This is the honest ceiling on print speed, and it comes before the flow multiplier for a reason: measure a wall while printing faster than the hotend can melt and you are measuring the melt limit, not your flow number. A hotend can only melt so much plastic per second; past that it under-extrudes regardless of what number sits in the slicer speed field. Beginners chase speed here and blame the extruder.
Phase 3 — Flowabout 30 minper filament
How to do it
Print a test that ramps flow rate progressively.
Find where the extrusion first goes thin or rough.
Set the filament max volumetric flow to roughly 90% of that.
Check the PRINTER or extruder max volumetric speed too. The slicer applies whichever of the two is lower, so a stale printer-level limit quietly caps every filament you own.
Sanity check: speed × layer height × line width must stay under this number.
Keep the next step, the flow multiplier, comfortably under this ceiling — otherwise you will be measuring this limit instead of that number.
How to read the result
The flow rate, in mm³/s, at which extrusion first becomes visibly inconsistent. Use about 90% of it.
Your slicer may do this for you
OrcaSlicer has a max volumetric speed test under Calibration.
Redoing this invalidates
Calibration is a chain. Change this and the results below were measured against the old value: