[en] A machine tool, claimed to be the world's largest, for machining nuclear reactor core support units in a single piece, is described. The supports are fabricated in two sections and welded together before machining and forming a hollow workpiece 3m thick and 35 ft high. The machine is a two-column bridge with a 20 ft dia rotary table which moves under the fixed columns. Driven with a 150 hp dc motor with the speed under numerical control, it is rotated at speeds for timing and boring up to 23 rev/min, or for milling down to 0.2 rev/min, with a slow indexing speed range from 0.00045 to 0.045 rev/min. (U.K.)