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Flow rate in machine settings


batesman
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Posted · Flow rate in machine settings

Howdy!

 

On my Ender 2, I need to set the flow rate in Cura 3.6 to 104.5%. No problemo, right? Well, instead of doing it on a per print / per profile basis, I'd like to set it and forget it. So I learned that I can use M221 S104.5 in Marlin to set the flow rate directly in the Gcode of the printer profile. That way, my flow rate is set for each print right? Cool. Well then I started thinking (and this is where I mess myself up)..."If I set the flow rate percentage to 104.5% in the machine settings, but then the flow rate is defined as 100% (default value) in the slicer, which one wins?"

 

Any ideas on this? Do Gcode settings in the machine profile take precedence over what is defined in the slicer profile? How can I accomplish my goal and still be lazy?

 

Thanks in advance!

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    Posted · Flow rate in machine settings

    Got my answer (don't know why I didn't think of this before). I set the flow to 80% in the profile and left the machine settings at 104%. Then I printed a 25 mm cube with .48 wall thickness. The extruded wall thickness was .40 so...There you go. Profile settings override machine settings.

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    Posted · Flow rate in machine settings

    No.  They multiply together.

     

    So in cura if you set flow to 80%, Cura multiplies all the E values (extruder positions) by 80% such that you get 80% flow.

     

    With the M221 gcode, Marlin (the firmware on the computer) multiplies each of these E values again by the current Marlin flow value.  The Marlin flow value of course is set by M221.

     

    If you go into the TUNE menu on Ender (does ender have a tune menu?  Probably). and adjust the flow, it will set the Marlin flow value at that moment and forget.  If later an M221 value appears - that will override.  If later you set it in the TUNE menu again, then at that moment it will override again.

     

    But the flow in Cura is baked right into the E values.

     

     

     

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    Posted · Flow rate in machine settings

    Yup  I set Cura flow to 100% and then before starting my print I set flow in Repetier Host to 70% and after the first layer I set Repetier Host back to  100%, so I get the 1st layer at 70% and everything else at 100%

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    Posted · Flow rate in machine settings

    Again, no.  It's not overriding.  They are multiplying.  104% times 80% gives you 83% which is close enough to 80% that you don't notice the difference.

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    Posted · Flow rate in machine settings

    So the M221 is telling the printer to multiply all the extruder moves by 104%.  The 80% in cura affects the actual E values (the machine doesn't know about the 80% as the 80% part is baked right into the extruder positions in the gcode).  And cura doesn't know what M221 does.

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    Posted (edited) · Flow rate in machine settings

    I have a related question:

    Suppose in my Ender3 I set M221 S85 in the cura machine code, to set the flow rate to 85%, then use the hand wheel on the printer to select  "Tune" and then "Flow" and reset it from 85% to, say, 95%, then what flow rate do I wind up with, 95%, or .85 x .95 = .8075 ~ 81%?

    Note: And, does it matter if I print via USB or if I use an SD chip to carry the cura-generated code to the printer port?

    I have been ass-uming that I would get 95%, an increase of flow rate (which is reflected in the printer setting in the tune/flow menu), but now I wonder if it would actually decrease due to the potential multiplication of the two numbers.

    I guess this is more an Ender3 question than Cura, but I think it is relevant to the original question starting this thread.

    What say you?

    Edited by csterlin
    Added note,,,
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    Posted · Flow rate in machine settings

    I can't answer your override/multiplier question directly, but I have been following the excellent guide at https://teachingtechyt.github.io/calibration.html#flow which has you print a topless cube with a single wall. Adjust the layer width to match your nozzle (and make some other adjustments), then print and average the measure of the thicknesses of all the walls. Plug in that number, and the webpage will calculate your needed flow rate.

    You could use this to determine the override/multiplier issues.

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    Posted (edited) · Flow rate in machine settings

    "...which has you print a topless cube with a single wall."

    I would respectfully disagree.

    When the ratio of "Volume of Extrusion Out" to "Volume of Filament In" is 1:1 you are at 100% flow.

     

    1.75 diameter filament has a cross sectional area of PI x r² = 2.405mm²

    The cross section of any extrusion is "Line Width"  x "Layer Height".

     

    When a "single line wall" is extruded it is unconstrained on both sides and so it spreads out from the perfect "rectangular" shape into a flattened oval.  It WILL be wider, but the volume is correct at "100% Flow" provided two things have been done correctly:

    1. You have calibrated the E-steps on the printer.
    2. You have measured the exact diameter of the filament and entered that number in the "Diameter" box of the Printer Settings in Cura ("Printer Settings" must be loaded from the MarketPlace).

    An extrusion that is 0.20 high x 0.40 wide x 100.00mm long is 8mm³.

    The filament is 2.405mm³/mm

    8mm³ / 2.405mm³/mm = 3.32640mm of filament.

    If I tell Cura (and consequently the printer) to run at 85% flow then where does that missing 15% of the volume come from?  It can only come from the Line Width.


    To calibrate the flow - Calibrate the E-steps, get the filament diameter right, and then....

    Load a regular flat topped calibration cube in Cura and scale the cube to 75 x 75 x 1mm tall and slice it with all Cura flows at 100% and then print it.  Look at the top skin with a decent magnifying glass (a microscope is best) and it will tell you if you need to tweak the "Flow".  Trust your eyes.  If it looks good, it's good.

     

    If I tell Cura to use 0.40 line width:  The index distance between the extrusions of a skin will be 0.40mm.  If I also tell Cura to run at 85% flow (because a single wall "calibration" cube told me to) then each extrusion will be 0.34mm wide.  That is going to leave a noticeable gap between the lines of extrusion and is by definition "under-extrusion".

     

    But all your single wall prints will have precisely .40mm thick walls.

     

     

     

    Edited by GregValiant
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