Dave Paine
Thrust bearings may help if you are looking to get a smoother articulation.

I am using these in an articulated arm for hollowing tools.

Works well. I can tighten the pivot bolts so the arm can articulate, but with no vibration when used.

This design is using the tailstock to mount the arm. I could easily modify for a sanding arm to mount in the banjo.

Send me an email if you want to discuss this. I am happy to help. I love making new one-off projects.