Yesterday I wrote about working with TPU.

This material caused me so many problems in the beginning that I thought it might be worthwhile to talk about it in more detail today.

One of the pieces that I optimize is the tension put on the filament from my extruder. I use a dual gear extruder rather than an extruder with just a gear on one side. This increases the surface area that is in contact with the filament and allows me to put less of a “bite” on the filament, making it less likely to get deformed.

Additionally, I optimize the tension screw so that my gears just barely make marks on the filament.

The underlying issue that I’m trying to solve is that the material is soft. If I place too much pressure on the filament it can flatten out and then it won’t extrude properly or might even cause a clog.

Along the same lines, I optimize my retraction settings. If you have the option of using a direct drive extruder vs. a bowden extruder, you should do so. If you don’t, that’s ok. It’s not ideal, but we can make it work. With a bowden tube using normal PLA my retraction settings are normally around 6mm and 40mm/s. When I set up with TPU, however, I use 1-2mm retraction and no more than 20mm/s. Additionally, most slicers have a setting that limits the number of retractions in a section of filament. I typically limit the retraction to no more than 3 retractions per 10mm. This is to avoid grinding a flat spot onto the filament from repeated retractions as the part is being printed.

In my post yesterday I mentioned that I increase my temperature and reduce my speed, but I didn’t mention any specific values. It varies, but I normally like to run TPU or silk PLA that contains TPU at around 210-220 and I run it pretty slow, usually around 20-30 mm/s. These specific settings all require some testing and optimization, but this should give you a good starting point. The general idea is to make sure that the material is melted enough when it gets to the hotend that it won’t cause the filament to bind or bend. Same thing with the speed, if you try to push too much filament through the filament ends up bending and causing clogs.