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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Continuous Resin Printer Shows The Speed

Redditor [No-Championship-8520] aka [Eric Potempa] has come up with an interesting DIY take on the Continuous Liquid Interface Production (CLIP) process currently owned and developed by Carbon Inc.

The usual resin 3D printer you may be familiar with is quite a simple machine. The machine has only one axis, which is the vertically moving build platform. A light exposes a photosensitive resin that cures on and is then pulled up off of a transparent window, before the next layer is exposed.

Typical resin printer setup

CLIP is a continuous resin printing process that speeds up printing by removing this peeling process. It utilises a bottom membrane that is permeable to oxygen. This tiny amount of oxygen right at the boundary prevents the solidified resin from sticking to the bottom, allowing the Z axis to be moved up continuously, speeding up printing significantly.

The method [Eric] is using is based around a continuously rotating bath to keep the resin moving, replenishing the resin in the active polymerisation zone. The bottom of the bath is made from a rigid PDMS surface, which is continuously wiped with a squeegee to replenish the oxygen layer. He notes the issues Carbon are still having with getting enough oxygen into the build layer, which he reckons is why they only show prints of smaller or latticed structures. His method should fix that issue. The build platform is moved up slowly, with the part appearing in one long, continuous movement. He reports the printing speed as 280 mm/hour which is quite rapid to say the least. More details are very scarce, and the embedded video a little unclear, but as one commentator said “I think we just saw resin printing evolve!” the next snarky comment changed the “evolve” to “revolve” which made us giggle.

Now, we all know that 3D printing is not at all new, and only the expiration of patents and the timely work by [Adrian Bowyer] and the reprap team kickstarted the current explosion of FDM printers. Resin printers will likely be hampered by the same issues until something completely new kickstarts the next evolution. Maybe this is that evolution? We really hope that [Eric] decides to write up his project with some details, and we will be sitting tight waiting to pore over all the gory details. Fingers crossed!

Scanning electron micrograph of a microfabricated lens array

Getting A Fly’s-Eye View With Microfabricated Lens Arrays

Atomic force microscopy, laser ablation, and etching with a witches brew of toxic chemicals: sounds like [Zachary Tong] has been playing in the lab again, and this time he found a way to fabricate arrays of microscopic lenses as a result.

Like many of the best projects, [Zach]’s journey into micro-fabrication started with a happy accident. It happened while he was working on metal-activated chemical etching (MACE), which uses a noble metal catalyst to selectively carve high-aspect-ratio features in silicon. After blasting at a silver-coated silicon wafer with a laser, he noticed the ablation pits were very smooth and uniform after etching. This led him to several hypotheses about what was going on, all of which he was able to test.

The experiments themselves are pretty interesting, but what’s really cool is that [Zach] realized the smooth hemispherical pits in the silicon could act as a mold for an array of microscopic convex lenses. He was able to deposit a small amount of clear silicone resin into the mold by spin-coating, and (eventually) transfer the microlens array to a glass slide. The lenses are impressively small — hundreds of them over only a couple hundred square microns — and pretty well-formed. There’s always room for improvement, of course, but for an initial attempt based on a serendipitous finding, we’d call it a win. As for what good these lenses are, your guess is as good as ours. But novel processes like these tend to find a way to be useful, and the fact that this is coming out of a home lab doesn’t change that fact.

We find this kind of micro-fabrication fascinating. Whether it’s making OLED displays, micro-machining glass with plasma, or even rolling your own semiconductors, we can’t get enough of this stuff.

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Flat-Pack Pasta: Like Ikea Furniture Without The Weird Wrench

When it comes to food packaging, there’s no bigger scam than potato chip bags, right? People complain about the air (nitrogen, actually) inside, but it’s there for a reason — nitrogen pushes out oxygen, so the chips live in a state of factory-fresh dormancy until you rip open the bag and release the gas. If you want flat-pack chips, there’s always those uniformly-shaped potato slurry wafers that come in a can. But even those usually manage to have a few broken ones.

On the other hand, no one complains about the extra space in their box of fusilli — that would be silly. But seriously, successfully shipping fragile foods requires either flat packing or a lot of extra space, especially if that food comes in a myriad of fun 3D shapes like pasta does. Everybody knows that 3D pasta is superior to flat pasta because it holds sauces so much better. The pasta must be kept intact!

The great thing about pasta as a food is that it’s simple to make, and it’s more nutritious than potato chips. Because of these factors, pasta is often served in extreme situations to large groups of people, like soldiers and the involuntarily displaced. But storing large quantities of shapely pasta takes up quite a bit of space. And because of all that necessary air, much of the packaging goes to waste.

So what if you could keep your plethora of pasta in, say, a filing cabinet? A research team led by the Morphing Matter Lab at Carnegie Mellon University have created a way to make flat-pack pasta that springs to life after a few minutes in boiling water.

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Self-assembling Polymers Support Silicone 3D Prints

We all know what the ultimate goal of 3D printing is: to be able to print parts for everything, including our own bodies. To achieve that potential, we need better ways to print soft materials, and that means we need better ways to support prints while they’re in progress.

That’s the focus of an academic paper looking at printing silicone within oil-based microgels. Lead author [Christopher S. O’Bryan] and team from the Soft Matter Research Lab at the University of Florida Gainesville have developed a method using self-assembling polymers soaked in mineral oil as a matrix into which silicone elastomers can be printed. The technique takes advantage of granular microgels that are “jammed” into a solid despite being up to 95% solvent. Under stress, such as that exerted by the nozzle of a 3D printer, the solid unjams into a flowing liquid, allowing the printer to extrude silicone. The microgel instantly jams back into a solid again, supporting the silicone as it cures.

[O’Bryan] et al have used the technique to print a model trachea, a small manifold, and a pump with ball valves. There are Quicktime videos of the finished manifold and pump in action. While we’ve covered flexible printing options before, this technique is a step beyond and something we’re keen to see make it into the hobby printing market.

[LonC], thanks for the tip.

Flexible, Sensitive Sensors From Silly Putty And Graphene

Everyone’s favorite viscoelastic non-Newtonian fluid has a new use, besides bouncing, stretching, and getting caught in your kid’s hair. Yes, it’s Silly Putty, and when mixed with graphene it turns out to make a dandy force sensor.

To be clear, [Jonathan Coleman] and his colleagues at Trinity College in Dublin aren’t buying the familiar plastic eggs from the local toy store for their experiments. They’re making they’re own silicone polymers, but their methods (listed in this paywalled article from the journal Science) are actually easy to replicate. They just mix silicone oil, or polydimethylsiloxane (PDMS), with boric acid, and apply a little heat. The boron compound cross-links the PDMS and makes a substance very similar to the bouncy putty. The lab also synthesizes its own graphene by sonicating graphite in a solvent and isolating the graphene with centrifugation and filtration; that might be a little hard for the home gamer to accomplish, but we’ve covered a DIY synthesis before, so it should be possible.

With the raw materials in hand, it’s a simple matter of mixing and kneading, and you’ve got a flexible, stretchable sensor. [Coleman] et al report using sensors fashioned from the mixture to detect the pulse in the carotid artery and even watch the footsteps of a spider. It looks like fun stuff to play with, and we can see tons of applications for flexible, inert strain sensors like these.

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Tissue-Engineered Soft Robot Swims Like A Stingray

We’re about to enter a new age in robotics. Forget the servos, the microcontrollers, the H-bridges and the steppers. Start thinking in terms of optogenetically engineered myocytes, microfabricated gold endoskeletons, and hydrodynamically optimized elastomeric skins, because all of these have now come together in a tissue-engineered swimming robotic stingray that pushes the boundary between machine and life.

In a paper in Science, [Kevin Kit Parker] and his team at the fantastically named Wyss Institute for Biologically Inspired Engineering describe the achievement. It turns out that the batoid fishes like skates and rays have a pretty good handle on how to propel themselves in water with minimal musculoskeletal and neurological requirements, and so they’re great model organisms for a tissue engineered robot.

The body is a laminate of silicone rubber and a collection of 200,000 rat heart muscle cells. The cardiomyocytes provide the contractile force, and the pattern in which they are applied to the 1/2″ (1.25cm) body allows for the familiar undulating motion of a stingray’s wings. A gold endoskeleton with enough stiffness to act as a spring is used to counter the contraction of the muscle fibers and reset the system for another wave. Very clever stuff, but perhaps the coolest bit is that the muscle cells are genetically engineered to be photosensitive, making the robofish controllable with pulses of light. Check out the video below to see the robot swimming through an obstacle course.

This is obviously far from a finished product, but the possibilities are limitless with this level of engineering, especially with a system that draws energy from its environment like this one does. Just think about what could be accomplished if a microcontroller could be included in that gold skeleton.

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