How much drag is too much?
I currently have the MMU3 on my MK4S in the OPE. Everything is in the enclosure (spools, buffer, etc). While this shortened the filament path from stock (less PTFE tube), some filament types have more drag on the tubes than others. While I haven't run into issues yet, I do worry about excess wear or print defects if the extruder gear is having to work harder. I noticed this was the case even with the stock buffer setup (some silk filaments were almost impossible to feed through) so I'm not concerned the custom setup is worse off, just not sure when I should start to be concerned. I did have one hiccup on a five color print last night where the stuck filament sensor tripped and paused the print on a gold silk filament that honestly felt terrible to feed in so I wasn't surprised.
Not sure what other people have experienced with their setups in terms of filament drag and I'm sort of curious.
RE: How much drag is too much?
I have seen the nextruder pull so hard the PTFE tube collapsed, but with the right combination of conditions the feeding can fail. I have a drybox, buffer and MMU. I first found freiction feeding problems with Glow in the Dark filament. It had high resistance in the PTFE tubes and kept stripping in the nextruder. I have come across it again with a PETG filament that feels more like a stranded rope on the OD vs. smooth PLA/PETG. Keeping the PTFE tubes as short as possible and avoiding tight turns helps reduce the overall drag.
Another factor is many small details. I printed an item that had simulated rivet heads. Hundreds of tiny drops of filament on one layer. Hundreds of retracts and feeds with very small filament advancement. This combined with the high friction in the PTFE tubes caused the nextruder to work the same area over and over and grind a spot out of the filament and fail to feed.
I have ordered a "high quality" .3mm ID/4mmOD ptfe tubing for feeding from spool to MMU to see if that will help with these problem filaments.
RE: How much drag is too much?
I tried 3mm ID in hopes that it would help and the difference was negligible. I also noticed I had loading issues because the filament would snag on the cassettes shoulders just outside of the PTFE tubes since they had a larger opening.
I have ordered a "high quality" .3mm ID/4mmOD ptfe tubing for feeding from spool to MMU to see if that will help with these problem filaments.
RE: How much drag is too much?
I also noticed I had loading issues because the filament would snag on the cassettes shoulders just outside of the PTFE tubes since they had a larger opening.
I noticed that also, I plan on smoothing the transition area in the cassetts since there are steps from the layering. Little things can make a big difference.
RE: How much drag is too much?
I gave up with the cassettes, too much hassle to load for limited benefit. I keep my reels in a drybox ( https://www.printables.com/model/551828-unoriginal-prusa-drybox) with auto rewinders ( https://www.printables.com/model/269390-integrated-auto-rewinder-for-spool-tank), works better than when I used the cassettes.
RE: How much drag is too much?
I don't have the room around my machine for an additional dry box, hence why I decided to get everything in the enclosure. Self rewinding spool holders in the enclosure would be awesome though. Do the spool holders themselves add drag though?
RE:
Not that I've noticed.
I've got my drybox on a shelf above the printer with the filament feeding down at the back of the shelf into the cutout at the top back of the enclosure so the feed from the reel to the MMU does not have any tight corners