when I polish aluminum I go from 220-3000 (up to 400 on the oscillating sander then the higher grits go on the vibratory sander. Then I use 'mothers aluminum polish'. This is ALOT of work though. If you leave it at a modest level (1500 or so) with the vibratory sander, it looks kinda cool on big surfaces (patchy). Only reason I use the vibratory sander is because they don't seem to sell hook and loop sand paper locally for higher grits then 400, but I HIGHLY recommend the new diablo brand sand paper 'net' pads. They are like 2x as expensive but the dust goes through the sand pad into the extractor.. its great. They make em from like 80 to 400 IIRC.
Dealing with hard anodized aluminum is a PITA mechanically. I have not tried it with chemicals but I had a really nasty scratched up hard anodized aluminum surface and I sanded it down. Took forever, felt like it was destroying sand paper, uneven sanding, unpleasant etc.
Alumninum is weird because I have seen people just skip alot of the sand paper steps and go crazy on a buffing wheel and it gets similarly sparkling results. But, I try to avoid buff polishing because it makes plumes of dust. Like for manifolds.. people just seem to take them dirty and put them right on the wheel after some wire brushing to get them shiny, but its like hours on the buffing wheel.
(the actual setup that you SHOULD (*if you are a billionaire*) have is insane, think gloves+apron integrated into each other with giant dust extractors behind the wheel sucking tons of air). I try not to use it and shower immediately since my setup is ghetto. I think 'real' machine shops that do alot of work have their own lowly paid polishing guys + dedicated room for polishing, since its such a nasty operation on the wheel if done dry (which is why I like mag+aluminum polishing compound, since its a smear). My shops is trashed after heavy polishing wheel use.. if its nice I try to take it outside on a stone wall to work there.
Keep in mind if you are serious about polishing, there are three (basic that I know of) steps to it that use sisal, stitched and loose wheel, depending on removal rate. Sisal wheels are very aggressive, while the loose wheel is dainty.. and they are compound, material and surface finish specific. Like, I don't think it makes sense to use black polishing compound (very hard) on a loose buff wheel, and its only recommended to use it with hard sisal (the stuff ropes are made from).. harbor freight even sells like 6 compounds.. plastic, non ferrous, hard clean, medium clean, standard jewelers rogue, etc.
Where to go from sand paper to polishing depends on geometry, surface finish and probably other factors. I feel like you would need to do it alot to know what works best. When I bearly knew about the tools, I got a near perfect finish on a damaged multimeter with just tooth paste. I almost feel like you might want to sand, then polish to know where to sand, then polish again with some things (maybe its just me). I noticed this with copper structures, you can reduce the work load alot if you just do a light polish first, clean, to find trouble spots, then work on them with more aggressive methods (sand, different wheel, different compound) to match the finish, rather then to do the whole thing (its a crazy amount of work to make a nice finish on a big object). It's also EXTREMELY boring. I feel like I am going crazy if I just try to follow a step set and doing at least some unnecessary work. And you also need experience to know the wheel speed and pressure to apply, when to clean, etc.. easy on paper and cheap on first thought but its neither if you want to do a reasonable amount of work.
Not to mention, it hurts your hands/fingers. At this point I cringe at the thought of scrubbing stuff. On the plus side, after you polish and clean a bunch of tools, chassis, car.. you really start to be careful about damaging equipment because you put so much work into it.. usually means you work a bit safer since you clear the area you are working in and stuff like that (not because you care for personal safety of course, just because something might get... SCRATCHED!
The worst is thinking 'yeah thats easy to fix, I will just bang on it a bunch and fix it on a rainy day (teenage you). Well that day is going to rain with tears.
I swear standing infront of that wheel covered in dust messes with your head after a while.
On an interesting note, I wonder if someone has a particulate sensor and can take a measurement in a shop after polishing occurs. I have a feeling its very bad.
Also, consider using a sharpie or something to mark up stuff thats not totally trashed so you reduce your work load.
And for bare aluminum, the mothers mag + aluminum polish compound has some protectant in it (silicone based IIRC), so if its your last step it should be some what protected. I bought proxxon tools on eBay that have aluminum base with some kind of stains, I just used the mag/al polish on it and it restored it to the holographic status (its fly cut, so its not a 'mirror', more like a hologram.. but it would be mirror like if it was ground/lapped/etc).
For using wet polishing compounds like that, I recommend the milwakee polisher/sander tool that runs on batteries with the side grip. I think you will find doing it with a drill will PISS YOU OFF SEVRELELY. Die grinder/polisher/etc are GODSENDS. I only ever use the drill to do something if I need an extension rod.
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