Loading TPU on a Core One
I loaded some TPU into my Core One about a month ago. It tangled inside the gearbox and I had to disassemble the entire nextruder to get it out. During the loading process the tangled filament apparently destroyed the load sensor. After discussion with Prusa Chat, I had to order a new heatsink/loadsensor. That has now been installed and the Core One freshly calibrated. I am trying to load TPU again but I can't get the filament past the second filament sensor built into the nextruder head. I have tried trimming the filament to a taper, cutting it blunt, disabling the filament sensor, opening the gate - nothing is letting me get the filament to the point where the menu says "Continue." Anyone have any tips?
Thanks.
There ought to be a warning on every spool of flexible filament - this is not easy to use - Prusa's note on p49 of your 3D PRINTING HANDBOOK doesn't leap out either ...
If you have disassembled/rebuilt the nextruder the most likely cause is a wrong nextruder idler pressure - the two spring loaded screws at the top need to be set correctly -
First heat the nextruder to the working temperature of the highest temperature filament you have used recently (tell the load procedure that's what you are loading - but load a length of scrap PLA) then purge the PLA and immediately unload it - this clears any residue from the path, all flexible filaments need this step.
Disconnect the PTFE tube from the top of the nextruder, feed the filament through the delivery tube and pull out a few extra centimeters to work with (if the pull is very difficult you may need to replace the internally worn PTFE or bypass it for this filament) Now trim the end at 45° and try loading directly to the nextruder.
Repeatedly try loading the TPU, adjust the idler pressure between each try - turn both screws by the same amount and keep careful count of the turns in case you have to go back - at this stage we don't know whether the idler is too tight or too loose so you might have to try both ways ... between each apparently successful try open the idler and check the filament is following the correct path.
Finally reconnect the tube and start your print.
Cheerio,
RE: Loading TPU on a Core One
If you can't get past the second sensor, there's a mod that replaces the spring with opposed magnets to get the force down. I don't see why using a weaker spring wouldn't also work. I'll probably try that at some point. I've printed TPE-83A by just pushing it straight into the Nextruder with the Teflon tube removed and it did go past the factory sensor with no mods. I'd expect little trouble with TPU-95, but we've got some TPU-70-something at work that I suspect I could never print without extensive modification of the Nextruder, basically all new parts surrounding the gear and bearings.
RE: Loading TPU on a Core One
What a pain in the you-know-what. I never had any problems printing TPU with my Mk4S. I’ll look for the magnet mod.