A note on stiction between plastic-paint interfaces
I recently found an embroidery stand frame at the second-hand shop for $25, and spent a day or two stripping off the old-timey varnish and refinishing it with a tough white enamel paint.
Along the way, I designed and printed new tri-lobe locking knobs to replace the plain wooden discs that the stand came with. These discs were hard for me to grasp in my hands.
When I fitted these knobs to the stand, especially the horizontal one that controls the tilt of the table, I found that the glass-smooth surface of the knobs that I printed had a huge amount of stiction against the smooth surface of the enamel paint. I had to use a hammer on that horizontal axis knob to overcome the stiction and remove it.
I printed some 1.2 mm thick plastic washers to separate these surfaces. The glass-smooth surface of the washer goes against the paint, basically gluing it in place, and the knob rides on the rougher upper surface of the washer. This solves the issue entirely.