Hi Skwerm,

Here's how I would resolve the problem, but others might probably come with better solutions.
My guess is that the sphere seams will create trouble for the boolean subtraction.



So I rebuild the groove, using half sphere (but taking care to avoid seams)



I have attached the .3dm file too (without the fillet operation)

-- EDIT

Ok, looks like the groove need to be build a little bit more carefully, because while the fillet operation works, it generates naked edges :S