Making A Metal Hand Doorknob

Regular doorknobs are widely reviled for their bare simplicity, but by and large society has so many other problems that it never really comes up in day to day conversation. Fear not, however, for [Matthew] has created something altogether more special: a doorknob in the shape of his own outstretched hand.

The build was inspired by a similar doorknob at the WNDR museum in Chicago, and its one you can recreate yourself, too. It’s achieved through a multi-stage mold making process. [Matthew]’s first step was to make a flexible mold of his hand using Perfect Mold alginate material to do so.

Once solidified, [Matthew’s] hand was removed and the mold filled with wax. The wax duplicate of [Matthew]’s hand was then used to create an investment plaster mold for casting metal. Vents were added in the end of each fingertip in the mold to allow molten metal to effectively fill the entire cavity.

Once the investment mold was solid and dry, the wax was melted out and it was ready for casting. A propane furnace was used to melt the casting metal and fill the mold using a simple gravity casting method. [Matthew] ended up making two hands, one in aluminium and one in copper. Some cleanup with grinders and a wire wheel, and a replica of [Matthew]’s hand was in his hands!

The finished piece looks great attached to a door knob, and we’re sure it’s quite satisfying shaking hands with your hefty metal self every time you open the door. It bears noting that the same techniques can be used with 3D printing, too! If you pull off your own great home casting project, be sure to drop us a line. Video after the break.

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Hackaday Links: September 19, 2021

Things might be getting a bit dicey out in Jezero crater for Ingenuity. The little helicopter that could is starting to have trouble dealing with the thinning Martian atmosphere, and may start pressing against its margin of safety for continued operation. Ingenuity was designed for five flights that would all take place around the time its mothership Perseverance touched down on Mars back in February, at which time the mean atmospheric pressure was at a seasonal high. Over the last few months, the density of the Martian atmosphere has decreased a wee bit, but when you’re starting with a plan for a pressure that’s only 1.4% of Earth’s soupy atmosphere, every little bit counts. The solution to keeping Ingenuity flying is simple: run the rotors faster. NASA has run a test on that, spinning the rotors up to 2,800 RPM, and Ingenuity handled the extra stresses and power draw well. A 14th flight is planned to see how well the rotors bite into the rarefied air, but Ingenuity’s days as a scout for Perseverance could be numbered.

If you thought privacy concerns and government backdoors into encryption technology were 21st-century problems, think again. IEEE Spectrum has a story about “The Scandalous History of the Last Rotor Cipher Machine,” and it’s a great read — almost like a Tom Clancy novel. The story will appeal to crypto — not cryptocurrency — fans, especially those fascinated by Enigma machines, because it revolves around a Swiss rotor cipher machine called the HX-63, which was essentially a refinement of the original Enigma technology. With the equivalent of 2,000-bit encryption, it was considered unbreakable, and it was offered for sale to any and all — at least until the US National Security Agency sprung into action to persuade the inventor, Boris Hagelin, to shelve the HX-63 project in favor of electronic encryption. The NSA naturally helped Hagelin design this next generation of crypto machines, which of course all had backdoors built into them. While the cloak and dagger aspects of the story — including a possible assassination of Boris Hagelin’s son in 1970, when it became clear he wouldn’t “play ball” as his father had — are intriguing, the peek inside the HX-63, with its Swiss engineering, is the real treat.

One of the great things about the internet is how easy it is to quickly answer completely meaningless questions. For me, that usually involves looking up the lyrics of a song I just heard and finding out that, no, Robert Plant didn’t sing “Whoopie Cat” during Misty Mountain Hop. But it also let me answer a simple question the other day: what’s the largest single-piece metal object ever created? I figured it would have to be a casting of some sort, and likely something from the middle of the previous century. But as it turns out, the largest casting ever appears to have been manufactured in Sheffield, England in 2015. The company, Sheffield Forgemaster International, produced eleven castings for the offshore oil industry, each weighing in at over 320 tonnes. The scale of each piece is mind-boggling, and the technology that went into making them would be really interesting to learn about. And it goes without saying that my search was far from exhaustive; if you know of a single-piece metal part larger than 320 tonnes, I’ll be glad to stand corrected.

Have you heard about “teledriving” yet? On the face of it, a remote-controlled car where a qualified driver sits in an office somewhere watching video feeds from the car makes little sense. But as you dig into the details, the idea of remotely piloted cars starts to look like one of those “Why didn’t I think of that?” ideas. The company behind this is called Vay, and the idea is to remotely drive a ride-share vehicle to its next customer. Basically, when you hail a ride, a remote driver connects to an available car and drives it to your location. You get in and take over the controls to drive to your destination. When you arrive, another remote drive pilots the car to its next pickup. There are obvious problems to work out, but the idea is really the tacit admission that all things considered, humans are way better at driving than machines are, at least right now.

Casting Silicone Parts With 3D-Printed Inserts For Stiffness

Prolific maker [Jan Mrázek] shared his process for casting soft silicone parts that nevertheless have some added stiffness, which he accomplished by embedding porous, 3D-printed “ribs” into the pieces during the casting process. The 3D-printed inserts act as a sort of skeleton, and as a result, the parts have a soft silicone surface but gain structure and rigidity that simply wouldn’t be obtained if the part were cast entirely in silicone. The nice thing is that no new materials or tools were needed; [Jan] 3D printed both the molds for the parts as well as the structural inserts. It’s always nice when one can use the same tool and materials to accomplish different functions.

The parts [Jan] is making are interesting, as well. He observed that the process of swapping resin in his printer’s build tank was an unpleasant experience for a number of reasons, chief among them being that resin is sticky and messy, and the shape of the build tank doesn’t make pouring resin from it a clean job.

His solution was to design a pour spout that could be pressed onto the build tank, and some specially-designed squeegees to allow scraping the tank clean with ease. Silicone is the ideal material for the parts because it turns out that sticky resin beads nicely on silicone’s surface. Anywhere else, resin tends to spread out and form a sticky mess, but on silicone resin it forms tidy drops and is much easier to clean up.

It’s a technique worth keeping in mind, because one never knows when it could come in handy. Fabricating soft robots for example tends to involve silicone casting and clever techniques. See [Jan]’s parts in action in the video, embedded below.

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Casting A Simple 3D Print In Aluminium

3D printing with plastics and resins is great for quickly prototyping parts with all manner of geometries, but strength and durability of the parts produced is often limited. One way around this is to use your 3D printed parts as patterns for casting in something tougher like aluminium. That’s precisely what [Brian Oltrogge] did to produce an attractive wall hook from a 3D printed design.

The process starts with the design and printing of a wall hook, with [Brian] taking care to include the proper draft angles to allow the pattern to be properly removed from the mold. The print is carefully sanded down and post-processed to be highly smooth, so that it doesn’t spoil the mold when its removed for the casting process. From there, a sand casting mold is built around the pattern using sodium silicate in a 3-4% mix by weight with fine masonry sand. Once ready, the pattern is removed, and the mold is assembled, ready for the pour.

[Brian] completes the process with a simple gravity casting method using molten aluminium. The part is then removed from the mold, and filed down to improve the surface finish from the sand casting process. It’s then polished up to a nice shine and hung on the wall.

[Brian] does a great job of explaining the basics of what it takes to get gravity casting right; draft angles in particular are something often ignored by beginners, yet are crucial to getting good results. You needn’t just settle for casting inanimate objects though; we’ve featured DIY casting processes for gears before, too. Video after the break.

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Modular Box Design Eases Silicone Mold-Making

Resin casting is a fantastic way to produce highly detailed parts in a wide variety of colors and properties, and while the process isn’t complicated, it does require a certain amount of care and setup. Most molds are made by putting a part into a custom-made disposable box and pouring silicone over it, but [Foaly] was finding the process of making and re-making those boxes a bit less optimized than it could be. That led to this design for a re-usable, modular, adjustable mold box that makes the workflow for small parts considerably more efficient.

The walls of the adjustable box are four identical 3D-printed parts with captive magnets, and the base of the box is a piece of laser-cut steel sheet upon which the magnetic walls attach. The positioning and polarity of the magnets are such that the box can be assembled in a variety of sizes, and multiple walls can be stacked to make a taller mold. To aid cleanup and help prevent contamination that might interfere with curing, the inner surfaces of each piece are coated in Kapton tape.

The result is a modular box that can be used and re-used, and doesn’t slow down the process of creating and iterating on mold designs. The system as designed is intended for small parts, but [Foaly] feels there is (probably) no reason it can’t be scaled up to some degree. Interested? The design files are available from the project’s GitHub repository, and if you need to brush up a bit on how resin casting works, you can read all about it here.

Casting Skateboard Wheels With A 3D Printed Mold

We’ll admit that most of the Hackaday staff wouldn’t get too far on a skateboard, but that doesn’t mean we can’t appreciate the impressive DIY wheels that [Chris McCann] has managed to cast using 3D printed molds. From unique color combinations to experimental materials, the process certainly opens up some interesting possibilities for those looking to truly customize their rides. Though it’s worth noting there’s a certain element of risk involved; should a set of homemade wheels fail at speed, it could go rather poorly for the rider.

Both the STL and STEP files for the mold have been released under the Creative Commons Attribution 4.0 license, meaning anyone with a 3D printer can follow along at home. Unfortunately, it’s not quite as simple as clicking print and coming back to a usable mold. Because of the layer lines inherent to FDM 3D printing, the inside of the mold needs to be thoroughly sanded and polished. [Chris] mentions that printing the mold in ABS and using vapor smoothing might be a workable alternative to elbow grease and PLA, but he hasn’t personally tried it yet.

Once you’ve got the three part mold printed, smoothed, and coated with an appropriate release agent like petroleum jelly, it’s time to make some wheels. The core of each wheel is actually 3D printed from PETG, which should give it pretty reasonable impact resistance. If you have access to a lathe, producing aluminum cores shouldn’t be too difficult either. With the core loaded into the mold, urethane resin is poured in through the top until all the empty space is filled.

But you’re not done yet. All those little air bubbles in the resin need to be dealt with before it cures. [Chris] puts his filled molds into a pressure chamber, though he mentions that vacuum degassing might also be a possibility depending on the urethane mixture used. After everything is solidified, the mold can easily be taken apart to reveal the newly cast wheel.

While there’s often some trial and error involved, 3D printing and resin casting are an undeniably powerful combination. If you can master the techniques involved, you can produce some very impressive parts that otherwise would be exceptionally difficult to produce on a hacker’s budget. Especially when you’re ready to start casting molten metal.

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Peeking Inside A VW Gearbox Reveals Die Casting Truths

Recently, I was offered a 1997 Volkswagen Golf for the low, low price of free — assuming I could haul it away, as it suffered from a thoroughly borked automatic transmission. Being incapable of saying no to such an opportunity, I set about trailering the poor convertible home and immediately tore into the mechanicals to see what was wrong.

Alas, I have thus far failed to resurrect the beast from Wolfsburg, but while I was wrist deep in transmission fluid, I spotted something that caught my eye. Come along for a look at the nitty-gritty of transmission manufacturing!

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