Lost Foam Casting In Action

Even though not all of us will do it, many of us are interested in the art of casting metal. It remains a process that’s not out of reach, though, especially for metals such as aluminium whose melting points are reachable with a gas flame. The video below the break takes us through the aluminium casting process by showing us the lost-foam casting of a cylinder head for a BSA Bantam motorcycle.

The foam pattern is CNC milled to shape, and the leftover foam swarf is removed with a hot wire. The pattern is coated with a refractory coating of gypsum slurry, and the whole is set up in a tub packed with sand. We get the impression that the escaping gasses make this a tricky pour without an extra sprue, and indeed, they rate it as not perfect. The cooling fins on the final head are a little ragged, so it won’t be the part that goes on a bike, but we can see with a bit of refining, this process could deliver very good results.

For this pour, they use a gas furnace, but we’ve seen it done with a microwave oven. Usually, you are losing wax, not foam, but the idea is the same.

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Hackaday Podcast Episode 267: Metal Casting, Plasma Cutting, And A Spicy 555

What were some of the best posts on Hackaday last week? Elliot Williams and Al Williams decided there were too many to choose from, but they did take a sampling of the ones that caught their attention. This week’s picks were an eclectic mix of everything from metal casting and plasma cutters to radio astronomy and space telescope budgets. In between? Some basic circuit design, 3D printing, games, dogs, and software tools. Sound confusing? It won’t be, after you listen to this week’s podcast.

Check out the links below if you want to follow along, and as always, tell us what you think about this episode in the comments!

Download an audiophile-quality oxygen-free MP3 file here.

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More Microwave Metal Casting

If you think you can’t do investment casting because you don’t have a safe place to melt metal, think again. Metal casting in the kitchen is possible, as demonstrated by this over-the-top bathroom hook repair using a microwave forge.

Now, just because it’s possible doesn’t mean it’s advisable. There are a lot better ways to fix something as mundane as a broken bathroom hook, as [Denny] readily admits in the video below. But he’s been at the whole kitchen forging thing since building his microwave oven forge, which uses a special but easily constructed ceramic heat chamber to hold a silicon carbide crucible. So casting a replacement hook from brass seemed like a nice exercise.

The casting process starts with a 3D-printed model of the missing peg, which gets accessories such as a pouring sprue and a thread-forming screw attached to it with cheese wax. This goes into a 3D-printed mold which is filled with a refractory investment mix of plaster and sand. The green mold is put in an air fryer to dry, then wrapped in aluminum foil to protect it while the PLA is baked out in the microwave. Scrap brass gets its turn in the microwave before being poured into the mold, which is sitting in [Denny]’s vacuum casting rig.

The whole thing is over in seconds, and the results are pretty impressive. The vacuum rig ensures metal fills the mold evenly without voids or gaps. The brass even fills in around the screw, leaving a perfect internal thread. A little polishing and the peg is ready for bathroom duty. Overly complicated? Perhaps, but [Denny] clearly benefits from the practice jobs like this offer, and the look is pretty cool too. Still, we’d probably want to do this in the garage rather than the kitchen.
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A red hot crucible is held with metal tongs above a white plaster mold. The mold is held in a bright pink silicone sleve atop a metal pan on a wooden workbench. Red cheese wax holds the sleeve to a metal funnel connected to a vacuum cleaner.

Lost Print Vacuum Casting In A Microwave

Hacks are rough around the edges by their nature, so we love it when we get updates from makers about how they’ve improved their process. [Denny] from Shake the Future has just provided an update on his microwave casting process.

Sticking metal in a microwave certainly seems like it would be a bad idea at first, but with the right equipment it can work quite nicely to develop a compact foundry. [Denny] walks us through the process start to finish in this video, including how to build the kilns, what materials to use, and how he made several different investment castings using the process. The video might be worth watching just for all the 3D printed tools he’s built to aid in the process — it’s a great example of useful 3D prints to accompany your fleet of little plastic boats.A hand holds a very detailed copper ring. It is inscribed with the words "Open Source Hardware" and the open gear logo associated with open source hardware. It looks kinda like a class ring.

A lot of the magic happens with a one minute on and six minutes off cycle set by a simple plug timer. This allows a more gradual ramp to burn out the PLA or resin than running the microwave at full blast which can cause some issues with the kiln, although nothing catastrophic as demonstrated. Vacuum is applied to the mold with a silicone sleeve cut from a swimming cap while pouring the molten metal into the mold to draw the metal into the cavities and reduce imperfections.

We appreciate the shout out to respirators while casting or cutting the ceramic fiber mat. Given boric acid’s effects, [PDF] you might want to use safety equipment when handling it as well or just use water as that seems like a valid option.

If you want to see where he started check out this earlier version of the microwave kiln and how he used it to make an aluminum pencil.

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Slab Casting – A New Way To Combine 3D Printing And Ceramics

Slip casting can be messy both in processing and in making the original plaster mold. What if there was a better way, thanks to 3D printing?

[Allie Katz] has developed a new technique using 3D printed slab molds to make ceramics. By combining the ability of 3D printing to make intricate designs and the formability of clay, they have found a way to make reproducible clay objects without all that tedious mucking about with liquid clay.

[Katz] takes us through a quick “Mould Making 101” before showing how the slab casting press molds were made. Starting with a positive CAD design, the molds were designed to eliminate undercuts and allow for air infiltration since a plastic mold can’t suck the water out of the clay like a plaster one would. Some cookie clay cutters were also designed to help with the trickier bits of geometry. Once everything was printed, the molds were coated with cornstarch and clay was pressed in. After removal, any final details like handles can be added and the pieces are then fired as normal.

If you’d like to see some more 3D printing mixed up with ceramics, check out 3D printing glass with a laser, reliable ceramic slurry printing, or this TPU-based approach.

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Teletext In Ireland, Another Broadcasting Leftover Bites The Dust

Over the years we’ve reported on the passing of a few of the broadcasting technologies of yesteryear, such as analogue TV in America, or AM radio in Europe. Now it’s the turn of an early digital contender, as one of the few remaining holdouts of old-style teletext is to shut down its service. The Irish broadcaster RTÉ is to turn off its teletext service Aertel, which has been live in some form continuously since 1986.

Like all European countries, Ireland has had only digital TV for quite a few years now. The linked RTÉ piece implies that the Aertel service has been carried as the old-style data in the frame blanking period even when part of a digital multiplex rather than the newer digital teletext system, so we’d be really grateful if some of our Irish readers could flick on their TVs and confirm that.

In an internet-connected world it seems quaint that a limited set of curated pages could once have been such a big deal, but it’s easy to forget that for many the teletext system provided their first ever taste of online information. As it shuffles away almost unnoticed we won’t miss counting through the page numbers cycling by in the top corner as we waited for our page to load, but it’s worth marking its final passing from one of the few places it could still be found.

Teletext does pop up in a few projects here, most recently as the display engine for a game of DOOM.

Nuke Your Own Uranium Glass Castings In The Microwave

Fair warning: if you’re going to try to mold uranium glass in a microwave kiln, you might want to not later use the oven for preparing food. Just a thought.

A little spicy…

Granted, uranium glass isn’t as dangerous as it might sound. Especially considering its creepy green glow, which almost seems to be somehow self-powered. The uranium glass used by [gigabecquerel] for this project is only about 1% U3O8, and isn’t really that radioactive. But radioactive or not, melting glass inside a microwave can be problematic, and appropriate precautions should be taken. This would include making the raw material for the project, called frit, which was accomplished by smacking a few bits of uranium glass with a hammer. We’d recommend a respirator and some good ventilation for this step.

The powdered uranium glass then goes into a graphite-coated plaster mold, which was made from a silicone mold, which in turn came from a 3D print. The charged mold then goes into a microwave kiln, which is essentially an insulating chamber that contains a silicon carbide crucible inside a standard microwave oven. Although it seems like [gigabecquerel] used a commercially available kiln, we recently saw a DIY metal-melting microwave forge that would probably do the trick.

The actual casting process is pretty simple — it’s really just ten minutes in the microwave on high until the frit gets hot enough to liquefy and flow into the mold. The results were pretty good; the glass medallion picked up the detail in the mold, but also the crack that developed in the plaster. [gigabecquerel] thinks that a mold milled from solid graphite would work better, but he doesn’t have the facilities for that. If anyone tries this out, we’d love to hear about it.