Facebook PixelA cement mixer truck converted into a polishing machine for small boulders
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A cement mixer truck converted into a polishing machine for small boulders

Image credit: LCDRI Cement Ball Mill

Darko Savic
Darko Savic Aug 18, 2021
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The idea is to convert an old concrete mixer truck into a polishing machine for small boulders. Basically a huge rock tumbler. The machine would then be used to polish small boulders into beautiful oversized gemstones.

There are 2 novelties to the proposed idea:
  1. creation of large gemstones to be sold for ornamental use
  2. DIY conversion of fairly accessible parts into an industrial machine that would otherwise be extremely expensive
Ball mills such as the one featured on the header image exist. So do big commercial tumblers. I imagine they are extremely expensive.

I have yet to see a polished boulder that looks like a gemstone. I don't think this has been purposefully done before.

Tumbled rocks

People collect interesting rocks and pebbles, then tumble them at home into gemstones. I've bought a few on various fairs and art shops.

I imagine there would be a market for huge ornamental gemstones placed on driveways, shopping malls, etc. Tumbling something like this would be amazing:

Converting a concrete mixer

Finding an old cement mixer in a junkyard might be tricky, but they are out there.

The rest is a matter of stripping and repurposing parts into an oversized version of this.

A solar powered electric motor would be used to slowly but persistently rotate the entire thing for weeks. The opening on the rear end would be enlarged by cutting of 1/3rd of the drum.

The boulders would be loaded in and out with a forklift and pulleys.
Creative contributions

What the final product could look like

Darko Savic
Darko Savic Sep 08, 2021
These look like polished boulders. Something that could be made in the proposed tumbler

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A polishing blanket that is embedded with motors to be used for the same purpose

Samuel Bello
Samuel Bello Sep 10, 2021
Other than using a tumbler to polish rocks, smaller rotating machines that are covered with sandpaper can be used to polish them. An example of such a scenario is the one shown in this video where a Dremel rotary tool is used to polish a small piece of rock. The proposed blanket will work based on the same principle but there will be a lot of small motors between the layers of the blanket.

Since this comes as a blanket the safety glasses and the mask used in the video will not be necessary as the blanket will protect the user from the fragments that fly off the rocks. To polish a lot of small rocks, they can be enclosed in the blanket and shaken with a different motor so that the polishing is even for all the rocks and not only for the rocks near the surface.

For much larger rocks, the blanket can be placed on the rock to polish different parts of the rock until the whole rock or just the desired part is polished. Whole mountains can even be polished for the aesthetic effect.

Advantages over using parts of a cement mixer
  • The equipment used is going to be much smaller and lighter so it is easily transported to where it is needed.
  • A blanket embedded with motors is flexible and will not only polish regular shaped stones, it can be used to polish objects with complex shapes that have crevices. An example of such objects is a stone statue.
  • The equipment is not DIY but it is going to be cheap and easy to rent out. This is quite convenient since the demand for polished rocks is low.
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Darko Savic
Darko Savic3 years ago
A tumbler not only polishes the rocks but also rounds them. It would take a lot of precision work to grind a large rock into a nice shape that looks like it's been transformed by a river over centuries. A tumbler does that, but fast.
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