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A Cross Section of a Typical Oliver Evans Mill

A Cross Section of a Typical Oliver Evans Mill

Text and Drawing

Theodore R. Hazen

This drawing shows a cut-away section of a mill equipped with the Oliver Evans system of machinery, revealing some of the internal workings of the mill. The mill is shown with three pairs of millstones, however,at one time the mill may have had four pairs of millstones. The machinery shown was installed in a restoration. For simplification, not all of the machinery is shown. With the Oliver Evans machinery installed in a mill,such a mill with three pairs of millstones can produce flour to supply seven bolters (sifters) with ground flour. The millstones, on the first floor of the mill, are the primary machinery and use 60% of the total available power. The secondary machinery, the elevators, conveyors (augers), hopper-boy, bolters, etc., uses the remaining 40% of the power generated by the water wheel.

Grain would be brought to the mill by wagon, carried into the ENTRANCE door on the first floor. The miller would weigh the sacks of grain. The miller would then pick up each sack and dump it into the RECEIVING HOPPER on the first floor. There is a gate in the bottom of the receiving hopper which controls the flow of grain down the chute which feeds the ELEVATOR. The grain flow can be shut off, or just opened in varying amount so that each elevator cup is properly filled. The grain flows down the chute to the mill's basement, there the empty cups that have come from the mill's attic turn right side up as they pass over the bottom pulley in the elevators boot. As the cups come up from under the pulley they are filled by the chute.

Cups on the continuous moving belt carry the grain up through the floors of the mill to the mill's ATTIC. As the cups of the belt turn over the top driving pulley, the full cups are over turned and their material empties out down a chute. The chute feeds the grain into the GRAIN CLEANER. The grain cleaner or rolling screen is a double mesh wire covered cylinder. The wire cylinder strains or filters our any dirt, seeds and any other foreign matter from the grain. At the end of the grain cleaner is a smutter or fanning mill, which removes the smut, mold, fungus and any dirt clinging to the grain. Then from the smutter the grain falls through a CHUTE to the SECOND FLOOR and into grain BINS directly above the millstones. From the hopper shaped bottom bins on the SECOND FLOOR, the grain falls down a vertical chute on the FIRST FLOOR (which is removable for millstone dressing). The vertical chute has a gate in it to control the flow and cut off the grain. These chutes fill the MILLSTONE HOPPER that sits on a wooden frame called a horse. The horse sits on the round wooden millstone cover called a vat. Hung from under the horse is a wooden device called a shoe. The shoe regulates the flow of grain into the millstones.

The three pairs of mill STONES are on the FIRST FLOOR. The grain is fed into the turning upper stone called the runner stone. The wooden shoe is vibrated back and forth by a turning device mounted in the center of the upper turning millstone, called the damsel. The grain is moved between the upper turning millstone and the bottom stationary stone, called the bed stone. These 2 stones are from 3/8" an inch apart in the center eye, to about one sixteenth apart at the outer edge of the two stones. On the surface of both millstones are cut grooves in the millstones which cut the grain like a pair of scissors. The upper runner stone is turning about 125 revolutions per minute, and the kernels of grain make a spiral path outward between the millstones. Each kernel is between the stones for 3 1/2 revolutions. The two millstones never touch and you do not get any of the stone into the flour, about as much stone as you get steel from your butter knife when you butter your bread. There are three millstone CRANES used to lift off the upper runner stone for millstone dressing.

The meal leaves the millstones all around the outer edge and as it does it falls down a chute attached to one side under the millstone cover. The ground grain is slightly warm and moist, so in the basement it is fed into the bottom of another elevator. The elevator carries the meal up to the ATTIC where a chute pours it into the outer edge of a low tub enclosing the HOPPER-BOY. The hopper-boy is a turning rake that cools and drys the meal so it won't stick in the bolting screens. From a chute attached just off center if the hopper-boy the cooled meal falls down a chute into the BOLTER on the SECOND FLOOR. The bolter is a long round reel covered with various side mesh screens. From the head of the reel, the screens vary from fine to medium mesh in the side of the openings to allow the finest (smallest particles) flour to pass through the screen, then continuing down the inside of the reel (the next larger size particles) the middlings pass through the medium sized screen. And finally out the lower tail of the reel falls the (largest size particles) bran. The three grades of materials falls down different chutes into conveyors just under the SECOND FLOOR. The turning conveyors move the material horizontally into the three different produce BINS on the FIRST FLOOR. The miller would afterwards pack the flour into barrels, and the bran and middlings into sacks.

The entire process is connected from beginning to end. The water turns the wooden WATER WHEEL OUTSIDE and the GEARS in the mill's BASEMENT that power the millstones, and the power is sent upward through the mill by the MAIN SHAFT to power the other machines. Water and gravity make the whole process work. Where at one time before Oliver Evans introduced these labor saving machines, milling was a very laborious trade. Oliver Evans made a science of what was once a traditional hand craft, where the miller had only his own strength and that of his helpers.


1. The above drawing and text by T. R. Hazen appeared in "How Does It Work?" (text and drawing), Peirce Mill (folder), Parks & History Association, Georgetown, Washington, D.C. 1987, reprint 1989.

The Same Typical Oliver Evans Mill Shown in Side Cross Section

The Automation of Flour Milling in America

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Copyright 1996 by T. R. Hazen