small, the extruder retracts and advances the filament repeatedly while it waits for the minLayerTime to expire. This has flattened the filament several times causing failure to extrude (just before the print finishes of course).

I have tried using the default combing/retraction settings, and I have lengthened "Minimum travel" and "Minimal extrusion before retracting", and both enabling and disabling "Combing", but none of those settings seem to have any effect.

Any ideas how I can stop this behavior of both retraction AND advancing BEFORE moves?

 

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This sounds crazy. I've never heard of this. Did you choose "ultimaker 2" for you machine? What is the retraction length and speed set in the menus on the actual printer? I recommend 4.5 to 5.5mm.

Look through the gcode with a text editor. The retraction/unretraction commands are G10 (retract) and G11 (unretract). You could look for those codes.

 

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I had this effect once. It was caused by the minimum extrusion amount between two retracts. The situation was that a short travel, a very short printing distance and a longer travel followed each other. Retraction was performed on the first short travel due to the minimum travel length. Then the print distance was performed but as it was very short it was not really visible. After that the longer travel was performed but as the minimum printing amount between two retracts was not reached the longer travel was performed without retraction. All together it looked like it would retract, prime and then travel.

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I had this effect once. It was caused by the minimum extrusion amount between two retracts.

Hey that looks like a situation I had too on a crazy print with a lot of custom supports.

crazy 35 hours print with XT

 

Even stranger, it appears that when the print gets to the top-most layers where each layer is small, the extruder retracts and advances the filament repeatedly while it waits for the minLayerTime to expire. This has flattened the filament several times causing failure to extrude (just before the print finishes of course).

Flattening the filament could be due to too much tension in the feeder or some soft filaments like FlexPLA does flatten easily when a few retractions are performed on the same spot.

Try playing with the minimum travel and minimum extrusion before retracting settings.

 

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