top of page


Mill Operation


Custom windmills are not just giant pinwheels that blow in the wind; they are, truly, factories.  Like any machine in a factory, the parts of a windmill need to be inspected, cleaned, and lubricated before operation can begin.  These complex machines require the miller to retain a unique and thorough knowledge of physics, meteorology, agriculture, and sailing.  The following page details how an Illinois windmill is typically operated, from morning inspection to bagging ground grain. 



Mill Inspection


Upon arrival, the miller will inspect the exterior of the mill for any obvious wind damage to the cap, sails, tie beams, or tower; immediate repairs are arranged, since damage to any of these critical areas would prevent milling. 


Inside, the teeth of every cogged wheel need to be checked for cracks or breakage.  On most windmills, the teeth can be easily replaced by removing wooden wedges within the wheel that holds them in place (a good miller will always have spare parts for common repair items). 





Millers must also visually inspect the bearings and contact points of all the moving parts.  Cracks and other visible wear must be remedied immediately to prevent costly repairs.  Lubricants, used to reduce friction between parts and ensure a smooth run, must be applied at either end of the wind shaft, drive shafts, quants, tentering machinery, and the machines for preparing and bagging grain


A spray can of WD-40 is not enough for windmill parts.  Although some millers throughout the world have turned to industrial gear oil or lithium-thickened grease, lard is the traditional lubrication of choice.  Sheep lard is used between the wooden sheers of the cap and the dead curb ring of the tower so that it will be easier to turn the cap into the wind.  Hog lard is best between metal parts, especially on an iron wind shaft.  Beeswax lubricates the teeth on the cog wheels.



Safety Precautions


Even with the band brake applied, the sails can turn in high winds.  To keep the machinery from turning, the stone-nut(s) may be engaged, and wooden chocks or pawls are wedged into the brake wheel.  Once the mill inspection is completed, these devices are disengaged or removed.


Outside, safety chains must be removed from the capstan wheel (or winch) at the end of the tail pole.  Additionally, the sails must be unchained from the stage or anchor point (sail anchoring also doubles as a lightning ground on windmills with metal sail stocks).



Grinding Stones


The grinding stones periodically need to be cleaned and, depending on the amount of work performed, need to be “dressed,” referring to the act of chiseling new cracks and grooves to form a grinding pattern.  When working together, the two stones literally cut into grain with a scissor-like action, pulverizing it.  This is not unlike a burr coffee grinder: in fact, commercial burr grinders (like those at Starbucks) are based on traditional mill stone design.


In order to access the stones, the vat needs to be removed.  The vat is a round wooden box that encases each pair of grinding stones, designed to trap and sweep ground flour into a chute for bagging.  Sets of locks on the vat are unlatched, and each half is removed to expose the stones.


Each windmill is equipped with a specialized crane to aid the miller in lifting the two-ton stones by hand.  With the vat removed, a pair of bails (a large, tong-like device) is attached to the runner stone.  The bails are joined by a threaded rod that runs through the upper arm of the crane.  When the miller turns the stone by hand (which is perfectly balanced between the bails), he can lift or lower the stone as necessary.  Once free from the bed stone, the runner can be swung out of position and pivoted for maintenance.

The cogged teeth of the great sput wheel in De Immigrant are covered in beeswax.

Photo by Tom Haskell

This wooden pawl was installed in the cap of De Immigrant to prevent the brake wheel from turning when not in use.

Photo by Tom Haskell


The vat and crane in their normal positions

The wooden vat is removed and bails are attached to the threaded rod.

Bails are attached to the sides of the runner stone.

The runner stone is turned by hand, rising as the threaded rod travels.

The stone is swung out for maintenance.


Illustration by Tom Haskell

Pre-Operating Procedures
Luffing the Cap


Capstan wheels (left) and winches (right) are both used for the same purpose: to tug the tail pole into the direction the miller wishes to turn the cap.  In both cases, a chain or cable is tied to an anchor point (usually, a bolt or clamp built into the eight corners of the stage) and threaded through the tail pole.  When the wheel or winch turns, it winds the cable taught, pulling the tail pole closer to the anchor; the tension is so great that the tail pole pivots the cap. 


In 1745, an English miller, Edmund Lee, invented the tail fan—an additional, smaller set of sails (somewhat resembling the wind wheel of an American wind engine) that automatically turns the cap into the wind without any action by the miller.  A few destroyed mills—such as Holstein’s, Brockman’s, and Bartels’—all used tail fans.  Note that these windmills do not have tail poles or bracing.


The photos of the Fabyan Windmill below demonstrate the process known as winding or luffing the cap into the new direction of the wind.  They were taken from the same spot on the ground as the cap was being turned from the south to the southeast: 

Photos by Tom Haskell

Photos by Tom Haskell

Reefing the Sails


Once the sails are facing the wind, the next step is to determine how strong the wind is.  The miller determines the amount of canvas to be drawn over the sails based not only on the wind’s speed, but also on the size of the mill and the amount of work it needs to perform.  A large custom windmill ready to grind and operate wind-driven grain preparing machines will require more wind power than a small wind engine will for pumping water.


Regardless of usage, the canvas sail cloth (and the required rigging) is always left on the sails; the canvas is rolled and wrapped through the sail bars along the whip.  The design of the sails may resemble that of a ladder, and for a good reason—unfurling the canvas requires the miller to climb each sail, one at a time, to make adjustments.  In very high winds, the miller will probably choose not to run the sails with canvas; in fact, he may even remove portions of the wind board, which is located on the leading edge of the sail. 


In lower wind speeds around 35 miles per hour, the miller would need a full wind board and may also choose to unfurl part of the canvas.  Covering about one-quarter of the sails in canvas is known as the first reef position; in moderate winds, the curved sword-point canvas covers roughly half of the sail; very low winds require the dagger point, covering three quarters of the sail; and little to no wind requires the full sail.  Once the miller has manually adjusted all four sails, operation can begin.


Photos by Tom Haskell

Partial Wind Board

(not in use, or over 40 mph)

First Reef

(30 - 40 mph)

Sword Point

(20 - 30 mph)

Dagger Point

(10 - 20 mph)

Full Sail

(under 10 mph)

Illustration by Tom Haskell



The sails are also used to describe the miller’s state of business.  Below are the four typical sail positions of windmills, which are (from left to right): long rest (Saint Andrew’s cross), short rest (Saint George’s cross), celebration, and mourning.
During celebration, the miller would dress the sails in full canvas and fly the colors of the national flag (the grand opening of the Fabyan Windmill is an example of this).  In mourning, the wind boards on the sails determined how close the deceased was to the miller (the more wind-boards removed, the closer the relation).  If the miller himself died, his windmill would turn slowly as all others remained motionless.

Saint Andrew's Cross

(long rest - closed)

Saint George's Cross

(short rest - stand by)


(flying national colors)


(full sail, no rotation)

Illustration by Tom Haskell

cutaway view

Cutaway view of the Fabyan Windmill as it currently appears in Geneva, IL. The basement level was not present when the mill was located in Lombard; thus, the machinery found in the basement would have been located on the first floor when it was built. Note too that it was unusual to have an auxiliary iron drive shaft for equipment that would have been turned by wooden gears.

Illustration by Tom Haskell

Custom Windmill
Grinding Machinery


A—The internal brake lever that releases the brake.


B—The brake wheel, which is surrounded by the brake.


C—The wind shaft holds the sails together.


D—The wallower transfers power from the brake wheel to the main drive shaft


E—Main drive shaft, delivering power to all moving parts below.


F—Friction wheel, which turns the sack hoist.  On some windmills, this is a crown wheel that turns grain elevators.


G—Great spur wheel, which transfers power to the stone nuts.


H—When engaged, the stone nuts receive power from the great spur wheel to turn the grinding stones.


I—Quant, or stone spindles, a wooden or iron rod running from the stone nut to the grinding stone


J—Auxiliary drive nut, used to power a drive shaft for other machinery.


K—Auxiliary drive shaft.


L—Corn dump bin, where the corn cobs are deposited for processing.


M—Corn sheller, removes kernels of corn from the cob


N—The corn grain elevator lifts the processed corn to the third floor, where it is dumped into a bin for grinding.


O—Wheat dump bin, where whole wheat grains are deposited for processing


P—The smutter is a device that removes the chaff (or shell) that surrounds the wheat berries (used in making flour) via centrifugal force.


Q—The wheat grain elevator lifts the processed wheat berries to the third floor.


R—The cleansed wheat is then dumped into the grain garner.


S—Wheat then travels down a chute to the grain hopper for grinding.


T—Grinding stones come in sets of two; the runner stone (in this case, the upper or overdrift stone) is the one that is turned by the quant.


U—The stationary stone, or bed stone (in this case, the lower stone) remains in place.


V—Vat, a removable wooden enclosure for the grinding stone, designed to catch the flour or meal after it is processed and scoop it into the next chute.


W—Bolting machine, which contains a screen used to sift and separate flour by fineness.


A corn scalping reel (not pictured), on the first floor, performs the same task as the bolting machine, but separates fine corn meal from coarse feed.

Grinding Grain


In most cases, nearly all of the controls the miller may need are accessible at the stage level (on all Illinois windmills, the second floor).  From the stage, the miller tugs down on the brake rope to lower the brake lever (A).  With the brake wheel (B) free to rotate, the sails begin turning.  The brake wheel, which is located directly on the wind shaft (C), turns the wallower (D).  The wallower connects directly to the main drive shaft (E) that turns all other gearing within the mill.


Since most windmills grind at least two types of grain (usually corn and wheat), two separate but similar grinding systems are present.  With wheat grinding, the farmer first empties sacks of grain into the wheat dump bin (O).  The whole wheat travels down a chute into the smutter (P).  Using a series of screens and centrifugal force, the wheat is first separated from dirt, debris, and other impurities.  The wheat berries are then separated from their shell (or chaff), and a fan blows the waste material out of the mill. 


A friction or crown wheel (F) may be present to turn the pulleys within the grain elevator heads or to engage a sack hoist.  In either case, its purpose is to raise prepared grain to the upper floors for grinding.  The cleaned wheat is lifted via grain elevator (Q) to the third floor and dumped into the grain garner (R).  Berries then drop into the hopper (S) for grinding. 


Corn follows a similar path: the farmer dumps whole ears of dry corn into the bin (L).  After being separated from their cobs and other debris by the corn sheller (M), kernels of corn are taken to the upper floors via the corn grain elevator (N).  Like the wheat process, corn is dumped into a garner and then into a hopper for grinding.


The great spur wheel (G), the largest cogged wheel of the mill, delivers the power necessary to turn the heavy grinding stones.  When engaged, the spur wheel turns the stone nuts (H) and the auxiliary drive nut (J).  The auxiliary drive shaft (K) powers machines in the lowest levels of the mill, including the smutter and corn sheller; the stone nuts turn the quants (I).  Through an automatic process (the “shaker”), the grains in both hoppers are tapped into the eye of the grinding stones, and flour or meal is produced through the cutting action by the upper runner stone (T) against the stationary bed stone (U).


The stones are encased within a removable wooden casing known as the vat (V).  The vat must be present to contain the flour or meal as it is ground and to scoop it into the wheat bolter (W) or corn scalper for bagging. 




Precautions While Milling
Tentering the Stones


On some mills, a fly-ball governor (pictured to the right) controls the distance between the grinding stones—a process known as tentering.  As the wind speed (and thus the mill’s speed) increases, the distance between the stones must be greater to accommodate the increased amount of grist entering the vat. 


While grinding, the miller needs to know how close the stones are, even if the windmill is equipped to do so automatically.  By keeping his “nose to the grindstone,” the miller can adjust the stones if he smells flour burning from friction.  If the mill suddenly loses wind power, the stones would also have to be adjusted—quickly—else the mill can literally “come to a grinding halt.”



Storms and Tail Winds


Stormy weather can be dangerous for windmills: high winds blowing from different directions can easily try turning the sails, which can strain the machinery; lightning strikes can set the mill ablaze; and heavy rains can flood the main level.  Needless to say, these conditions prevent milling and cause significant delays during the fall harvest.


The sails are susceptible to damage from dangerously high winds, icing, and stress; thus, sails are constructed of inexpensive pine that can be easily replaced.  Most importantly, the sails cannot spin out of control, or they can cause the wind shaft to rotate out of its bearing.  To counter this, the miller counts the number of times a sail passes a window (on a four-sailed windmill, dividing the number of times the sail passes in one minute, divided by four, yields revolutions per minute).   


When weather prevents operation, all a miller can do is roll up the canvas and “quarter” the cap.  Quartering involves turning the cap 90 degrees from the general direction of the wind.  This way, the wind will neither turn the sails from the front nor from the back. 


The worst possible damage to the mill can occur from tail-winds.  Hoover Dam was constructed specifically to accept stress from the waters of Lake Mead.  Could you imagine if the dam was suddenly forced to hold water back from the opposite side instead?  Windmills, similarly, are built to accept the wind head-on; but a tail wind can push the sails—and, in fact, the entire cap—right off the tower of the mill. 





The brake wheel (A) is so named not because it alone has any stopping power, but because this wheel is surrounded by a band brake.  A wooden brake (B) encircles the brake wheel, and expands or contracts against it to slow the rotation of the sails.  One point is fixed to the cap, and the other end is fixed to the brake lever (C).  When the lever is applied, the brake clamps against the wheel. 


If the wheel were to stop on a dime during grinding, the momentum contained in the sails would be so great that they would break free of the wind shaft and become deadly projectiles.  Conversely, applying the brake too slowly causes the wooden parts to smolder.  Thus the miller needs to pulse the brake lever in a steady manner to ease the rotation of the sails without setting the cap on fire.



Machinery, Services, and Tools


Some millers knew that being closed meant taking a great business loss.  Since windmills are considerably more unreliable than water mills, some added engines to drive the grinding stones when there was no wind.  No surviving windmills still use steam engines, but the chimney still stands next to the Peotone Windmill, and an old steam engine drive shaft is still present in the west wall of the Fischer Windmill’s tower.


Not only could a farmer get his grain ground, sifted, and bagged, but he could employ someone to sharpen his tools or mend his clothes while he waited.  The cutaway diagram of the Fabyan Windmill illustrates every part of the grinding process.  It is also unique in that has: a basement level, where the grain preparation equipment is; grain elevators, which were only present in a few mills; and an auxiliary drive shaft to drive the grain-preparing equipment and sharpening stone.


Tools were necessary for daily operation, and for shaping replacement parts for the windmill.  Specialized hack saws, wrenches, and chisels were used for cutting wooden parts, tightening the metal fasteners in the gearing, cranking the tail pole winch, and dressing the stones. 

The brake system within

the cap of De Immigrant.

Photo by Tom Haskell

This fly-ball governor prevents De Zwaan in Holland, MI from "coming to a grinding halt".

Photo by Tom Haskell

The wheat bolter in the Fabyan Windmill

Photo by Tom Haskell

A hopper and vat in the Fabyan Windmill

Photo by Tom Haskell

bottom of page