Neander97 / Historical Trivia: The mechanical principles underlying the working of a water-powered mill are, from the hindsight of the 20th century, quite simple. Whether undershot or overshot, the water propels the wheel, which transfers the water's power to the drive-shaft, which turns the millstones. Of course, waterwheels were employed to do more than mill grain, by the 10th century C.E. waterwheels were supplying power for bellows and trip hammers and soon after were powering wood saws and metal lathes.

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Waterwheels and Mills

see also: Waterwheels and Mills: A Select Bibliography

In all likelihood, the earliest tools employed by humankind for crushing or grinding seeds, nuts, and other food-stuffs consisted of little more than a flat rock, upon which the material was crushed by pounding with a stone or tree branch. Indeed, "wild" chimpanzees have been observed employing just such flat rocks and branches to open hard-shelled nuts. The first substantive improvement on the rock and branch type-crusher was the mortar and pestle. The archaeological records shows that as early as 30,000 years ago, Cro-Magnon artists employed the mortar and pestle to grind and mix the pigments they used to create their magnificent "cave-art."

Far more efficient than the flat rock or even the mortar and pestle was the handmill, quern, or as it is known in the New World, the mano and matate, which appears to have long pre-dated the agricultural revolution (see Figures 1 & 2). The handmill consists of a flat rock, often hollowed or concave, on which the grain, seeds, or other materials is placed, and a grinding stone, which is rolled across the grain, thus reducing the grain to flour. Although the handmill is still, today, in use in many parts of the world, approximately 2,000 years ago humankind began to harness water-power to turn the stones that ground its grain.

By 200 B.C.E. water-powered grist mills began to appear in substantial numbers in Egypt and by the First Century C.E. waterwheels and water-powered mills were common throughout the Mediterranean littoral. It is believed that the waterwheel spread into the Mediterranean community from Western Anatolia, where, it is believed, the technology was borrowed from the Persians, who, may have in turn, learned of the waterwheel from the Chinese. The earliest known examples of waterwheels were of the horizontal design, that is to say, the paddle wheel lay flat in the water and acted directly on the spindle or drive shaft (See Figure 3).

As early as the First Century C.E., the horizontal waterwheel, which is terribly inefficient in transferring the power of the current to the milling mechanism, was being replaced by waterwheels of the vertical design. In general, there are two types of vertical waterwheels, the undershot (See Figure 4) and the overshot (See Figure 5), which is the more energy efficient of the two. Both varieties of the vertical waterwheel require the use of gears to transfer the motive force of the water to the milling mechanism.

There are several disadvantages to the undershot waterwheel. One being in the manner in which the water's force or power is utilized. The undershot waterwheel rests directly in the stream and depends upon the force of the water to push the wheel. In addition to inefficiently harnessing the stream's motive force,the undershot wheel also requires a rather substantial and constant of water, and thus becomes even more inefficient or even useless at times of low stream-flow.

Because of the need for a constant and steady water supply, it is most often the undershot wheel that is found in association with a millpond. The overshot waterwheel, on the other hand, more efficiently harnesses the motive force of the stream and is far less dependent upon streamflow. In fact, the overshot wheel can be operated at some distance from the actual stream or water source. Water to power brought to the overshot wheel by means of a flume or pipe. From the flume, the water drops onto the wheel's paddles, thus harnessing both the force of the water and of gravity.

The mechanical principles underlying the working of a water-powered mill are, from the hindsight of the 20th century, quite simple. Whether undershot or overshot, the water propels the wheel, which transfers the water's power to the drive-shaft, which turns the millstones (See Figure 6). Of course, waterwheels were employed to do more than mill grain, by the 10th century C.E. waterwheels were supplying power for bellows and trip hammers (See Figure 7) and soon after were powering wood saws and metal lathes.

In the Late Middle Ages, gristmill complexes often took on an almost industrial character. In Figure 8 we see the complexity of such an operation. Note the two undershot water wheels, with accompanying spindles and lantern gear, at the center of the figure. The pack animals haul the grain to scales. After being weighed and recorded by the tally-master, the grain was fed to millstones via the two hoppers. Note also the spare millstone.

Sources:

Frances and Joseph Gies, CATHEDRAL, FORGE, AND WATERWHEEL: TECHNOLOGY AND INVENTION IN THE MIDDLE AGES (1994).

L. Sprague de Camp, THE ANCIENT ENGINEERS (1974).

Henry Hodges, TECHNOLOGY IN THE ANCIENT WORLD (1992).

Sir Joseph Flawith Lockwood, FLOUR MILLING (1945).

John E. Pfeiffer, The Emergence of Man (1969).

see also: Waterwheels and Mills: A Select Bibliography

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