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My Rock Tumbler's Motor is Hot! Is That Normal?

Most motors will be hot to the touch when operating. Here are a few tips for safe operation.
Thumler's thermally protected motors
Thermally protected replacement motors for Thumler's Tumblers. Top left:   fits the A-R1,   A-R2,   and   A-R12.   Top right:   fits the Model B (high speed).   Bottom right:   fits the UV-10 Industrial.   Bottom left:   fits the Model B (low speed). We sell replacement motors for a limited number of tumblers from Thumler's, Lot-o-Tumbler and Lortone. The motors that we sell are intended for use on these tumblers. If you need a motor for any other tumbler, please contact the manufacturer of that tumbler.

Rock Tumbler Motors Run Hot

Many owners of rock tumblers notice that their motors are very warm, even hot, while they are operating. They usually become concerned about this, and that is understandable.

Most rock tumblers have air-cooled motors that are designed to run hot to the touch. You will probably not burn your fingers if you touch the motor quickly. However, if you allow your fingers to remain in contact with the motor for more than a moment, the heat will be uncomfortable. That motor temperature is normal.

Thermally Protected Motors

High-quality rock tumblers have thermally-protected motors. These motors will shut off if they become overheated. This is a safety feature intended to prevent fires. It can also extend the life of your motor in some situations..

We sell several Thumler's Tumblers that are shipped from the factory with thermally protected motors. They are the Thumler's A-R1, A-R2, A-R12, Model B, U-V10 Industrial Model, and U-V18 Industrial Model. We believe that these are some of the highest quality motors used in hobbyist rock tumblers today.

thermally protected on the motor nameplate
Thermally protected motors usually have the words "thermal protection" or "thermally protected" on the motor nameplate. Thermal protection is a safety feature and a feature that can extend motor life in some situations. Motor manufacturers want you to know if the motor is thermally protectited - it is a sign of quality.

Our Experience with Hot Motors

We have been using Thumler's Tumblers for about 50 years and, over the past decade, we have sold thousands of their tumblers. We have never heard of a fire or an electrical problem being attributed to a Thumler's Tumbler. We have never heard of a fire or an electrical problem being attributed to a Lot-o-Tumbler.

At almost any time, we have between one and four rock tumblers running at our office. This is a combination of Thumler's Tumblers, Lot-o-Tumblers, and Lortone tumblers. We have been doing this for years. We estimate that the tumblers at our office have experienced a total running time of at least 50 years. Out of all of that time, we have only experienced an overheated rock tumbler on one occasion.

That overheating was on a Thumler's A-R2, when one of the barrels got wedged between the drive shaft and the idler shaft. That kept the drive shaft from turning but the motor kept running and working hard trying to turn that stuck driveshaft. The motor overheated. The motor stopped operating. We found the tumbler stopped that evening and it would no longer operate. We had to replace the motor.

We have had good luck with our tumbler motors. This good luck may be in part to our habits of keeping our rock tumbling area clean, and regular motor lubrication.

Things You Should Watch For

If a motor on a rock tumbler - or a motor on any appliance - begins to overheat, you will likely smell it. Overheating motors often emit an odor of hot oil or burning plastic. If you experience this, do not touch the appliance. If you know how to turn off the electricity to that part of your home, turn it off. If that is not possible, don't touch the appliance, but unplug it from the wall outlet. If you see smoke or deformed plastic, or feel heat before touching the plug, do not touch it. Get assistance from someone who can turn off the electricity and evaluate the situation.

Then, as soon as possible, contact an electrician for advice. If your tumbler was the source of the odor, contact the manufacturer.

In many cases, an overheating motor simply has hot bearings that are producing a burnt oil smell. It can also be dust or dirt in the motor that is getting hot and emitting an odor. However, if you are not experienced at solving electrical problems, it is best to get expert advice.

Things That Can Cause Overheating

Here are some things that can cause your rock tumbler to overheat. Do your best to avoid them!
Any machine operated by electricity can be a fire hazard under the right conditions, many of which are listed above.

There is one situation that should concern you. If you detect a hot oil or burnt plastic odor coming from your motor, or see smoke, that is a time to unplug the motor and contact the manufacturer.

Be Concerned About Motor Safety

Here are some general tips to keep your rock tumbler operating safely. Some of them also prevent overheating.

A safety-conscious person who does the above can reduce the risk of fire, reduce the risk of injury, and prolong the life of the tumbler.

Quality, Care and Gentle Use

We advocate buying a quality tumbler, made by a company that has been in business for a long time.

Some manufacturers design and build with a goal of producing the lowest-cost item in the market. The most expensive part of most rock tumblers is the motor, and using a low-quality motor is a place where costs can be cut. You get what you pay for.

We also advocate "care and gentle use" of the items that you purchase. It does not matter if it is a rock tumbler, a car, or a toaster. Treat your rock tumbler with respect. Keep it clean. Lubricate it regularly. Doing these things will often enable you to enjoy your possessions for a much longer time.

Some Motor Trivia

Most modern homes have at least two dozen small air-cooled motors working in them every day. These motors are in furnaces, air conditioners, refrigerators, ceiling fans, space heaters, recliners, washing machines, dryers, waste disposals, ovens, microwaves, attic fans, hair dryers, garage door openers, pumps, toys, and more. Most people are surprised to learn how many motors are working in their home.

Motors in the home cause occasional fires. They are the small machines that we live with, so we should buy quality products, install them properly, operate them gently, and maintain them according to the manufacturer's instructions.

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