Compressible TPU Washers

[626Pilot]

I've been working on improving my printable magnetic arm effector. One of the issues I've identified is that it's difficult to get the ball joints, which screw into captive locknuts inside the effector, to be perfectly level. PLA and PETG will only compress a tiny amount (a few microns) before they break. I was unable to find any 10x3x1mm washers on Amazon or McMaster-Carr, so I turned to thermoplastic polyurethane (TPU). At first, I tried printing a 100% solid washer, but that didn't compress much either. After experimenting with settings for awhile, I figured out that the inside needed to be as hollow as possible.

These settings worked well for me:

- Extruder: SeeMeCNC EZR-Struder (has to be flex-filament compatible!)
- Washer STL: 3.2mm ID, 9mm OD, 1.2mm thick
- Filament: SainSmart black TPU (presumably any TPU will do)
- Layer height: 0.1mm
- Num Loops: 1
- Skin Thickness: 0.1
- Infill: 33.3%

This results in washers that will allow about 50 microns of compression, give or take. This is more than enough for adjusting the ball joints. The washers don't spring back 100% if they are compressed a lot, but they will recover enough to allow loosening if they aren't wrenched on too hard. The tops of the washer are not solidly filled because the skin is so thin, but this is okay. It doesn't compromise function, and it may allow a tiny amount of air to escape from the inside during tightening.

TPE, a softer flex filament, is less resistant to abrasion than TPU. I decided not to try it for that reason. It COULD work, but the washers have to be able to stand up to shearing and compression forces at the same time.