Production. Milling machines and machine castings. Welders, too, are busy men in machine tool plants. Most of the oil and coolant tanks, guards and hundreds of other parts are made in the sheet metal and welding shop where men work with steel as cabinetmakers work with wood. Some machine tools, longer than a freight car, have beds so large that they can't be cast, and are therefore welded up from steel plates as much as two to three inches thick