How a Threshing Machine Works

Inside the box: explaination of how a threshing machine works

| January 2000

The first threshing methods involved beating grain by hand with a flail, or trampling it by animal hooves. An early threshing machine, patented in 1837 by Hiram A. and John A. Pitts, Winthrop, Maine, was powered by horses walking on a treadmill. Improvements were made to the original machine until late in the 1800s. The threshing machines used early in the 20th century were basically the same, except for the power source. About 1890, steam engines replaced horses and mules, and around 1915, tractors with diesel, kerosene or gasoline became more prevalent. In the early 1920s, combines – a combination harvester and thresher – made their debut, but they did not replace threshing machines completely until about the middle of the century.

A threshing machine is used to separate the grain from the straw and other light materials. It is, essentially, a three-step process:

In the first stage, bundles of grain and straw were pitched into the feeder (or hopper). The feeder controlled the rate of feed passing into the machine to prevent overloading. In reality, the rate at which the bundles were pitched into the hopper probably had more effect on the rate than the hopper itself.

In the second stage, the separator, a rapidly rotating set of blades (visible at the end of the feeder), first tore the bundles apart, breaking the twine and snapping the heads from the straw, then beat the straw and heads onto a grooved plate, knocking kernels from the heads without crushing them. The straw then passed over a straw rack that removed most of the straw from the kernels. Whatever passed through fell onto a series of progressively smaller shaking screens, removing most of the remaining straw and chaff from the kernels.

In the third stage, the cleaner, kernels that passed through the last screen were moved over a stream of air that blew the remaining straw and chaff away. The cleaned kernels then fell into a hopper to be elevated to a measuring device before being dumped into sacks or conveyed to a granary. The straw and chaff were blown out onto the straw stack by a larger, stronger blower. FC


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