Designing A Pen Clip That Never Bends Out Of Shape

March 3, 2026 by Lewin Day 9 Comments

If you’ve ever used a ballpoint pen with a clip on the top, you’ve probably noticed they bend pretty easily. The clip relies on you only bending it a small amount to clip it on to things; bend it too far, and it ends up permanently deformed. [Craighill] decided to develop a pen clip that didn’t suffer this ugly malady.

The wire clip design easily opens wide because the spring wire is not actually deforming much at all. Credit: YouTube video, via screenshot

The problem with regular pen clips comes down to simple materials science. Bend the steel clip a little bit, and the stress in the material remains below the elastic limit—so it springs back to its original shape. Push it too far, though, and you’ll end up getting into the plastic deformation region, where you’ve applied so much stress that the material is permanently deformed.

[Craighill] noted this problem, and contemplated whether a better type of clip was possible. An exploration of carabiner clips served to highlight possible solutions. Some carabiners using elastically-deformed closures that faced the same problem, while others used more complicated spring closures or a nifty bent-wire design. This latter solution seemed perfect for building a non-deforming pen clip. The bent wire is effectively a small spring, which allows it to act as a clip to hold the pen on to something. However, it’s also able to freely rotate out from the pen body, limiting the amount of actual stress put on the material itself, which stops it entering the plastic deformation region that would ruin it.

It’s some neat materials science combined with a pleasant bit of inventing, which we love to see. Sometimes there is joy to be had in contemplating and improving even the simplest of things. Video after the break.

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Electrical Steel: The Material At The Heart Of The Grid

February 15, 2024 by Dan Maloney 32 Comments

When thoughts turn to the modernization and decarbonization of our transportation infrastructure, one imagines it to be dominated by exotic materials. EV motors and wind turbine generators need magnets made with rare earth metals (which turn out to be not all that rare), batteries for cars and grid storage need lithium and cobalt, and of course an abundance of extremely pure silicon is needed to provide the computational power that makes everything work. Throw in healthy pinches of graphene, carbon fiber composites and ceramics, and minerals like molybdenum, and the recipe starts looking pretty exotic.

As necessary as they are, all these exotic materials are worthless without a foundation of more familiar materials, ones that humans have been extracting and exploiting for eons. Mine all the neodymium you want, but without materials like copper for motor and generator windings, your EV is going nowhere and wind turbines are just big lawn ornaments. But just as important is iron, specifically as the alloy steel, which not only forms the structural elements of nearly everything mechanical but also appears in the stators and rotors of motors and generators, as well as the cores of the giant transformers that the electrical grid is built from.

Not just any steel will do for electrical use, though; special formulations, collectively known as electrical steel, are needed to build these electromagnetic devices. Electrical steel is simple in concept but complex in detail, and has become absolutely vital to the functioning of modern society. So it pays to take a look at what electrical steel is and how it works, and why we’re going nowhere without it.

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a flexible film with a matrix of illuminated color LEDs being stretched

Truly Flexible Circuits Are A Bit Of A Stretch

April 3, 2023 by Michael Shaub 5 Comments

Flexible PCBs have become increasingly common in both commercial devices and DIY projects, but Panasonic’s new stretchable, clear substrate for electrical circuits called Beyolex takes things a step further. The material is superior to existing stretchable films like silicone, TPU, or PDMS due to its high heat tolerance (over 160° C) for the purposes of sintering printable circuit traces.

But, a flexible substrate isn’t very useful for electronics without some conductive traces. Copper and silver inks make for good electrical circuits on stretchable films, and are even solderable, but increase resistance each time they are stretched. Recently, a team out of the University of Coimbra in Portugal has developed a liquid metal ink that can stretch without the resistance issues of existing inks, making it a promising pair with Panasonic’s substrate. There’s also certain environmental benefits of printing circuits in this manner over traditional etching and even milling, as you’re only putting conductive materials where needed.

After the break, check out Panasonic’s earlier videos showing some of their demo circuits that include a stretchable NFC antenna harvesting electricity even while submerged in water and an LED matrix performing while being, bent, rolled, and stretched. We’re excited to see where this technology leads and when we hackers will be able to create our own stretchable projects.

A great many flexible PCB projects have graced Hackaday, from early experiments to sophisticated flexible PCB projects. Heck, we had a whole Flexible PCB Contest with some awesome flexible projects.

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The Physics Behind The Collapse Of A Huge Aquarium

December 20, 2022 by Jenny List 144 Comments

At the end of last week Aquadom, the world’s largest cylindrical aquarium, unexpectedly shattered and caused an emergency as it flooded both the Berlin hotel that housed it and the surrounding streets. From an engineering perspective it’s a fascinating story, because its construction was such that this shouldn’t have happened. We have an analysis of what might have gone wrong from [Luis Batalha] (Nitter), and from it we can learn a little about the properties of the plastic used.

The aquarium was made of an acrylic polymer which has an interesting property — at a certain temperature it transitions between a glass-like state and a rubber-like one. Even at room temperature the acrylic is well below the transition temperature, but as the temperature drops the acrylic becomes exponentially more brittle. When the outside temperature dropped to well below zero the temperature also dropped in the foyer, and the high water pressure became enough to shatter the acrylic.

Sadly few of the fish from the aquarium survived, but fortunately nobody was killed in the incident. News coverage shows how the force of the water destroyed the doors and brought wreckage into the street, and we’re guessing that it will be a while before any other hotel considers such a project as an attraction. Meanwhile we’ve gained a little bit of knowledge about the properties of acrylic, which might come in handy some day.

Header: Chrissie Sternschuppe, CC BY-SA 2.0.

Defective 3D Printing For Great Strength

February 2, 2022 by Al Williams 6 Comments

Most of us want our 3D prints to be perfect. But at Cornell University, they’ve been experimenting with deliberately introducing defects into printed titanium. Why? Because using a post-print treatment of heat and pressure they can turn those defects into assets, leading to a stronger and more ductile printed part.

The most common ways to print metal use powders melted together, and these lead to tiny pores in the material that weaken the final product. Using Ti-6Al-4V, the researchers deliberately made a poor print that had more than the usual amount of defects. Then they applied extreme heat and pressure to the resulting piece. The pressure caused the pores to close up, and changed the material’s internal structure to be more like a composite.

Reports are that the pieces treated in this way have superior properties to parts made by casting and forging, much less 3D printed parts. In addition, the printing process usually creates parts that are stronger in some directions than others. The post processing breaks that directionality and the finished parts have equal strength in all directions.

The hot isostatic pressing (HIP) process isn’t new — it is commonly used in metal and ceramic processing — so this method shouldn’t require anything more exotic than that. Granted, even cheap presses from China start around $7,000 and go way up from there, but if you are 3D printing titanium, that might not be such a big expenditure. The only downside seems to be that if the process leaves any defects partially processed, it can lead to fatigue failures later.

We wonder if this development will impact all the car parts being printed in titanium lately. If you need something to print in titanium, consider hacking your rib cage.

Simple Setup Answers Complex Question On The Physics Of Solids

February 1, 2022 by Dan Maloney 17 Comments

Thought experiments can be extremely powerful; after all, pretty much everything that [Einstein] came up with was based on thought experiments. But when a thought experiment turns into a real experiment, that’s when things can get really interesting, and where unexpected insights crop up.

Take [AlphaPhoenix]’s simple question: “Are solid objects really solid?” On the face of it, this seems like a silly and trivial question, but the thought experiment he presents reveals more. He posits that pushing on one end of a solid metal rod a meter or so in length will result in motion at the other end of the rod pretty much instantly. But what if we scale that rod up considerably — say, to one light-second in length. Is a displacement at one end of the rob instantly apparent at the other end? It’s a bit of a mind-boggler.

To answer the question, [AlphaPhoneix] set up a simple experiment with the aforementioned steel rod — the shorter one, of course. The test setup was pretty clever: a piezoelectric sensor at one end of the bar, and a hammer wired to a battery at the other end, to sense when the hammer made contact with the bar. Both sensors were connected to an oscilloscope to set up to capture the pulses and measure the time. It turned out that the test setup was quite a challenge to get right, and troubleshooting the rig took him down a rabbit hole that was just as interesting as answering the original question. We won’t spoil the ending, but suffice it to say we were pleased that our first instinct turned out to be correct, even if for the wrong reasons.

If you haven’t checked out [AlphaPhoenix] yet, you really should. With a doctorate in material science, he’s got an interesting outlook on things, like calculating pi using raindrops or keeping the “ultra” in ultra-high vacuum. Continue reading “Simple Setup Answers Complex Question On The Physics Of Solids” →

Tech In Plain Sight: Primitive Engineering Materials

December 22, 2021 by Al Williams 33 Comments

It isn’t an uncommon science fiction trope for our hero to be in a situation where there is no technology. Maybe she’s back in the past or on a faraway planet. The Professor from Gilligan’s Island comes to mind, too. I’d bet the average Hacakday reader could do pretty well in that kind of situation, but there’s one thing that’s often overlooked: materials. Sure, you can build a radio. But can you make wire? Or metal plates for a capacitor? Or a speaker? We tend to overlook how many abstractions we use when we build. Even turning trees into lumber isn’t a totally obvious process.

People are by their very nature always looking for ways to use the things around them. Even 300,000 years ago, people would find rocks and use them as tools. It wasn’t long before they found that some rocks could shape other rocks to form useful shapes like axes. But the age of engineered materials is much younger. Whether clay, metal, glass, or more obviously plastics, these materials are significantly more useful than rocks tied to sticks, but making them in the first place is an engineering story all on its own.

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