Color Change extrudes a small piece of filament moving back to the print.  

RE: Color Change extrudes a small piece of filament moving back to the print.

I tend to add a tiny cube to the print and make sure in the preview that the slicer fills it in first on color changes. I found this to be the best way to avoid those "droppings"

RE: Color Change extrudes a small piece of filament moving back to the print.

I have the same issue.  I just get ready for it to drop and grab it before the print head moves to print.  Like you said, this is not an oozing situation, it is being ejected by the print head.

Just upgraded to MK4S from an MK4, which had the same issue.  Using PrusaSlicer 2.8.1.

RE: Color Change extrudes a small piece of filament moving back to the print.

I put my brass brush underneath before I hit the button.  It's always done this, even on the XL and mk3's after a color change or running out of filament.  I believe it does it to make sure you don't have any missed extrusion on your print. 

I have had happen where I paused a print, and the nozzle oozed while paused.  That oozing makes it so that there's an empty spot insude the nozzle.  When I hit resume there ends up with a very small section with no extrusion on the part as the nozzle has to fill back up before plastic is extruded. 

This is why if I need to pause a print I make sure to do it while it's printing infill so the mixed extrusion won't be seen. 

RE:

Posted by: @brian-12

I put my brass brush underneath before I hit the button.  It's always done this, even on the XL and mk3's after a color change or running out of filament.  I believe it does it to make sure you don't have any missed extrusion on your print. 

I have had happen where I paused a print, and the nozzle oozed while paused.  That oozing makes it so that there's an empty spot insude the nozzle.  When I hit resume there ends up with a very small section with no extrusion on the part as the nozzle has to fill back up before plastic is extruded. 

This is why if I need to pause a print I make sure to do it while it's printing infill so the mixed extrusion won't be seen. 

Using the brass brush makes more sense than burning my fingers grabbing hot filament.  DOH!

I still see no reason for the extruder to push out more filament.  It had just done a purge.  And yes, sometimes there is still a small bit dangling from the nozzle after the purge, depending on the filament (I find the higher the the nozzle temperature the more likely there will be a "dangler").

I wonder if they are doing a retraction after the purge and then pushing the filament back in when resuming the print?  If that is the case, I wonder if some custom G-Code could be added to move the head to a waste area and deposit the extruded bit before resuming the print?

I am going to get the MMU soon, and I wonder if this is still an issue with the MMU?

RE: Color Change extrudes a small piece of filament moving back to the print.

This is not a issue with the MMU

RE: Color Change extrudes a small piece of filament moving back to the print.

Posted by: @joantabb

This is not a issue with the MMU

 

Thank you.  Good to know.  I know what I am getting for Christmas. 🙂

RE: Color Change extrudes a small piece of filament moving back to the print.

Posted by: @reb-3

Thanks, I found some older threads and apparently this has been an issue for awhile and nothing can really be done about it.  This seems to be by design in the firmware.  I personally don't like it,  

I believe it to make sure there is no blank extrusions on your print.  Like I mentioned earlier depending on how long the nozzle sits before you resume printing you could end up with a spot with no extrusion from oozing 

By having this in the software it does a quick small purge immediately before resummoning resuming printing.

RE: Color Change extrudes a small piece of filament moving back to the print.

Brian, what you are saying makes sense.  It would be nice if they cleared the extruded part before resuming printing.  I get that it is tricky, but I would like that attempt made as opposed to just plopping that strand on the print.

RE: Color Change extrudes a small piece of filament moving back to the print.

How do you make it print to the cube first?

Posted by: @foxrun3d

I tend to add a tiny cube to the print and make sure in the preview that the slicer fills it in first on color changes. I found this to be the best way to avoid those "droppings"

RE: Color Change extrudes a small piece of filament moving back to the print.

How do you make it print to the cube first?

That is a tricky one. I wish I had a clear-cut recipe for it but at least in my hands it's been largely try and error. Changing the order of objects in the object list on the tight combined with rearranging objects and checking what gets printed first in the preview usually does the trick. I also have a stored template project that is set up correctly and use replace STL but when you have to add more objects to it it's back to try and error.  

RE: Color Change extrudes a small piece of filament moving back to the print.

AFAIR this extra extrusion after the purge was explained by someone from Prusa to build back/stabilize the nozzle pressure. I use the last bit of purge extrusion to hold onto the pressure purge bit, and yank both off when the nozzle is about to touch the printed part.