How to Site a Mill
MILL SITE. A mill seat is a suitable place for a water mill. A
mill site is the mill seat and the above mill dam. The mill dam is an interruption
in the flow of water, raises and maintains the water flow so as to make
it available to turn a water wheel.
WATER POWER SYSTEMS. Three functions of a water power system is to
deliver large amounts of water to a water wheel, remove the energy from
the water through the action of the water wheel, and disposing of the used
water or returning it to the stream below the mill.
Water power systems consist of a number of elements. The "DAM"
serves two purposes: first, to raise the water; second, it creates an impoundment
or reservoir which acts as an energy bank. Water flows the same day and
night, so it is saved during the night to be used the next day. In "SPILL
WAYS", gates are used to raise or lower the water level and flow.
Some are built to hold planks called "FLASH BOARDS" which
can be put on or taken off to regulate the water level of the pond or reservoir.
They are removed at times of freshets or flood stages. The "RACE"
has two types, "HEAD," and "TAIL" RACE.
The race carries the water from the dam to the mill site. A race may be
from a few feet to miles in length depending on the distance between the
dam and the mill site. The same race may serve one mill or many mills. At
the mouth of the race there is often a "TRASH RACK," which
stops floating logs and large debris from damaging the water wheel. Behind
the trash rack and at the end of the race are "GATES."
The gates allow the mill operator to control how much water is in the race
and enters the water wheel. These two types of gates are called "HEAD
GATE" and "SLUICE GATE" (or "CONTROL GATE.")
A "FLUME," "SLUICE" or "PEN STOCK"
carries the water at an elevated level above ground to the water wheel.
Flumes are either open or closed, while a pen stock is in the form of water
tight pipe. Pen stocks are either cast iron pipe, sheet iron pipe, concrete
pipe, or the traditional wooden pipe. Later mills had dams with water being
led to the wheel by a short race or flume. After the water flows through
the water wheel it is then returned to the stream below the mill. It flows
through a "TAIL RACE."
A water wheel or turbine must have the used water removed from the wheel
so sufficient fall is given to the tail race to quickly carry the water
away from the water wheel, while the head race maintains the height and
level of the water from the dam to the wheel. There are two basic types
of water motors, "VERTICAL WATER WHEELS" and "HORIZONTAL
WATER WHEELS." The three common types of vertical water
wheels are the "UNDERSHOT," the "BREAST,"
and the "OVERSHOT." The two common horizontal water wheels
are the "TUB WATER WHEEL," and the "TURBINE WATER
The two basic principles which operate on all water wheels is "IMPACT"
(or "FLOW"), and "FALL." The difference
in elevation between the water level in the mill pond and where it leaves
the water wheel is called the "HEAD." The end of the flume
is called the "WATER BOX." This is where the control gate
The general rule is that if the difference between the top of the dam and
the water surface at the tail race is less than 6 feet, and the water could
only flow under the wheel, you would use an undershot water wheel, or horizontal
water wheel. If the difference is less than 10 feet and a flume or sluice
is able to carry water to the top of the wheel, but the water would be high
enough to fill up some of the wheel's buckets, you use a breast water wheel.
If the difference is greater than 10 feet and the water would be high enough
to fill up the wheel's buckets at the top of the water wheel, you use an
overshot water wheel. Breast water wheels are more efficient than undershot
water wheels, but the overshot water wheels are the most efficient.
Until the late 1700's millwrights thought the undershot was the most efficient
type of water wheel because the rushing and bubbling water looked powerful.
In Europe the most common type of water wheel was often the undershot, because
of its additional use in tidal and boat mills. The undershot was the basic
water wheel all millwrights learned to construct. Some millwrights in Europe
only learned to construct undershot water wheels so when they came to America
they might construct an undershot water wheel operating from a 40 foot fall.
The development of the "ELBOW BUCKET" was a great advancement
over the "FLAT PADDLE" open bucket or "FLOAT,"
primarily used on the undershot water wheels.
In the United Kingdom and Europe the undershot, breast shot, and pitch back
water wheels were classified as undershot because the water flowed under
these types of water wheels. There are two types of traditional undershot
water wheels, the undershot and the flutter wheel. There are three types
of traditional breast shot water wheels, the low breast, middle breast and
high breast water wheels. There are two types of traditional overshot water
wheels, the overshot and the pitch back water wheels.
In the early 1800's the most common water wheel used to power American
industry was the breast water wheel. It was not until the 1840's did millwrights
discover which type of water wheel was the most efficient in different places
according to the available head, not the available flow. Wooden water wheels
had several drawbacks: they rotted out every ten to twenty years, and they
could not be operated in cases of ice, imbalance and debris. From the 1820's
to 1840's water wheels began to be constructed with cast iron shafts and
hubs. In the 1870's all steel water wheels eliminated the problems with
imbalance, rot, ice and debris.
Water power systems have both disadvantages and advantages. The advantages
are many. They use energy that is free, they do not pollute, they do not
use up the energy source, they return it to the stream unchanged, and they
add oxygen to the water which helps aquatic life. However, a disadvantage
is that they are effected by droughts, and floods. At one time there were
thousands of small water powered mills in use. As a general rule water powered
mills from northern Virginia north into Maryland, Pennsylvania, New Jersey,
New York, and New England, often had their water wheels inside of the mill
building to protect them from ice and freezing. Mills south of northern
Virginia usually had their water wheels outside of the mill structure. Historically
some water mills constructed a roof or awning over the water wheels to protect
the wheels. These roofed covered wheels might be either wide overshot, breast
shot or undershot water wheels. When a traditional wooden water wheel (which
was enclosed within the mill) was replaced by the modern Fitz Water Wheel
they too occupied the same original space as the old wheels.
The improvements seen in Oliver Evans' Automated Mill were developed
from 1782-83. The first edition of Evans work was published in "The
Young Mill-Wright and Miller's Guide," in 1795. Most mills constructed
until the 1870's were probably similar to the internal workings of an Oliver
Evans Mill. Most mills prior to Oliver Evans involved much manual labor
in the moving of grain and flour within the mill building. Many mills were
clustered along tiny mill streams. Before Oliver Evans, many industrial
complexes remained small and sometimes very isolated. With the improvements
of Oliver Evans, mill centers developed in areas either near the supply
of grains or close to the markets or sea ports. At the beginning of the
American Civil War, Richmond was the largest flour milling center in America.
Wheat grown in Virginia was superior to that grown in other areas for bread
baking. Besides Richmond, Virginia, and the Shenandoah and Cumberland Valleys,
other regions also had Oliver Evans influenced mills in the late 1700's
and early 1800's; such as in the Brandywine Valley north of Wilmington,
and in the Baltimore area. Virginia, Maryland, and Delaware led the way
with America's first installation of automated mill systems.
For the millwrights to harness the power of water to operate a mill, they
had to consider several elements. The mill stream had to have a fairly dependable
flow of water, and with sufficient fall to turn a water wheel without creating
the necessity for erecting huge dams. The stream had to provide a natural
dam site for the stability of the dam once built. Broad valley floors provide
poor sites for damming, whereas valleys with a natural constriction not
only limit the necessary size of the dam but provide more effective anchoring
points for the structure. A good mill pond location immediately upstream
of the mill dam must provide for the impoundment of enough water to operate
the machinery even during periods of relative drought. In areas were the
incline of the stream bed and where the ponds are confined between steep
they could not hold much water unless the dam was quite high. An area above
a natural constriction would be ideal to create a mill pond. Lower dams
were better for construction and repair costs, besides the dam structure
would have considerably less risk of undue water pressure, ice jams, and
Mill ponds situated in narrow valleys must be backed up a considerable distance
in order to impound sufficient water for the daily mill operation. The slope
of the valley floor ideally should not be raised high above the dam site.
A valley floor whose slope raises high above the top of the dam will require
an equally high dam structure. The terrain should open up just above the
dam site. When the pond is filled with water, it should be at a moderate
elevation. Mill ponds situated in broad valleys could impound sufficient
water within a very short distance above the dam, thus reducing the area
and height of the mill dam.
Dams which are built of wood are anchored against wood and stone abutments
to the creek banks. These abutments provide greater stability for the dam
structure and tend to prevent erosion and the undermining of the dam caused
by high water running around the abutments. Dams built of log or timber
cribbing are filled with stone rubble and faced on the upstream side with
fitted boards to resist leakage. Wood dams are not as durable as stone dams,
but are very strong and are more easily rebuilt if the dam is destroyed
by spring floods.
At least two outlets are required for each dam. The first is the spill way
which allows the surplus water to flow past and over the dam once the pond
is full. The second is where the water will flow to the mill via a mill
race, flume, or sluice. This second outlet can be a simple ditch, often
lined with stone or wood, or may be a complex wooden stave flume or plank
box sluice. A third outlet would be a natural overflow or seepage for the
rising spring floods, often away from the area of the milling complexes.
The miller who operated the mill and the millwright who constructed the
mill were each masters of milling. A miller was expert with his controlling
devices: the wheels, shafts gear trains, and the knowledge of how to adjust
his massive millstones to less than a wheat grains thickness apart. Well-balanced
millstones can be a paper's thickness apart. The millwright through the
apprentice system (prior to Oliver Evans' book) learned the advanced technical
knowledge necessary to milling more so then anyone in the colonies. The
millwright knew how to find natural ravines where dams could be built to
feed water to a mill as much as a mile away and maintain the height of the
water to the top of a water wheel. The millwright could lay out mill races
or canals at a constant elevation, following the natural contours of the
hillsides to bring the water to the mill at a point downstream where the
water would fall or drop on the wheel. The dropping point was a "FALL"
in millwright terminology. The water had to not only fall over or upon the
water wheel, but it also had to drain away downstream as efficiently as
possible. The millwright had to ensure that the water did not form a sluggish
puddle under the wheel to slow its rotation and diminish its power. The
mystery once solved allowed successful placement of a mill where none was
ever known to exist. Millwrights would use all of the knowledge to make
eventual solutions so that a system of shafts and gears would be used to
transmit power from the water wheel to one or more sets of millstones. As
the water wheel turned, the main shaft would be mounted to run the millstones
as well as to power additional machines of the mill by means of a system
of belts and pulleys.
Oliver Evans' book "The Young Mill-Wright and Miller's Guide"
also solved the great hydrostatic paradox of the time. The hydraulics problem
was to determine which water wheel to use, the overshot, the pitch back,
the breast shot, or the under shot. And then once the water wheel type was
determined, it was critical to judge which size of millstones was appropriate
for the water wheel chosen. This knowledge prior to Evans was only accessible
to the master millwright. Many early colonists built both tub mills and
vertical mills. A "TUB MILL" was the most primitive type
of mill, with its water wheel inside the building itself. The wheel was
mounted on the same shaft as the turning runner millstone. The wheel was
placed in a tub to cut down on the waste of water. Since the wheel is set
parallel to the ground, a tub mill was classified as a "HORIZONTAL
MILL." The water was funneled through a flume to the blades on
the water wheel and the sheer force of the moving water made the wheel turn.
The main shaft and the runner millstone mounted on it turned at the same
speed as the water wheel. This unsophisticated system was also called a
"GREEK MILL," "NORSE MILL" or "SWEDE'S
MILL." This type of mill could be easily transported to a better
site if the water power proved inadequate. A typical tub mill structure
measured about 12 by 14 feet. The familiar "VERTICAL MILL"
has its water wheel mounted on the side of the mill building perpendicular
to the earth, with the axle mounted horizontally. The vertical mill wheel
made it necessary to build a gear system to change the horizontal rotation
of the main shaft into a vertical motion that could be used inside the mill
to power the millstones. The smallest and the largest vertical mills have
a gear system, incorporating wooden (squirrel cage) pinion gears (called
"TRUNDLES") that were mounted at the bottom of the shafts
that turned the runner millstone. The colonial millwright could plan a mill
that would not only turn corners with motive power, but also make the millstones
revolve at a rate faster than the slow but steady turning water wheel. When
Oliver Evans patented his improvements in 1787 they increased the efficiency
and cost effectiveness of mills. Oliver Evans published his book on mill
construction and operation in 1795. This handy guide for putting up mills
may account for the underlying similarity among 19th century mills that
on the exterior look very different. Many millwrights simply would copy
the cross-section drawings of the layout of Oliver Evans' machinery directly
from his book.
Mills in America passed through at least four major eras of technology:
1. The traditional pre-settlement European technology ("LOW MILLING,"
"FLAT MILLING," or "AMERICAN MILLING"
2. The Oliver Evans "AUTOMATED MILLING SYSTEM" of 1787.
3. The NEW PROCESS MILLING SYSTEM of the 1850's and 1860's ("HALF-HIGH
MILLING" technology) which involves regrinding middlings on
smaller diameter millstones.
4. The Roller Mill system of the 1870's ("HIGH GRINDING,"
or "GRADUAL REDUCTION" technology), which incorporated
the New Process milling system and the use of the "ROLLER PROCESS."
This process of "WHEAT SAW MILLING" was developed by Hungarian
engineers in the mid-century.
There is a close connection between the agricultural hinterland and the
flour hungry seaports such as New York, Wilmington, Baltimore, and Richmond.
The Napoleonic wars ran the price of American flour prices up per barrel,
and even after the war. The larger mills were called "MERCHANT MILLS"
whose owners were capitalists with large investments. They bought wheat
and manufactured it into flour for retail sale to the neighborhood and bulk
sales by barrel to brokers. The "CUSTOM MILLS" or "COUNTRY
MILLS," on the other hand, were the small operations where the
miller ground grain for customers and kept a fraction of the output as his
fee or "TOLL," rather than charging in cash for grinding.
Some country mills made no fine flour at all, just grinding corn, buckwheat,
rye, oats, and animal feeds. After the 1920's, larger mills' flour production
began the end of the era of small rural Virginia mills. Buildings began
to either decay or were put to other uses. The western wheat and flour milling
centers (such as in Minneapolis) began to win over the ancient eastern milling
industry. Virginia mills operated on a local trade and on feed production.
The packaged western flour shipped by rail undersold that made by local
Virginia millstone and roller mills milling wheat grown often within sight
of these Virginia mills. A pattern of bankruptcies and trustee's sales developed,
with mills selling at lower prices at each successive auction and many of
the mills being stripped of the machinery which was moved elsewhere.
Some of the terminology of flour milling may be perplexing to the modern
reader. For example, the mill building itself was long referred to as "THE
MILL HOUSE," but later "THE MILL HOUSE"
came to mean the "MILLER'S HOUSE," or dwelling rather than
the functioning mill. "A SET OF MILLS" often meant merely
one mill building, possibly equipped with more than one set of grinding
mechanisms, often meaning equipped with a saw mill besides a grinding operation.
"A DOUBLE MILL" was referred to in the plural although
only one mill structure occupied that particular site. A double mill may
mean two water wheels operating two separate sets of gearing and millstones,
or a double mill may also mean a mill which includes two separate milling
operations such as grinding and sawing mills in the same structure. In describing
the mill's machinery or equipment of a mill, a "RUN OF STONES"
meant one complete set of grinding stones, the upper "RUNNER"
stone and the lower "BED" stone. A "TWO RUN OF
STONES" indicated two complete and separate units in the same mill,
four millstones in two pairs. The "RUN" of the mill is
what the mill grinds or the amount of grain ground by the millstones in
a given period. A "RUN" is another name for a "PAIR"
of millstones. A "MILL RUN" is another name for
the "HEAD RACE" and also "MILL RUN" refers
to what the mill was grinding each day. There is the "HEAD"
or fall of water and the "head" of the barrel which the miller
places his flour. To run the millstones too "THIN" means to run
the stones with too little feed which could ruin the millstones. A "MILL
BILL" is not a statement of charges or a list of items but another
name for a "MILL PICK" which is used to "DRESS"
or sharpen the millstones. Going "THROUGH THE MILL" does
not mean touring the mill structure but the grain that has traveled "THROUGH
This water wheel suffers from the most common problem with wooden water
wheels. The water enters the buckets forward of the vertical center of the
water wheel. The water should leave the end of the chute behind the vertical
center so the water wheel gets full benefit of the fall of the water. In
may water wheels that the water enters the buckets in front of the vertical
center much of the water can fly over or overshoot the wheel and be wasted.
See: Fitz Steel Overshoot Water Wheels, Bulletin No. 70, Decmeber
1928, by the Fitz Water Wheel Company, Comparison
With Wood Wheels
1. Selection of a mill seat or privilege. Does the stream site have an
abrupt descent on the stream bed, a succession of lesser falls, or an extended
rapids offering a concentration of fall favorable to power development.
2. The greater the height of the fall, the less the volume of water required
to obtain a given amount of power, thus reducing the size and expense of
the hydraulic facilities from the millpond and tail race.
3. Mill sites are more numerous and sharply defined in hilly terrain and
in the upper portions of a river system than in lower valleys with gentler
slopes and a typically sedentary character.
4. Typical mill installation consists of a water wheel erected besides or
beneath a mill structure; a dam at some suitable point up stream to divert
more or less of the flow into the headrace; and to increase the amount of
fall (usually to create a pond for storage of the nighttime stream flow);
a canal called a millrace, or headrace, to carry the water to the mill with
minimal loss of fall; a pen stock, or sluice, with gate, to convey the water
to the wheel; and a tail race to carry the water discharged from the wheel
with energy largely spent, back to the stream below the mill. A typical
mill race and sluice box has 1" to 0" fall.
5. Further appurtenances are needed such as gates to regulate water flow,
waste ways for contingencies of flood and high water, and trash racks to
keep floating debris and ice from clogging pen stocks and water wheel.
6. Dams are a barrier constructed of locally available material, such as
stone, timber, brush and soil, in various arrangements erected across the
stream with its ends well anchored in the stream banks on either side. Dams
may be a low structure. They are intended to divert water into a head race
to maintain the fall and develop horse power.
7. Dams raise the water level and backs water up stream depending upon the
height of the dam structure and the character of the local terrain. They
create a storage reservoir known as a millpond. This accumulated water will
run the mill for hours.
8. The simplest type of mill dam is a crude obstruction of tree trunks,
branches, and stones, the openings chinked with gravel, sand, clay, or loam.
9. Timber dams were the most common. A timber crib is filled with stones
10. Crib dams use narrow channels and high banks on each side. The dam consists
of two cribs secured to the natural embankment made of material that the
water will not penetrate. The two cribs have a V shaped connection between
them with an apron extending 3 or 4 feet forward of the cribs. The V shape
and the two cribs form an arch which holds the pressure of the water
11. Masonry Dams were never as common in America as they were in England.
12. Earthen dams generally have a stone or covered spill way.
13. Abutments at the stream banks and tumbling aprons of timber dams are
covered with planks or rocks to prevent the water passing over the dam from
undermining the dams foundations.
14. The dam should not be too close to the mill. A breach or leak on the
fore bay may wash away the mill. The mill should be placed to protect it
from floods and high water.
15. Waste water should be free to pass by the mill and not injure it.
16. Wide low dams handle high water or flooding best. Streams with narrow
dams during periods of high water or floods will overflow its banks.
17. The dams should have a good foundation. Mill walls should have a separate
foundation from the foundation which holds the husk or Hurst frame. It they
rest on a common foundation the machinery vibrations will shake down the
building around it.
18. Historic Note. The 19th century parcels tend to be internal subdivisions
of larger 18th century parcels, such as major lots or military land grants.
These larger parcels tend to have been surveyed. Therefore, reconstructing
these larger 18th century units can often allow one to accurately locate
and correctly position the smaller, otherwise ambiguous, later subdivisions.
Since mill dams were often built at the edges of parcels, where those edges
intersected the mill stream, the reconstruction of 19th century property
lines that may no longer exist can be critical in discovering unmapped dam
and pond locations. Hypothetical site plans and hypothetical delivery system
suggest and underscore the hypothesis that industrial parcels frequently
begin at mill dam locations and that reconstructing parcel intersections
with mill streams may often locate previously unmapped dams and ponds of
earlier mill sites.
19. Stone should be part of the abutment material in order to establish
a stable anchoring point for a mill dam, particularly critical at the sharp
bends in the creek or stream and at steep banks.
20. The site should be accessible to the supply of grain, transportation
(can you build a road to the mill), and flour markets.
The following is a list of items to consider and identify when establishing
a new mill site.
1. Size of mill structure.
2. Number of millstones (types of millstones for different types of flours).
3. Roller mills.
4. Combination millstones and roller mills.
5. Horse power requirements of machinery in the mill (what is the grindings
surface of the millstones).
1. Animal and human.
3. Water: stream and tidal.
7. Gas: liquid and natural.
Water Wheel or water motors
1. Type of water wheel: a) horizontal: norse mill, tub wheel, turbine; b)
vertical: undershot, flutter, low breast, mid breast, high breast, pitch
2. Width of water wheel (if the water wheel is vertical).
1. Types of dams: log, timber, crib, earthen, stone or masonry.
2. Size the area which the dam back floods.
3. Spill way, overflow.
4. Wash out gate.
1. Head race: a) in ground mill races- earthen, earthen lined with stone,
wood or brick; b) elevated or buried channels; c) wooden sluice box; d)
pen stock, either round wooden pipe, concrete pipe, round masonry stone
or brick, or metal pipe of either sheet metal or cast iron pipe.
2. Tail race: open earthen race or enclosed underground race.
1. Trash racks.
2. Head gates.
3. Control gates.
4. Flood gates.
Type of milling operations
1. Custom mill.
2. Merchant mill.
3. Feed Mill.
4. Combination mill.
POWER= Cubic feet per minute x 62.125 (weight per cubic foot of water) x
and divide by 33,000 pounds
Head would equal the 16 foot diameter water wheel plus one foot below the
water wheel for the water to flow into the tail race, one foot of water
above the water wheel for the water to enter the water wheel, and three
feet of water standing in the sluice box. This would equal 21 feet of needed
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