A ball mill efficiently operated performs a wide variety of services. in small milling plants, where simplicity is most essential, it is not economical to use more than single stage crushing, because the steel-head ball or rod mill will take up to 2″ feed and grind it to the desired fineness. in larger plants where several stages of coarse and fine crushing are used, it is customary to crush from 1/2″ to as fine as 8.Amit 135 lesson 7 ball mills circuits – mining mill . for the initial chargin of a mill coghill and devaney defined the ball size as a function of the top size of the feed ie d †“v 040 k ˆšf db ball size cm. more detail ball mills.