Polishing radio telescope bearing. This 17.5-foot hemispherical bearing is being machined to form the structural heart of the 140-foot (43-meter) telescope at the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia, USA. When complete, it will support the full rotating weight of 2700 tons on a .005-inch thick oil film between it and the main hydrostatic pad supports. Cast by General Steel Industries it was then finished and polished by Westinghouse. Nearly 17 tons of metal were ground off during this process of getting the surface smooth with no bump more than .003 inches. The bearing still weighs in excess of 150 tons, and is one of the largest steel castings ever poured. Construction of the 140-foot telescope at Green Bank was completed in 1965.