Extrusion multiplier seems to be ignored  

RE: Extrusion multiplier seems to be ignored

I've re-checked several times and I'm sure I'm not imagining it! 

My PrusaSlicer is outputting bgcode by default (because my printer is Prusa CoreOne?) so I've used Prusa G-code viewer to convert the bgcode file to ASCII and then searched for "M221", and I see "M221 S100" even though my PrusaSlicer filament extension multiplier is 0.6.  Obviously I can edit it to "M221 S60" and then convert the file back to bgcode, but it's simpler to tune it on the printer.  But why should I have to?  Is nobody else experiencing the same?

RE: Extrusion multiplier seems to be ignored

Don't do that.  If you set your extrusion multiplier in the software Prusa Slicer filament profile to 0.6 and you ALSO set M221 S60 then you are setting it twice (0.6 *0.6=0.36).  

By setting the extrusion multiplier in the filament settings then the actual extruded amount in the generated gcode is reduced.  So the E values for each extrusion move are adjusted.  It DOES NOT set the M221 value for that.  By setting M221 you are instructing the firmware of the printer to reduce those E values 'on the fly'.  Do one OR the other.  It is quite common to set the M221 value back to a known starting point at the end (or start of a print)  and that is part of a Printers Start or End gcode block.  So yes it being reset is probably expected. The M221 flow rate is persistent across prints and only lost if you power cycle the unit which is why its common to reset it.  

I don't have a Core 1 but installing the printer profile shows that the Start GCode block does have the line to reset the flow back to 100% included.

RE: Extrusion multiplier seems to be ignored

Thanks Neophyl for your explanation.  I see now the 'M221 S100' line in the gcode, after all the 'thumbnails' (whatever they are!).  So you're saying that's my printer's default Start code?  That's exactly what's overriding my filament extrusion multiplier setting, so why do they program it to do that?

I've checked the 'Printers' tab in PrusaSlicer and I can't find any way to tell it to stop overriding my extrusion multiplier setting.

RE: Extrusion multiplier seems to be ignored

Its programmed that way as you should be setting the extrusion multiplier in the filament settings.  That's what its there for on a per filament basis.  For many/most filaments leaving it at 1 is needed.   For example if you changed it to 0.6 for printing LWA and then swapped to say normal PLA then you would be massive under extruding.  By configuring it per filament and leaving the printer at M221 S100 flow rate its correct for each print as the adjustments is baked into the gcode.  Not to mention that something like LWA will probably also need other settings adjusted too.  Far better to tune the filament profile properly than change the printer profile.  

As I said before if you have your LWA filament profile set to an EM of 0.6 you don't and shouldn't set it via M221.  The amount of plastic extruded will already be reduced on each gcode line.  M221 is for quick and dirty adjustments or for where an extruder is so mechanically out of tolerance that its is consistently over/under extruding with all filaments.  Although in that case the usual remedy is to tune the steps per mm rather than mess with M221.

Altering your printers start or end gcode is not advised unless you know what you are doing and so you cant see those settings unless you are in expert mode.  Like many other settings.  

RE: Extrusion multiplier seems to be ignored

That's exactly the point Neophyl.  I am setting the extrusion multiplier to 0.6 in the Prusaslicer filament profile before slicing but the bgcode file that's created contains only "M221 S100" in the start sequence, and no subsequent command line to reduce the EM to 0.6 or 60%.

RE: Extrusion multiplier seems to be ignored

I think you have missed the point of my posts.  Setting the Extrusion Multiplier does NOT set M221.  Its is not supposed to alter that value, it never was supposed to.  That is not the mechanism to reduce the extrusion rate on a sliced file.

With the Filament Profile configured 0.6EM, for each and every extrusion line in the gcode the E value gets reduced individually.  For example if you were to slice a basic cube with an EM of 1.0 you would get something like the following as an example -

;TYPE:Perimeter
;WIDTH:0.449999
G1 F2616
G1 X113.132 Y116.868 E.80343
G1 X113.132 Y93.132 E.80343
G1 X136.868 Y93.132 E.80343
G1 X136.868 Y116.808 E.8014

The same cube with a filament Extrusion Multiplier of 0.6 contains

;TYPE:Perimeter
;WIDTH:0.449999
G1 F2616
G1 X113.132 Y116.868 E.48206
G1 X113.132 Y93.132 E.48206
G1 X136.868 Y93.132 E.48206
G1 X136.868 Y116.808 E.48084

Notice ALL the E values are reduced in the file.  If you care to do the math you will see the values are reduced by 0.6 (rounded up from .482058 to .48206).   This is with the EM set to 0.6 and the M221 set to S100.  The M code is NOT involved at all in reducing extrusion in normal use.  It is only used after the fact on an already existing gcode/bgcode file for a quick and dirty adjustment.

If you were to ALSO set the M221 value to S60 then you would get 0.6 of those reduced values so the real extrusion factor would be 0.36 of the normal value with an EM of 1.0 .  Do you see the mechanism now ?

Please do some research on how a slicer and Gcode works before playing with settings and values hidden in the expert sections.  

RE: Extrusion multiplier seems to be ignored

You're right, I have misunderstood thus far.  So the PrusaSlicer EM is not modifying or setting M221 in the gcode -- it is modifiying the E function of each individual line of code.  Thanks for your patience in clearing that up for me.

So, since I'm setting EM to 0.6 and then also tuning it to 0.6 in my CoreOne+ control panel to get a good print with this particular filament, it seems like EM 0.36 should be the correct value with no adjustment in the control panel.

I must admit I've got so used to things working straight out of the box (I don't know why I didn't have to make those adjustments when using this filament with my Ender3) that I haven't delved too far into slicing theory.

RE: Extrusion multiplier seems to be ignored

I've not used LW-PLA as I have never had a use case for it but I am familiar with the literature on its properties.

I understand that its foaming properties are tied heavily to temperature. It stands to reason that different hot end designs with different melt zone distances etc will cause the filament to react differently in those different printers.  

0.36 EM does seem to be on the extreme side of things, but I am a big believer in real world testing to see what actually works for a particular setup so if you have performed your tests and that is what it works out at for you then so be it.  

Most filament manufacturers data (when its even supplied) on print settings are based on whatever hardware they have used.  Usually they don't mention what setup they used for their testing.  Given that Enders are a VERY common printer choice being cheap and plentiful it wouldn't surprise me if the recommendations are based on a printer which is an Ender (or similar given how many copies there are too).  You just never know.

Same with the supplied Prusa Profiles, the prusa brand filaments generally have more testing on one of their own printers but other brands they generally just use manufacturer data or sometimes user supplied data.  It is why I never ever rely on either, I always do some simple test prints first with a new filament to see if my own usual 'defaults' are suitable.  Can't beat empirical data.  There are large differences between by old Mk3 with steel nozzle and my sv08 for the same filaments.  So many factors.  

RE: Extrusion multiplier seems to be ignored

Thanks again Neophyl.  I agree 100% that you can't beat empirical data.  So I'll be slicing a test piece with EM 0.36 and work forwards from there.

RE: Extrusion multiplier seems to be ignored

Posted by: @abenn

[...] My PrusaSlicer is outputting bgcode by default (because my printer is Prusa CoreOne?) [...]

Not because your printer is model XY...because you didn't change the slicer configuration: https://help.prusa3d.com/article/binary-g-code_646763

😉

RE: Extrusion multiplier seems to be ignored

Posted by: @alphasigma

Not because your printer is model XY...because you didn't change the slicer configuration: https://help.prusa3d.com/article/binary-g-code_646763

Thanks alphasigma.  A while back I tried to print one of my old .gcode files and got an error message that it was incompatible, so I assumed that bgcode had been selected by the slicer to be compatible with the selected printer.  Presumably the incompatibility was something else, so I'll output as gcode next time I slice a file, and see what happens.