Hi All.
Considering this was my mess I probably am disqualified from guessing but I will share some info that might help narrow things down a little.
I used a 2 flute high helix solid carbide end-mill.
The spindle speed was 5700 rpm.
The cut speed average was 24 ipm.
The stock started out at 2" x 2" x 3.5" - 6061 about 70% was removed.
The rough down was .250 depth of cut with .1 step over.
This was the 8th part cut that day.
It was 95 degrees in the shop.
The mill was controlled with a Grex and Mach.
I was wearing shorts and was probably drinking beer by then.
It filled a 20 gallon shop vac bag about 3/4 the way up. And it took me many hours to clean the mill.
Hope that helps!!
Oh and here is another pic that will make it easier to count the chips on the floor

Chad