Cross Section of a Typical Oliver Evans Mill
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.
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