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What is the best way to polish aluminum castings?

If you are working from bare castings, it is very hard to do correctly in your garage or shop. Take them to a shop that specializes in plating and polishing. Those guys will put a mirror finish on them for you with a lot less effort that you are going to have.

If you are just buffing off the oxidation and tarnish, I just use a cloth wheel on a table grinder type of motor and use a very fine buffing/polishing compound. I often double up the cloth wheel so there are two of the same size side by side, which gives me more surface area to work with.

If your taking a fairly decent looking original casting that is a little oxidized and don't want to make it look like it just came out of the factory you can also get some great results by using a product called Tarnite or Nevr-Dull found at your local hardware store.
Brings out a nice clean look but keeps a little of the original patina.

gamblingman wrote:If you are working from bare castings, it is very hard to do correctly in your garage or shop. Take them to a shop that specializes in plating and polishing. Those guys will put a mirror finish on them for you with a lot less effort that you are going to have.

If you are just buffing off the oxidation and tarnish, I just use a cloth wheel on a table grinder type of motor and use a very fine buffing/polishing compound. I often double up the cloth wheel so there are two of the same size side by side, which gives me more surface area to work with.

I really don't think you would want a mirror finish on them because I don't believe they came from the factory that way. A mirror finish would involve removing some of the metal to get it perfectly smooth. JMHO

Nevr-dull or Simi-chrome both are good and are available at hardware stores. . Best is still a polishing wheel and polishing compound. You can get small amounts of compound and buffing wheels at a wholesale jewelers supply if you have one.