Posted by: @conrad-2

 It's trivial to take the cover off, pop off the tube and feed from the top, in fact sometimes I just leave the spool on the side and let the stuff just drape up over the edge, though that's probably poor practice.

This is what I do for TPU and PEBA Air.

Posted by: @hyiger

Once I installed the MK4S Bogie Idler & Main Plate mod and Nextruder Filament Sensor Magnet Mod, top-loading (bypass PTFE) of softer TPU is not an issue. Even without these mods, I don't recall having and issues loading 95A through the Bowden tube. 

Thanks for this sugegstions.  I have had some issues with softer TPU, but not 95A.  

I have printed some commercial projects for a company that makes patient lifts.  They want them out of ABS and TPU.  I tend to print the TPU on my Centauri Carbons, but have done several on my Core Ones.  The only failures I had were due to wet filament (I thought).    When I go with softer TPU, I have had additional difficulties.  

I’ve just completed my first print with TPU 30D and wanted to share a few observations, mainly around filament loading.

Setup: Nextruder + PTFE (Bowden) tube

Issues & findings:

1. I was not able to push the filament through the PTFE tube while it was connected to the print head.
   What worked was:
   - unscrewing the fitting from the Nextruder
   - removing the elbow connector
   - manually feeding the filament through
   Then I reinstalled the elbow and fitting (without mounting it back onto the Nextruder yet) and manually inserted the filament into the extruder.
   
   
2. The filament started twisting and wrapping around the drive gears.
   Recovery without disassembly:
   - released the tension lever
   - removed the tangled filament
   - used tweezers to guide the filament directly into the hotend path
   - manually advanced the extruder (E axis)
   - re-engaged the tension lever once properly seated
   - continued feeding until extrusion from the nozzle
   
   
   

Plan going forward:

• Repeat the same loading procedure for soft TPU
• Print a wing nut for the PTFE fitting to allow tool-free removal

Hope this helps someone working with very soft TPU.
Good luck!
HP

I use Overture N95A filament and the Generic Flex Profile with a 0.6mm high flow brass nozzle.  I keep the TPU in an air tight container with an EVA-DRY renewable desiccant when not in use.

Loading: I cut about a 60 degree angle on the filament, usually I can get it past the Core One + first filament sensor without disabling it with the internal toggle switch if I push it hard enough.   Sometimes the Nextruder itself doesn't sense the filament but retracting slightly and pushing it sometimes works or disabling filament sensors always works (I think that option is available after selecting HELP).  Last resort would be disassembling the Nextruder to clean out debris from the filament sensor. (https://help.prusa3d.com/article/nextruder-filament-sensor-core-one-core-one-l-mk4-s-mk3-9-s-xl_465702)

Core One unloading TPU  in the middle of a print succeeds the first time the majority of the time while unloading from an idle printer fails the majority of the time.  For a filament change in the middle of a print, if the filament did not unload, I select RETRY while pulling on the filament, this always works if I get to the printer quickly.  I don't bother opening the idler in this case.   Before I figured this out I would do multiple retries and the TPU would sometimes go the wrong way around, requiring the planetary gear to be disassembled to fix. 

Unloading TPU from an idle (cold) printer works about 10% of the time. When the TPU doesn't unload I quickly go to CONTROL->MOVE AXIS->E/Extruder(I'm doing this from memory so the menu might be different) and rotate the knob clockwise while pulling on the filament. This always works for me.

I print TPU on the textured steel sheet using heavy duty non-scented hairspray for a release layer. This makes removing the print much easier.

I hope this helps.

1. Dry Filament.  I print directly from DryBoxes that are at 10%.  I used this design: https://www.thingiverse.com/thing:4976052

2. Sharp angle on the filament tip when loading.  The 95A will feed through the PTFE tube and first sensor without issue.  Feeding it by very small amounts allows it to make it past the second sensor and get picked up by the feed gear.

3. Used Generic Flex profile and the included CHT nozzle.  My Core One was a kit, so there was also some playing around with the idler screws.  The instructions are a bit vague on what the "factory" setting is.

4. Unloading is a pain as the TPU will form a blob that doesn't want to come out of the top of the extruder (just before the PTFE tube).  It is sometimes possible to open the idler and fish the filament out, cut off the end, then pull it through.  Resist the urge to just pull it out.  The filament will likely snap and leave that blob in the extruder.

5. Clean the extruder and nozzle after each print.  I had a tough time with under extrusion.  The first couple of prints might work great, but without the nozzle cleaning, it would eventually start to under extrude.  Note that I haven't had a successful cold pull on the Core One.  This would probably be the best for cleaning things out.

Hope this helps.