Loadcell on mounting bracket
Clamp with notches
The extruder drive force pulling the filament is being measured in the picture above. A clamp is securely attached to the filament and it is pulling on a loadcell, a devise to accurately measure force, which is clamped to the desk.
The filament was not entering the extruder "hot end" so the measurements were not affected by the extrusion process.
The Measured Data
Since the spring rate is known from the previous mentioned measurements, the applied spring force can be calculated from the spring compression data. That was done and it generated the graph below.
The Calculated Data
Now the next question is "How much extrusion force is needed for different material, settings and printing speed?