Under extrusion after zhop
Hello,
I am having trouble getting clean prints after my MMU upgrade, right now it appears that there is an underextrusion problem after a zhop - see attached photos. I am using the default setting in Slic3r for MMU single extruder and any suggestions are greatly appreciated.
thanks,
Nathan
Re: Under extrusion after zhop
I am having a similar issue and I would like some feedback also.
I have a Prusa i3 mk2s with MMU with latest drivers and firmware.
I noticed that whenever there is a retraction the extrusion afterwards appears to start late. That is to say that material does not come out of the nozzle when its supposed to, but later, resulting in under extrusion right after a unretract. Attached you will find the .stl of a file i created to test this, the gcode created through Prusa Control and one of the photos i took of the results.
Reading though the gcode it seems to me that the retract commands are excessive and/or wrong but I'm no expert so I'm asking for your opinions here.
Below is the start gcode where it makes the priming line and then starts the skirt.
G1 Z0.250 F7200.000
G1 X50.0 E80.0 F1000.0
G1 X160.0 E20.0 F1000.0
G1 Z0.200 F7200.000
G1 X220.0 E13 F1000.0
G1 X240.0 E0 F1000.0
G1 E-4 F1000.0
;BEFORE_LAYER_CHANGE
;0.2
G1 Z0.200 F7200.000 ; move to next layer (0)
;AFTER_LAYER_CHANGE
;0.2
G1 E-4.00000 F3000.00000 ; retract
G1 Z0.800 F7200.000 ; lift Z
G1 X54.042 Y63.005 F7200.000 ; move to first skirt point
G1 Z0.200 F7200.000 ; restore layer Z
G1 E4.00000 F3000.00000 ; unretract
M204 S1000 ; adjust acceleration
G1 F1800
G1 X54.663 Y62.526 E0.02461 ; skirt
G1 X55.407 Y62.276 E0.02461 ; skirt
G1 X195.787 Y62.246 E4.40153 ; skirt
It seems to me that it retracts twice E-4 right at the end of priming and right before moving to the skirt starting point and then the unretract to start the skirt is lacking material.
E-4(retract after prime)->
E-4(retract before skirt)->
E4(unretract,is currently at -4mm, no material coming out)->
E0.02461(is at -3.97539,no material coming out)->
E0.02461(is at -3.95078, no material coming out)->
E4.40153(ends at +0.45075 so should have plastic extruding at the end of the move.)
Am i following the gcode correctly? it feels like something similar goes on throughout the print. What is wrong here?
Re: Under extrusion after zhop
I can see this happening with my MMU also. After the initial purge the skirt is not drawn and material starts to flow first when the actual object is drawn. I really do not know if this is happening during the print also but I have serious issues with print quality (same as many in the blockage-thread). Have you talked with the support about your findings? It looks like a patch is needed
Re: Under extrusion after zhop
I have sent them an email describing the issue with a link to this thread. Let's see what the verdict will be.
Re: Under extrusion after zhop
What I have found through some experimentation to mitigate these issues and what I have noticed is, I had to completely remove the final E-4 in the starting gcode to remove the starved extrusion at the beginning of the print and I had to lower general retraction to 2.8mm. Anything near or above 4mm results in starved extrusions especially in small moves. Also changed retract speed to 40mm/s and deretract to 20mm/s.
Still in contact with Prusa about this as well so will update from there when I have something usefull.
Re: Under extrusion after zhop
I think the latest build of Slic3r has corrected the extra E-4. I have verified that it is not part of the gcode in my calibration sample
"Removed the hard-coded priming line when both single_extruder_multi_material and wipe_tower are enabled,
and the print prints with a single extruder only"
https://github.com/prusa3d/Slic3r/releases
Re: Under extrusion after zhop
In i3 MK2 MM Single mode profile it is still there, producing the same results for me after testing it. I still have to reduce retractions and completely remove the last E-4 of the starting gcode to avoid delayed extrusions after retracts during print and delayed extrusion after wipe line.
Re: Under extrusion after zhop
I think the latest build of Slic3r has corrected the extra E-4. I have verified that it is not part of the gcode in my calibration sample
"Removed the hard-coded priming line when both single_extruder_multi_material and wipe_tower are enabled,
and the print prints with a single extruder only"
https://github.com/prusa3d/Slic3r/releases
That version definitely fixed the E-4 issue but otherwise is super buggy unfortunately. Seems like there were a lot of good improvements in there related to the multi material stuff. I hope they clean it up soon 🙂
Re: Under extrusion after zhop
I have exactly the same problem but with a Prusa Clone with a single extruder... i get Underextrusion exactly like in your photos after retractions/ travel moves... i have 0.8 mm retraction distance and 50mm/s retraction speed... the only way to mitigate this is to use Restart distance after retract... but for me it is a Workaround... did you found a solution ?
I tried several retraction settings...
also i found the retraction in the G code a bit weird.
I am getting G1 E-0.8 F3000 for a retraction
then a G1 E 0.8 F3000 for deretract
but then the retraction is not E-0.8 anymore but just E ( X-0.8) where X is the Last extruded g code line...
I am also using Slic3er Prusa Edition