If you have a 4 in or hand grinder, you can use a 80 grit alum oxide or ceramic coat disc or a flap disc. You can also use a 4 in x .90 cutting disc,which cuts or grinds both sides. These items are made by SAIT and are very enexpensive. I have these, but should be able to locate at a bearing house somewhere close to your area. about 4.00 should cover any of the above. If you dont have a hand grinder, get a very course rock so the aluminum will not load up the rock.

Thanks for the reply. No, I don't have a hand grinder (is that what these wheels are for?) only a bench grinder. The part that I want to grind is about 6" X 6" and sort of egg shaped. The aluminum is 3/16" thick. I did a rough cut to get the general shape and now I need to remove from 1/16" to 1/2" all the way around.

I choose aluminum for this project partly because I heard it was easy to work with because it is so soft. So far that's true except for this whole grinding thing!

3M makes a wheel for grinders that is specifically designed for aluminum. I kind of resembles a large brillo pad in its texture. If you would like more information on them drop me an email.sadickers@yahoo.com