Water-cooling A 3D Printed Rocket Isn’t Quite Practical

May 23, 2026 by Zoe Skyforest 23 Comments

Consumer-grade 3D printers are useful for lots of things, but they kind of fall down when it comes to making stuff that survives high temperatures. [Mr. More Gooder] wasn’t deterred from a rocket build using FDM printed parts though, instead relying on water cooling to try and beat this practical limit.

The concept is simple enough—[Mr. More Gooder] printed a propane-burning combustion chamber and nozzle out of plastic that you’d totally expect to melt when the flames started. Thus, the nozzle was given fittings to allow water to be continually pumped through to try and drag away enough heat to let the rocket survive more than a few seconds. Unfortunately, during testing the uncooled combustion chamber quickly melted. A redesign with water cooling throughout performed a little better, until the water jacket began to leak into the main chamber and extinguished the flames. Melted plastic could be seen dripping out of the nozzle shortly after ignition, too.

Even if the nozzle did hold up for a longer period of time, it’s worth noting this is probably not a viable route towards a flight-ready engine. Mostly because you would need a huge supply of water to keep the components cool which would add a great deal of weight to any such build. There’s a reason NASA doesn’t recycle old drink bottles to make rocket engines, after all.

In any case, we love to see all sorts of rocket experiments, even the unsuccessful ones.

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Biofeedback Butterfly Beats With A Pulse

May 19, 2026 by Zoe Skyforest 1 Comment

Biofeedback is the idea of making one conscious of a biological process or feature, and then using this to try and exert control over the very same. [Mariia Hruntes] demonstrates this ably with a fluttering build of her own design.

In this case, the biological process being made clear is that of the user’s heartbeat. This is tracked with a MAX30102 pulse oximetry sensor, which can be used to measure both heart rate and blood oxygen levels if so desired. It’s hooked up to an Arduino Uno, which polls for pulse rate data, and then actuates an SG90 micro servo in turn. This operates the wings of a 3D printed butterfly, such that they flap in pace with the wearer’s pulse. The goal is to observe this, and then try and calm one’s self to relax and slow the flapping through the power of the mind.

It’s a simple build, but one that clearly demonstrates the concepts of biofeedback in action. We’ve seen similar principles applied to everything from aiding sleep to improving the practice of mediation. If you’re working on your own neat biofeedback project, be sure to let us know on the tipsline.

How To Avoid Failed Screw Holes In 3D Printed Parts

May 7, 2026 by Donald Papp 21 Comments

Screws are useful fasteners for 3D prints, but the effectiveness of a screw (not to mention the ease or hassle of insertion) depends on the hole itself. This comprehensive guide on how to design screw holes in 3D printed parts takes guesswork out by providing reference tables as well as useful general tips.

The guide provides handy tables saying exactly how big to design a hole depending on screw type, material (PLA, PETG, or high-flow PETG) and whether the hole is printed in a vertical or horizontal orientation. This takes the guesswork out of screw hole design.

There’s no reason to guess the right size of hole for a screw, just refer to some handy tables.

The reason for different numbers is because multiple (but predictable) variables affect a 3D-printed hole’s final dimensions. Shrinkage, filament properties, and printing orientation can all measurably affect small features like screw holes; accounting for these is the difference between a good fit, and cracking or stripping.

In addition to the tables, there are loads of other useful tips. Designing lead-ins makes screws easier to insert and engage, and while increasing walls is an easy way to add strength it’s also possible to use 3D-printed microfeatures which are more resistant to distortion and don’t depend on slicer settings. There’s even suggested torque amounts for different screw and material types.

Sure, the most reliable way to get a hole of a known size is to drill it out yourself. But that’s an extra step, and drill bits aren’t always at hand in the desired sizes. The guide shows that it is entirely possible to print an ideal screw hole by taking a few variables into account.

If your design calls for screws, be sure to check it out and see if there’s anything you can use in your own designs.

3D Printed Train Whistles Sound Out At Full Scale

May 7, 2026 by Tyler August 10 Comments

The age of steam is long gone, but there are few railfans who don’t have a soft spot for the old rolling kettles. So you’d best believe when [AeroKoi] talks about 3D printed train whistles, that’s steam whistles. Generally speaking, Diesels have horns.

You would not expect printed plastic to hold up to live steam– but that’s why [AeroKoi] uses compressed air. Besides, it’s a lot easier to both justify and maintain an air compressor than a boiler in the shop. At least some hobbyists say it doesn’t make a huge difference with brass whistles, so it should be good enough for plastic. What’s interesting is that even with 120 PSI blasting through them, these multi-part prints held together and sounded amazing.

[AeroKoi] does demonstrate there was a learning curve to climb before he had a good whistle design, and shows you what features worked best. He shared two successes on Thingiverse: A 6-Chime whistle from the Sante Fe Railroad, and a Northern Pacific 5-chime whistle, both 4″ in diameter and printed in vertically sectioned parts. The Northern Pacific is not to be confused with the totally different Union Pacific Railroad, whose famous “Big Boy” also had a whistle feature in the video — though evidently he’s not as happy with it, since he did not share the design.

Those are all North American designs, but there’s no reason this technique wouldn’t work to replicate a more European sound; one of his early experiments was kind of going in that direction already. Of course if you want a perfect replica, the old ways are the best ways: cast brass and live steam. We’ve had a few articles about train whistles in the past, one of which was a doorbell.

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A hexagonal brass enclosure surrounds an aluminium fan with three blades. The fan has an integrated outer rim with a series of small holes around the rim.

Building A Rim-Driven Jet Engine

April 19, 2026 by Aaron Beckendorf 18 Comments

Rim-driven thrusters turn the normal propeller-motor arrangement inside out; rather than mounting the motor at the center of the propeller, they use a large hollow motor, with the blades attached to the inside of the rotor. They’re mostly used in ship propellers, though there have been some suggestions to use them in electric aircraft. [Integza], always looking for new and unusual ways to create propulsion, took this idea and made it into a jet engine.

Rather than using an electric motor, the fan in this design is propelled by miniature rocket nozzles along the edge. The fan levitates on a layer of high-pressure gas between the fan rim and the housing. To prevent too much pressurized gas from escaping, the fan and housing needed to fit together closely, but with minimal friction. A prototype made out of acrylic and resin and powered by compressed air proved that the idea worked, but [Integza] wanted to make to this a combustion-powered engine.

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LED Matrix Clock Proudly Shows Its Inner Wiring

March 31, 2026 by Donald Papp 25 Comments

Some projects take great care to tuck away wire hookups, but not [Roberto Alsina]’s Reloj V2 clock. This desktop clock makes a point of exposing all components and wiring as part of its aesthetic. There are no hidden elements, everything that makes it work is open to view. Well, almost.

The exception is the four MAX7219 LED matrices whose faces are hidden behind a featureless red panel, and for good reason. As soon as the clock powers up, the LEDs shine through the thin red plastic in a clean glow that complements the rest of the clock nicely.

[Roberto]’s first version was a unit that worked similarly, but sealed everything away in a wedge-shaped enclosure that was just a little too sterile, featureless, and ugly for his liking. Hence this new version that takes the opposite approach. Clocks have long showcased their inner workings, and electronic clocks — like this circuit-sculpture design — are no exception.

The only components, besides the Raspberry Pi Zero W and the LED matrices, are the 3D-printed enclosure with a few hex screws and double-sided tape. Design files and code (including the FreeCAD project file) are available should you want to put your own spin on [Roberto]’s design.

This Front Panel Makes Its Own Clean-Edged Drill Guides

March 30, 2026 by Donald Papp 8 Comments

We haven’t seen an instrument panel quite like [bluesyann]’s, which was made by curing UV resin directly onto plywood with the help of a 3D printer and a bit of software work. The result is faintly-raised linework that also makes hand drilling holes both cleaner and more accurate.

The process begins by designing the 2D layout in Inkscape, which has the advantage of letting one work in 1:1 dimensions. A 10 mm diameter circle will print as 10 mm; a nice advantage when designing for physical components. After making the layout one uses OpenSCAD to import the .svg and turn it into a 3D model that’s 0.5 mm tall. That 3D model gets loaded into the resin printer, and the goal is to put it directly onto a sheet of plywood.

A little donut shape makes a drill centering feature, and the surrounding ring keeps the edges of the hole clean.

To do that, [bluesyann] sticks the plywood directly onto the 3D printer’s build platform with double-sided tape. With the plywood taking the place of the usual build surface, the printer can cure resin directly onto its surface. Cleanup still involves washing uncured resin off the board, but it’s nothing a soak in isopropyl alcohol and an old toothbrush can’t take care of.

[bluesyann] has a few tips for getting the best results, and one of our favorites is a way to make drilling holes easier and cleaner. Marking the center of a drill hit with a small donut-shaped feature makes a fantastic centering guide, making hand drilling much more accurate. And adding a thick ring around the drill hole ensures clean edges with no stray wood fibers, so no post-drilling cleanup required. Don’t want the ring to stick around after drilling? Just peel it off. There’s a load of other tips too, so be sure to check it out.

A nice front panel really does make a project better, and we’ve seen many different approaches over the years. One can stick laminated artwork onto an enclosure, or one can perform toner transfer onto 3D printed surfaces by putting the design on top of the 3D printer’s build surface, and letting the heat of molten plastic do the work of transferring the toner. And if one should like the idea of a plywood front panel but balk at resin printing onto it, old-fashioned toner transfer works great on wood.