Your machine's 1600 rpm limit is what's killing you. You say you're using a "slot drill", and I'm not familiar with that term. If I were doing this at those speeds, I'd probably stop using carbide and go with a 1mm HSS-Co (high speed steel with cobalt) 3 or 4 flute ball end mill. A HSS-Co cutter can't run at the same speeds as carbide, but they are a lot less money and have a much-higher transverse rupture strength than carbide.
Run it a touch slower, perhaps at 1200 rpm. Load the tool at no more than .008mm per tooth, so 9.6mm/min. It'll take a long time to get finished, but less headaches and money spent.