Non-ferrous metals like aluminum, brass, copper, etc., should be fine. Ferrous metals are another issue all together, and you're going to have a tough time building a jack-of-all-trades machine that covers the gamut.
Wood routing rpm isn't an issue for carbide tooling in non-ferrous materials by the way. Shops routinely machine these materials at 30k+ on machines built to handle pretty much any ferrous material; Roeders, Matsuura LX-series, etc..
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