This may be a little over the top but this is what I did as a test project for a friend.
A friend of mine came over with a wasted brass tower all dented up, egg shaped with the chrome peeling off, that alone is a finger slicer.
I had an idea and machined a 1/8" aluminum washer that had a I.D. large enough to allow for the plasma nozzle to center cutting area distance, added this to the hole diameter. Ran this washer thru a set of slip rollers to match the radius of the tower.
Secured this guide washer to the tower with a "C" clamp a piece of wood inside the tower with a matching radius to prevent a "C" clamp contact mark coming thru the tower. A quick loop against this guide produced a perfect circle within 7 seconds. A minute with a half round file for a bur and slag free hole. A test project that worked off a wild hair idea.
This with a Hypertherm Max 20 plasma cutter that was used but in like new condition that I found in a estate antique funiture store a friend has as his business. I paid $125 for a perfectly operating machine that checked out by my Miller service repair friend, Miller used to repair Hypertherm plasma cutters. I got a lucky find on this machine. Sad part it's rated clean to .200" but can cut .250 not as clean. A Miller 375 would make me happy as it's able to cut clean to .375", cut .500" but not as clean. Add this to my big future wish list of items.
Bier Jagdwaffe... Bier 30 zeit.....~~=o&o>..........