Well. i did mine with a lathe , holding a grinder steady on the ring ... make sure you hold it steady , and rest grinder on tool rest . Really not a big deal , just have a steady hand, and a sharp eye !! then finish with an 80 grit , finish disc... i ended up with a much "smoother finish then factory machining .... just an idea , or at least an option!! ....Definately worth getting , i now am looking for some spots that normally would'nt go into !! Cheers