Flat Belt Basics: Subtle Adjustments Contribute to Efficient Belt Operation

Let's Talk Rusty Iron


| January 2010



A correctly aligned tractor and separator

A correctly aligned tractor and separator.

courtesy Sam Moore

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.