For Ali I use half the cutter diameter as the DOC, but I use Open Architecture cutters like these https://www.sorotec.de/shop/Cutting-...s/2-Flute-ALU/ Spindle is 12000 rpm and feed is 5mm/sec. It seems slow, but maybe I am just cautious. Most of what I do is one off. Lots of air to clear chips, and my coolant is WD40 and this gives OK results on that soft sheet ali 1050 grade.

But it did take a few broken cutters to get there.