I have an assembly with two parts.

These parts have been "pre machined" in prep for welding.

Now i assemble the parts and created a "final machine" revolve cut in the assembly to show it as finished part.

My problem is, i would like to fill in where the weld preps were on the pre machined parts, i'd even like a 3mm radius between plate and shaft, but there is no revolved Boss/Base feature in assemblies.