In aluminum, on a bridgeport, you could be machining at 30-50 IPM or so with good carbide endmills. I would think 33 IPM might be a little slow, especially when considering 'rapids.' You might be better off with a 4000 count/rev. encoder, which would give you 20,000 counts per inch, or a command step of 0.00005". Not too shabby, IMHO. That would give you a max speed of around 67 IPM.
My name is Electric Nachos. Sorry to impose, but I am the ocean.
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(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)