My father's machine shop has a lathe that can handle 47" diameter turning stock. I know they have turned some things 18-20' long. If need be they can turn longer stuff. It is two phase electric not the normal three phase. Came out of The Naval Yard in Philly originally I was told. The motor is like a small car. Pre WWII and was moved on a flat car and lifted off and into the shop by a crane. Fun to work with big tools.