Some lathes have a vertical spindle instead of a horizontal one, with a large rotating table on which the work is clamped. These huge machines, called vertical boring mills (Figure l-5),are the largest of our machine tools. A 25-ft-diamiter table is not unusual. Huge turbines,weighing many tons,can be placed on the table and clamped in position to be mechined. The machining of such castings would be impractical on a horizontal spindle lathe.