(Here's the whole article that I didn't finish last week.)
So first, let’s settle just who Oliver Evans was. Oliver was born on Sept. 13, 1755 in Newport, Delaware. At the age of 16 he was apprenticed to a wheelwright where he became familiar with the wagonmaking business. He then took a job where the fine wires were made that were used to card wool or cotton in preparation to spinning them into yarn or thread. While there he designed a machine that bent and cut the staple-like wires at the rate of 1,500-per-minute.
In 1782 Oliver and his brother Thomas moved to Tuckahoe, Md., where they opened a small store. He must have visited a local grist mill, probably to obtain flour for his store, because it was here that he first got his ideas that led to the automated flour mill.
He was soon called home to join his older brothers in the construction of a mill on property along the Red Clay Creek that they had purchased from their father. When finished, the mill operated the same as all other mills were operating, but over the next few years Oliver put into operation some of his ideas that resulted in a fully automated milling process.
In mills of the late eighteenth century, sacks of wheat were carried up steep stairs to the top floor, opened and dumped into a hopper that fed a rolling cylindrical screen that removed chaff and dirt. It then dropped down through a chute into a hopper that fed the millstones on the second-level. The ground wheat, now called meal, descended through another chute to another chest in the basement. The warm and moist meal was shoveled out of the chest into buckets that were hoisted back up to the third floor. There the meal was spread out onto the floor to cool and dry a bit before it was pushed into a hole in the floor and down a vertical chute to the bolting cylinder. There the fine flour was separated from the lower-grade middlings and bran, which spilled out the end of the reel and were used as animal feed. The flour was shoveled out of the chest beneath the bolter into wooden barrels, which were then closed for shipment to market.
As you might imagine, not only was this entire process a lot of work but it also left a lot of opportunity for contamination of the product and, even then, people didn’t like having specks of they didn’t know what in their flour. However, up until then there was not much industrial innovation. People tended to do things the same way it had always been done.
Evans' new system made no changes in the way that grain was cleaned, ground, bolted (that is, sifted through bolting cloth) and packed. The five improvements were all in the way that grain or flour was moved from one process to the next in the mill. The first was the bucket elevator.
The improvements that Evans came up with were the bucket elevator*, the “hopper-boy,” which cooled and dried the flour, the screw conveyor*, the “drill,” or horizonal conveyor*, and the descender, or belt conveyor. (These three items * are incorporated in Abbott’s mill). In 1790, when the federal patent office opened, Evans filed an application and was granted the third patent issued in the United States for his “New Method of Manufacturing Flour and Meal.”
At Abbott’s Mill, elevators are used in many places. Just the cornmeal grinding (millstone) operation incorporates five elevators. Four of them are over 30 feet tall and go from the basement floor, all the way into the top of the attic. The fifth elevator is only about 8 feet tall and carries cornmeal from one of the other elevators, up to a small attic storage bin that’s just a little higher.
Attic level
<--The attic storage bin is on the left
Second floor
Ground level
Basement level
However, in the roller mill operation, there are a great deal more elevators, plus two other Oliver Evans improvements. As I explained last week, as soon as grain enters the mill it is dumped into a hopper feeding an elevator, which carries the grain up to the grain separator in the attic. From there gravity takes over for a while until the grain makes its way through the scourer. It then begins the journey through as many as nine elevators as it is slowly reduced in size and sifted and resifted several times. Each time it goes through one of the six roller mills, it must then enter a different elevator, to be carried up to the next trip through the “Gyrator” and back to a different set of rollers. And then the “overs,” the middlings and bran, enter their own elevator to be carried up to the flour dresser (or bolter) in the attic. And finally the flour enters yet another elevator, to be carried up to one of the two flour bins.
But, we aren’t finished with elevators just yet. There’s also another elevator tucked away that’s part of a short “mystery” operation. In the back room on the ground floor, (where the mill model is) there is a floor hatch that leads to a small bin in the basement that feeds the largest elevator in the mill. (Largest, meaning bucket size.) This elevator goes up to a fairly large storage bin on the second floor. Whatever went in that bin could be retrieved from a chute right next to the floor hatch.
My guess is that it was used to temporarily store animal feed that was made from ground-up corncobs and other stuff. That’s just a somewhat educated guess, but no one has come up with anything better, yet. What do you think? You can leave your comment below.
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Elevators work fine for moving material vertically to a higher location, but what if you need to move it horizontally? That’s what the other two Oliver Evans improvements do. At Abbotts Mill, there is a screw conveyor, which Evans called simply “the conveyor”, and there is also a horizonal conveyor, which Evans called “the Drill".
The Archimedean screw had been invented by the legendary Greek inventor Archimedes sometime in the second century BC, (that’s over 2200 years ago.) It has historically been used to raise water to a higher level, but no one had ever thought to use it to move grain or flour.
Evans saw a screw conveyor being used by the four Ellicott brothers, Quaker millers near Baltimore, and obtained their permission to include it in his mill designs. Their design was of a continuous helical screw, similar to the modern one below.
Evans found that angled wooden paddles prevented the warm, moist flour from caking up, but the principal was the same.
At Abbott’s Mill, a screw conveyor was used to move grain from under the wheat separator in the attic, to different storage bins on the second floor where there isn’t enough vertical distance to use chutes. The screw is 7 1/2 feet long and operates in two directions from a starting point near the center.
The last of Oliver Evans’ improvements to be found at Abbott’s Mill is a short horizonal conveyor, or “Drill” as he called it. (I have no idea why he called it a drill, but that was 130 years ago, so who knows.) It consists of a wooden box, 5 inches wide by 8 inches high and about 40 inches long. Near each end is an axle that crosses the box and inside is a pulley at each end that a cotton belt rides on (just like in the elevators).
Attached to the belt are small, wooden paddles that sweep the “floor” of the box, drawing the flour from one end of the box to the other, where it falls down a very short chute into the bolter. I have visited many other mills, but I've never seen a "Drill" in any of them. Maybe they were there, but not that I ever noticed.
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This Sunday I'll be representing SPOOM-MA (the Society for the Preservation Of Old Mills-Mid Atlantic chapter) at the Mid-Atlantic Grain Fair. I'll take notes and pictures and share them here next week.