Feedback - Feed and spindle speed for milling aluminum and brass

My camera just returned from its California vacation (at the manufacturer's repair center), and I took a couple of snapshots to
illustrate the chattering I was asking about. If you're interested, you're invited to use the link in my sig.
The problem definitely seems to have been the flexibility of the CNC router I used. That machine is adequate for wood and better than a hacksaw - but it does leave a lot to be desired for metalworking.
Even though parts are rough and unfinished (and, yes, "mushy" to metal supremicists), the new machine appears fully capable of doing the job for which it was designed. I loaded up TurboCNC and was well pleased with the initial testing. My very first hand-coded g-code program ran properly first time!
I think the next set of metal parts will be done on a machine actually designed for cutting metal - most likely a mini-mill retrofitted with these same steppers and control box; and with a less haphazard cooling/chip removal capability.
Again, thanks to all for the help!
-- Morris Dovey DeSoto Solar DeSoto, Iowa USA
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