What Happens in a Rock Tumbler?

Rock tumblers are very simply devices that look and sound more complicated than they actually are.

Essentially, rock tumblers mirror what happens in nature over hundreds of years.

Finding a perfectly round and smooth stone on the beach or by a river is a rare treat, and knowing that this is the result of hundreds or thousands of years of work by Mother Nature makes it even more special.

Rock tumblers speed up this process, giving you beautifully smooth and polished stones without needing to wait for Mother Nature to do her job.

While the river or sea ‘tumbles’ the rocks over time, with the water smoothing the edges of the pebbles, rock tumblers achieve this process in a matter of weeks.

So how do they work? Rock tumblers consist of a motor and a barrel, which is either made from plastic or rubber.

The barrel is loaded with rocks, water and grit, and the motor is turned on and run at different stages for a few days or weeks, depending on the type of tumbler you are using.

Rotary vs Vibratory

We’ll go into this in more detail in another article, but the type of rock tumbler you own will determine the exact process used to tumble the rocks.

Rotary tumblers slowly rotate, with the rocks rubbing against the edge of the barrel as they are turned.

Vibratory tumblers on the other hand, vibrate at very high speeds. The rocks smooth by rubbing against each other over and over.

The different actions of the two tumblers means that rotary tumblers often produce beautifully rounded stones, while vibratory tumblers produce stones similar to their original shape.

Both rotary and vibratory tumblers require grit and water to function, although rotary models require a lot more grit. The grit helps to smooth the stones, while the water allows the barrel to behave in the same way as the river bed.

Course grit is used at the start of the project, to break down the sharp edges of the rock. Every few weeks, finer grit is added to the tumbler, until the final stage in where the grit used is almost like a powder.

There’s various types of grit available, depending on whether they are used for smoothing or polishing, and this can be easily and cheaply purchased either at rock shops or on Amazon.

A quick note that using grit from the river bed does not work!

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