Hi Don,
Welcome to a nice little corner of the internet.
My personal and completely arguable goto rules for feeds and speeds for 1/16" to 1/8" endmills in aluminium are to target a chipload in the 0.0005"-0.001" range. Assuming your endmills are two-flute, that translates to a feedrate of [0.0005 to 0.001] * 2 * 20000RPM = 20 to 40ipm, so those values in the CC screenshots look about right.
Now for DOC, I go for 5 to 10% of endmill diameter in metal for regular toolpaths:
- so that DOC 0.02" for a 0.062" endmill sounded way too ambitious
- and 0.009" DOC for the 0.08" endmill is about right (11%) but still a little high to my taste, for a first try.
Pretty sure it did not break because of heat, but because of excessive deflection (how long was the endmill stickout?) or high tool engagement in one of the corners of that toolpath.
EDIT: so my point is, reduce your DOC further, find a setting that works, and optimize DOC later.
Check out Winston’s videos if you haven’t already