While changing to black filament, I measured the force required to pull the (natural PLA) filament through the translucent guide tube arching over the M2’s chassis from the spool to the extruder:
A strike-anywhere kitchen match (bet you can’t buy those any more!) provided more than enough heat to bend the end of the filament into a loop suitable for the pull scale:
- Tube reasonably straight: 0.5 lb = 2.2 N
- Tube arched to middle of X axis: 1 lb = 4.5 N
- Tube sharply bent to X axis nearest spool: 1.5 lb = 6.7 N
The force increases slightly while tugging filament off the spool, as the spool does not rotate freely on the printed arm jutting out from the frame, but those numbers are in the right ballpark.
The effective diameter of the extruder drive gear is about 11.5 mm, so overcoming the tube friction requires somewhere between 10 and 40 mN·m of torque. That’s applied at the one point in the whole system most likely to show the result of uneven loading, because it directly affects the pressure of the molten plastic behind the nozzle.
That’s considerable motivation to get rid of the filament guide tube…