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eric-lester

Changing Colors Mid-print with New UM2 Firmware

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So with the newest version of Cura came an update for my UM2 firmware. I like the changes and was especially happy about the ability to change material mid-print. I decided to try it out by trying to print a simple traffic cone in red with white bands. I used the "Pause at height" plugin in Cura, and the printer stopped at the right height, and I was able to change to a new color. The issue is that once the material has been changed, it retracts a bit when you choose the type. As a result, no material is extruded for (in my case) the first layer and a half. This made getting adhesion between layers obviously impossible, and I gave up after the second time it happened. Is there any way to fix it? I even turned off retraction, but that doesn't do anything in this case as the command to retract filament after a material change seems to rest entirely in the UM2's firmware.

P.S. I know that I could do a workaround with a new feeder and force the last few mm's through, but I don't want to go that route just yet.

 

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Strange, I saw exactly the opposite behavior: After pressing resume, the nozzle went back to the place it stopped and then extruded a lot of material like it does normally in the front left corner before starting a print but this time on the printed object. Luckily I used little infill, so all of it just sunk into the infill.

 

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...

The issue is that once the material has been changed, it retracts a bit when you choose the type.

...

 

AFAIK the "standard" change material wizard is used during the pause. It retracts the loaded filament 20mm (the same value as the "end-of-print-retraction").

The "pause at height" plugin has an option "Retraction amount". Just increase this value for your needs and it should work.

For UltiGCode-Flavor this is a volumetric value (IMHO) - so you can use a value of approx. 130 (mm3) for 2.85mm filament.

I think there is an additional "normal" retract too (4.5mm? - done by the plugin) - so eventually you have to increase the value even a bit further.

 

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The "pause at height" plugin has an option "Retraction amount". Just increase this value for your needs and it should work.

 

Hmm. I tried doing the exact opposite...that is decreasing retraction length for the plugin. You're gonna have to explain how increasing it could possibly help here. Also, if the material change is done after the pause, does that change even matter?

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Hmm. I tried doing the exact opposite...that is decreasing retraction length for the plugin. You're gonna have to explain how increasing it could possibly help here. Also, if the material change is done after the pause, does that change even matter?

 

Well, the increased retraction amount on pause doesn't matter, 'cause you remove the material anyway. But on resume the same amount of retraction is reverted (by the plugin) and this compensates the "end-of-print" retraction. Simple but effective.

BTW: this behavior of the change material wizard is not that bad. It prevents oozing pretty well...

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Jerryrigged a solution by means of removing the bowden end from the print head while material is being forwarded during the change. I let out a great excess so that even after retraction it's too long. Slowly reinserting the bowden pushes the extra plastic through the nozzle, keeping the chamber full so that resuming the print already has material primed and loaded. A bit cumbersome to be honest, but the seamless results make it all worthwhile :)

11084597_758353297603070_1279756632_n.jpg

 

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