Needle scrapers are great, if you want to get down to bare cast iron. I also use them on things like angle iron to remove most of the mill scale. One thing to be aware of on the more modern machine tools is the smoothing coat. They bondo up any really bad casting defects and then shoot the whole machine with a coat of "leveling primer" which is basicaly just a spray version of body filler, usualy to a depth of 1/16-1/8". If you take this off, the machine may not look quite right, unless you want to smear it back down with bondo and sand it. My recomendation on machines like that is to just sand off the top layers of paint, bondo up the scars that you feel you can't live with, and paint it. I work on a lot of antique machines, so they don't have this to begin with.