3d printed engine block sanders

My son and I are making this engine https://www.thingiverse.com/thing:644933 by https://www.thingiverse.com/ericthepoolboy
we were having a tough time sanding out the parts for the pistons so they move smooth. I made the ID sander to help but my son thought the we should be able to made one for the pistons. I went back to Tinkercad and this is what we came up with. it works great. I did print this with a 50% infill and 4 walls just to make sure it could handle the drill. just wanted to share.