Lost PLA Casting Brings out the Beauty of Macromolecules

Biochemistry texts are loaded with images of the proteins, nucleic acids, and other biopolymers that make up life. Depictions of the 3D structure of macromolecules based on crystallography and models of their most favorable thermodynamic conformations are important tools. And some are just plain beautiful, which is why artist [Mike Tyka] has taken to using lost-PLA casting to create sculptures of macromolecules from bronze, copper, and glass.

We normally don’t cover strictly artistic projects here at Hackaday, although we do make exceptions, such as when the art makes a commentary on technology’s place in society. In [Mike]’s case, not only is his art beautiful and dripping with nerd street cred, but his techniques can be translated to other less artsy projects.

kcsa_5_bigFor “Tears”, his sculpture of the enzyme lysozyme shown in the banner image, [Mike] started with crystallographic data that pinpoints every peptide residue in the protein. A model is created for the 3D printer, with careful attention paid to how the finished print can be split apart to allow casting. Clear PLA filament is used for the positive because it burns out of the mold better than colored plastic. The prints are solvent smoothed, sprues and air vents added, and the positive is coated with a plaster mix appropriate for the sculpture medium before the plastic is melted out and the mold is ready for casting.

[Mike]’s sculpture page is well worth a look even if you have no interest in macromolecules or casting techniques. And if you ever think you’ll want to start lost-PLA casting, be sure to look over his build logs for plenty of tips and tricks. “Tears” is executed in bronze and glass, and [Mike]’s description is full of advice on how to handle casting such vastly different media.

Thanks to [Dave Z.] for the tip.

Foundry From Scrapped Oven for Cheap, Clean Castings

Home-built foundries are a popular project, and with good reason. Being able to melt and cast metal is a powerful tool, even if it’s “only” aluminum. But the standard fossil-fuel fired foundries that most people build are not without their problems, which is where this quick and clean single-use foundry comes into play.

The typical home foundry for aluminum is basically a refractory container of some kind that can take the heat of a forced-air charcoal or coal fire. But as [Turbo Conquering Mega Eagle] points out, such fuels can lead to carbon contamination of the molten aluminum and imperfections when the metal is cast. With a junked electric range, [Turbo Conquering Mega Eagle] fabricates a foundry that avoids the issue in an incredibly dangerous way. The oven’s heating element is wrapped around an old stainless saucepan, fiberglass bats from the stove insulate the ad hoc crucible, and the range’s power cord is attached directly to the heating element. The video below shows that it does indeed melt aluminum, which is used to sand cast a fairly intricate part.

We can’t see getting more than one use out of this setup, though, so it’s only as sustainable as the number of ranges you can round up. But it’s worth keeping in mind for one-off jobs. For a more permanent installation, check out this portable propane-powered foundry. And to see what you can make with one, check out this engine breather cast from beer cans.

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Tools of the Trade — Injection Molding

Having finished the Tools of the Trade series on circuit board assembly, let’s look at some of the common methods for doing enclosures. First, and possibly the most common, is injection molding. This is the process of taking hot plastic, squirting it through a small hole and into a cavity, letting it cool, and then removing the hardened plastic formed in the shape of the cavity.

The machine itself has three major parts; the hopper, the screw, and the mold. The hopper is where the plastic pellets are dumped in. These pellets are tiny flecks of plastic, and if the product is to be colored there will be colorant pellets added at some ratio. The hopper will also usually have a dehumidifier attached to it to remove as much water from the pellets as possible. Water screws up the process because it vaporizes and creates little air bubbles.

Next the plastic flecks go into one end of the screw. The screw’s job is to turn slowly, forcing the plastic into ever smaller channels as it goes through a heating element, mixing the melted plastic with the colorant and getting consistent coloring, temperature, and ever increasing pressure. By the time the plastic is coming out the other end of the screw, and with the assistance of a hydraulic jack, it can be at hundreds of tons of pressure.

Finally, the plastic enters the mold, where it flows through channels into the empty cavity, and allowed to sit briefly to cool.  The mold then separates and ejector pins push the part out of the cavity.

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DIY Nozzle Socks For Your 3D Printer

If you have a 3D printer, your nozzle and heater block are invariably covered in a weird goo consisting of decomposed and burnt plastic. There’s only one way around this – a nozzle sock, or a silicone boot that wraps around the heater block and stops all that goo from accumulating.

Right now, E3D sells silicone nozzle socks for their normal-sized heater blocks, with a release for their maxi-sized Volcano blocks coming shortly. [Ubermeisters] couldn’t wait, so he designed a 3D printed mold to cast as many Volcano nozzle socks as he could ever need.

The mold itself is taken from the mechanical drawings of the E3D Volcano hotend, printed in Proto Pasta HTPLA. To create the nozzle sock, this mold is filled with a goo made from GE Silicone I, mineral spirits, plaster of Paris, carbon powder, aluminum powder, titanium microspheres, and bronze powder colorant from Alumalite.

The mold is sprayed with release, filled with silicone goo, and slowly brought together. After a few hours, the silicone has cured, can be removed from the mold, and the flash can be cut away from the finished part. The end result is great — it fits the Volcano hotend well, and shouldn’t be covered in melted, burnt plastic in a week’s time.

All the files for the Volcano nozzle sock mold can be found on YouMagine. Alternatively, you could wait another month or two for E3D to release their ‘official’ Volcano nozzle sock.

Portable Lightweight Foundry

[Makercise] is getting ready for Maker Faire. One of the things he’d really like to do is some casting demonstrations. However, he has no desire to take his expensive and heavy electric kiln based foundry to Maker Faire. So, he made his own.

He got into metal casting during his excellent work on his Gingery lathe series. He started off by modeling his plan in Fusion 360. He’d use a 16qt cook pot turned upside down as the body for his foundry. The top would be lined with ceramic fiber insulation and the lid made out of foundry cement. He uses a Reil style burner, which he also modeled as an exercise. This design is light and even better, allows him to lift the top of foundry off, leaving the crucible completely exposed for easy removal.

All went well with the first iteration. He moved the handles from the top to the bottom of the pot and filled it with insulation. He built legs for the lid and made a nice refractory cement bowl on the bottom. However, when he fired it up the bowl completely cracked along with his crucible. The bowl from design flaw, the crucible from age.

A bit put off, but determined to continue, he moved forward in a different direction. The ceramic insulation was doing so well for the top of the foundry that he decided to get rid of the cement altogether and line the bottom with it as well. The lid, however, would be pretty bad for this, so he purchased another pot and cut the top portion of it off, giving him a steel bowl that matched the top.

The foundry fires up and has worked well through multiple pours. He made some interesting objects to hopefully sell at Makerfaire and to test the demonstrations he has planned. The final foundry weighs in at a mere 15lbs not including the fuel cylinder, which is pretty dang light. Video after the break.

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Metal Casting With Single Shelled PLA Masters

[3DTOPO] does a lot of metal casting (video link, embedded below). That’s obvious by the full and appropriate set of safety gear, a rarity on YouTube.

They had all the equipment to do it the normal way: craft or CNC out a master, produce a drag and a copy, make any necessary cores, and finally; pour the mold. This is a long and tedious process. It has a high rate of error, and there is a parting line.

Another set of methods are the lost ones. With these methods the master is produced out of a material like foam or wax. The master is surrounded by refractory and then melted, burned, or baked out of the mold. Finally the metal is poured in. Theoretically, a perfect reproduction is made without ever having to open the mold.
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Learn Resin Casting Techniques: Cold Casting

Sometimes we need the look, feel, and weight of a metal part in a project, but not the metal itself. Maybe you’re going for that retro look. Maybe you’re restoring an old radio and you have one brass piece but not another. It’s possible to get a very metal like part without all of the expense and heat required in casting or the long hours in the metal fabrication shop.

Before investing in the materials for cold casting, it’s best to have practical expectations. A cold cast part will not take a high polish very well, but for brushed and satin it can be nearly indistinguishable from a cast part. The cold cast part will have a metal weight to it, but it clinks like ceramic. It will feel cool and transfers heat fairly well, but I don’t have numbers for you. Parts made with brass, copper, and iron dust will patina accordingly. If you want them to hold a bright shine they will need to be treated with shellac or an equivalent coating afterward; luckily the thermoset resins are usually pretty inert so any coating used on metal for the same purpose will do.

It is best to think of the material as behaving more or less like a glass filled nylon such as the kind used for the casing of a power tool. It will be stiff. It will flex a relatively short distance before crazing and then cracking at the stress points. It will be significantly stronger than a 3D printed part, weaker than a pure resin part, and depending on the metal; weaker than the metal it is meant to imitate.

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