Michael,
My original question was more for my "how to machine it" understanding and not that "how it should be filleted" should be different.

With that constant fillet, being the fillet that is desired, I have 2 options. I could do it with a 3d toolpath from a 3d model that has the fillet that looks like this:



Or I can cut the curve itself from the cutout:



This is esentially the 1.25 inch circle "surface projected" onto that sphere. We could get the 2d shape of that by wrapping the 2d sphere to the cylinder with a math function of:

wrap dimension*(360/(Pi*2))/radius

Then we could run a 2d toolpath that looks like this: (the light blue represents the cylinder unwrapped)





While turning round stock around its axis. Then a 1/8 inch fillet tool could just make 1 sweep around the edge and be done.

Would it be possible to get both types of fillet for the same situation though?

Thanks,
Burr