Hi Richard and thanks for the great info.
I'm using an IMCO 32646 1/8 2 flutes. I Also used Onsrud 1 flute (63-606) with same results, except that I had to run at lower feedrate (half), because it has half flute.
I followed your advice and measured the thickness of the chips and I measured 0.09mm (=0.0035 in) wich is right on the target (0.002 to 0.004 in specs). I don't see any melting sign as far as I can see. So far so good.
I'm building electronic audio stuff, and I use my CNC for panel cutting and decoration. The aluminum I cut is only 2mm thick. That is possibly helps for the melting issue.
you can see the result here to understand the context: