Abrasive belts are widely used in sanding and grinding equipment, and all require tension to operate. They need to be tensioned just enough so that the belt does not slip on the drive wheel or become detached from the machine. Belt tension is fixed on some sanders. However, most sanders are equipped with a tensioning device. This article focuses on how much tension a belt sander should have, and how to achieve it.

Low vs. High Belt Tension

When belt tension is not fixed, determining the optimum setting can be a matter of trial and error. Below is an overview of the signs that your setting is too low or too high.

1. Low Belt Tension

There are a variety of symptoms associated with low belt tension, including belt tracking problems. For example, tracking off in the same direction every time may indicate excessive wear on the tracking wheel or roll or a side-to-side variation in length. Other signs include:

• When the belt folds over, it breaks. A combination of roll wear and low belt tension can also cause this problem.
• Wear is evident on the printing on the back of the belt. It slips on the drive roll, which wears off the print on the back.
• The parts being finished have skip marks. The marks may have been caused by the belt losing speed or stopping, which can occur when the belt slips on the drive roll. In high-load situations, this can be a typical problem.
• When the head starts up or parts are processed, a short, high-pitched whining occurs. In this case, too, the belt may have slipped off the drive roll. The belt whines when it has minimal tension.

Over time, low tension can reduce the working life of the belt. This is because less pressure is applied when the belt slips and the abrasive does not have the chance to break down and sharpen like it’s supposed to.

2. High Belt Tension

Tracking cylinders are typically much smaller than tension ones, so high belt tension can overwhelm them. Bearings on the drive, tracking, and idler rolls of the head may also break down prematurely. On any type of grinding or sanding equipment, the higher the belt tension, the more wear there is on all related bearings.

Other signs that belt tension is too high include:

• The sanding belt breaks easily. When a belt is overtightened, it is less able to absorb high or fluctuating shock loads.
• Wear occurs on all rolls within the head. The belt typically wears at the outside edges of the rolls where it tracks back and forth. As belt tension increases, such wear increases excessively.

For screw-adjusted tension devices, it can be difficult to determine the proper tensioning amount unless you have considerable experience with that machine. After the machine is turned off, the belt should rotate five or more times. The tension may be too high if the belt stops very quickly.