Mike you are absolutely correct regarding re-sizing. (It seems like the simple solution until you realize scale is not the same as deflating.)
And yes,.. overcutting would be a better description.
So,.. if I have you correct;
If I set up roughing parameters telling it I am using 1/8 inch ball nose....
I then load a 1/4 inch ball nose into my spindle.
But, how would this make the cut 1/8 deeper in Z ?.... I think I follow what you mean as far as this compensating for x and y in the tool radius, but it wouldn't compensate for Z (would it?) *I suppose Z could be compensated for by resetting Z-zero by -.125** (shrug?... this would mean cutting .125 into the spoilboard for the rough cut.. I would thenneed to reset Z-zero +.125 for the finished cut ??)
Thank you both for your input and time.