Max extrude only velocity

General Discussion
1 
#max_extrude_only_velocity:
#max_extrude_only_accel:
#   Maximum velocity (in mm/s) and acceleration (in mm/s^2) of the
#   extruder motor for retractions and extrude-only moves. These
#   settings do not have any impact on normal printing moves. If not
#   specified then they are calculated to match the limit an XY
#   printing move with a cross section of 4.0*nozzle_diameter^2 would
#   have.

I don’t really understand this. Can someone explain how the maximum velocity gets calculated on a printer with a .4mm nozzle?

2

Max limits for extrusion without movement e.g. load/unload filament?

3

Yeah how do I actually calculate the maximum velocity? (for retraction purposes)

4

This question doesn’t make any sense. If you want to retract at 50mm/s, then set max_extrude_only_velocity to 50.

5

What I’m asking is how is the default calculated?

6

max_velocity * ((4 * nozzle_diameter^2) / filament_area)

Example: 300 * (.64 / 2.405) = 80mm/s
300mm/s max velocity, 0.4mm nozzle, 1.75mm filament diameter

EDIT: Fixed the formula. You can see it in extruder.py.

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