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Make Your Rock Tumbler Belts Last a Long Time

rock tumbler belts
Rock tumbler belts come in a wide variety of sizes, shapes and styles. Be sure to use one that is designed for your tumbler. The proper belt and good tumbling practice can make your belt last a long time.

A Tumbler Belt Can Last For Years

Your rock tumbler should not be a belt eater.

If you have a quality rock tumbler such as a Thumler's Tumbler or a Lortone Tumbler, and you use high quality belts - then you should get two, three or more years of service out of a belt. We use our tumblers regularly and most of our belts last for several years.

We provide some belt care tips below. Then, then after the tips, we explain some of the deeper problems that cause rock tumbler belts to fail. If you apply this information, we believe you will get a longer life out of your rock tumbler belts.

Belt Maintenance Tips:

1) Oil and grit will destroy your belt. If you get even a little oil or a little grit on the belt, clean it immediately by following the instructions below. Oil will cause your belt to deteriorate and it will also cause it to slip on the pulleys. Grit will quickly abrade your belt.

2) Clean your belt by placing it in a bowl of soapy warm water and washing it with a soft cloth. We use a few drops of Dawn or Palmolive dishwashing soap in about one cup of water. We clean our belts anytime we notice that they are dirty. If you have multiple tumblers, clean all of their belts while you have the bowl and soapy water ready.

3) Clean your pulleys by scrubbing them with a Q-Tip dipped in a weak solution of water and a mild dishwashing soap. Clean the motor pulley and the drive shaft pulley every time you clean your belt. If you don't clean them, then dirt on the pulley will immediately transfer onto your clean belt.

4) Clean your bearings after each 30 days of tumbler use, or, after each batch of rocks. Wipe the excess oil and dirt from the outside of your tumbler's bearings with a soft dry cloth or a dry strip of paper towel. If they have accumulated a lot of dirt, clean them with a soft rag soaked with a solution of mild dishwashing soap.

5) Lubricate each bearing after they have been cleaned, then lubricate each bearing with ONE drop of SAE 20 oil. Immedately after you apply the drop of oil, spin the bearing or turn the shaft several times to distribute the oil around the inside of the bearing. Wipe off any excess oil with a dry piece of cloth or a strip of dry paper towel. Clean and properly lubricated bearings will turn smoothly and reduce the amount of work that your belt must do to drive the tumbler.

The maintenance tips above should be used for any rotary rock tumbler.

Most rock tumbler belt problems fall into one of these categories: Let's consider these one at a time below...

Machine Problems

A very common problem that causes tumbler belt failure is a belt that is too tight. On most tumblers you can easily adjust the tension on the belt by loosening the mounting screws on the motor and moving the motor. Move it away from the drive shaft to tighten the belt and towards the drive shaft to loosen it. (See photo at right.)

The belt should not be extremely tight. You can test the tension by pressing on the top of the belt with your finger. The belt should have a little "give" when you press lightly. (See photo at right.) Adjust the belt so that it is tight enough to turn the drive shaft pulley without slipping under the load of a tumbler barrel.

While you are looking at the tension on the belt look at the pulleys. There should be one pulley on the end of the motor shaft and another on the tumbler's drive shaft. These pulleys should be in perfect alignment when the belt is on and the motor is running. (See photo at right.) If they are not in perfect alignment the belt will be subject to stress and abrasion. (A sign of abrasion is a belt wearing on one side or tiny particles of belt on or under one of the pulleys.) If your pulleys do not line up perfectly you can loosen the set screw on one of them and slide it in the proper direction for alignment.

Finally, a rough spot on one of the pulleys could be damaging the belt. Run your finger or a piece of cloth over all parts of the pulleys that the belt contacts. If there is a sharp edge you might feel it with your finger or the cloth might snag. Smooth any sharp spots with a piece of sandpaper.
stretched rock tumbler belt
Pictured above is a belt that has sat stationary on a tumbler for years (left) and a brand new belt (right).

Belt Problems

Some belts break because they are old or low quality. Others fail because they are the incorrect belt for your tumbler. Old belts can be stiff or cracked and break with a small amount of use. Low quality belts can stretch, break or wear quickly.

We recommend buying a fresh belt from a busy rock tumbler dealer who sells a lot of them. Substitute belts designed for vacuum cleaners or other appliances rarely fit precisely or last very long. We receive new belts directly from the manufacturer or distributor every few months and rotate our stock.

It is never a bad idea to have an extra belt on hand. Every tumbler belt will fail if it is used long enough. However, we don't advise purchasing six, eight or ten extra belts (unless you have six, eight or ten tumblers) because the belts could get old before you need them. One in reserve is usually a good number. Two is for those who remember the motto: "Be prepared." :-)
rock tumbler belts
This photo is looking down on the machine, viewing the motor pulley and the drive shaft pulley. Notice how they are in perfect alignment.

Operation Problems

Operation problems are duties that the person who runs the tumbler should perform. The most important is keeping the tumbler clean. If grit or dirt builds up on the pulleys they will contribute to belt wear.

Oil, lubricants, strong detergent and cleaning solutions can dissolve or weaken a belt. The belt should be cleaned with a dry cloth or paper towel. If it is oily it can be cleaned with a very mild dishwashing soap without additives such as Dawn.

Overloading the tumbler barrel can cause a belt to slip, break or wear. Overloading can happen when you fill the barrel too full. It can also happen if you are tumbling a material such as hematite that has a high specific gravity. When tumbling heavy materials reduce the amount of rock in the barrel to stay within machine capacity.

Finally, extreme temperatures can cause belt problems. If your tumbler is in an unheated building in winter, freezing temperatures can make the belt stiff and brittle. This can lead to wear. Another problem would be freezing of the water in the tumbler barrel. This can damage the barrel, pop the lid or cause the barrel to deform and jam the machine.

A Goal for Tumbler Operators

Nobody enjoys checking their tumbler to find the motor running and a stationary barrel. Following the precautions above should make that a very rare experience for you.

Happy Tumbling! Authors

Hobart King Hobart M. King has decades of rock tumbling experience and writes most of the articles on He has a PhD in geology and is a GIA graduate gemologist. He also writes the articles about rocks, minerals and gems on