When doing them by hand, the secret is to go slow, let the bit do the work, and don't force it. They can get away from you very easily and nick other places that you have done. Do a little at a time also. If you have a die grinder, you 're gonna need a good rotary file to get it done, and it needs to be specifically for aluminum. Reason being, is when it gets hot from the cutting, it will want to gum up the bit if you're using one for cast iron....the aluminum ones have bigger teeth that clean themselves out easier.
AND THE NUMBER ONE RULE!!!! WEAR EYE PROTECTION!!!!!!!!!!
but if you don't feel like going through all that, then hit me up, I'll give you the hook up.
