In combination with changing my Ultimaker 2 extended to use 1.75 mm filament I added this feature so it would successfully print flexible filament (TPU). The original setup from Ultimaker presented too much Bowden tube with a curve and this would make flexible filament to compress and create too much friction to pass successfully through to the print head. In addition the feeder design would allow the soft filament to buckle just above the pinch bearing and jam. The feeder provided here has zero open space to allow this problem. As seen in the OpenSCAD drawing a spring supports the stepper and feeder above the printer.
I have this setup on two Ultimaker 2 printers I use. It has worked well with both inexpensive TPU and ABS filaments for over 1800 hours of printing.
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