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Thumler's A-R2 Questions and Answers

Thumler's A-R2 Tumbler

What is Thumler's A-R2 Rock Tumbler?

The Thumler's A-R2 is a hobbyist grade rotary rock tumbler with two 3-pound capacity barrels. It has a durable metal base, rubber barrels, and a thermally protected motor designed for many years of use.

This small-capacity tumbler is recommended for beginners to experienced users. It can be shared by two people, used to tumble two different types of rough, or used for tumbling rocks at different stages of the rock tumbling process.

We have sold hundreds of A-R2 tumblers and have talked with many customers who use them. We have also used A-R2 tumblers ourselves to tumble hundreds of barrels of rough. This is the tumbler that we use for testing many of the tumbling roughs that we sell. One of our A-R2 tumblers has been running since the late 1960s. It has had some parts replaced, worn out a few belts and a couple barrels, and needed its motor replaced one time. But, how is that for long-term service?

Below we will address some of the most common questions and concerns we have heard about this tumbler.

Oiling Thumler's tumbler bearings
A squeaking tumbler is usually a sign that the bearings need to be oiled. The bearings should be oiled once a month.

Why is My Tumbler Squeaking?

We have had people write after starting their A-R2 tumbler asking, why is it squeaking so loudly? The answer 99% of the time is that the bearings need to be oiled. The bearings need to be oiled once a month for continuous smooth and quiet operation. The motor should also be oiled once a month to keep it in good working order. We have detailed instructions on how to oil a Thumler's tumbler.

Does the Motor Need Oiled?

Yes, the motor should be oiled once a month to keep it in good working order. There are two oil ports on the top of the motor. We have detailed instructions with photos about how to oil a Thumler's tumbler.

How Much Rough Do I Need?

People who are just getting into rock tumbling often ask how much rough should be put in the barrel. This cannot be answered with an exact weight because size, shape, and density of the material can vary greatly. The best answer is: the barrel should be between 1/2 and 2/3 full. Each barrel for this tumbler will usually take a little under two pounds of material to reach that level. We have an article and video that shows you what happens in a tumbler and why the 1/2 to 2/3 full level is so important here.

Tumble rocks of different sizes
A mix of particle sizes will give you better tumbling results.

How Big Can the Rough Be?

Our recommendation is you should not tumble a piece that is larger than half of the diameter of the barrel. Any larger than that, and there isn't much room for it to tumble in the barrel. For best results, you should have a range of sizes in the barrel. This is referred to as particle size balancing and will create many points of contact between the material for the grit to grind between the pieces.

Can I Run the A-R2 With Only One Barrel?

No. The A-R2 tumbler is designed for both barrels to be on the tumbler when in operation. If only one barrel is on the tumbler, it can "walk" off the rollers, probably causing a mess to clean up. If you only have enough rough material to fill one barrel, you can fill the second one with water and ceramic media (no grit).

A-R2 barrel placement

Place the Lids Towards Each Other

Placing the barrels on the A-R2 tumbler with the lids facing each other serves several purposes. Doing so will muffle the amount of noise produced from the rough rubbing on the plastic lids. Also if you have a leak or spill, it will be in the center of the shafts, keeping the mess from getting into the bearings and motor. Putting the lids facing each other will also keep the lid retainer ring lip from wearing away due to rubbing against the barrel guides. If the retainer ring won't stay on the barrel, you won't have a watertight seal.

Should the Barrels Rub Against the Guide?

It is normal for the barrels to rub against the barrel guides. The barrels will often "walk" to the right or left on the shaft rollers, and the guides are there to ensure that the barrels stay on the machine.

Rock tumbler barrel particles

Why is My Barrel Shedding Particles?

This is common and should not be cause for concern. When a new barrel rubs up against a barrel guide, the barrel guide will wear the barrel slightly. After several runs with the tumbler, the amount of barrel particles will reduce to a negligible amount.

Should the Motor Run Warm to Touch?

Yes. The A-R2 rock tumbler motor will be very warm to the touch when in operation. The motor is thermally protected and will automatically stop if it gets too hot. Thermal protection is a wonderful safety feature for any motor that will run 24 hours a day, 7 days a week.

The Motor is Running but the Barrels Are Not Turning

Several things can cause this problem, including: bearings need oiled, dirt or oil on the belt, or the belt is stretched / worn out and needs to be replaced.

First you should test to see if it is a bearing problem. With the machine plugged in and the motor running, give the barrels a little pressure down and roll them in the direction they normally turn. If this gets the barrels turning, then the bearings need to be cleaned and oiled.

Second thing to try is cleaning the belt and pulleys. Oil or dirt can cause the belt to slip. Shut the machine off and remove the belt. Using a light detergent such as Dawn dishwashing liquid, clean the belt and pulleys. A cotton swab works well to clean the grooves of the pulleys. Dry them thoroughly and put the belt back on to see if that gets the tumbler back up and running.

Third action is to purchase a new belt. Belts will wear and stretch over time and need to be replaced periodically.

Why is My Barrel Leaking?

There are many things that can cause the barrel to leak. We have an article to help diagnose the possible cause here.

Thumler's A-R2 Parts Diagram

Thumler's A-R2 tumbler parts diagram

1) Rubber Barrels - Two rubber barrels for quiet operation.
2) Plastic Barrel Lids
3) Barrel Retainer Rings - These hold the lid secure in the barrel, which creates the watertight seal between the lid and barrel.
4) Tumbler Motor - Durable thermally protected motor that will stop if it gets too hot.
5) Motor Pulley
6) Tumbler Belt - A slipping belt could be the result of oil or dirt on the belt and pulleys, or a sign it is stretched / worn out and needs to be replaced.
7) Drive Shaft - Has three rubber rollers, a drive pulley, two bearings and two shaft retainer clips. This is the shaft that makes the barrels rotate.
8) Idler Shaft - Has three nylon rollers, two barrel guides, two bearings and eight shaft retainer clips.
9) Bearings - Both shafts have a bearing on each end of them. These bearings hold the shafts in position on the base. They need to be oiled monthly to keep the tumbler operating smoothly and quietly.
10) Rubber Rollers - Located on the drive shaft to give traction to the barrel and cause it to rotate.
11) Nylon Rollers - Located on the idler shaft to reduce friction on the barrel for smooth rotation.
12) Barrel Guides - Keep the barrels on the rollers.
13) Shaft Retainer Clips - Hold components in place on the drive shaft and idler shaft.

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