Those machines made for wood won't work on metals. One step up from a fly cutter is a face mill; these can have multiple insert cutters and be fairly large. But they require a fairly substantial machine to run on - more so the larger they are. Another thing you might consider is a surface grinder; these are mostly used for steel, come with magnetic hold-down beds, and can be manually operated or automatic. If this is something you need to do a lot of, you might want to send it to a machine shop with specialized equipment that can do this for you in quantity. Here's an example of a company like that: [url=http://www.euclidprecision.com/surface-grinding.html/url] The surfaces they'll deliver are better than can be achieved by milling.