From The 3D Printer Brain

DupI3: FilamentSteps

Calibrating the Extruder Steps/mm or eSteps

Measure 120mm from top of extruder, using some control panel ( repetier host, s3d, mattercontrol ) extrude 100mm of filament:

• Manual method: Enter the following gcode in the manual gcode box then press enter or send: G1 E100 F150
• Or use the Extrude 100mm button on the Host (but make sure your extrusion speed is set to something reasonable like 3mm/s)
• Note: Because we are commanding INCOMING 1.75mm diameter filament, the raw incoming feedrate looks very slow and is, however, the output 0.4mm noodle of filament is moving at 65mm/s when the incoming 1.75mm filament is moving 3.4mm/s. This is why the MK10 listed maximum feedrate for XY motion is 65mm/s as that translates to the extruder doing it's maximum of 3.4mm/s pushing filament.

Now measure the distance from the top of the extruder to the mark you had made. It should be 20mm. If its not,

new_e_steps = old_e_steps * (100 / distance_actually_moved) … or, old_e_steps * (100 / (120 - distance_to_mark))

So now that you have the correct amount of filament being fed....... mostly. Take the new_e_steps and enter that into the Ext1 Steps / mm value in the Printer EEPROM setup from the Host or via the LCD (remember to save the EEPROM if using the LCD).

Repeat the test again to make sure it works and if it is still off do the math over and enter the new value to get even closer.

Video on how to calibrate an extruder