How do I turn off that giant "blob" production at the start of the print prior to the purge?
 
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How do I turn off that giant "blob" production at the start of the print prior to the purge?  

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nCeon
(@nceon)
Active Member
How do I turn off that giant "blob" production at the start of the print prior to the purge?

Ever since I have upgraded to the MMU2s all of my gcodes are produced from Slic3r with a huge blob produced prior to the purge line. Normally this is OK and actually seems to clean the nozzle but I am trying to print with a flexible filament and the absurdly fast extrusion during this step screws up the extruder 100% of the time (the flexible filament gets all jammed up)

I have gone into the gcode and there is no mention of this step that I can find.

 

How can I stop this?

Best Answer by Lichtjaeger:

I assume we are talking about this spot:

  • We start at { x=0; y=-3mm; z=0,4mm }.
  • If we look at the start gcode, the first purge command will be "Tc" (load to the nozzle). This is where the blob is.
  • Next, there is a quick move to { x=55mm} by the line "G1 X55.0 F2000.0" followed by going down to { z=0.3mm } by "G1 Z0.3 F1000.0".
  • Now the real purge line will start by "G1 X240.0 E25.0 F2200.0".

In earlier versions, even those first 55mm were drawn as a line. But I don't know if it is a slicer or a firmware thing.

But the problem with flex is how this "Tc" works at the moment. The filament is first pushed with rapid movements, then pulled and eventually pushed through the nozzle.

My tip for working with flexible materials: Do not slice in MMU single mode. Slice for MK3/2.5 without MMU and use the "load to nozzle" command of the panel. So it will not make this weird E moves when you start your prints. Don't forget to use "unload" when you're done with the flex material. 

Posted : 28/05/2019 5:31 pm
nCeon
(@nceon)
Active Member
Topic starter answered:
RE: How do I turn off that giant "blob" production at the start of the print prior to the purge?

For now my solution is to start the print, let it tangle all up in my bondtech gear during the "giant blob" phase, then pause the print and untangle it before restarting the print. It would be great to be able to avoid this....

Posted : 29/05/2019 2:37 am
PJR
 PJR
(@pjr)
Antient Member Moderator
RE: How do I turn off that giant "blob" production at the start of the print prior to the purge?

Are you using the Mk3S+MMU2S profile?

The "S" version has a shorter path between extruder and nozzle and will over-extrude on loads if you slice with the non-"S" profile.

 

Peter

Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…

Posted : 29/05/2019 8:32 am
nCeon
(@nceon)
Active Member
Topic starter answered:
RE: How do I turn off that giant "blob" production at the start of the print prior to the purge?

I am using the MK3SMMU2S profile and this is not extrusion on load (that works fine).

This step happens even if I have preloaded the filament to nozzle. The extruder will go to "home" and down to the plate, and extrude a big blob for several seconds prior to beginning the purge line, it is actually pretty effective at cleaning off the nozzle (which I assumed was it's purpose) when I am not using flexible filament.

Is this not normal behavior? This has happened with both Slic3r and the new Prusaslicer as well as 2 versions of the printer firmware.

This post was modified 5 years ago 2 times by nCeon
Posted : 29/05/2019 11:39 am
PJR
 PJR
(@pjr)
Antient Member Moderator
RE: How do I turn off that giant "blob" production at the start of the print prior to the purge?

Can you post a photo of the blob and also, can you attach a zipped G-code file which has the problem?

 

Peter

Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…

Posted : 29/05/2019 2:04 pm
Lichtjaeger
(@lichtjaeger)
Noble Member
RE: How do I turn off that giant "blob" production at the start of the print prior to the purge?

I assume we are talking about this spot:

  • We start at { x=0; y=-3mm; z=0,4mm }.
  • If we look at the start gcode, the first purge command will be "Tc" (load to the nozzle). This is where the blob is.
  • Next, there is a quick move to { x=55mm} by the line "G1 X55.0 F2000.0" followed by going down to { z=0.3mm } by "G1 Z0.3 F1000.0".
  • Now the real purge line will start by "G1 X240.0 E25.0 F2200.0".

In earlier versions, even those first 55mm were drawn as a line. But I don't know if it is a slicer or a firmware thing.

But the problem with flex is how this "Tc" works at the moment. The filament is first pushed with rapid movements, then pulled and eventually pushed through the nozzle.

My tip for working with flexible materials: Do not slice in MMU single mode. Slice for MK3/2.5 without MMU and use the "load to nozzle" command of the panel. So it will not make this weird E moves when you start your prints. Don't forget to use "unload" when you're done with the flex material. 

Posted : 29/05/2019 2:42 pm
nCeon and liked
nCeon
(@nceon)
Active Member
Topic starter answered:
RE: How do I turn off that giant "blob" production at the start of the print prior to the purge?

 This is exactly the issue and the solution I was looking for.

Thanks lichtjaeger!

Posted : 29/05/2019 3:06 pm
Hans
 Hans
(@hans-2)
New Member
RE: How do I turn off that giant "blob" production at the start of the print prior to the purge?

Has there been any improvement to the solution since 2019, I have this problem still, I just loosen my extruder gear tension which  sometimes works but more often it fails.

Posted : 08/01/2022 7:03 pm
toy4x4 liked
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