To operate the mill, the miller places the grain to be ground in the funnel-like hopper above his pair of millstones, after first taking out his toll (Turn Charge). The toll was usually about 1/16 of the grain. Then he opens the sluice gate that lets water into his water wheel. As the weight of falling water turns the water wheel (Click link above to see water wheel animation), large gears turning smaller gears make the shaft turn faster, much as the large gear on the peddles of a bicycle will turn the smaller gear on the wheel more rapidly. This power is transmitted to a vertical spindle, upon which rests a large, flat disc of stone, often weighing a ton or more. This stone spins just above, but not quite touching, an identical stone set stationary in the floor of the mill. Both stones have a pattern of grooves cut into their faces. As one stone turns above the other, their grooves cross much like scissor blades. Grain falling through the hole, or "eye", in the runner stone is cut apart as it passes between the two stones. The miller can adjust the distance between the stones to regulate how finely the grain is ground. The milled grains moves around the cover that is over the stones, until it falls through a hole into the meal chest. From there it can be scooped up into a sack to be taken home for baking.
Thanks to Sturbridge Village for animation.
Article adapted from S.V.
