This is my Trusty Delta 4″ x 36″ belt sander that has flattened hundreds of harmonica combs and lower reed plates ove the years. A real time saver, once you get the hang of using it. You need several different belts with different grits, including fine grit. I removed a sanding disk that was attached to the unit. (the grey plate in front on the left covers the area where the disk sander was). Also took off the piece that goes over the sanding belt to keep things from getting snagged by the belt and sent flying.
If you use a belt sander set up like this one, you can expect to send a bunch of reed plates and combs flying across the room until you get your technique together. I also removed flesh from my fingertips more than once. You have been warned!
One last tip – it is worth it to buy expensive high quality belts for your harmonica work. Keep a couple of cheaper ones on hand for household projects and other non-harmonica work. Do that and your best belts will last for years.