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Yeah, really feels that a shear or guillotine would be the best bet here if I was wanting straight cuts!
Just snapped a 0.8mm corn cob end mill...probably went a little fast.
Aluminium mills pretty well on these small lower powered machines or so i'm told...might have a dabble with that if my single flute test doesn't work, on the off chance it helps with the learning curve. Or brass, as you say.
Stonehedge-
Brass should be fine given a suitable feed rate. With a corn cob tool, aluminium may need a lubricant to avoid the teeth clogging - similar to file pinning. I used to task students with chasing the tool with a small paintbrush and paraffin if they wanted to use aluminium, mainly to clear the swarf. The next problem then was cleaning the bed sufficiently for double sided tape to work on the next job...
MrE
I was using a Roland PNC 2300 and tools similar to this:
https://www.prytec.com.au/product/160/Roland-Engraving-Cutters-for-Aluminium--Brass/
-all now very obsolete!
Attempts at manual control never gave a good outcome, and larger tools (more than 3mm diameter) generally tore the copper free regardless of machine or method of holding.
For anything larger / structural / more decorative than a circuit board I would try to teach precision smacking with the correct hammer followed by various grades of abrasive, or advise students to use brass or aluminium as an alternative to copper.
Brass might work - IIRC a brief etch in warm ferric chloride will preferentially remove the zinc leaving a (thin) layer with a high proportion of copper and the appearance of a dull copper finish.