to create undercuts like that. Picture a shaft with a larger ball on the end. These are commonly made for grinders, although I haven't seen them with the sparser flutes generally used for endmills.
Another way you could get this effect is by tilting the workpiece after cutting the ridges, so that you can access the sides with a ball-nosed (but not offset) cutter. But you'd have to do this twice, and it would be hard to maintain registration.
A third way to go would be to have a special form tool made, with the profile of the side of the ridges ground into its edge. This will cost some money, but this guy doesn't think he's getting this odd job done cheap, does he?
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