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.

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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Bronze casting with MakerBot

That, dear readers, is the smell of a new Hackspace opening up in Davenport Iowa. It is also the lovely scent of burning plastic. Because how do you celebrate a new Hackerspace? By casting bronze coins of course!

Begin by having a MakerBot extrude plastic coins, then compact the plastic coin in sand to produce a mold. Heat up your bronze in a trashcan furnace and pour it into the mold. The plastic melts away and you’re left with a bronze coin.

There are probably some safety measures and precautions that should be followed as well…