[ItBites]

David,

Not sure what temper you are using, but typically in a billet that thick, the center does not have the same temper as the outer couple of inches (can be gummy to machine too). When I have made big parts from a solid billet, I usually machine to near-net shape (the part moves after this due to removing internally stressed material), then re-heat-treat (it walks a little more during the re-heat treat). Then come back for the finish machining to final dimension, after all the stresses are stable again. This is normally followed and required practice for aerospace structures, but maybe not for this application?

Having seen you are an Engineer, I assume you have considered this. Was wondering what your plan was.