Farm Collector

Flat Belt Basics: Subtle Adjustments Contribute to Efficient Belt Operation

This summer I received a letter from Farm Collector reader Donald Wood, Danville, Calif., wondering if I could do a column on flat belts.

Don has used such belts and raised several interesting questions about them.

First, a belt can be defined as being a continuous strip of flexible material placed around two pulleys under a certain amount of tension to transmit power from one pulley to the other. This definition also describes chain, rope and V-belts, but we’ll stick to the flat belts used to power many farm machines, such as threshers, balers, hammer mills, husker-shredders and silo fillers.

Belts were made of leather, canvas and rubber. Leather was considered the best, but was the most expensive and required more care. Double thickness leather belts were made for heavy-duty use on large diameter pulleys but weren’t flexible enough for smaller pulleys. Few leather belts are seen today.

Canvas belting is made of several layers of canvas stitched along both edges as well as several times down the center. Canvas is the cheapest belt material, and usually is treated with oil or painted to make it waterproof. A 4-ply canvas belt is considered as strong as single-ply leather.

Probably the most common belt found today is the rubber belt. Made with a foundation of several layers of cotton duck to which a rubber compound is applied and vulcanized, a rubber belt is impervious to steam and water, and will not slip as readily as a leather belt. Three-ply rubber and single-ply leather belts have equivalent strengths.

Meeting end to end

Endless rubber belts are often spliced by stitching before being vulcanized, while leather belts may be spliced by tapering the thickness of each end, then overlapping and cementing those ends together. The two ends of an endless belt are often joined by hand lacing with leather thongs or very pliable wire, although “store-bought” metal lacing is probably more popular today, as few folks today know how to hand-lace the things.

The metal lacings consist of a series of loops applied to each end of the belt by hammering them into the belt material or using a special machine to press them into place. The belt ends are brought together so the loops interlace and a rawhide or steel hinge pin is inserted through the loops to hold them together. This method of connecting has the advantage of being easy to disconnect and is quite flexible.

Leather belts should be run with the hair (smooth) side toward the pulley and must be kept clean and flexible. The old belt dressing contained a good deal of resin, along with cod-liver and neat’s-foot oil (I looked up the ingredients in modern spray-on belt dressings and it’s a bunch of obscure chemicals that I don’t recognize). Rubber belts shouldn’t need any dressing as they shouldn’t slip if tight enough. In fact, sticky belt dressings have a tendency to pull off the outer layer of rubber and hasten the deterioration of a rubber belt. All belts should be kept clean and free of oil and grease. Leather belts should not be allowed to get wet.

Right side up

When a belt is running under load, there is a tight side and a slack side to the belt preventing transmission of 100 percent of the power. The tight side stretches under the tension, while the slack side contracts, resulting in belt creep, which is normal and is not the same as belt slip, the result of improper tensioning of the belt.

Belts should be run only tight enough to prevent slippage. A long belt doesn’t need to be as tight as a short belt because of its weight. If a belt is run too tight, however, it puts undue strain on the belt, pulleys, shafts and bearings. On the other hand, a loose belt has a tendency to flap and is easily thrown off if a sudden load is encountered. In the old days of steam threshing engines, the threat of fire from exhaust sparks was serious. Belts were long (as much as 150 feet) in order to keep the engine as far from the separator as possible. With gas or oil tractors, the possibility of exhaust sparks is much less and a 50-foot belt is plenty long enough; I’ve run a thresher with a 25-foot belt, and short belts are commonly used on hammer mills and silo fillers.

If possible, the lower side of a belt should be the driving side. The direction in which the machine must be run and the direction of the driving pulley must be taken into consideration. If necessary, the direction may be reversed by putting one twist in the belt, which also helps keep a long belt from flapping in a cross wind. However an uncrossed belt is more efficient as both heat and friction are generated at the point where the two sides of a crossed belt rub together.

Varied factors impact performance

In the old days, the thresherman always tried to set his separator so the wind came from the direction of the engine, preferably with a little “quartering.” This lessened the effects of a cross wind on the belt and kept the straw and chaff from being blown back onto the crew, while at the same time it blew the smoke and hot ashes from the engine away from the separator at an angle.

Velocity, speed, width and amount of tension determine the amount of power that can be transmitted by a belt. Length affects it as well, as a longer belt is heavier and thus requires more power to whirl it around the pulleys.

It’s very important that the driving and driven pulley are accurately aligned and on the same plane to prevent the edges of the belt from running partially off the inside of the pulleys and being damaged by rubbing against some part of the machinery, or running completely off the outside of the pulleys. A handyman-type jack can be a convenient way of moving the front of the tractor to one side or the other in order to attain perfect alignment.

As I wrote in the threshing chapter of my book, Implements for Farming with Horses and Mules, “A little caution and good judgment, along with a lot of practice, are required to quickly and properly line up and set a tractor and belt-driven machine.” And that’s all I know about flat belts and their use. FC

Sam Moore grew up on a farm in western Pennsylvania. He now lives in Salem, Ohio, and collects antique tractors, implements and related items. Contact Sam by e-mail at
  • Published on Nov 20, 2009
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