This is an attempt to get a mirror finish on stainless starting from scratch 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.

This is sold as “3M Safety Walk” (applied on steps to keep your feet from slipping). It makes for a good rough sandpaper and looks to be more coarse than 60 grit.

The surface was wet sanded with cutting oil and the 3M paper wrapped around a file for rigidity. Followed by 60 and then 220 grit paper.

Then polished with Mothers polish and a dish sponge. It made a decent satin finish but that is not the goal.

Surface was then wet sanded with cutting oil and a Scotchbrite scouring pad. Best shine yet but scratches are still too deep.

More white compound revealed some pitting but the shine is getting better.

The aluminum oxide disc was a bad idea. It knocked down some of the valleys but dimpled the surface

The surface was then wet sanded with 320 grit and polished with white compound. The surface feels like glass but the lines are still in it.