What is a Gristmill
A gristmill grinds grain into flour. The name refers to the grinding equipment as well as the building. Gristmills, powered by water wheels, have been around for many centuries, some as early as 19 BC. In the United States, they were common by the 1840s. Later mills were operated by other means. Since running water was not abundant in the Mansfield area, Ralph Man and Julian Field built a steam-powered mill, one of the first of its kind in this area. The grinding process remained the same, but the power supply to drive the mill stones and mechanisms was different. There was plenty of wood in the area for fuel and water for the boilers.
How They Work
At the heart of the gristmill are the grinding stones. There are two stones, an upper and a lower stone. Each stone is 4 to 6 feet in diameter, 18 to 24 inches thick and they weighed as much as a ton. Millstones were made of ordinary granite or sandstone, quarried so each stone is a single piece. They fit together, with one laying on top of the other. The bottom stone is called the bed stone and is fixed in position. The top stone is called the runner stone and it rotates on top of the bed stone. The runner stone had a hole in the center and grain was fed into the hole from a hopper and then the grain was ground between the two stones.
The stones had to be furrowed or grooved. The runner stone had furrows cut in the bottom and the bed stone had patterns cut in the top. The grooves served as channels through which air could pass and carry off heat generated during the grinding and they also served as pathways to carry off the flour.
Rule of Thumb
There was a vertical spindle that passed through both stones and turned the runner stone. The distance between the stones could be adjusted slightly, for different kinds of grain-corn, wheat, etc, by lowering or raising the beam on which the bed stone rested. By feeling the texture of the meal between his thumb and fingers, a "rule of thumb", the miller could determine how much to adjust the stones. The miller also had to be watchful of the flour and meal coming out of the stones to be sure that it did not get too hot and burn or even catch fire from the friction of the grinding stones. His sense of smell was important at this stage of the process and, therefore, he had to keep his "nose to the grindstone."
The flour or meal moved outward from the center of the stones by centrifugal force as the runner stone turned and ground it. After leaving the stones edges, the flour was confined by a wooden casing, called the vat, that covered the stones. It then fell down a chute to a bin on the floor below where it could be put in sacks or barrels.
Vern Raven, July 15, 2015