Hi,
I try to have say an internal scrap part stay fixed when milling aluminium. It sort of comes down to 'evacuating' chips, when slotting
or any internal milling evacuating chips is about the most significant thing you can do to ensure a good result, failure to do so
invites 'built up edge' and usually disaster for the part and the tool.
When milling an external contour or surface its less critical, usually compressed air or coolant flow is sufficient to clear the chips and
larger scrap bits tumble away from the tool.
Most of the parts I make are milled out of billet so the part stays attached to the parent material which  I then part off with a hacksaw
or a 125mm cutting disc with a mandrel which fits into the spindle. Works well IF and ONLY IF the spindle is trammed to the table, I had
some sticky moments learning that rule!

Craig