I saw this video https://www.youtube.com/watch?v=V6T0U9yEw0I a few years ago but didn't really have a use for it but now with 3d printing and using PLA I needed a small sander that wasn't too fast, normal sanders move so fast it just melts the plastic.
Enter the Spin Brush sander I used an old Spin Brush because that is what I had and I have a rounded back and forth sanding surface and a flat square sanding area in one toothbrush, the edges are extended out to get into the tight areas where the head of the brush just can't fit.
I included the Sketchup file in case you need to modify it as the toothbrush I used is almost eight years old, who knows if they have changed since then.
Here is a video of it working https://youtu.be/B9w12FLegwE

I printed it with PLA with Cura 0.4mm nozzle, 0.2mm layer height, 90% infill.
I pulled the bristles out with some needle nose pliers, you need to get a good grip, it was far easier than cutting them off though.
I glued the disks on to the SpinBrush with some super glue.
For the the sandpaper I have some stick on that I cut the shapes out of but a bit of glue stick and holding it on for a minute works well also, with the glue stick it leaves paper when you pull it off but nothing a drop of water won't take care of.