DIY Newton’s Cradle Uses Parts Designed on a Smart Phone

Injection Molded Parts

As far as physics demonstrations go, the Newton’s Cradle is probably one of the most recognizable. Named after Sir Isaac Newton, the Newton’s Cradle demonstrates the law of conservation of momentum using swinging ball bearings.

[Scorchworks] decided he wanted to build his own Newton’s Cradle. The frame appears to be cut from MDF or particle board and then screwed together. That material is really easy to obtain and also to work with using inexpensive tools. The tricky part was the ball bearings. Most of the time when you see a Newton’s Cradle, the ball bearings have a small hole drilled in the top with an eye hook attached. The string is then attached to the eye hook.

[Scorchworks] decided to do something different. His plan was to make custom injection molded plastic rings that would fit perfectly around the ball bearings. The most interesting thing is that he designed the injection molding plates entirely on his smart phone while at his child’s baseball practice. To do this, [Scorchworks] used his own Android app, ScorchCAD. ScorchCAD is a free clone of OpenSCAD that is designed to run on Android devices. Most of the functionality of OpenSCAD has been implemented in ScorchCAD, though not all functions work yet. You can find a list of all the supported functions on the project’s website or in the Google Play store.

Once the plates were designed within ScorchCAD, [Scorchworks] exported the STL file and then used Meshcam to generate the gcode for his CNC milling machine. Once he had the plates machined, he just placed the ball bearing into the mold and injected the molten plastic around it. The plastic formed a perfectly shaped ring around the bearing with small loops for the string. [Scorchworks] repeated the process several times to get all of the ball bearings finished.

Finally, the bearings were strung up using some fishing line. A Newton’s Cradle is very sensitive to the positioning of the ball bearings. To account for this, [Scorchworks] tied each end of the fishing line to two different screws on top of the cradle. This way, each screw can be tightened or loosened to adjust the position of each ball bearing.

13 thoughts on “DIY Newton’s Cradle Uses Parts Designed on a Smart Phone

    1. It does. I think you were under the same impression that I got from this initially. The mold is for the ring that goes around the ball bearings, not for the bearings themselves.

      1. No, it doesn’t include the holes for the strings. I’m looking at the mold and the product. He had to punch or drill the string holes. The mold clearly has the loop area where the string holes would be as one big open fill in the mold.

        1. Either limitations of the cad software he used, or the mill and tooling he had on hand most likely.

    2. For DIY injection molding he might not have felt like relying on the plastic to make it into such a thin run, a good improvement would have been a starter indentation in the mold though so drilling would be painless/centered otherwise.

  1. Always great to see a guy’s first inorganic mold. A novel application.
    For someone wanting a slightly more aesthetic (and faster and cheaper) method, you can purchase a length of black heatshrink tubing of sufficient diameter. Slice it into ~1/4 to 3/8 th inch circles, punch two holes on each side near the top about 1/2″ apart on each slice and then string fishing line through each pair of holes. Tie it up, and hit it with the heat gun. You can use two layers of heat shrink if you want it to last.

    Superballs can be substituted to comic effect, if you make the supporting strings longer.

  2. Very neat, but I couldn’t help but notice an error in the article. Ball bearings are whole assemblies that allow low-friction movement. Bearing balls are the balls contained within ball bearings.

  3. A tungsten tipped masonry drill slowly advanced will allow a hole to be drilled through the hardened casing, and this is most easily done with the ball chucked in a lathe.

  4. I’ve wanting a way to tweak my openSCAD files while waiting at the DMV and the likes for ages. Thankfully someone made it for me hahaha

    too bad it is closed source. i’d love to improve on those missing methods.

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