1.2mm³/s minimum extrusion speed?

[Adam - V3D]

Through recent experiments with extrusion i've come across a strange issue with minimum extrusion rates and unsure which parts of the system causes it.

As you can see from the chart below. The target extrusion time for all tests was 5 seconds but only tests 7 onwards lasted for 5 seconds as others seem to hit minimum extrusion limits and were sped up to 1.2mm³/s and thus completed faster.

Seems like its still plenty fast enough for a stepper motor. interpolation is enabled so there are plenty of microsteps available. I'm pretty stuck for ideas where this could be coming from.

G-code and firmware attached below.
config.g
Low Flow Limit Test.gcode

[dc42]

@adam-v3d the minimum feed rate for any move defaults to 30mm/min (0.5mm/sec). You can use the I parameter of M203 to reduce it, with an absolute minimum of 0.6mm/min (0.01mm/sec). Send M203 without parameters to check what the minimum feed rate is set to.

[Adam - V3D]

@dc42 Perfect, this is exactly the thing. Thankyou!