I will never pay the price of a steel lap again. I bought some when I did not know any better. Unless your topper on aluminum is way out a final pre-polish with 3,000 on a Batt lap will flatten things out. Lately I have been using a copper lap and charging it with 600 for final cutting. Love it so far and if one does a lot of cutting the savings is substantial. A seller in China has them on Ebay and the 2 I have are really flat. When the cutting slows down just charge it with diamond powder and you have a new lap.