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.

Mini-Molder: Blow Molder Scratch-Built by Single Hacker

 

We caught up with [James Durand] at Maker Faire. He was one of the rare Makers (no mention of selling or future crowd funding) that had a booth at Maker Faire — he was exhibiting a blow molding machine that he built from scratch.

The fabrication process is 100% [James]. Every custom part was designed and milled by him. All of the assembly techniques were his to learn along the way. And we didn’t see anything that isn’t production ready. We’re both impressed and envious.

About three years ago he got the itch to build the mini-molder after learning about the Mold-A-Rama machine — a blow-molding vending machine that was popular a half century ago. A bit of his journey is documented as a molding category on his blog. For the most part it sounds like 1.5 years spent on the CAD design really paid off. He did share one element that required redesign. The initial prototype had a problem with the molds being pushed up when they came together. He tweaked the mechanism to close with a downward motion by flipping the hinge design. This seems to hold everything in place while the drinking fountain chiller and water pump cool the mold and the plastic model within.

Injection Molding With Hot Glue

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Injection molding is simply forcing a melted thermoplastic into a mold of some sort, letting it cool, and then prying the mold apart to get to the finished piece. Hot glue guns are basically handheld thermoplastic extruders, so when [scorch] dug up some old injection molds he had sitting around, it didn’t take long to put two and two together.

Injection molds aren’t something any normal person has sitting around, but a few years ago [scorch] found two books published by Gingery, the same people who have published instructions on how to build a metalshop from scrap. [scorch] created his molds on a small CNC mill – a Sieg X3 – and his initial experiments with injection molded plastic were fairly successful, even if the molds were made from self-cast billets.

After molding a few hot glue LEGO parts with his equipment, [scorch] had a look around the Internet and noticed this was nothing new. One company even sells a hot glue gun-based injection molding kit using polyethylene glue sticks. Their demo video (seen below) seems much more complicated than [scorch]‘s efforts, so  we’ll say he came out ahead on this one.

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3D Printed Injection Molds

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A team at Budapest University has successfully created a functional injection mold for prototyping by using a Stratasys 3D printer.

Prototype injection molds are expensive. They are typically machined out of steel or aluminum which is both costly and time consuming, due to the complex geometries of most molds. [Dr. Jozsef Gabor Kovacs] works in the Department of Polymer Engineering at Budapest University, which is where he came up with the innovative approach of using 3D printing to produce a prototype mold.

The mold was printed in Digital ABS PolyJet Photopolymer plastic using a Objet Connex 3D printer. The injection material used was polyacetal; which has a fairly low melting point of 175°C. By using this method they were able to go from a prototype mold to a test part in less than 24 hours. We don’t even want to think about how expensive that would be to expedite from a machine shop.

After the break you can watch the entire production process from printing to molding.

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Retrotechtacular: The 10-year anniversary of plastic

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This footage called Industry on Parade is a unique look back at the golden age of plastics. We also value the footage as a look at America’s manufacturing sector at its height.

We remember a middle-school teacher recalling his father — who was a research scientist working at Dow — bringing home a pair of discs for him to play with. His first ever encounter with plastic. Here we see a snapshot ten years after plastic manufacturing went mainstream. It starts off with a tour of an injection-molding factory. The screenshot seen above is from the second vignette which tours a production line for naval ship models which will be used to train Navy personnel and as props for strategic planning maps. The film wraps up with the production of plastic fabrics starting with raw materials and ending with synthetic bug screen.

Just to prove it’s an authentic blast from the past, hang in there for the last two minutes when you get an anti-communism PSA. Classic.

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Home injection molding

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[Kenneth Maxon] is a wizard who only does things one way, beautifully. While out of the average hacker’s production capabilities, his injection molding machine is amazing to behold. The machine has all features a commercial model would. It heats and cools the mold, produces over a ton of pressure to inject plastic with, and ejects parts automatically to name a few.

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