classic hacks

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Perfecting The Shape-Changing Fruit Bowl

March 13, 2026 by 9 Comments

Fruit bowls have an unavoidable annoyance– not flies and rotten fruit, those would be avoidable if your diet was better. No, it’s that the bowl is never the right size. Either your fruit is sad and lonely in a too-large bowl, or it’s falling out. It’s the kind of existential nightmare that can only be properly illustrated by a late-night infomercial. [Simone Giertz] has a solution to the problem: a shape-changing fruit bowl.

See, it was one thing to make a bowl that could change shape. That was easy, [Simone] had multiple working prototypes. There are probably many ways to do it, but we like [Simone]’s use of an iris mechanism in a flat base to allow radial expansion of the walls. The problem was that [Simone] has that whole designer thing going on, and needs the bowl to be not only functional, but aesthetically pleasing. Oh, and it would be nice if expanding the bowl didn’t create escape routes for smaller fruits, but that got solved many prototypes before it got pretty.

It’s neat to see her design process. Using 3D printing and CNC machining for prototyping is very familiar to Hackaday, but lets be honest — for our own projects, it’s pretty common to stop at “functional”. Watching [Simone] struggle to balance aesthetics with design-for-manufacturing makes for an interesting 15 minutes, if nothing else. Plus she gives us our inspirational quote of the day: “As much as I feel like I’m walking in circles, I know that product development is a spiral”. Something to keep in mind next time it seems like you’re going around the drain in your own projects. Just be warned, she does have a bit of a potty mouth.

We’ve featured [Simone]’s design decisions here, if you’re interested in seeing how she goes the rest of the way from project to product. We’re pretty sure her face-slapping-alarm clock never made it into the SkyMall catalog, though.

Continue reading “Perfecting The Shape-Changing Fruit Bowl” →

A Rotary Dial The 3D Printed Way

March 11, 2026 by 3 Comments

There’s a meme which may have a basis in truth, of a teenager left clueless when presented with a rotary telephone. The dial, in reality a mechanical pulse chain generator, was once ubiquitous enough that having one in your parts bin was anything but unusual. If you’re curious about their inner workings in 2026 though, you may be out of luck. Never fear though, because [Moeya 3D Designs] is here with a fully 3D printed version. It’s not as compact as the original, but it’s all there.

If you’re not put off by the anime-style Japanese voice over on the video below the break and you can enable subtitles for your language, you get the full explanation. There’s a ratchet and spring on the dial, which when released drives a gear train that ends in a cam that would operate a switch for the pulses. Another set of gears drives a very neatly designed centrifugal speed governor, and we see the effect immediately when it is removed. We’re not sure who will go for this project, but we surely like it.

There are two videos below the break, with the dial shown off in the first and the design process in the second. Meanwhile we’ve talked in the past about the networks behind the dials. Continue reading “A Rotary Dial The 3D Printed Way” →

It’s 1979 – What Exactly Did That ∫ Key Do?

March 10, 2026 by 14 Comments

[Michel Jean] asked a question few others might: what exactly is going on under the hood of a classic HP scientific calculator when one presses the ∫ key? A numerical integration, sure, but how exactly? There are a number of useful algorithms that could be firing up when the integral button is pressed, and like any curious hacker [Michel] decided to personally verify what was happening.

[Michel] implemented different integration algorithms in C++ and experimentally compared them against HP calculator results. By setting up rigorous tests, [Michel] was able to conclude that the calculators definitely use Romberg-Kahan, developed by HP Mathematician William Kahan.

Selected by HP in 1979 for use in their scientific calculators, the Romberg-Kahan algorithm was kept in service for nearly a decade. Was it because the algorithm was fast and efficient? Not really. The reason it was chosen over others was on account of its robustness. Some methods are ridiculously fast and tremendously elegant at certain types of problem, but fall apart when applied to others. The Romberg-Kahan algorithm is the only one that never throws up its hands in failure; ideal for a general-purpose scientific calculator that knows only what its operator keys in, and not a lick more.

It’s a pretty neat fact about classic HP calculators, and an interesting bit of historical context for these machines. Should you wish for something a bit more tactile and don’t mind some DIY, it’s entirely possible to re-create old HP calculators as handhelds driven by modern microcontrollers, complete with 3D-printed cases.

Thanks to [Stephen Walters] for the tip!

Clear Resin Casting Replicates Old Acrylic For Selectric Repair

March 10, 2026 by 23 Comments

IBM Selectric typewriters have a lot of unique parts that can be tricky to source, but one we didn’t think of was the clear acrylic(?) dust covers, that are apparently very hard to find in good shape. [Eric Strebel] has a few Selectrics that all have issues with these parts. While you could come close to recreating this piece with acrylic sheeting carefully bent to match the original shape, [Eric] has a different hammer to try in a new video: replicating it with a resin casting.

He uses de-gassed tin-cure silicone to create a mold for the original, with a bit of 3D printed PLA and foam board to hold the silicone to create the mold. That’s done in two steps to create a two-part mold, which is separated and cleaned before the resin goes in. The original part is actually a smoky plastic, rather than fully clear, but [Eric] is able to match it perfectly using a colourant in his clear ̶e̶p̶o̶x̶y̶ polyurethane resin. The resin is put into the mold with a simple gravity pour, though he does have a vibrator on it to help it flow. Curing is done under heat and pressure– 60 PSI. The results are amazing; once he adds a touch of paint to match the black finish on one face of the original, it’s very difficult to tell [Eric]’s casting from his master piece, except that the cast replicas are in better shape.

This particular part works very well for casting and not much else. While you could match the large curve by heat-bending a piece of smoky acrylic, there are lips along the edges of the part that would be tricky to reproduce. [Eric] also needed several, for his multiple typewriters, and this method is very efficient at producing multiple units since the mold is reusable.

While you might not have an IBM Selectric that needs a dust cover, this technique is equally applicable to all sorts of clear shapes. If you’re new to resin casting, we have a handy guide to replicating plastic parts to get you started in this kind of work. It’s not just large parts that can be replicated: you can even copy phonograph records, such is the fidelity of resin casting.

Continue reading “Clear Resin Casting Replicates Old Acrylic For Selectric Repair” →

A 3D-printed mechanism is clamped between the jaws of a pair of calipers, which are surrounded by 3D-printed covers. A hammer is resting against one of the jaws, and a man's gloved hand is holding the calipers.

Embossing Precision Ball Joints For A Micromanipulator

March 4, 2026 by 5 Comments

[Diffraction Limited] has been working on a largely 3D-printed micropositioner for some time now, and previously reached a resolution of about 50 nanometers. There was still room for improvement, though, and his latest iteration improves the linkage arms by embossing tiny ball joints into them.

The micro-manipulator, which we’ve covered before, uses three sets of parallel rod linkages to move a platform. Each end of each rod rotates on a ball joint. In the previous iteration, the parallel rods were made out of hollow brass tubing with internal chamfers on the ends. The small area of contact between the ball and socket created unnecessary friction, and being hollow made the rods less stiff. [Diffraction Limited] wanted to create spherical ball joints, which could retain more lubricant and distribute force more evenly.

The first step was to cut six lengths of solid two-millimeter brass rod and sand them to equal lengths, then chamfer them with a 3D-printed jig and a utility knife blade. Next, they made two centering sleeves to hold small ball bearings at the ends of the rod being worked on, while an anti-buckling sleeve surrounded the rest of the rod. The whole assembly went between the jaws of a pair of digital calipers, which were zeroed. When one of the jaws was tapped with a hammer, the ball bearings pressed into the ends of the brass rod, creating divots. Since the calipers measured the amount of indentation created, they was able to emboss all six rods equally. The mechanism is designed not to transfer force into the calipers, but he still recommends using a dedicated pair.

In testing, the new ball joints had about a tenth the friction of the old joints. They also switched out the original 3D-printed ball mount for one made out of a circuit board, which was more rigid and precisely manufactured. In the final part of the video, he created an admittedly unnecessary, but useful and fun machine to automatically emboss ball joints with a linear rail, stepper motor, and position sensor.

On such a small scale, a physical ball joint is clearly simpler, but on larger scales it’s also possible to make flexures that mimic a ball joint’s behavior.

Back To Basics: Hacking On Key Matrixes

March 3, 2026 by 12 Comments

A lot of making goes on in this community these days, but sometimes you’ve just gotta do some old fashioned hacking. You might have grabbed an old Speak and Spell that you want to repurpose as an interface for a horrifyingly rude chatbot, or you’ve got a calculator that is going to become the passcode keypad for launching your DIY missiles. You want to work with the original hardware, but you need to figure out how to interface all the buttons yourself.

Thankfully, this is usually an easy job. The vast majority of buttons and keypads and keyboards are all implemented pretty much the same way. Once you know the basics of how to work with them, hooking them up is easy. It’s time to learn about key matrixes!

Continue reading “Back To Basics: Hacking On Key Matrixes” →

Have You Ever Used A Tick Stick?

February 28, 2026 by 20 Comments

Picture this: you have an irregular opening you need to fabricate a piece to fill. Maybe it’s the stonework of a fireplace; maybe it’s the curved bulkhead of a ship. How do you get that shape? The most “Hackaday” answer would be to 3D scan the area, create a CAD model based on the point cloud, and route the shape with CNC. Of course, none of those were options for the entirety of human history. So how do you do it if you don’t have such high-tech toys? With a stick, as [Essential Craftsman] takes great pains to show us in the video below.

It’s not just any stick, of course. Call it a “tick stick”, a “speil stick”, or a “joggle stick” — whatever you call it, it’s just an irregularly shaped piece of wood. The irregular shape is key to the whole process. How you use it is simple: get some kind of storyboard — cardboard, MDF, whatever — that fits inside your irregular void. Thanks to the magic of the stick, it need not fit flush to the edges of the hole. You put the tick stick on the storyboard, press the pointy end against a reference point on the side of the hole, and trace the stick. The irregular shape means you’re going to be able to get that reference point back exactly later. Number the outline you just made, and rinse and repeat until you’ve got a single-plane “point cloud” made of tick stick outlines.

Your storyboard is probably going to look mighty confusing, but that’s what the numbers are for. Bring your storyboard and your tick stick onto the workbench and whatever you want to cut out– plywood, cardboard, 1/4″ steel armor plate, you name it–and simply repeat the process. Put the tick stick inside outline #1 and mark where the pointy end lands on the material. Then do it again for the other outlines, reproducing the points you measured on the original piece. After that, it’s just a game of ‘connect the dots’ and cutting with whatever methodology works for your substrate. A sharp knife will work for cardboard, but you’ll probably want something more substantial for steel plate.

It’s not often you’re going to need the tick stick– the [Craftsman] reports only needing it a few times over the course of a decades-long career, but when you need it, there’s not much else that will do the job. Well, unless you have a 3D scanner handy, that is. Continue reading “Have You Ever Used A Tick Stick?” →