This is working for me..
For deep scratches and if painted first start with a Josco Brumby Poly pad medium grit, not the cheaper paper based ones as they don't last and the finish is variable.
They come in several sizes to suit angle grinder mounts. Normally 100mm or 127mm. use selectively only on the areas where deep scratching is.
http://www.josco.com.au/newsite/jia/products/abrasives/abrasives_jbfd.htmNext use the fine grade poly disk and work back the deeper areas you used the previous pad and a all over light touch up.
Grab the Josco buffing kit, designed to suit a hand drill mount, has two buff wheels and 2 polishing compounds. Spend as much time as you can using both.... no point saving the buff compounds and wheels.
http://www.josco.com.au/newsite/jia/products/polishing/polishing_pk.htmHere's mine not finished yet, drain etc to do and final buff up...
boiler.jpg
cheers
bt1