Production. Milling machines and machine castings. Precision gears are essential for machine tools to ensure accurate, smooth, quiet operations and long life. This gear grinder -- itself a machine tool -- is perfecting the working surfaces between the teeth of a milling machine gear. The milky liquid is coolant used to control the temperature at the grinding point so that the delicate physical character of the metal, produced by predetermined and careful heat treating, will not be disturbed. Location: a large Midwest machine tool plant