I made a 4 or 5" disc out of a drain cover and ran it on my 4.5" angle grinder to try out. I need to play around with it more before I say if it works or not. It did save buying a big angle grinder and an expensive disc. I think the drain covers also come in 6" too.

Eric
http://s1199.photobucket.com/user/sparky234/library/My%2057%20Chevy%20Stepside?sort=3&page=1
'57 Chevy 3100 (Little Red)
'81 RD350 LC - Fun, Fun, Fun
'83 GS1100E - Pocket Rocket