This sander works well for sanding plastic it doesn't make it too hot like a Dremel. it sands at the right speed to have great control. I haven't tested with other grits of sandpaper yet. I have also sanded wood filler with it. It worked so well for me I am posting it now, but I plan to add more as I use it more.
The Electric Toothbrush is from Family Dollar $4. but many may work it has a 13mm round head I did not use the square brush yet. you would even be able to submerge the head under water for wet sanding.

Items you need:

 PLA Filament 2mm x 8mm bolts (Or other if you   drill the holes for them.) Epoxy (I used 5 minute by JB Weld) Adhesive (3M Super 77) Sandpaper

Printing: PLA with 6 wall thickness, 20% infill. this made it very strong for me

I used 2mm by 8mm socket head cap screws for placement and support of the Main adaptor. then snip the heads off then epoxy the adaptor in place.

1. After printing cut the bristles off the toothbrush leaving the plastic they are embedded in.
2. Place the Main adapter over the round end (slot up and facing outward as in the picture) and drill the two holes. Start small that's why they are smaller than the final screw.
3. Thread two 2mm bolts in the holes and clip the head off of them.
4. test fit the Main Adaptor. then glue in place with epoxy.
5. Spray the sandpaper with glue. I used 3M super 77. and place your sanding pads on the paper and cut around them with Exacto style knife.
6. Have more fun sanding!!!