3D Printing And Metal Casting Are A Great Match

December 15, 2025 by Donald Papp 21 Comments

[Chris Borge] has made (and revised) many of his own tools using a combination of 3D printing and common hardware, and recently decided to try metal casting. Having created his own tapping arm, he tries his hand at aluminum casting to create a much more compact version out of metal. His video (embedded below) really shows off the whole process, and [Chris] freely shares his learning experiences in casting his first metal tool.

The result looks great and is considerably smaller in stature than the 3D-printed version. However, the workflow of casting metal parts is very different. The parts are much stronger, but there is a lot of preparation and post-processing involved.

Metal casting deals with molten metal, but the process is otherwise very accessible, and many resources are available to help anyone with a healthy interest.

The key to making good castings is mold preparation. [Chris] uses green sand (a mixture of fine sand and bentonite clay – one source of the latter is ground-up kitty litter) packed tightly around 3D printed parts inside a frame. The packed sand holds its shape while still allowing the original forms to be removed and channels to be cut, creating a two-part mold.

His first-time castings have a rough surface texture, but are perfectly serviceable. After some CNC operations to smooth some faces and drill some holes, the surface imperfections are nothing filing, filler, and paint can’t handle.

To cast molten metal, there really isn’t any way around needing a forge. Or is there? We have seen some enterprising hackers repurpose microwave ovens for this purpose. One can also use a low-temperature alloy like Rose’s Metal, or eschew molten liquid altogether and do cold casting, which uses a mixture of resin and metal powder instead.

The design files for [Chris]’s tapping arm are available from links in the video description, and he also helpfully provides links to videos and resources he found useful. Watch it in the video, embedded just below.

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Trace Line Clock Does It With Magnets

December 8, 2025 by Donald Papp 9 Comments

We love a good clock project, and [byeh_ in] has one with a design concept we don’t believe we have seen before. The Trace Line Clock has smooth lines and a clean presentation, with no sockets or visible mechanical fixtures.

Reading the clock is quite straightforward once one knows what is going on. At its heart, the unmarked face is much like any other analog clock face, and on the inside is a pretty normal clock movement. The inner recessed track on the face represents hours, and the outer is minutes. The blue line connects the two, drawing a constantly changing line.

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How To Design 3D Printed Pins That Won’t Break

December 1, 2025 by Donald Papp 9 Comments

[Slant 3D] has a useful video explaining some thoughtful CAD techniques for designing 3D printed pins that don’t break and the concepts can be extended to similar features.

Sure, one can make pins stronger simply by upping infill density or increasing the number of perimeters, but those depend on having access to the slicer settings. If someone else is printing a part, that part’s designer has no actual control over these things. So how can one ensure sturdier pins without relying on specific print settings? [Slant 3D] covers two approaches.

The first approach includes making a pin thick, making it short (less leverage for stress), and adding a fillet to the sharp corner where the pin meets the rest of the part. Why? Because a rounded corner spreads stress out, compared to a sharp corner.

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The Eleven-Faced Die That Emulates Two Six-sided Dice

November 28, 2025 by Donald Papp 28 Comments

Rolling two six-sided dice (2d6) gives results from 2 to 12 with a bell curve distribution. Seven being the most common result, two and twelve being the least common. But what if one could do this with a single die?

This eleven-sided die has a distribution matching the results of 2d6.

As part of research Putting Rigid Bodies to Rest, researchers show that a single eleven-sided asymmetric shape can deliver the same results. That is to say, it rolls numbers 2 to 12 in the same distribution as 2d6. It’s actually just one of the oddball dice [Hossein Baktash] and his group designed so if you find yourself intrigued, be sure to check out the 3D models and maybe print your own!

The research behind this is a novel method of figuring out what stable resting states exist for a given rigid body, without resorting to simulations. The method is differentiable, meaning it can be used not just to analyze shapes, but also to design shapes with specific properties.

For example, with a typical three-sided die each die face has an equal chance of coming up. But [Hossein] shows (at 8:05 in the video, embedded below) that it’s possible to design a three-sided die where the faces instead have a 25%-50%-25% distribution.

How well do they perform in practice? [Hossein] has done some physical testing showing results seem to match theory, at least when rolled on a hard surface. But we don’t think anyone has loaded these into an automated dice tester, yet.

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Stack N’ Rack Your Hardware With The HomeRacker Project

November 27, 2025 by Donald Papp 9 Comments

Things are cooler when rack-mounted, and [KellerLab] aims to make that all far more accessible with the HomeRacker, a modular and 3D-printable rack building system designed to let you rack-mount to your heart’s content. While it can handle big things, it seems especially applicable to tasks like mounting one’s home network equipment and Raspberry Pi machines.

A rack is a great place for those Raspberry Pi servers and home networking equipment, but it can also handle bigger jobs.

The basic system (or core) consists of three different parts: supports, connectors, and lock pins. The supports are the main structural bars, the connectors mostly go at the corners, and the lock pins ensure everything stays put. The nominal sizing is a 15 mm x 15 mm profile for the supports, with lengths being a multiple of 15 mm.

All is designed with 3D printing in mind, and requires no tools to assemble or disassemble. There are design elements we really appreciate, like how parts are printed at an angle, which improves strength while eliminating the need for supports. The lock pins (and the slots into which they go) are designed so that they are effective and will neither rattle nor fall out.

But the core system is just the foundation. There’s plenty of modularity and expansions to handle whatever one may need, from Gridfinity shelves and drawers to various faceplates and other modules. There are some example applications available from [KellerLab]’s HomeRacker models page, like CD shelf, under-desk drawer, or filament rack.

[KellerLab] welcomes any collaboration, so check out the GitHub repository for CAD references and design files.

One last point to make about the value of printing objects like this at an angle: not only can the resulting layer lines provide better strength and reduce or eliminate the need for supports, but printing at an angle can help hide layer lines.

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This Bedtime Bot Enforces Better Sleep Hygiene

November 27, 2025 by Seth Mabbott 5 Comments

[Will Dana] is engineering his way to better sleep hygiene. Not satisfied with a simple bedtime reminder notification — such things are easily dismissed, after all — [Will] is offloading self-control onto a robot which will take his phone away at bedtime.

Scrolling in bed is allowed up to a prescribed time. At that time, a rack and pinion-mounted arm rises up from behind his mattress, presenting an open hand, ready to accept the object of his addiction. At this point, a countdown begins. If he does not hand over the device in a matter of seconds, the robot escalates by flashing obnoxiously bright lights in his face.

The nocturnal technology detox is not absolute, however. A button allows [Will] to temporarily retrieve his phone after it has been confiscated. This safety override accounts for the Inevitable situation where he will need to send a last-minute text before nodding off. The flashing light disincentive countdown is restarted upon retrieval, ensuring that [Will] does not cheat his own system for additional scroll time.

As a brief sidebar, [Will] does a nice job explaining how pulse-width modulation works for the purpose of controlling the speed of the rack and pinion mechanism.

For more of [Will’s] projects see this iPad suspension system a Lamp that tracks the location of the ISS and a drum that uses the piezoelectric effect to charge mobile devices.

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3D Printing A Piano Action

November 13, 2025 by Bryan Cockfield 14 Comments

Part of the reason there are always free pianos on your digital classifieds listing of choice is that, at least economically speaking, a piano is less of a musical instrument and more of a complicated machine that can and will wear out (not to mention the physical difficulty of actually moving one). Once a piano reaches that point, whether through age, use, or neglect, at that point it’s to intents and purposes worthless. But still, they’re essentially just machines. [Toast] figured that, since 3D printers not only can print all kinds of other machines and musical instruments alike, he would take a stab at combining these two and made his own 3D printed piano.

A piano’s action is the mechanical linkage between the keys and the strings of the piano themselves. Over many hundreds of years this has developed into a complicated series of levers which not only rapidly strike strings when a key is pressed, but also mute the strings while the key is not being pressed and strike the strings in a way that the hammer won’t be pressed into the strings if the player leaves their finger on a key. Rather than try to recreate all of this in meticulous detail, [Toast] has swapped out the strings for a series of tubes which, unlike strings, do not much change their musical behavior if the hammer remains on the tube after being struck. This greatly simplifies the action (and cost) of his miniature piano.

The piano works by positioning hammers above these tubes, which strike downwards when a musician depresses the keys. Rubber bands return the hammers to their upright positions after the key is lifted. The instrument went through a few stages of design as well where [Toast] refined the size and shape of the tubes as well as improved the way by which the hammers are attached to the keys.

Is it still a piano if it has pipes instead of strings? Perhaps, but at the very least we can all agree that he’s built a working keyboard action capable of producing music, if not an outright definitionally-accurate piano. It’s an interesting build that we hope to see more iterations of in the future, if not to build a more functionally accurate 3D printed piano action then to see what is possible from a 3D printer in the piano space. Despite their complexity and weight, pianos are a fundamental and popular instrument in the Western music tradition and we’ve seen many interesting builds around them like this modern player piano built with a series of solenoids. Continue reading “3D Printing A Piano Action” →