Taz 6 PLA Filament Grind

Hello everyone. This is probably a decade old problem with PLA filament, and this is what I have done trying to solve it; yet still failed.

1st time when this happened, I was printing something with a lot of thin fins. Each fin was only 2mm wide and a few mm long. I thought it was the constant retraction caused grinding. I cleaned the feeder screw and went on printing something else, the grinding did not happen. Then it came back on something very boxy shape. That means it’s not the shape of the print that causes grinding.

I then moved to the filament spool holder. A lot of modifications I found on TAZ printers have spool holder on top of printer, with spool axis along Y. This way, the filament unwinds into feeder without twisting. I thought the grinding was caused by the twisting torque by having spool axis along X. I made a spool holder on the side holding spool with its axix along Y. It did not grind in thin prints, but grinding came back. That means it is not the twisting in filament that causes grinding.

There are people putting the reason for grinding to “heat creep”, stating hot end heatsink fan is not powerful enough to cool the heatsink, so heat creeps up into filament tube and causes filament to expand, thus jams in tube, and feeder screw keeps pushing filament to grind. There are fan shroud modifications to fit 80mm fan to cool hot end heatsink. I found JLC_Designs’ solution:
https://forum.lulzbot.com/t/taz-5-80mm-fan-shroud-files-linked/1662/1
downloaded and printed in ABS with enclosure, still some minor wrap, but not a problem. Then I realized it was for TAZ5, and not compatible with TAZ6.

To quickly solve the “heat creep” problem, I designed an 80mm fan shroud, screws directly to stock 40mm fan mounting holes, and put a crappy 80mm computer case fan on external power supply. It was not a powerful fan, but I thought it should move much more air than stock 40mm fan. I will share my design later. The first attemp to print failed due to filament grinding at around 20% of height. I then put a higher RPM, but louder, 80mm fan on it. The same print came out with no problem at all after 4 hours. After removing the part, without touching anything else, I started another 10hr print, thinking it should be ok. 9 hours later, this morning, I found it failed at 40% of height due to filament grinding.

What did I do wrong? How can we solve filament grinding for PLA? I think I have exhausted all my options. Please help.

Update#1
I will add a filament filter based on this video:
https://www.youtube.com/watch?v=aFsgWr7gApM&ab_channel=BarnaculesNerdgasm

I can print eSUN PLA+ just fine, but IC3D PLA and Atomic Filament PETG always gave me grinding issues.

Recently I used a filter and filled it with olive oil and all my problems went away.

Try it out, I have it stuck to the end of the tubing and it stays perfectly, even when I switch filaments. Should’ve made this from the start.

Other causes of grinding to examine:
Overextrusion (most likely cause if its failing on long thin tall parts) causing the hotend to back up due to layer thickness too high and the nozzle end getting effectivly plugged.
Idler tension too low
Idler tension too high (immidiate grindout)
Idler bearing gummed up and jammed.
Hobbed bolt gummed up and not biting in
Thermristor failing or partially failing
Heater core failing or partially failing
Excessive fan cooling at the hot end tip causing resolidification.