Note that these speeds are generally the fastest speeds which should be used and ought to be treated as upper limits. In industry, maximizing production and throughput are usually top priority and the tendency is to push machines as hard as possible. Lower speeds will give longer tool life.
Some materials though may not give best results when machined at too slow of a speed. Brass is notable in this way.
Cutting speed is given as "sfm" (surface feet per minute)
Alloy (tough) steels - 50-60 sfm Cast iron - 60-80 sfm Cold Rolled Steel (CRS) - 80 sfm Mild Steel - 120 sfm Bronze - 150 sfm Aluminum - 300 sfm Brass - 600+ (as fast as you can spin)The calculation is simple: sfm = pi * d * rpm / 12
Alan Koski (10-13-2010) provided a table with information specific to his mill.
For aluminum, here are the speeds which could be used with some common cutters:
And here are the speeds for mild steel:
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