Watch Bondo Putty Get Sprayed Onto 3D Prints

August 31, 2025 by Donald Papp 18 Comments

3D prints destined for presentation need smooth surfaces, and that usually means sanding. [Uncle Jessy] came across an idea he decided to try out for himself: spraying Bondo spot putty onto a 3D print. Bondo spot putty comes from a tube, cures quickly, and sands smoothly. It’s commonly used to hide defects and give 3D prints a great finish. Could spraying liquified Bondo putty onto a 3D print save time, or act as a cheat code for hiding layer lines? [Uncle Jessy] decided to find out.

Gaps and larger flaws still need to be filled by hand, but spray application seems to be a big time saver if nothing else.

The first step is to turn the distinctive red putty into something that can be sprayed through a cheap, ten dollar airbrush. That part was as easy as squeezing putty into a cup and mixing in acetone in that-looks-about-right proportions. A little test spray showed everything working as expected, so [Uncle Jessy] used an iron man mask (smooth surfaces on the outside, textured inside) for a trial run.

Spraying the liquified Bondo putty looks about as easy as spraying paint. The distinctive red makes it easy to see coverage, and it cures very rapidly. It’s super easy to quickly give an object an even coating — even in textured and uneven spots — which is an advantage all on its own. To get a truly smooth surface one still needs to do some sanding, but the application itself looks super easy.

Is it worth doing? [Uncle Jessy] says it depends. First of all, aerosolizing Bondo requires attention to be paid to safety. There’s also a fair bit of setup involved (and a bit of mess) so it might not be worth the hassle for small pieces, but for larger objects it seems like a huge time saver. It certainly seems to cover layer lines nicely, but one is still left with a Bondo-coated object in the end that might require additional sanding, so it’s not necessarily a cheat code for a finished product.

If you think the procedure might be useful, check out the video (embedded below) for a walkthrough. Just remember to do it in a well-ventilated area and wear appropriate PPE.

An alternative to applying Bondo is brush application of UV resin, but we’ve also seen interesting results from non-planar ironing.

Continue reading “Watch Bondo Putty Get Sprayed Onto 3D Prints” →

Lynx-R1 Headset Makers Release 6DoF SLAM Solution As Open Source

August 27, 2025 by Donald Papp 8 Comments

Some readers may recall the Lynx-R1 headset — it was conceived as an Android virtual reality (VR) and mixed reality (MR) headset with built-in hand tracking, designed to be open where others were closed, allowing developers and users access to inner workings in defiance of walled gardens. It looked very promising, with features rivaling (or surpassing) those of its contemporaries.

Founder [Stan Larroque] recently announced that Lynx’s 6DoF SLAM (simultaneous location and mapping) solution has been released as open source. ORB-SLAM3, modified for Android-based hardware (GitHub repository), takes in camera images and outputs a 6DoF pose, and does so effectively in real-time. The repository contains some added details as well as a demo application that can run on the Lynx-R1 headset.

The unusual optics are memorable. (*Hands-on Lynx-R1* by Antony Vitillo)

As a headset the Lynx-R1 had a number of intriguing elements. The unusual optics, the flip-up design, and built-in hand tracking were impressive for its time, as was the high-quality mixed reality pass-through. That last feature refers to the headset using its external cameras as inputs to let the user see the real world, but with the ability to have virtual elements displayed and apparently anchored to real-world locations. Doing this depends heavily on the headset being able to track its position in the real world with both high accuracy and low latency, and this is what ORB-SLAM3 provides.

A successful crowdfunding campaign for the Lynx-R1 in 2021 showed that a significant number of people were on board with what Lynx was offering, but developing brand new consumer hardware is a challenging road for many reasons unrelated to developing the actual thing. There was a hands-on at a trade show in 2021 and units were originally intended to ship out in 2022, but sadly that didn’t happen. Units still occasionally trickle out to backers and pre-orders according to the unofficial Discord, but it’s safe to say things didn’t really go as planned for the R1.

It remains a genuinely noteworthy piece of hardware, especially considering it was not a product of one of the tech giants. If we manage to get our hands on one of them, we’ll certainly give you a good look at it.

Butta Melta Stops Rock-solid Butter From Tearing Your Toast

August 25, 2025 by Donald Papp 53 Comments

Ever ruin a perfectly serviceable piece of toast by trying (and failing) to spread a little pat of rock-solid butter? [John Dingley] doesn’t! Not since he created the Butta Melta to cozily snug a single butter serving right up against a warm beverage, softening it just enough to get nice and spreadable. Just insert one of those foil-wrapped pats of butter into the Melta, hang its chin on the edge of your mug, and you’ll have evenly softened butter in no time.

The Butta Melta is intentionally designed with a bit of personality, but also has features we think are worth highlighting. One is the way it’s clearly designed with 3D printing in mind, making it an easy print on just about any machine in no time at all. The second is the presence of the hinge point which really helps the Butta Melta conform to a variety of cup designs, holding the payload as close as possible to the heat regardless of cup shape. A couple of minutes next to a hot beverage is all it takes for the butter to soften enough to become easily spreadable.

You may remember [John] (aka [XenonJohn]) from his experimental self-balancing scooters, or from a documentary he made about domestic ventilator development during COVID. He taught himself video editing and production to make that, and couldn’t resist using those skills to turn a video demo of the Butta Melta into a mock home shopping style advertisement. Watch it below, embedded just under the page break, then print one and save yourself from the tyranny of torn toast.

Continue reading “Butta Melta Stops Rock-solid Butter From Tearing Your Toast” →

LeRobot Brings Autonomy To Hobby Robots

August 23, 2025 by Donald Papp 6 Comments

Robotic arms have a lot in common with CNC machines in that they are usually driven by a fixed script of specific positions to move to, and actions to perform. Autonomous behavior isn’t the norm, especially not for hobby-level robotics. That’s changing rapidly with LeRobot, an open-source machine learning framework from the Hugging Face community.

The SO-101 arm is an economical way to get started.

If a quick browse of the project page still leaves you with questions, you’re not alone. Thankfully, [Ilia] has a fantastic video that explains and demonstrates the fundamentals wonderfully. In it, he shows how LeRobot allows one to train an economical 3D-printed robotic arm by example, teaching it to perform a task autonomously. In this case, the task is picking up a ball and putting it into a cup.

[Ilia] first builds a dataset by manually operating the arm to pick up a ball and place it in a cup. Then, with a dataset consisting of only about fifty such examples, he creates a machine learning model capable of driving the arm to autonomously pick up a ball and place it in a cup, regardless of where the ball and cup actually are. It even gracefully handles things like color changes and [Ilia] moving the cup and ball around mid-task. You can skip directly to 34:16 to see this autonomous behavior in action, but we do recommend watching the whole video for a highly accessible yet deeply technical overview.

Continue reading “LeRobot Brings Autonomy To Hobby Robots” →

RepRapMicron Promises Micro-fabrication For Desktops With New Prototype

August 22, 2025 by Donald Papp 15 Comments

3D printing has transformed how hobbyists fabricate things, but what additional doors would open if we could go even smaller? The µRepRap (RepRapMicron) project aims to bring fabrication at the micron and sub-micron scale to hobbyists the same way RepRap strove to make 3D printing accessible. New developments by [Vik Olliver] show a promising way forward, and also highlight the many challenges of going so small.

How exactly would a 3D printer do micro-fabrication? Not by squirting plastic from a nozzle, but by using a vanishingly tiny needle-like effector (which can be made at any workbench via electrochemical erosion) to pick up a miniscule amount of resin one dab a time, curing it with UV after depositing it like a brush deposits a dot of ink.

By doing so repeatedly and in a structured way, one can 3D print at a micro scale one “pixel” (or voxel, more accurately) at a time. You can see how small they’re talking in the image in the header above. It shows a RepRapMicron tip (left) next to a 24 gauge hypodermic needle (right) which is just over half a millimeter in diameter.

Moving precisely and accurately at such a small scale also requires something new, and that is where flexures come in. Where other 3D printers use stepper motors and rails and belts, RepRapMicron leverages work done by the OpenFlexure project to achieve high-precision mechanical positioning without the need for fancy materials or mechanisms. We’ve actually seen this part in action, when [Vik Olliver] amazed us by scribing a 2D micron-scale Jolly Wrencher 1.5 mm x 1.5 mm in size, also visible in the header image above.

Using a tiny needle to deposit dabs of UV resin provides the platform with a way to 3D print, but there are still plenty of unique problems to be solved. How does one observe such a small process, or the finished print? How does one handle such a tiny object, or free it from the build platform without damaging it? The RepRapMicron project has solutions lined up for each of these and more, so there’s a lot of discovery waiting to be done. Got ideas of your own? The project welcomes collaboration. If you’d like to watch the latest developments as they happen, keep an eye on the Github repository and the blog.

One-Motor Drone Mimics Maple Seeds For Stability

August 20, 2025 by Donald Papp 14 Comments

We’ve seen aircraft based on “helicopter” seeds (technically samara seeds, which include those of maples and elms) before, but this recent design from researchers at the Singapore University of Technology and Design (SUTD) shows how a single small motor can power a spinning monocopter capable of active directed flight, including hovering.

The monocopter is essentially an optimized wing shape with a single motor and propeller at one end. Hardware-wise it might be simple, but the tradeoff is higher complexity in other areas. Physical layout and balance are critical to performance, and software-wise controlling what is basically a wing spinning itself at high speed is a complex task. The payoff is highly-efficient flight in a package that self-stabilizes; it weighs only 32 grams and has a flight time of 26 minutes, which is very impressive for a self-contained micro aircraft.

We saw what looks like an earlier version of this concept from SUTD that was capable of directed flight by modifying the airfoil surface, but like the seeds it was modeled after, it’s more of a glider. This unit has the same spinning-seed design, but is actively powered. A significant improvement, for sure.

For those who prefer their DIY micro aircraft a little more traditional-looking, be sure to check out the design details of a handmade and fully operational 1:96 scale P-51 Mustang that weighs only 2.9 grams. It even has retractable landing gear! When one can manage to keep mass to a bare minimum, a little power goes a long way.

Hide Capacitive Touch Buttons In Your Next 3D Print

August 20, 2025 by Donald Papp 15 Comments

Capacitive touch sensors are entirely in the domain of DIY, requiring little more than a carefully-chosen conductive surface and a microcontroller. This led [John Phillips] to ask why not embed such touch buttons directly into a 3D print?

Button locations and labels can be made as part of the 3D print, which is handy.

The process is not much different from that of embedding hardware like magnets or fasteners into 3D prints: one pauses the print at convenient spot, drops in the necessary hardware, then resumes printing. It’s more or less the same for embedding a touch-sensitive button, but [John] has a few tips to make things easier.

[John] suggests using a strip of copper tape, one per touch pad, and embedding it into the print near the surface. His preference is three layers in, putting the copper tape behind 0.6 mm of plastic when using standard 0.20 mm layer heights.

Copper tape makes a good capacitive touch sensor, and the adhesive on the tape helps ensure it stays in place as the 3D printer seals it in on subsequent passes.

Copper tape is also easy to solder to, so [John] leaves a small hole over the copper — enough to stick in a wire and tack it down with the tip of a soldering iron and a blob of solder after the print is complete. It might not be ideal soldering conditions, but if things get a little melty on the back side it’s not the end of the world.

On the software side capacitive touch sensors can be as simple as using an Arduino library for the purpose but [John] rolled his own code, so give it a peek.

This reminds us a bit of another way to get a capacitive touch sensor right up against some plastic: a simple spring can do the trick.