This is an attempt to get a mirror finish on stainless and without any scratches.
Hand sanding only was used in the pics below on a scrap piece of angle.
This shows a progression starting from raw filed material as in a newly fabricated part.

Starting as shaped with a file

A course sanding block smoothed it out some but it's too flexible and began rounding the corners		Finish still scratched but beginning

3M polishing compound applied with the sanding block	That brought out more shine.	However, it did nothing for the scratches.

3m applied with a Dremil tool and a felt disc.	Leaves a better shine.

Then, white polishing compound was used from a Harbor Freight kit. Held in a vise for easy access.		But the scratches are still too deep.