Figuring Out Cut Depth & Speed

If you try to cut too deep or too fast, the mill vibrates too vigorously too trust.  Tired of figuring combinations by trial and error, I did some experiments.  It appears that when cutting 6061 aluminum with a .5 end mill, the inches/minute x depth of cut has to be less than .02 to work well.  Actually .15 is a bit better.

UPDATE: Black Delrin (which is some sort of reinforced acetal) can easily handle 2.50 as the product.