Move exceeds maximum extrusion (AA mm^2 vs BB mm^2)

Knowledge Base
1

Move exceeds maximum extrusion (AA mm^2 vs BB mm^2)

Background

Klipper has a safety mechanism that checks if a single move extrudes an unhealthy amount of filament or if the extrusion of multiple moves add up to such an amount.

This limit is calculated according to following formula:
Maximum Extrusion = 4.0 x Nozzle_Diameter^2 = 4.0 x 0.4^2 = 0.640 mm²

For the standard 0.4 mm nozzle the default values calculates to:
Maximum Extrusion = 4.0 x 0.4^2 = 0.640 mm²

Reasons

  • Misplaced M83 (Relative Extrusion). This by far the most common reason
  • Too extreme prime lines, e.g. high E values across a short movement
  • Too extreme purge settings during filament change
  • Weird Slicer settings affecting the extrusion or flow rate
  • Mismatching extrusion modes (absolute / relative) between slicer and Klipper
  • Changed nozzle for a higher diameter but not adapting the configuration

Potential solutions

  • Usually working with M82 (Absolute Extrusion) is preferred
    • Check start-gcode, start macro etc. for M83 commands and remove them
    • Check slicer setting and verify that the slicer is set to absolute extrusion
  • Check prime line / purge gcode if a high volume is extruded over a short distance
  • Check for slicer settings that may affect the extrusion logic
  • Check the printer.cfg if the nozzle_diameter setting is correct
  • Cranking up the max_extrude_cross_section setting in [extruder] section is not a solution. The underlying problem may cause issues later

Additional Background

If there is interest, how for example a prime line is calculated in the context of this error message, this is the math:

Input Parameters

  • Nozzle Diameter: 0.4 mm
  • Filament Diameter: 1.75 mm
  • Extrusion Width: 0.48 mm
  • Layer Height: 0.2 mm
  • Print Speed: 80 mm/s
  • Extruded Length: 15 mm
  • Movement Length: 30 mm

Calculation

max_extrude_cross_section [mm²] = 4.0 x Nozzle_Diameter^2 = 4.0 x 0.4^2 = 0.640 mm²

Extruded_Volume [mm³] = Extruded_Length [mm] x (Filament_Diameter [mm] / 2)^2 x Pi = 15 mm x (1.75 mm / 2)^2 x 3.14 = 36.1 mm³

Actual_Extruded_Cross_Section [mm²] = Extruded_Volume [mm³] / Movement_Length [mm] = 36.1 mm³ / 30 mm = 1.2 mm²

  • If one single gcode command (e.g. starting at X=0 / Y=0: G1 X0 Y30.0 Z0.3 F1500.0 E15), would request a movement of 30 mm while trying to extrude 15 mm filament (gcode: E15) it would result in a Actual_Extruded_Cross_Section of 1.2 mm²
  • Klipper would react with an error message saying Move exceeds maximum extrusion (1.2mm^2 vs 0.640mm^2)
  • To solve the issue, either the Movement_Length needs to be increased by a factor of 1.875 to minimum 56,25 mm or the Extruded_Length decreased by the same factor to E8
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