I'm still somewhat new to 3D printing with FDM machines, but what I've come to realize is that filament spools are hateful things. Especially a very full spool.
The fundamental problem is that it's not possible to wind a filament spool perfectly such that the filament never crosses over or under itself. And even if it were, if you don't keep constant tension on the filament, it will unwind and tangle on the spool. Also, the filament seems to have twists which cause it to want to reverse the direction that it coils in, creating a kink or a knot.
The key to avoiding this problem is two-fold:
- On the one hand, keep the filament path into the printer as short as possible. Try to keep the filament path clear of anything around which the filament might tighten itself.
- On the other hand, keep the filament loose on the spool.
Loose filament actually wants to to straighten itself out into orderly coils. It's only when the filament is held taught that it wants to kink, knot, and jam. At the same time, unless the filament is contained by the sides of the filament spool, it will still want to snag or constrict around objects along the filament path.
For a New or Full Filament Spool
Don't try to print off a full filament spool. The filament is not adequately contained by the sides of the filament spool, and wants to leap over the sides. It will then wrap itself around the spindle, kink, knot, and all manner of nasty things as it is pulled ever tighter by the extruder.
Instead, after slicing, look at the summary info in your slicer and find out how filament is required. Measure out double that amount, and coil it loosely around an empty filament spool. I.e, don't actually lock it onto the filament spool.
If you don't have an empty spool yet, then the best thing to do is just let it dangle loosely from the printer, and clear the path into the printer as much as possible. You'll need to watch that it hasn't tangled from time to time.
If you hear the filament making noise, better take a look! But, it's much easier to straighten out filament that's not attached to a spool -- especaially a full spool.
For a Used Filament SpoolYou can print directly off of a half-used spool. But apply this trick before you start the print, and periodically while the print progresses.
Grab hold of the free end of the filament in your hand, and then back-wind the filament spool. This loosens up the filament. As you back-wind the filament, it will help if you scrape your finger back and forth across the spool, to loosen up tight spots. Keep doing this until you have enough filament loose on the spool to complete the print.
Check on the spool from time to time to make sure that there is still ample filament loose on the spool.