How to Make a Miniature Never-Ending Metal Marble Run

This miniature marble machine’s DIY process is astonishing!
Christopher McFadden

Love marble? Prefer to send them careening at breakneck speed around a marble run? How about making one that never ends? 

Then this little DIY project should be right up your alley.

However, like any project of this nature, you are going to need to gather a few materials fist. For this one, the creator, Daniel de Bruin, used a large number of junk pieces, but you can buy some of the components, and gear, needed from these links: 

Once you've got everything you need, it is time to crack on with the build. 

Depending on the parts you could salvage, the first part is to design a 3D-printable model to hold the ball bearing ring and gear together in one unit. 

ball bearing machine bits
You will need a smaller ball bearing and larger toothed cog to form the main gear of this machine, Source: Daniel de Bruin/YouTube

The basic idea is to have two main 3D-printed rings, one of which contains the ball-bearing ring to act as a kind of axle. This first inner plastic ring will also pin a rotating magnetic tipped arm to pick up and move the metal balls around.


The other, larger plastic ring will hold the inner ball bearing assembly, and outer toothed cog together so they can rotate together.

ball bearing machine 3d printed bits
The final 3D-printed and assembled plastic rings, ball bearing, and outer toothed cog assembly, Source: Daniel de Bruin/YouTube

This part will form the core of the machine to hold and rotate an arm that will pick up and move the metal balls from a receptacle at the bottom of the track to the start of the track. 

As no model has been provided, and the parts you source will vary, this will need some trial and error on your part. If this sounds confusing, you can watch the video in slow motion to get an idea of how it works.

Alternatively, you could mock up a model using cardboard, or similar material, prior to 3D modeling. If you are interested, the printer used in this build was a Prusa Mini 3D Printer. You can use whichever printer you have to hand, of course. 

However you designed it, the next step is to assemble the ball bearing, 3D plastic rings, and outer cog together into one piece. 

metal ball machine ring
Closer view of the assembly, Source: Daniel de Bruin/YouTube

The next step is to make the magnetic tipped raising-arm. The creator fashioned the arm using a length of 0.6 mm galvanized steel. With the desired length cut, make an L-shaped bend in one end and fix it into place on the inner 3D-printed ring, as shown in the video.

marble machine arm
Making the arm, Source: Daniel de Bruin/YouTube

You can see that the creator cut a few small pieces of heat-shrinkable wire sleeve for this, but you can affix however you please. The 3D model of the inner ring also had a pair of holes opposite the min arm slot to accommodate a U-shaped piece of galvanized steel to keep the arm secure in one position. 

marble track machine arm fastner
Affixing the arm into place on the inner plastic ring, Source: Daniel de Bruin/YouTube

Now you can glue a small magnet to the free end of the arm. This should be larger than 0.6 mm but smaller than the metal balls you plan on using for the track. 

The track will also need to be wider than the magnet too but thin enough to let the balls run down them, so bear that in mind later on when designing the track. You will notice that the creator also crafted a small piece of plastic with a cavitied end.

This is to slightly weaken the magnet's influence on the metal ball. 

This plastic cap needs to be thin enough for the magnet to actually attract and lift the metal balls, but thick enough to enable a smooth release of the ball at the start of the track.

metal marble machine arm complete
The complete arm assembly. Not the mini-magnet and plastic cap, Source: Daniel de Bruin/YouTube

The next step is to create the base for the entire setup. You can use whatever material you want, to whatever dimensions. Wherever you decide to place the ball-moving part of the machine, you will need to drill three parallel holes into the board.

Cut three pieces of 0.6 mm galvanized steel, two the same length, and one shorter. These will hold the main ring and arm assembly in place. 

Ensure that they are long enough to enable the main arm assembly to freely rotate about its axis. The height at which you mount the main wheel and arm assembly will depend on your track design.  

metal ball track struts
Source: Daniel de Bruin/YouTube

Next, cut three small lengths of steel wire and affix to the opposite side of the inner plastic ring, as shown in the video (and below). These will be used to solder the main ring and arm assembly to the supporting struts. 

metal ball machine ring in place
Source: Daniel de Bruin/YouTube

Next, it is time to build the main motor assembly that will turn the wheel continuously. Grab any old electrical motor, or source the one suggested, and affix the nylon helical screw to the motor axle. 

You can use other alternatives, but ensure they can be fitted to the motor and will turn the outer cog of the central arm assembly. Affix the motor and vertical screw assembly into place on the board so that the screw can turn the arm assembly smoothly. 

This may take some trial and error. You could design and 3D print some form of mounting bracket too. 

marble machine motor
Mount the motor and screw assembly in place, Source: Daniel de Bruin/YouTube

Next up, if desired, you can add some supporting struts to the main assembly for added stability. 

metal ball machine struts
Source: Daniel de Bruin/YouTube

The next phase is to actually build the metal ball track. This can be to any design you see fit, but it must finish at the base of the central wheel and start at some point along with the path of the downward rotation of the wheel. 

Remember that once free of the raising arm, the ball will need to roll down the track under the influence of gravity. Ensure the design has an overall downward gradient from start to finish. 

This creator used lengths of 0.6 mm galvanized wire in either straight or curved sections. Each track consisted of two main bars soldered together with the semicircular lengths of cut spring coils. 

metal ball machine track
Building the track, Source: Daniel de Bruin/YouTube

This will be a laborious task, so we hope you enjoy fine soldering work. The track can be made in modular pieces, with each section soldered to the preceding part. 

metal ball machine track length example
Example of a completed track length, Source: Daniel de Bruin/YouTube
metal ball machine track under construction
Track construction underway, Source: Daniel de Bruin/YouTube

Rinse and repeat until the entire track is completed to your liking. In this example, the marble run ends with a flourish through the center of the ball bearing ring. 

Once a ball has reached the end, it falls from the main track and is maneuvered via a receiving ramp into a plastic receptacle at the base of the main wheel and raising arm assembly.

The pit or receptacle should be designed in such a way that the metal ball comes to rest directly underneath the path of the moving arm so it can be picked up by the magnet as it passes. This will likely take some trial and error work.  

metal ball run pit
Source: Daniel de Bruin/YouTube

With the main assembly and track complete, now all you need to do is wire up the motor to a battery, add some metal balls, and enjoy your creation!

marble run machine pit and arm
The final main assembly, pit, ramp, and motor should look something like this, Source: Daniel de Bruin/YouTube

Who knows, your friends might be so impressed they may commission you to make them one too!

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