Sweep Power Steps It Up

Horse powered sweep power boosed farm production

| January 1999

In the early 1800s, the drive to increase farm production put horses to work in treadmills. But soon even basic horse power was not enough.

As threshing machines became larger and more sophisticated, with feed and straw conveyors, as well as the new "vibrators" (or straw walkers), horse-powered treadmills could not keep up. Sweep powers were the immediate answer. It's unknown when the sweep power was introduced, but an 1836 illustration of a Gaar thresher shows a four-team sweep power driving a ground jack through a tumbling rod. A belt from the pulley on the ground jack drives the thresher.

A typical sweep power consisted of a heavy wooden frame that could be mounted on wheels for portability. A large, cast iron bull gear was mounted horizontally on that frame so it could rotate. On the bull gear were heavy sockets to which were attached wooden sweep arms. The teeth on the bull gear engaged small diameter pinion gears on either end of a cross shaft, in the center of which was a large spur gear. The spur gear turned a small pinion gear underneath the frame that drove the output shaft. A tumbling rod from the output shaft ran directly to the driven machine, or else it drove a pulley on a ground jack to which the machine was belted.

One or two horses were hooked to each wooden sweep and driven around in a circle, having to step over the tumbling rod on each round. For stability, the power was dug in, or staked and braced, to keep the whole thing from turning. To prevent problems from missteps, some operators built wooden or earth bridges. The gear reductions and the length of the sweeps were engineered to give the proper RPM at the tumbling rod, while the teams walked at a pace of 2 1/4 miles per hour.

The driver had no reins, just a whip and his voice to control his animals. In the book Machines of Plenty, Stewart Holbrook likened him to a circus ringmaster. Of course, his charges couldn't escape or attack him, being firmly attached to their sweeps, but it was his duty to keep the teams marching at a steady pace, no matter what the power demands of the thresher. With a mixture of cajolery, threats and imprecations, plus judicious flicks of his whip, the driver kept his animals to the task as he watched them go round and round and round ...

Sweep powers were built in many sizes, ranging from one-horse up to 16-horse and, although I haven't heard of any designed for dogs, goats or humans, anything was possible.