What cause the filament to "coil" during printing?
I can straighten it out but it comes back.
RE: What cause the filament to "coil" during printing?
Over Time it gets a memory of being curved on the spool. It may also have been put on the spool warm making it conform to the spool curve. It is harmless as long as it isn't snagging anything. A little resistance on the feed spool will straighten it some. It does add a little to the drag in a PTFE tube. Just the nature of spooled filaments.
RE: What cause the filament to "coil" during printing?
I print probably 100 spools per year for the last 4 years. This is the first I ever had the issue.
All the same prusa pla filament. So, probably a manufacturing abnormality OR the MK4 nextruders are a contributing factor.
RE: What cause the filament to "coil" during printing?
My theory is that if the filament isn't in the center of the extruder gear, or has unequal pressure on the two idler screws, the gear imparts a torque on the filament making it eventually jump the spool. On a Mk3's, the gear position on the motor shaft can be off; on Nextruder models it should be pretty well centered, but I'm still thinking the can add twist if the idlers and gear aren't perfectly aligned.
Then again, it might be filament isn't perfectly round, an extrusion flaw when made. Though, I've noticed on my Mk3 the filament always jumps off the spool the same direction, so it's hard to blame random filament flaws. My Core One is too new for any data.