A Glowing Potato Peeler Makes A Nernst Lamp

Over the last couple few decades there has been a great shift in electric lighting, first towards more compact and efficient fluorescent lights, and then towards LED bulbs. The old incandescent bulbs, while giving a pleasant light, were not by any means efficient. Digging into the history books the incandescent bulb as we know it was not the only game in town; while suspending a filament in a vacuum stopped it from being oxidized there was another type of light that used a ceramic element at atmospheric pressure. The Nernst lamp required its filament to be heated before it would conduct electricity, and [Drop Table Adventures] has made one using the blade from a ceramic potato peeler.

The right ceramic is not the problem given the ease of finding ceramic kitchen utensils, but two problems make a practical light difficult. The copper connections themselves become too hot and oxidize, and preheating the ceramic with a blowtorch is difficult while also keeping an even heat. Finally, they do manage a self-sustaining lamp, albeit not the brightest one.

If you think the Nernst lamp sounds familiar, maybe it’s because we covered it as part of our retrotechtacular series.

Continue reading “A Glowing Potato Peeler Makes A Nernst Lamp”

A flip-top foundry for metal casting

Flip-Top Foundry Helps Manage The Danger Of Metal Casting

Melting aluminum is actually pretty easy to do, which is why it’s such a popular metal for beginners at metal casting. Building a foundry that can melt aluminum safely is another matter entirely, and one that benefits from some of the thoughtful touches that [Andy] built into his new propane-powered furnace.

The concern for safety is not at all undue, for while aluminum melts at a temperature that’s reasonable for the home shop, it’s still a liquid metal that will find a way to hurt you if you give it half a chance. [Andy]’s design minimizes this risk primarily through the hands-off design of its lid. While most furnaces have a lid that requires the user to put his or her hands close to the raging inferno inside, or that dangerously changes the center of mass of the whole thing as it opens, this one has a fantastic pedal-operated lid that both lifts and twists. Leaving both hands free to handle tongs is a nice benefit of the design, too.

The furnace follows a lot of the design cues we’ve seen before, starting as it does with an empty party balloon helium tank. The lining is a hydrid of ceramic blanket material and refractory cement; another nice safety feature is the drain channel cast into the floor of the furnace in case of a cracked crucible. The furnace is also quite large, at least compared to [Andy]’s previous DIY unit, and has a sturdy base that aids stability — another plus in the safety column.

Every time we see a new furnace design, we get the itch to start getting into metal casting. And with the barrier to entry as low as a KFC bucket or an old fire extinguisher, why not give it a try? Although it certainly pays to know what can go wrong before diving in.

Continue reading “Flip-Top Foundry Helps Manage The Danger Of Metal Casting”

Printing Ceramics Made Easier

Creating things with ceramics is nothing new — people have done it for centuries. There are ways to 3D print ceramics, too. Well, you typically 3D print the wet ceramic and then fire it in a kiln. However, recent research is proposing a new way to produce 3D printed ceramics. The idea is to print using TPU which is infused with¬†polysilazane, a preceramic polymer. Then the resulting print is fired to create the final ceramic product.

The process relies on a specific type of infill to create small channels inside the print to assist in the update of the polysilazane. The printer was a garden-variety Lulzbot TAZ 6 with ordinary 0.15mm and 0.25mm nozzles.

Continue reading “Printing Ceramics Made Easier”

3D Printed Vortex Cooled Rocket Needs To Stop Leaking

Rocket engines are known for one thing above all else, and that’s getting hot. It’s this very property that makes them such a challenge to build and run from a materials engineering standpoint. It’s hard enough to build one with advanced metal alloys, but [Integza] presses on with trying to make one on a 3D printer. Progress is being made, but success remains elusive.¬† (Video, embedded below.)

To try and mitigate the thermal effects of burning propellants in his engine design, [Integza] looked to vortex cooling. This is where oxygen is swirled around the outer edge of the combustion chamber in a vortex, acting as a buffer layer between the burning fuel and the chamber walls. With 3D printed chamber components, keeping temperatures as low as possible is key, after all. Unfortunately, despite using a special ceramic-laden resin for printing and lathering the rocket components in various refractory materials, it wasn’t possible to stop the chambers leaking. Solid combustion was possible for a few seconds at a time, but eventually each motor tested turned into a ball of flames as the walls broke down.

Thankfully, nobody was hurt in testing, and [Integza] has a clear idea of the problems that need to be fixed in the next iteration. We’ve featured other vortex cooled rockets before – the theory is sound. As always, the devil is in the implementation.

Continue reading “3D Printed Vortex Cooled Rocket Needs To Stop Leaking”

Homebrew Doorknob Caps For High-Voltage Fun

Mouser and Digi-Key are great for servicing most needs, and the range of parts they offer is frankly bewildering. But given the breadth of the hardware hacking community’s interests, few companies could afford to be the answer to everyone’s needs.

That’s especially true for the esoteric parts needed when one’s hobby involves high voltages and homemade lasers, like [Les Wright]. He recently came up with a DIY doorknob capacitor design that makes the hard-to-source high-voltage caps much easier to obtain. We’ve seen [Les] use these caps in his transversely excited atmospheric (TEA) lasers, a simple design that uses high-voltage discharge across a long, narrow channel filled with either room air or nitrogen. The big ceramic caps are needed for the HV supply, and while [Les] has a bunch, they’re hard to come by online. He tried a follow-up using plain radial-lead ceramic capacitors, and while the laser worked, he did get some flashover between the capacitor leads.

[Les]’s solution was to dunk the chunky caps in acetone for a week or so to remove their epoxy covering. Once denuded, the leads were bent into a more axial configuration and soldered to brass machine screws. The dielectric slug is then put in a small section of plastic tubing and potted in epoxy resin with the bolts protruding from each end. The result is hard to distinguish from a genuine doorknob cap; the video below shows the build process as well as some testing.

Hats off to [Les] for taking pity on those of us who want to replicate his work but find ourselves without these essentials. It’s nice to know there’s a way to make unobtanium parts when you need them.

Continue reading “Homebrew Doorknob Caps For High-Voltage Fun”

Dog Bowls Show The Versatility Of Ceramic Slip Casting

Here at Hackaday, we feature projects that are built of just about every material imaginable. Silicon-spangled fiber-reinforced epoxy resin is our primary medium, but we see plastic, wood, steel, aluminum, and even textiles from time to time. It’s not often we see slip-cast ceramic molding, though, and when it pops up, it’s always good to take a look at this versatile manufacturing method.

The back-story on this one is that [thoughtfulocean], a mechanical engineer idled by COVID lockdowns, wanted custom water bowls for his dogs, one of whom is clearly a grumpy Ewok. The design started with a 3D-print of the final vessel, printed in sections and glued together. These were used to create a two-piece plaster mold into which a watery slurry of clay, or slip, was poured. The plaster mold dehydrates the slip, leaving behind a semi-solid layer of clay of the desired thickness once the excess slip is poured off. The resulting casting is then fired in a kiln and glazed.

Of course, [thoughtfulocean] ran into a few problems along the way. The first mold was warped thanks to the mold box bowing under pressure from the plaster, so the whole molding process had to be revamped. The finished bowl also shrunk less than expected after firing, which led to some more revisions. But the finished bowl look really nice, and the included pump and filter keeps the Ewok’s water free from the yuck a dog’s face can introduce. As a bonus, it sounds like [thoughtfulocean] might have created a marketable product from all this. Take that, COVID!

Slip-casting ceramic may not be all that common around here, but ceramic as a material isn’t exactly a stranger. And who says slip casting is limited to ceramic? After all, we’ve seen a similar method used with plastic resin.

[via r/engineering]

No Doorknobs Needed For This Nitrogen Laser Build

Sometimes the decision to tackle a project or not can boil down to sourcing parts. Not everything is as close as a Digi-Key or Mouser order, and relying on the availability of surplus parts from eBay or other such markets can be difficult. Knowing if and when a substitute will work for an exotic part can sometimes be a project all on its own.

Building lasers is a great example of this, and [Les Wright] recently looked at substitutes for hard-to-find “doorknob” capacitors for his transversely excited atmospheric lasers. We took at his homebrew TEA lasers recently, which rely on a high voltage supply and very rapid switching to get nitrogen gas to lase. His design uses surplus doorknob caps, big chunky parts rated for very high voltages but also with very low parasitic inductance, which makes them perfect for the triggering circuit.

[Les] tried to substitute cheaper and easier-to-find ceramic power caps with radial wire leads rather than threaded lugs. With a nominal 40-kV rating, one would expect these chunky blue caps to tolerate the 17-kV power supply, but as he suspected, the distance between the leads was short enough to result in flashover arcing. Turning down the pressure in the spark gap chamber helped reduce the flashover and prove that these caps won’t spoil the carefully engineered inductive properties of the trigger. Check out the video below for more details.

Thanks to [Les] for following up on this and making sure everyone can replicate his designs. That’s one of the things we love about this community — true hackers always try to find a way around problems, even when it’s just finding alternates for unobtanium parts.

Continue reading “No Doorknobs Needed For This Nitrogen Laser Build”