I thought I would buy a 3 kg spool because lazy, don't be me.
I thought I would buy a 3 kg spool because lazy, don't be me.
Just thought I would quickly share what can happen if you're not paying attention with a heavy mass spool if you're not careful. I have all my spools on a dowel rod attached to the top of my printer enclosure and fed through an opening in the top. Never had the slightest issue with 1 kg spools, and I thought I would save a little bit of money and time changing filament by trying a 3 kg spool. It spins perfectly fine without friction, but the much heavier mass is enough to cause it to have significant strain on the extruder pulling it in to the hot end. You can see in the result where I provided strain relief by hand while watching it print. 
Can you tune it out by bumping your extrusion multiplier? I've run 3 kg spools more or less exclusively for like 5 years now. They ride on ball bearings though. I do print the occasional 1 kg spool and don't have issues swapping back and forth.
You'd probably have to keep tuning as the weight of the spool decreases.
Its more practical to print a spool holder with bearings for it. Thingyverse has some good onesIt's* more practical
You might try greasing the dowel.
So... KY? Astroglide?
PTFE super lube. Won't degrade and stink up the place. It's the same lube you put on linear bearings.
Lithium grease would probably be best for a serious answer, but Crisco would probably be ok too.
Bugger. Have you got a workaround? Or are you now an automated feeder for the next 2kg?
You mentioned already having smaller spools, can just transfer some of it there. Best of both worlds, if a little tedious
One day filament will come with DRM so you can't print it backwards. Only a pirate would do that!
That's probably what I'll end up doing
I have my 3kg spools above the printer as well, not having your issue, I think the difference is I'm using a guide pulley on a skate bearing to direct the filament straight into the extruder.
Ig you think that's bad wait until you get multiple retractions going that the rocking motion of the 3kg Is probably going to be enough to pull the filament right out of the extruder.
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Others have suggested greasing the dowel or using bearings, and if the issue was friction, then they'd be right.
If the issue is inertia, then this won't help. Accelerating a given mass to a given velocity requires a certain amount of energy, no matter what.
What could help is something similar to a Huygen drive, where the filament is looped around a large wheel (large enough that the filament can curve around it without breaking) which is able to move against a spring or counterweight. This would allow the movement of the spool to be "averaged out" rather than accelerating and decelerating sharply on every extrusion and retraction.