Speeds and feeds are critical to good cuts, especially in copper.

Run the figures through a speeds and feeds calculator to see what you should theoretically be running at (https://fswizard.com/# is good), but you may need to deviate from those somewhat.
A big problem is that you're machining copper, which can be very "gummy" to work with. It doesn't always cut cleanly, and it likes to stick to the cutter.
Speeds and feeds are critical so that you're continually cutting, and not rubbing, but you also have to ensure chips are not sticking to the cutter (a touch of WD40 will work well), and chips are being cleared (just enough air flow to ensure chips are getting blown away from the cutting area is enough).


That's the fundamentals. There is at least one other semi-regular on here who works on such a small scale, so they may be along soon with some tips.