3D Printed Molds For Casting Rose’s Metal

Have you ever played with Rose’s metal? It’s a fusible alloy of bismuth, lead, and tin with a low melting point of around 100 °C. Historically, it’s been used as a solder for cast iron railings and things, and as a malleable pipe filler material to prevent crimping while a pipe is bent.

[Ben Healey] has been playing around with Rose’s metal and some PETG printed molds, making everything from Star Wars Imperial credits to chess pieces to leather stamping tools. In the video after the break, [Ben] takes us through the process, beginning with mold-making from STLs — something he picked up from another YouTuber.

He recommends adding registration marks to multi-part molds in order to keep everything lined up, and adding a small recess in the seam for easy separation with a flat-head screwdriver. So far, the molds have held up to multiple pours, though [Ben] did print them rather thick and is glad he did.

As far as making liquid metal, [Ben] used a cast iron pot with a convenient pour spout, and a blowtorch. He added graphite powder to the molds in an effort to make them give up the goods more easily. To finish the pieces, [Ben] cut the flashing with tin snips and used sandpaper and a Dremel to smooth the edges. Copper plating didn’t work out, but [Ben] is going to try it again because he thinks he screwed something up in the process. He’s also going to try printing with TPU, which we were just about to recommend for its flexibility.

There are many ways to cast metal on the (relatively) cheap. Have you considered Kinetic Sand?

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Epoxy lenses

The Ins And Outs Of Casting Lenses From Epoxy

If you need a lens for a project, chances are pretty good that you pick up a catalog or look up an optics vendor online and just order something. Practical, no doubt, but pretty unsporting, especially when it’s possible to cast custom lenses at home using silicone molds and epoxy resins.

Possible, but not exactly easy, as [Zachary Tong] relates. His journey into custom DIY optics began while looking for ways to make copies of existing mirrors using carbon fiber and resin, using the technique of replication molding. While playing with that, he realized that an inexpensive glass or plastic lens could stand in for the precision-machined metal mandrel which is usually used in this technique. Pretty soon he was using silicone rubber to make two-piece, high-quality molds of lenses, good enough to try a few casting shots with epoxy resin. [Zach] ran into a few problems along the way, like proper resin selection, temperature control, mold release agent compatibility, and even dealing with shrinkage in both the mold material and the resin. But he’s had some pretty good results, which he shares in the video below.

[Zach] is clear that this isn’t really a tutorial, but rather a summary of the highs and lows he experienced while he was working on these casting methods. It’s not his first time casting lenses, of course, and we doubt it’ll be his last — something tells us he won’t be able to resist trying this all-liquid lens casting method in his lab.

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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.