I've recently been struggling to determine the maximum volumetric flow capability of my hotend using the spreadsheet produced by Stefan of CNC Kitchen. Firstly, Stefan's spreadsheet doesn't work with delta printers (or any other type that has X=0, Y=0 in the centre of the build plate). Secondly, having written my own spreadsheet based on Stefan's, my next problem has been that all the printed "nuggets" were the same size and almost half the weight that they should be with a range of volumetric flows from 6mm³/s to 20mm³/s. Visually, the extruder was spinning at the same rate for each setting.
Looking further, I discovered that, for RRF2.03 and later (I'm on 3.4.0), M203 used to set maximum feed rates, has a default minimum feed rate of 30mm/min. This can be changed with the I parameter (that's capital i) once one knows of its existence (it's clearly shown in the Duet3D GCode dictionary!) At the default feed rate, with Stefan's method, all volumetric flows will be constrained to a minimum of about 24mm³/s, which is optimistic for a V5/V6 hotend (hence my 50% extrusions)! This will apply to all printer types running RRF2.03 and later, not just deltas.
I've now set M203 I6 and the gcode runs my extruder at much more sensible speeds, producing printed nuggets with weights that are where I would expect them to be (and I now know how bad my hotend is!)
Hopefully, this note will help others.
