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.

After each test a new section of the filament was inserted to make sure the testing was done on a fresh section. Each setting was measured at least five times to make sure the data was repeatable.

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

Summary:
Interestingly, the extruder drive force is closely proportional to the spring pressure= bearing pressure. That relationship is expected with the assumption that the friction coefficient is constant. This information can be used to get the approximate force required for the spring pressure assuming that the Ultimaker version 3 knurled drive bolt is used.

Now the next question is "How much extrusion force is needed for different material, settings and printing speed?

Bertho Boman
Vinland Corporation
11600 NW 20^th Street
Fort Lauderdale
FL 33323
(954) 475-9093
Email: boman33 at Vinland dot com
www.vinland.com