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Why second purge on filament change during print?  

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jim-4
(@jim-4-2)
New Member
Why second purge on filament change during print?

I use the color change feature in the Prusa Slicer to change color at a certain level. When my object prints the Prusa stops at the specified layer and moves the extruder head up and pushes the bed back. It prompts me to unload the current filament, then to load the new filament. It pushes through a good bit of the new filament and asks if the color is correct. 

At this point there is a good amount of extruded filament to remove. After I click "yes" it extrudes another 2 cm or so of filament before returning to the print location.

Because of this second extrusion I have to sit with my long nose pliers under the hot end. I click "yes" wait for the second extrusion to finish and then grab the extruded filament as the extruder is heading off at speed to return to the print. If I don't do this, then the extruder head moves back to my print with 2 cm of extruded filament to glom onto the object.

I wonder why there is this second extrusion. It would seem ok with me to just continue when I press "yes" rather that have this additional extrusion. 

Postato : 25/06/2022 12:45 am
Diem
 Diem
(@diem)
Famed Member

It's pressurising the nozzle path.

Do not remove the filament before you click 'Yes', just take hold of it and when it moves off you will have the load extrusion *and* the pressurisation extrusion left in your hand.

Cheerio,

Postato : 25/06/2022 1:20 am
fuchsr hanno apprezzato
fuchsr
(@fuchsr)
Famed Member
RE: Why second purge on filament change during print?

What he said. Probably a precaution for those cases where someone may leave the printer and  is not answering the question right away. So by repressurizing the printer makes sure it's all set to continue properly. 

Postato : 25/06/2022 10:20 am
jim-4
(@jim-4-2)
New Member
Topic starter answered:
RE: Why second purge on filament change during print?

I tried your suggestion but it did not work. Holding the filament change extrude and then just waiting for the pressurization and movement left a 2 cm bit of extrusion on the hot end, heading to my print.

If this is a precaution for someone leaving the printer for a while, why not have the firmware time that and only do the extra extrusion in that case? 

Jim

Postato : 25/06/2022 5:30 pm
JoanTabb
(@joantabb)
Moderator
RE: Why second purge on filament change during print?

I understand that This is a marlin feature, as it also happens the same on other manufacturers printers. 
regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK

Postato : 26/06/2022 2:35 am
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