This Homemade Machine Makes Beautifully Spherical Rocks

How often do you come across really pretty rocks in nature? Probably not often, because they’re all cracked, lumpy, dirty, and dull. But there is beauty within even the most mundane stones — you just have to uncover it, like a sculptor chipping away everything that doesn’t look like an elephant. But what if your metaphorical elephant is spherical? Then this homemade machine is perfect for the job.

Making a decent sphere out of any material is difficult, because you don’t have a hard edge or face to use as a reference, or a good way to hold the material while also accessing the entire surface. But this is a particularly tricky problem for rocks, because they are famously hard. If you want to turn that rock you found into a stunning shiny sphere, how do you even start?

That’s what this video from Rob of Michigan Rocks explains. The machine Rob built is based on a similar design first posted seven years ago by James Muchmore. But Rob’s version is more affordable to build and he goes into a lot more detail about how it works.

And how it works is very interesting. It is essentially the same concept that machinists use to get really flat surfaces: slowly remove the high spots until everything is at an equal “elevation.” Rob’s machine applies that concept to a sphere by treating “high” as the furthest distance from the center.

The machine does that use three electric hand drills arranged around the sphere and pulling in towards its center using bungie cords. Those are very cheap battery-powered drills, but fed by DC power supplies. Each drill has a masonry-style hole saw that cups the stone. Water for lubrication drips down from a jug.

The effect is all three drills turning and pushing into the stone, which naturally rotates as they do. All the while, the teeth are grinding off the high spots. After it is roughly spherical, Rob can replace the saws with successively finer polishers until the stone is a nearly perfect sphere and very shiny.

And even very ordinary rocks look amazing when they’ve received this treatment.