HAHA! You really don't want to get into polishing if you can afford to have a shop do it. It's tedious, time consuming, wears ones fingers to the bone, gets black dust everywhere including on ones face and is just plain miserable job. If I wasn't on a fixed income you can bet every part of mine would go to a shop for polishing!
There are a number of threads here on polishing and all are very good . There is a ton of info on the net to.
If you wish to take on polishing aluminum get the biggest HP electric motor you can. I have a 2hp that will carry an 8 inch polishing wheel. The small HF polisher works okay but struggles with a six inch wheel. It does pull a 3 inch wheel pretty good. Then get some buffing wheels. I like the loose stitched wheels for 90% of my operations. Get some polishing compound. I start with a high abrasive then work to the final fine grain like a white or green compound.
It's important to massage out the nicks, dings, scratches and corrosion from the part. What 45 y/o bike doesn't have corrosion on the aluminum covers! An 80 grit is a good start, hand sand until you get a real nice uniformly bright surface with no discoloration. Discolored areas are usually the corrosion, it can be very deep! I have never filed or sanded through a cover yet. Use a file for deep gouges then use 80 grit to smooth out the file marks. As you use files or sand paper try to maintain the contour of the part; you don't want wavy areas.
Once you have achieved a uniform bright finish with the 80 grit move on to 100 grit and keep working to 500 grit, you can work all the way to 1500 grit if you prefer. As you progress you will likely see imperfection in the aluminum manifest, not much you can do here; you could try sanding them out which works about 33% of the time. I can usually get those discolored areas to brighten up during the cutting operation with a black compound and fine tuned during the polishing phase.
Sanding is an important step in polishing, time spent sanding will pay off in the finished product as it means less time working the buffer and a better finish. Like painting; the prep work makes the difference between a pro job and an okay job.
When you get the surface sanded to a uniform shine then you can polish with the buffer. Wear eye protection, a mask and heavy gloves. Choose the compound to start with; I either start with a fast cut compound and get the part smoothed then move to a medium cut compound. My final compound is a white fine that presents a high luster polished look. I have used a green compound some success but the white compound works 99% of the time.
In the initial stages with a cutting compound the part will get extremly hot to hold, try to carry the heat through out the process; you want to load the motor (pressing the part to be polished firmly against the buffer wheel) but not so much that it stalls or struggles to spin the buffer wheel. As you get near the high luster with the final polishing compound carry some heat but just enough to keep the part warm and I use light to almost no pressure against the buffer wheel.
A lot of folk use one wheel for one cutting compound and change wheels with the next compound. I used to do this as well but now I use the same wheel for coarse and medium cut compounds, for the final polish I use a fresh loose cotton wheel with the white compound.
For those nooks and crannies I use a dremel with a buffing pad, it's a real PIA.
One last tip; keep a firm grasp of the work, it will get hot and the buffer will catch the edge of the work and rip that part right out of your hand. Nothing worse than spend hours at the polisher only to have that part flug across the shop and it does so with some velocity!
Takes me about 6 hours to do a large cover.
