Over/under extrusio...
 
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Over/under extrusion after purge investigation.  

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BigBrain3D
(@bigbrain3d)
Supreme moderator Admin
Joined: 1 year ago
Posts: 198
05/04/2020 8:36 pm  

There have been reports on thingiverse of under/over extrusion after purge blobs are created. This is using PrusaSlicer and the retractable purge mechanism.

This thread is a for investigating the cause and finding a solution to this problem.

"It ALWAYS under extrudes after the blob on the first layer. But then it OVER EXTRUDES after that."-Jagr200

"At the first 2 layer i have under Extrusion and with the next layers massive over Extrusion."-MagicBugsBunny

" it extrudes the first layer correctly, AND changes tools/blobs correctly, but then the second layer does not extrude correctly at all. Filament simply doesn't get put down."-alicedprojects

"has anyone been able to figure out how to stop the printer from missing filament after changes? When I use the mechanism the next mm or so of printing is missing. I've tried to play around with the retraction settings with no luck."-Trutey

Attached is a picture of the issue on a 2 color safety pylon.

This topic was modified 7 months ago by BigBrain3D

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ODINITE
(@aaron-c-jensen)
New Member Customer
Joined: 8 months ago
Posts: 1
06/04/2020 5:53 am  

Off the top of my head, an accumulating error potentially points at an issue with relative mode vs absolute mode:

[ a quick recap of what I am talking about ]

https://www.sublimelayers.com/2017/10/to-extruder-relative-or-not-to-extrude.html

 

Another possibility is extruder temperature and retraction settings causing oozing:

[ https://www.matterhackers.com/articles/retraction-just-say-no-to-oozing ]

 

However, without seeing some of the source files (slic3r version, input file to slic3r, slic3r settings, gcode) to properly debug, I'm grasping at straws. I'd love to take a look if some more information was available.

 

All the best,

ODINITE


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AliceDProjects
(@alicedprojects)
New Member
Joined: 7 months ago
Posts: 1
07/04/2020 1:41 am  

Hi, same AliceDProjects from Thingiverse.

Thanks for investigating this issue.

First of all, one thing that I can see as an immediate issue is that Thingiverse's new UI has completely broken the GCode formatting on the part description on their site. It's completely unusable/unreadable.

What really needs to happen is that someone needs to create a GitLab Snippet or GitHub Gist (or heck, even a full repository) so nobody has to go hunting for the "correct" version of the GCode.

I just got my Prusa MK3S printing correctly again after a rebuild and it's going to be a while before I attempt installing the RPM again. Hopefully by then, a Snippet/Gist will be up with the correct GCode.

It's really easy, you can do it directly from a web browser. Just read: https://docs.gitlab.com/ee/user/snippets.html


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BigBrain3D
(@bigbrain3d)
Supreme moderator Admin
Joined: 1 year ago
Posts: 198
04/05/2020 6:40 pm  

@alicedprojects,

The gcode and assembly instruction have now been centralized here.

 


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Perro!
(@andynewlands)
New Member Customer
Joined: 4 months ago
Posts: 1
05/07/2020 4:14 pm  

I have a similar issue with over-extrusion, when using the RPM (hardward from BigBrain3D - other parts printed myself), with Prusa Mk3+MMU2S: I'm getting bulges/blobs on the corners of a 15x15x10 (15% infill) multi-colour slab, after the first few layers.  I do not encounter the same issue when using the normal wipe tower.

The RPM functions mosty fine (only ocassional 'snagging' of the blob), but I think the purge material is building up until it touches the hotend nozzle which, I'm begining to suspect, may be causing a slight excess pressure in the extruder which, in turn could cause over-extrusion just as printing resumes (just a thought).

 


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Daniel Martin
(@daniel-martin)
Active Member Customer
Joined: 8 months ago
Posts: 16
12/07/2020 7:23 pm  

hi, I have been having the same issues with when there is a colour change there is blobs appearing on my models this seam to be because by the printer over extruding after the purge is done.

 

 

https://www.dropbox.com/sh/uhvy2quoz1763zs/AAB6VhQRVHumA9B_aQ7hYGsea?dl=0


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Pavel Strzinek
(@pavel-strzinek)
New Member Customer
Joined: 7 months ago
Posts: 2
14/07/2020 7:37 pm  

Hello, I experienced under/over extrusion too and fixed it with this G-code addition placed at the end of Tool change G-code, just before the last {endif}. You can experiment with different G1 E values to your liking:

;*************** Prevent under-extrusion on first layer and over-extrusion on other layers *******
{if layer_num == 0}
M106 S0 ;turn off fan
G1 E1.1 F2100 ;deretract extruder
{else}
G1 E-0.8 F2100 ;retract extruder
M106 S[max_fan_speed]
{endif}

;*************** End Prevent under-extrusion on first layer and over-extrusion on other layers *******
This post was modified 4 months ago by Pavel Strzinek

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BigBrain3D
(@bigbrain3d)
Supreme moderator Admin
Joined: 1 year ago
Posts: 198
15/07/2020 4:16 pm  

Hi @pavel-strzinek,

Thank you for this information. We've updated the scripts on the instruction page with your code.

 

 


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Piotr Apanowicz
(@piotr-apanowicz)
New Member Customer
Joined: 1 month ago
Posts: 1
27/09/2020 4:29 pm  

I finally got RPM to eject blobs properly.  Now printing and as the layers progress the overextrusion blobs become more and more visible even with the code that is supposed to be preventing it.   Any other fixes I can try? 


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