One of the most necessary professions in the old days was that of the miller. Every village, no matter how small, had a miller. As noted in the book, Colonial Craftsmen And The Beginnings Of American Industry: "It was a small village indeed that had no mill. As has been said, the mill was usually a prime reason for the settlement."
Gristmills were constructed in a number of types, either driven by the wind or by water. The Dutch emigrants who settled along the eastern seaboard brought the windmill to America. The Germans and English favored water powered mills.
As its name implies, the windmill was powered by the wind. A large shaft was set protruding out of the side wall of the windmill. The shaft's end that was inside the mill was carved into cogs that mated with gears connected to the mill's grinding equipment. That grinding equipment included two large horizontally placed stones between which the grain would be ground into flour. The shaft, with its cogs and adjoining gearing, was positioned at the top of the mill; the force of gravity being employed to move the ground flour from the grinding stones at the top of the mill to the bins located on a lower level. Usually there were no more gears than absolutely necessary. In order to take full advantage of the wind's haphazard nature, fewer gears, into which the power would be transfered, were included in the design. On the outside, four large vanes were set at right angles into the horizontal shaft. The windmill's vanes were constructed of wood in a lattice structure and then covered with sailcloth. The vanes were set at a slight angle so as to catch the wind and always turn the shaft in the same direction. The arrangement of latticework ensured that the vanes would not be too heavy and thereby restrict movement. It also enabled the miller to make adjustments to compensate for extremely strong winds. He simply loosened the edge of the sailcloth on the outer end of the vane and gave it a few twists. That allowed the empty spaces of the latticework to be exposed, cutting down on the vane's resistance to the wind.
The entire windmill structure was usually constructed so that it could be pivoted in a circle. The mill structure would be built on a central stanchion. That was necessary so that the vanes could be aimed directly into the wind no matter from direction it was blowing.
The windmill was popular in the regions settled by the Dutch and Scandinavians, but due to the unreliability of the wind the windmill was likewise unreliable. It was the hardest to control of all the mill types. The miller, or his apprentice, constantly had to adjust the sailcloth and reposition the mill so as to keep the speed of the grindstones somewhat uniform.
The water powered mills were of three types: tub, undershot flutter and overshot.
Tub mills tended to be small constructions. They generally consisted of a vertical shaft with vanes positioned horizontally and placed underneath a natural waterfall. Tub mills were not very productive and were often superceded by a more substantial mill of either an undershot or an overshot wheel.
The undershot wheel was constructed as a paddle wheel with vanes radiating from a horizontal shaft. The end of the shaft holding the vanes would be positioned, like the tub mill, under a natural waterfall. The water would strike the vanes from the backside and flow under the shaft. The undershot wheel was often small and not much of an improvement, in terms of produced power, over the tub mill. The speed of the wheel was directly linked to the natural speed of the water rushing against it. A briskly flowing stream was often required for the undershot wheel.
The mill that produced the most power, required the least amount of stream force, and therefore was favored by millers who could afford the construction of them, was the overshot wheel type. The overshot wheel gristmill did not need to be built right alongside the waterway from which it was fed. A slow stream of water from a nearby dam, most often transported to the overshot wheel via a manmade trough, was all that was required to move the large overshot wheel. Therefore, the mill could be built some distance from the natural waterway.
The trough that carried the water from the dam to the mill was known as the race or "head" race. The point at which the water began to flow onto the wheel was called the raceway. At the raceway was a gate of solid wood which the miller raised in order to allow water in the race to pour over the wheel. The higher the gate was raised, the more water was allowed to flow onto the wheel. The gate, therefore, was called the "head flow control."
The race was usually constructed of wood planking simply nailed or pegged together. At first the race would have leaked quite of bit of the water, but eventually the planks would swell up and water loss would become minimal. The continual movement of water over the wood planks kept them swelled up and tight.
Throughout the day, when the mill was being operated, the water was allowed to flow freely from the dam and down the race. The day's usage might draw the dam down pretty low, but at night, when the race was blocked off, the dam refilled.
The overshot wheel type of mill utilized a large wheel, sometimes twenty feet in diameter, with small trough-shaped "buckets" encircling the outer edge. The actual structure of the wheel consisted of two "sides" formed in the shape of a circle. The trough shaped buckets were nailed in place between the two sides. If the head race was strong and constantly filled, the width of the wheel (i.e. length of the buckets) might be the same as the diameter of the wheel. The entire structure was attached to a horizontally placed main shaft by means of spokes radiating from the shaft. The wheel was often entirely or partially exposed on the outside of the mill structure, but it was not uncommon to be enclosed. By enclosing the wheel, there was less chance of it freezing up in the winter.
The volume and speed of water pouring over the wheel did not need to be large and fast. The mechanism that caused the wheel to turn was the fact that as the buckets at the top became filled with water, they overbalanced the empty lower ones.
The horizontal main shaft, onto which the wheel structure was built, extended into the mill structure. The main shaft was located at the bottom of the mill structure on a water powered mill. If it were located toward the top, as in the windmill, the race would have to be much higher. On the inside end of the main shaft were either carved or attached cogs. The cogs fit into the open spaces of a lantern gear assembly known as the "trundle head". From the trundle head rose the "spindle", a vertical shaft which extended the entire height of the mill structure, and onto which the mill stones were attached at the top. Various additional gears could be linked to the trundle head, and they in turn, linked to different pieces of machinery that needed to be operated. As the result of mechanics of attaching smallerand larger gears together, different speeds could be obtained for different pieces of machinery despite the fact that the speed of the turning main shaft remained constant.
In regard to speed, a large wheel, up to twenty feet in diameter, would make about two and a half revolutions per minute with only a small volume of water causing it to turn. The spindle tended to turn between five and eight times faster than the main shaft.
Two stones, often three feet in diameter and nearly a foot thick, made up the grinding mechanism of the grist mill. The bottom stone, called the "bedder" had a large hole in its center through which the spindle passed without touching. This stone was called the bedder because it was bedded onto the floor and kept stationary. The top stone was called the "runner". An iron plate, called a rynd, was attached to the spindle. It was likewise attached to the top surface of the runner stone. That attachment enabled the top stone to be turned at the same speed as the spindle.
The trundle head, at the bottom end of the spindle, rested on a beam which could be raised or lowered enough for the miller to make fine adjustments to the closeness of the bedder and runner stones. By adjusting the height of the runner, the stones could be separated completely so as to stop grinding altogether without stopping the turning of the mill wheel. At times, the grinding needed to be halted but the other machinery being run by the mill wheel needed to continue.
When the gristmill was new, the miller might obtain two stones quarried from nearby granite deposits. Granite stones did quite well, but as the miller became more affluent and was able to afford them, he would purchase imported French burr stones. French burr stones were fabricated from small sections of a stone that was a bit softer than granite. The sections were shaped into the disc shape and bound together with heavy iron bands. The French stones were coveted by millers because they could be cut sharp and stayed sharp longer than ordinary granite stones.
The faces of the mill stones were not completely flat. The bedder's top face was slightly concave. The runner's bottom face was slightly convex. The degree of curvature also varied slightly between the two faces so that there was an almost imperceptible closer fit at the edge than at the center. The grain was poured into the space between the two stones through the center hole in the runner. Since the space between the two stones was slightly greater at the center where the grain enterred than at the edge, it was ground more and more fine as it was channeled along the stones' grooves to the outer edge.
The mill stones had to be dressed - that is, a system of long grooves were cut into the bottom face of the runner and in the top face of the bedder. The grooves had to be cut in a particular way in order for the grain to be moved between the two surfaces as it was being pulverized into flour. Groups of grooves were cut parallel to a tangent to the center hole. The grooves themselves could not simply be cut in a v-shape. They needed to have one side sloping while the other was nearly vertical. The groove, in cross-section, resembled a check mark (ü ). While the miller himself might dress his own stones when necessary, the job was usually done by itinerant stone dressers.
A hopper was located on the top floor of the grist mill. The grain that was brought to the miller by the local farmer was poured into the hopper. A spout, called the "shoe", funneled the grain into the center hole in the runner. The centrifugal force exerted by the moving runner stone forced the grain to be pushed from the center toward the edge of the space between the two stones. In most grist mills a wooden box was constructed around the stones to contain the grain after if had been ground fine and forced from the stones. A chute led from the box to another bin on the floor below. At that point, the ground grain was sifted. Some millers utilized a "bolter" to sift and sort the grain into different sizes. The bolter was a long wooden box, whose bottom was covered with a series of fine to coarse mesh cloths and positioned so that it was slightly inclined. The bolter shook constantly. As the ground grain enterred its raised end, the finer flour was sifted out near the top of the bolter. Increasingly coarser flour was sifted out at points further down the bolter with coarse bran falling out at the lowest end.