I'm doing talk-to-text so bear with me
Basically you start out with a hammer and Dolly .. which you can get it like Harbor Freight or whatever for auto body work.. it's the same thing. Use that so you can knock down all your dents and creases and stuff like that and you just kind of gently work the metal till it looks as flat as it can be. If you don't your final piece will still show dents and its hard to polish around an anyways. Then I use a 8-inch general duty da sander. this is my preference . If you use something bigger like a 10 12 d's made for rough sanding body filler it has a longer stroke so you may want to start with a higher Grit paper like 120 and see how that goes before scaling back to something more hardcore.
After my initial hammer and Dolly work and eyeball freaking the metal straight by hand I just start sanding with either 80 grit 60 grit or like 36 grit depending how bad the piece is. Usually i start with 80 and see how that goes. Will start noticing almost right away areas that don't get touched by the sander . Its a great way to show you the low areas. I don't really fall in love with the direction of sanding...the more random the better. and whatever spots are low again we can rework with the hammer and Dolly and get those as flat as you can then go back to standing with either the 80 or 36 Grit. Once I can see that the piece has been fully sanded ,every area has been touched by the sander, ***and most important all blemishes sanded off ** we can move on to the rest of the process. The rest of the process is pretty much getting rid of those rough sanding marks left behind by the last grit of paper you used. 80 grit sander marks come off by using a higher grit. 120 removes marks left by 80 grit. 180 removes the 120 marks. 240 320 400 600 800 you get the idea.
If you really want to get crazy you can do a thousand grit wet but don't really have to...makes final polish a little easier.
Once you're this far you now have a piece that will take a very nice polish.
I like to do polishing on pieces like the one shown with a felt wheel and Jewelers Rouge. The Felt wheel bolts right onto my bench grinder. Then the Final Touch is the same felt wheel with some of that blue magic that I like so much and then I'll hand polish it one more time with Blue Magic and what you see is the results. Almost like a damn mirror just takes time. You can go extra crazy and get a super soft felt wheel to final polish but I'm cheap and lazy.
On the other hand if you want a more brushed look you can go back with a hand sanding block and like 800 grit and slowly put some straight striations back I to the metal to look a little more "production line made" you guys know I like extra shiny stuff lol.
Next time rework a piece ill try to remember to take pics or video.
I learned this trick while restoring impossible to find stainless trim on classic cars. Many times you just have to fix what's there because good used or new is unavailable or ridiculous priced.
I can also tell you don't use a random orbital, straight grinder, or straight line sander. The sanding marks left behind by those tools tend to be much more hardcore and in the end its very hard to get those marks out on your final polish. (You end up with a shiny piece with a crapload of sanding marks left behind).
I don't know what gypsy magic is in a da sander but the sanding scratches are so non directional that they're easier to polish out in the end. That's why bodyshops use them to cut back fresh clearcoat. Easier to buff that shine out in the end.
You guys really should have a da anyways...they make cabinet rework and parts sanding so easy. And sanding bondo also easier.