Extrusion Multiplier -- Prusa Summer Update -- I'm Confused
The "Prusa Summer Update" https://www.prusaprinters.org/prusa-research-summer-update-2018/
references this" Common Problems" video https://www.youtube.com/watch?time_continue=196&v=Lsa-PXAXdKY
which in turn references this Extrusion Multiplier Calibration article https://help.prusa3d.com/l/en/article/d9j1xdg7vj-extrusion-multiplier-calibration
I followed the steps to measure the extrusion as explained in the article and got a wall thickness of 0.43mm which the instructions told me to compare against the print settings wall thickness which is at the default 0.45mm. I'm then to adjust the filament multiplier to correct for the difference.
HOWEVER:
The G-Gode included in the above article, AND the Slic3r PE MK3 Printer Profile Start G-Code specify M221 95 which reduces the filament flow to 95%.
0.45mm x 0.95 = .4275 -- or in other words the thickness I measured.
Perhaps I'm overthinking things, but something just doesn't seem right.
Re: Extrusion Multiplier -- Prusa Summer Update -- I'm Confused
The M221 adjustment line has been added by Prusa to Slic3rPE at the end of the startup gcode (Printer Settings->Custom G-Code->Start G-code). From my reading on the issue, Slic3r tends to over-extrude, so this is a blanket fix albeit a kludgy one. My 1st inclination was to remove it, but then I thought Prusa might incorporate the fix more gracefully in a future release, so I've left it. My own adjustments are in addition to that adjustment, and should still work if they tweak the Slic3r algorithm in a future release. So yes, you might end up tweaking on top of their tweak but theirs may be tougher to remove at some point in the future.
Re: Extrusion Multiplier -- Prusa Summer Update -- I'm Confused
> From my reading on the issue, Slic3r tends to over-extrude, so this is a blanket fix albeit a kludgy one.
It is not Slic3r that over-extrudes. In my opinion, the plastic is too viscous to completely fill the gaps between the extrusion lines, so there will be some air bubbles trapped, and the excess material would overflow. Therefore it is safer to account for the air gaps with a tiny bit lower extrusion.
Re: Extrusion Multiplier -- Prusa Summer Update -- I'm Confused
Simplify 3D has been doing this .95 thing for years if my memory serves me. I recall a video from Thomas Sanladerer discussing this point quite some time ago. The code is there and can be changed. I believe it does the .95 change for .20 layer height only by the way.
Re: Extrusion Multiplier -- Prusa Summer Update -- I'm Confused
that sounds correct. for higher extrusion crosssections (thick nozzles, thick layers) the relative volume of trapped bubbles is tiny, so there is no need to correct for them.