It's a fair question. What kind of machine is used to turn a piston 38" in diameter?
The answer is that in the world of large-scale machining, a 38 inch piston is aggressively responding to email spam trying to increase its size.
To give you some idea of scale, check out this 88 incher.
I remember taking a trip to Norfolk when I was in college, working at a machine shop. I had to get a hydraulic cylinder with a 18" bore cleaned up. Many of the lathes had the headstock and tailstock at opposite ends of a building. Turning a propeller shaft over 25' was routine business.
The Norfolk Naval Shipyard focuses on length rather than girth. Tapping out with a 48" OD, they can turn the same over 80 feet in length. That's a shaft.