Or a belt sander or Linisher... Just need to have a smooth surface and even the sharpening stone idea is sound, just not sure I would attempt it with a shell holder chucked up in a drill but rather just manually slide it back and forth.The drill press idea is awesome! Thank you
I have even used a "Cutting Blade" in a 4" grinder and applied the object to be sanded down to the face of the disk... Against all rules and advice as there is a risk of breaking the blade with too much pressure on the surface but it will give a smoother surface than a regular grinding disk unless you can find a really fine one.
Belt sander or sanding disk has always been my "go to" for small amounts of material removal since I don't have a mill or surface grinder.