Treadmill Rock Tumbler

Repurposing a used treadmill motor and frame to tumble rocks in my shop.

Background:

I started making knives as a hobby back in August of 2022. I was using my belt grinder to assist in tumbling knives for a stone washed finish. While it was a good practice, I quickly found that having my belt grinder tied up for a period of time would slow down my production. I picked up a free treadmill off Facebook Marketplace. I created a standalone tumbling station to free my belt grinder back up!

Supplies:

I built this tumbler using an SRC electronic voltage regulator, a bridge rectifier, and a low cost power supply. You can use an old one if you have it available. You will also need some additional wire/tools to connect everything if you do not already have them. Below are links to the products I purchased for this project.

(These are all Amazon affiliate links that help support my content)

Electronic Voltage Regulator: https://amzn.to/3tr2hfo

Bridge Rectifiers: https://amzn.to/3vghmkm

Low Cost Power Supply: https://amzn.to/4ayQfl1

Disassemble parts and wire up the power supply:

Warning: I am not an electrician. Electricity CAN kill you. This write-up is for informational purposes. You are doing this at your own risk!

Sorry for my lack of pictures. I was asked for this write-up after I was already finished with this project. I will try to be as descriptive as possible.

Disassembly:

I started with opening the power supply, unplugging the fan, and removing the board and wiring harness inside of it. I replaced that board with the board of the SRC controller. (You can discard the board and wiring harness or keep it. It’s not needed anymore).

Once the power supply board is removed, I set that aside and started working on the SRC controller. I took off the cover by removing two screws holding it on. After the cover was removed, I unplugged the small fan, and removed the knob. (You can discard the small fan or keep it. It’s not needed anymore). Then, I reinstalled one of the small screws, (back left on the board next to the power inputs). After all that, I drilled out the opening where the knob would go on the power supply and filed the edges smooth.

I used two self-tapping screws to mount the power supply to the treadmill frame. Just drill those in and be sure to clean up any metal shavings before assembly.

Assembly and Wiring:

After I cleaned everything up, I mounted the SRC controller and bridge rectifier into the power supply with 3M double sided tape.

NOTE: When mounting the bridge rectifier, there is only one marking on the side to pay attention to. “AC” is on one of the corners, so pay attention to where you put that corner (that is where the blue wire is installed on my example). One of your output voltage wires must go to that. The diagonally opposite corner is where the other output voltage wire will go to.

I will start with power coming in. There are three wires coming in for power (black, white, and green). Green will go to a ground on the power supply. I took the black wire and went to one pole on the “On/Off” switch. The other pole of the “On/Off” switch went to the first AC input slot on the SRC controller board. The white wire goes to the second slot of the AC input. NOTE: (The black, and white wires are interchangeable on the AC input slots).

Working on the “Voltage Output” on the SRC controller, I have two wires coming out (blue, and white). The blue wire went to the “AC” corner on the bridge rectifier I mentioned earlier. The white wire went to the diagonally opposite corner. NOTE: (The blue, and white wires are interchangeable on the bridge rectifier AC locations).

Now the wires going to the motor get connected to the remaining two poles on the bridge rectifier. I put the black wire on the top right, and the red on the diagonally opposite corner. NOTE: (The red, and black wires are interchangeable on the bridge rectifier DC locations).

You can now plug the fan back into the SRC controller in the uppermost white receptacle on the board. Run the two self-tapping mounting screws back in, reinstall the power supply cover and you’re all set.

Download Wiring Diagram

Frame construction and mounting the rollers:

I reused the treadmill frame since it already had mounting locations for the motor and the rollers. The only modification I made to the rollers was drilling and tapping the roller that had the belt pulley. Only one side had a hole drill and tapped. Since there was not treadmill belt to keep tension on it, I had to drill and tap the other side in order to hold it in place, and keep tension on the belt coming off the motor.

I sectioned the rest of the frame, removing about four feet of tubing to shorten it. I relocated the mounting brackets for the second roller. Since the second roller has fine adjustment screws, the alignment of the rollers does not have to be 100% exact.

The only issue I have right now is that the container travels on the rollers while spinning. That can easily be fixed by attaching a stop that goes from the side of the frame and runs to the container.

Conclusion:

How I made this tumbler is not an exact science. These instructions do not need to be followed to the letter. You can absolutely take creative liberties with this. You can also take that same control box and motor and apply it to many other projects. It does not have to be just a tumbler. Many people have used this same power supply setup for belt grinders, drill presses, and even lathes! What will you use it for?

I want to thank each and every one of you that are interested in this project! I really enjoyed writing this out. Please feel free to use the contact link below and reach out! Any constructive criticism is welcomed. I will be happy to answer any questions that you may have.