Sanding/smoothness is key. The better you sand the less time it will take to polish and the polish job will show your efforts the more you sand.    Damn that sounds weird. Anyway... I haven't polished stainless yet. On aluminum I use a bar that's colored green. I bought it on eBay.

My experience/playing with it is here:
http://www.socaljetboats.com/index.php?topic=2367.0

That grinder I bought doesn't have enough power. I would start off with 600 grit on something like angle iron or plate, ending up somewhere around 1000 grit wet. Hit it with a buffing wheel and that green bar and it looks killer really quick.

Someone on here very recently polished a pump with great results, try to find their thread as well.

That bowl looks great. I have a way better start than than. My rail kit way already polished out at one time so basically I need to just buff it out again. I guess I should have specified what I am starting with. The metal is in good shape it just needs a buffing and I want to get some fine scratches out if possible.

flour , please elaborate i have never heard of this before

cool, thanks for the knowledge

Late post but found something that keeps things shiney with no work at all, try and find some of Amsoils MP (metal protector) spray, just spray it all over everything once its clean, it dries and lasts quite a while and its cheap!

Haven't found anything is doesn't work on (chrome, stainless, aluminum, copper, brass, cadium) I love this crap!

My last build I took all the aluminum and buffed it out as good as possible, then had it all powder coated clear. It dulls the shine just a tad, but from that point out I threw away all the polish I had and simply wiped it down witha  damp towel.
I watched my friends polish until their fingers bled and all that work was in the toilet as soon as it hit the water. Mine was a wipe down and looked like new with no effort.

Cool trick!