Im thinking of cutting a design in a metal sheet using the plasma cutter then buffing it to a sub to near mirror finish. Would this be possible or would the edges of the metal sheet look burnt/annealed? Would the edges be too jagged to do precise/thin designs?
Im thinking of doing this in steel or stainless steel sheet about 20-18 gauge.
I can’t speak as much to the edge finish with plasma cutting, but for a mirror finish you want stainless steel; regular 304 would be fine. It’s relatively easy to polish with a series of grinder flap discs and wheels. If there is discoloration from the plasma heat on the edges, it will likely be removed by mechanical polishing, or there are acid-based “pickling” agents designed to passivate welds which should remove the discoloration. I used to see that on food-safe machinery, but all our sheet metal was laser or water jet cut.
my advice is that the edges are going to look pretty rough when your done and they will need to be ground/sanded down. It would be wise to cut the shape out a little bigger than the final dimensions and grind to final size. If your concern is more about discoloration from tempering that will be removed as you polish as its only on the surface assuming we are talking about steel.