I have an H2C. I don’t have TPU assist. I don’t take the lid off. I successfully print 85A and softer with this strategy below. Note *** I typically use the right side 0.6mm nozzle for really soft TPU. I find the 0.4 nozzle gets unreliable with anything softer than 90A.
1 - Print off an H2 PTFE TPU Y adapter. There are a few on Makerworld. The one I use and can be seen in the pic below is this one in ASA - H2D Internal Y-Adapter for PTFE (ECAS04 Coupling) - Free 3D Print Model - MakerWorld. Remember the part that is straight is for the tube to the right side filament buffer, and the path that has a jog in it is for the TPU. Don’t worry about the comments, this model works, you need something else as outlined further down to make it work really well with soft TPU. Make sure you run some hard filament through the adapter a bunch of times after you’ve printed it to help smooth some of the walls and transition. You’ll need ECAS connectors for the model I use.
2 - Print off a finger powered filament pusher, this is important because it acts like the TPU assist helping to push the soft TPU with some pressure. As seen in one of the pics below, also requires PTFE (pneumatic) connectors - 3D Printed Manual Feeder - Free 3D Print Model - MakerWorld
3 - Connect the TPU bypass port tube to the manual filament pusher as in the picture
4 - Put your roll of TPU on a ball bearing based center spool drybox of some sort. Polydryer works great, AMS HT works great with the TPU mod, or whatever you’ve got, make sure there is absolutely minimal friction (as little as possible anyway, if it’s too smooth, you may get tangles on your spool if it spins too much on it’s own. This is crucial to ensuring low friction feeding of TPU
5 - Park your toolhead near front right. That’s where there is the least resistance of filament through the tubes
6 - Switch extruder to the right
7 - Start pushing the TPU through the manual pusher, and once it grabs, you can rotate the dial to push the tpu through. Don’t worry if it gets partially stuck somewhere, it is bound to happen when you start off. But with careful push and pull with your fingers, you should be able to see the TPU going through the tube to the toolhead. The critical part now, is to push hard enough to create pressure so that the filament sensor senses the TPU. Usually not a problem with 85A, but some softer TPU may take a bit of patience.
8 - once you see that the filament sensor has sensed the TPU, set the nozzle temp to whatever is appropriate for your TPU, I usually just use 240c.
9 - While pushing with the manual pusher, keep pressure on the filament and push the extrude down button a few times. Keep feeding pressure on the manual pusher with one hand and extrude button with the other
10 - Once you see filament oozing out, loading is done. You can now run your print. when you are done, Don’t attempt to use the auto-unload. Instead, heat the nozzle back up to 240c, and push the up extrude a few times until you can pull out the TPU from the tube and roll back into drybox, or roll back up the spool
hope this helps! Let me know if you have any questions
