Volumetric Extrusion settings

I want to start playing with the volumetric extrusion capabilities of Marlin, but it's a little unclear to me after reading what little bit of info is out there exactly how to set it up.

Triffid Hunter's calibration guide has a small updated section on it but it appears that was written right after Marlin supported it and possibly before Slic3r did.

I'm using Marlin bugfix-1.1.x and Slic3r 1.2.9.

From what I can gather, setting Slic3r to use VE under "Printer Settings->General->Use Volumetric E" will generate gcode that contains the extrusion amount in mm^³.

My issue is what exactly to put in the M200 command for filament size for Marlin. The small blurb in the Marlin docs make it sound like it should be my actual filament size (i.e. 1.75), but the RepRap gcode docs page seems to indicate it should be the generic 1.128 (sqrt(1 / pi) * 2 = 1.128 for an extrusion multiplier of 1).

So, I'm not sure whether to issue a

M200 D1.75

or

M200 D1.128

M200 D1.75

but actually measure your diameter, unless you have a perfect filament supplier...

[marlinfw.org]

Quote
Dust
M200 D1.75

but actually measure your diameter, unless you have a perfect filament supplier...

[marlinfw.org]

Thanks Dust, I will do that.

Bruce

Ok, one more question. I've determined that my maximum extrusion speed with no slipping is 5.3 mm/s at my ABS print temp of 245C. How do I convert that into mm^3/s for use in the Slic3rPE max volumetric speed in the filament settings?

If only talking about the extruder, assuming a 0.4mm nozzle, use the formula:

v=s*PI*r^2
therefore
mm^3 = 5.3*PI*(0.4/2)^2
= 0.666 mm^3

If someone else has better solution, I'm genuinely interested. I usually calculate volumetrics using run speed, so v = lws.
For example, if I want to run at 30mm/s with a layer height of 0.3mm and an extrusion width of 0.5mm, I'll set my volumetric speed to 4.5mm^3/s.