Why use springs on the extruder?

Why use springs instead of a "fixed" position for the pinch wheel bearing? From my admittedly limited experience I get the same end results from squashing the filament with a fixed bearing as I do from using a spring.

Is there some downside to plastically deforming the filament?

The only reason is to provide a somewhat constant pressure on the filament even if the filament is not a constant diameter, as can happen with cheaper filament. A lot of people can get away without the springs, as long as the filament is a constant diameter.

There's no downside to squishing the filament as long as it isn't causing excessive friction being pushed into the barrel.

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I used fixed position, and have occasionally had failures in the middle of a print where the pinch wheel grinds away a section and hence loses grip and feed stops.

I imagine using springs would push the pinch wheel into the ground away section so feed could continue.

Having said that, the feed failure may have been for some reason that the springs keeping pressure would simply result in the entife filament being ground away.

I think my latest failures, which have been happening about an hour into the print, are due to my motor heating up too much, which causes the bearing which opposes the pinch wheel to heat up (I am using an Adrians style extruder) which then softens the filament a little before it enters the thermal break... the pressure of the feed causes the now softened filament to bulge slightly before entering the thermal break and hence form a bit of a blockage. This slight increase in pressure coupled by the fact that now the filament is softened at the pinch wheel causes it to grind away, losing all traction and a feed failure results.

I have managed to turn my pot down and inserted some folded tin foil between the motor and the 'pinch wheel opposing bearing' with a great deal of the tin foil sticking out to wick off heat. This seems to have worked as I ran 2 1.5 hour consecuative prints with no failure

One more step closer to big print runs Just need to finish my filament feed mechanism first before it can run for many hours unattended... my prints are currently for this feed mechanism.