Building a Gristmill: How Does a Mill Work?

Pennsylvania man tackles design and construction of Colonial-era gristmill at Nittany Antique Machinery Assn.

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by Gary Gentzel Sr.

How does a mill work? Learn about the design of a colonial gristmill, and how an old grainmill works through this new construction in Pennsylvania.

After a long career at Pennsylvania State University, where he had worked in the Office of Telecommunications, Bob McLaughlin had a plan for a retirement project. He just needed a little help getting launched. “In 2007, I approached the Nittany Antique Machinery Assn. (NAMA), Centre Hall, Pennsylvania, and asked them if they’d be interested in me building a gristmill on their showgrounds,” he says. “But they’d have to pay for it.”

Bob had no farm background. He was not a collector of antique farm equipment and he didn’t belong to NAMA. Shoot, he didn’t know anyone who did. “I was hoping to find a place where I could help restore an old gristmill but that didn’t happen,” he says. “So I started thinking about NAMA. They put on tractor shows and demonstrations. And you know, the gristmill is the end to the whole process from planting to grinding.”

Don Athey, Kevin Shell and Bob McLaughlin standing outside the newly constructed mill.

Today, the gristmill built by Bob and a team of NAMA volunteers features the only wooden water wheel in central Pennsylvania. An unusual attraction, the replica of a colonial-era gristmill typically draws a couple hundred visitors during the annual NAMA show. “I don’t know too many others that were started from scratch,” he says. “Usually, people try to restore an old [grainmill], but there are a couple crazy guys like me.”

A process requiring patience

The word gristmill typically defines a process in which millstones are used to grind grain. The grain is fed into a hole (the eye) in the upper (or runner) stone and is ground into flour or meal between it and the lower (or bed) stone. A set of gears driven by the water wheel causes the upper stone to turn; the lower stone is fixed and does not turn. The millstones are enclosed in a hoop that directs the ground grain to a meal spout where it is collected.

A black wooden waterwheel attached to the gristmill.

Bob’s interest in gristmills dates back more than 30 years. A long-time member of the Society for the Preservation of Old Mills, Bob began attending conferences on the topic in 1990, so it was no huge leap for him to design the mill he had in mind for the NAMA showgrounds. But it didn’t happen overnight.

After winning NAMA support for the project in 2007, Bob found a set of millstones in 2010. During the next five years, the structure’s design was completed, timbers were cut and the foundation was completed. Construction of the mill took two years; two more years went by before the water wheel was constructed. Finally, in September 2018, the mill made its debut.

A lucky find

Millstones were an essential component for the replicated colonial gristmill, but they’re not the kind of thing you pick up at the local hardware store. “We knew what we were looking for,” Bob says, “but they’re fairly expensive. We were hoping for a donation of millstones.” That didn’t happen, but in 2010, he found a set being used as yard art at a local residence. The fact that the stones had originally been used in a gristmill in Clarion County, about 100 miles away, was a bonus.

The stones are not the highest quality, Bob admits, but they work. Measuring 42 inches in diameter, they are a medium size set for gristmill work. Grooves are chiseled in to the stones in precise patterns. Stones used to grind corn require bigger grooves; stones used to grind wheat have more shallow grooves. “Ours were probably corn stones,” he says. “They have fairly deep grooves.”

Early millstones used in America were typically shipped from France. On trans-Atlantic crossings, they were used as ballast. “Ours is described as ‘quarter-dress,'” Bob says. “The grooves are straight.” An unusual alternative style is the “sickle dress,” with curved grooves.

How does a mill work?

A closeup of the millstone gears from underneath.

Once millstones were obtained, the process of design began. Through his involvement with the old mill preservation group, Bob had some familiarity with the type of building needed. The timber-frame structure would be built with mortise and tenon construction.

A person standing over the milling stones, feeding corn in.

The first step was cutting timbers for the frame from red oak, using the club’s sawmill. “That saved us a little money,” Bob says. “Framing for mill machinery is usually white oak, for strength and durability, but it was just too expensive.” Bob conducted an engineering analysis early on. “I didn’t want there to be a post in the middle of the viewing area,” he says.

Closeup of corn moving from the hopper to the shoe, then being milled.

Bob had no previous experience with timber-frame building. NAMA member and professional carpenter Don Athey was eager to help, but the project would be his first experience with timber frame construction as well. “One of the guys watching said, ‘Gee, I never thought it would actually go together,'” Bob recalls. “I was very glad when it did.”

Closeup of the NAMA gristmill stones running.

The timbers were fastened with oak pins. “An Amish man made them for us, 25 cents each for 200,” Bob recalls. “We were all rookies. A bunch of the volunteers had construction experience but nobody was experienced with timber construction. It actually went pretty well. A local hardware company brought their crane and lifted timbers for the roof. That was a real godsend. I don’t know how we would have done it without that help.”

Viewing platform maximizes old grainmill visitor experience

The grain milling process is only a small part of answering the question, ‘how does a mill work?’ A concrete-block foundation supports concrete floors. The structure consists of a large open space with a viewing platform and basic mill machinery. Gears, pulleys and bearings for the mill’s drive train were sourced from a donation of two trailer loads of old grainmill parts. “All of the donated parts were in good shape,” Bob says. “We only had to make two pieces.”

The structure measures 16 by 30 feet (“Now everybody says we should have made it bigger,” he says) in a split-level design that includes an observation platform. “That way, people can see the drive train and look up and see the millstones,” he says. Positioned on a hill, the mill building rises 10 feet to the eaves on the sides of the building. “The roof is fairly steep,” Bob says. “It’s a 45-degree angle.”

Guests walking around the gristmill exhibit.

Made of red oak, the mill’s water wheel measures 18 feet in diameter by 2 feet wide; the shaft is 18 inches in diameter by 10 feet long. “The guys cut the shaft at the show,” Bob says. The water wheel churns through a pool of 5,000 gallons of water hauled from a pond at nearby Penn’s Cave. Eventually, a pump will be used to recirculate the water.

For now, an antique tractor is used to provide power for the mill. “We’re still working on the water wheel’s drive train,” Bob says, “so we’re running the mill with a tractor and a belt pulley through the other side. We’ve run it on steam and stationary engines and it’s worked well on both. We use a 6hp engine; I think the minimum needed is about 3hp.”

In business for the long haul

Other than a structure Bob built to feed grain to millstones, there is little else in the gristmill. That simplicity has paid off. “Our first attempt at grinding was during the September 2018 show,” Bob says, “and we have run it every year since.”

A white stone that is flat on the left and has a deep hole on the right with markings from being used to grind grains. There is a sign labeling it as an Indian Mill, with an approximate date of origin of 1600 -1700.

Thus far, the mill has only been used to grind corn, but there was some trial and error in learning about how does a mill work. “We’ve had pretty good success with corn,” Bob says. “We tried wheat one time. Apparently, wheat is different than corn. We had wheat berries flying everywhere. It was kind of a disaster.”

A three-man team meets weekly to maintain equipment and prepare for shows; the three also run the mill during NAMA shows. “We’re gradually getting more volunteers,” Bob says. And who knows? Any day now, somebody could open the gristmill’s door and find his retirement project. FC

For more information, email Bob McLaughlin at

The 48th annual Nittany Antique Machinery Assn. Fall Show will be held September 8-11, 2022. For more information, visit Nittany Antique Machinery Association on Facebook; online at Nittany Antique.

Leslie C. McManus is the senior editor of Farm Collector. Contact her at

  • Updated on Aug 4, 2022
  • Originally Published on Jul 19, 2022
Tagged with: corn mill, Gristmill, mill, restoration
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