The edge mill is a grinding device that uses round stones or weights to crush minerals and grains. It has been powered by animals, wind, water, steam, and electric motors. The mill was also used in the manufacture of explosives such as gunpowder.
An edge mill, or chilian mill, is a grinding device used to crush or grind minerals and grains. The mill uses a pair of round stones or edge-set weights that rotate about a central pivot in a shallow, round millbed. The grain or ore is poured into the grinding bed where the edges of the rolling stones crush it. Early examples of the edge mill were powered by animals, wind, or water, with later power sources including steam and internal combustion engines or electric motors. In the early to mid 1900s, the edge mill was also frequently used in the manufacture of explosives such as gunpowder.
Stones have been used as universal milling agents since the beginning of time. Round stones rolled over grain spread across a flat surface proved to be one of the most efficient methods of milling, with stone mills still in daily use in many regions of the world. The edge mill was one of the most efficient types of stone mill. Mills consist of a driven vertical shaft through which an axis passes at right angles. A pair of large round stones or weights with holes in their centers are then fitted to the shaft, one slightly closer to the central shaft than the other.
As the driven shaft rotated, the stones rolled around their axis on their edges in a flat, round millbed. The mill bed typically had a low edge which formed a shallow trough to prevent the milled material from spilling out. Various types of ore and grain were poured into the mill bed where the rolling stones crushed them between their edges and the surface of the bed. The fact that one wheel was placed closer to the central shaft than the other meant that the stone’s tracks overlapped, covering a larger area in the process. The different edge textures and adjustable stone heights gave the mill operators a degree of control over the fineness of the material being ground by the mill.
Over the centuries various sources of energy have been used to drive the edge mill. Early mills were driven by oxen, donkeys or horses, with later types driven by windmill mechanisms or water wheels. As technology advanced, the edge mill was usually powered by electric motors and steam, petrol or diesel engines. In addition to grinding ore and grain, these mills were used extensively in the production of chemicals and explosive components. Many plants producing high quality black powder for explosives and ammunition manufacturing used the edge mill to grind the powder components before blending.
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