Making beautiful things from epoxy and wood happens to be [Peter Brown’s] area of expertise. He was recently quested with reverse engineering the ring design of the Canadian manufacturer secret wood — a unique combination of splintered wood and epoxy — and achieved impressive results.
When Sparkfun visited the factory that makes their multimeters and photographed a mysterious industrial process.
We all know that the little black globs on electronics has a semiconductor of some sort hiding beneath, but the process is one that’s not really explored much in the home shop. The basic story being that, for various reasons , there is no cheaper way to get a chip on a board than to use the aptly named chip-on-board or COB process. Without the expense of encapsulating the raw chunk of etched and plated silicon, the semiconductor retailer can sell the chip for pennies. It’s also a great way to accept delivery of custom silicon or place a grouping of chips closely together while maintaining a cheap, reliable, and low-profile package.
As SparkFun reveals, the story begins with a tray of silicon wafers. A person epoxies the wafer with some conductive glue to its place on the board. Surprisingly, alignment isn’t critical. The epoxy dries and then the circuit board is taken to a, “semi-automatic thermosonic wire bonding machine,” and slotted into a fixture at its base. The awesomely named machine needs the operator to find the center of the first two pads to be bonded with wire. Using this information it quickly bonds the pads on the silicon wafer to the board — a process you’ll find satisfying in the clip below.
The final step is to place the familiar black blob of epoxy over the assembly and bake the board at the temperature the recipe in the datasheet demands. It’s a common manufacturing process that saves more money than coloring a multimeter anything other than yellow.
Word clocks are cool, but getting them to function correctly and look good is all about paying attention to the details. One look at this elegant walnut-veneered word clock shows what you can accomplish when you think a project through.
Most word clocks that use laser-cut characters like [grahamvinyl]’s effort suffer from the dreaded “stencil effect” – the font has bridges to support the islands in the middle of characters like “A” and “Q”. While that can be an aesthetic choice and work perfectly well, like in this word clock we featured a few months back, [grahamvinyl] was going for a different look. The clock’s book-matched walnut guitar back was covered in tape before being laser cut; the tape held the letters and islands in place. After painstakingly picking out the cutouts and tweaking the islands, he used clear epoxy resin to hold everything in place. The result is a fantastic Art Deco font and a clean, sleek-looking panel to sit on top of an MDF light box for the RGB LED strips.
The braided cloth cable adds a vintage look to the power cord, and [grahamvinyl] mentions some potential upgrades, like auto-dimming and color shifting. This is very much a work in progress, but even at this point we think it looks fabulous.
Working with high voltage is like working with high pressure plumbing. You can spring a leak in your plumbing, and of course you fix it. And now that you’ve fixed that leak, you’re able to increase the pressure still more, and sometimes another leak occurs. I’ve had these same experiences but with high voltage wiring. At a high enough voltage, around 30kV or higher, the leak manifests itself as a hissing sound and a corona that appears as a bluish glow of excited ions spraying from the leak. Try to dial up the voltage and the hiss turns into a shriek.
Why do leaks occur in high voltage? I’ve found that the best way to visualize the reason is by visualizing electric fields. Electric fields exist between positive and negative charges and can be pictured as electric field lines (illustrated below on the left.) The denser the electric field lines, the stronger the electric field.
The stronger electric fields are where ionization of the air occurs. As illustrated in the “collision” example on the right above, ionization can happen by a negatively charged electron leaving the electrically conductive surface, which can be a wire or a part of the device, and colliding with a nearby neutral atom turning it into an ion. The collision can result in the electron attaching to the atom, turning the atom into a negatively charged ion, or the collision can knock another electron from the atom, turning the atom into a positively charged ion. In the “stripping off” example illustrated above, the strong electric field can affect things more directly by stripping an electron from the neutral atom, again turning it into a positive ion. And there are other effects as well such as electron avalanches and the photoelectric effect.
In either case, we wanted to keep those electrons in the electrically conductive wires or other surfaces and their loss constitutes a leak in a very real way.
It’s not transparent aluminum, exactly, but it might be even better: transparent wood. Scientists at the University of Maryland have devised a way to remove all of its coloring, leaving behind an essentially clear piece of wood.
By boiling the block of wood in a NaOH and Na2SO chemical bath for a few hours the wood loses its lignin, which is gives wood its color. The major caveat here is that the lignin also gives wood strength; the colorless cellulose structure that remains is itself very fragile. The solution is to impregnate the transparent wood with an epoxy using about three vacuum cycles, which results in a composite that is stronger than the original wood.
There are some really interesting applications for this material. It does exhibit some haze so it is not as optimally transparent as glass but in cases where light and not vision is the goal — like architectural glass block — this is a winner. Anything traditionally build out of wood for its mechanical properties will be able to add an alpha color channel to the available options.
The next step is finding a way to scale up the process. At this point the process has only been successful on samples up to 1 centimeter thick. If you’re looking to build a starship out of this stuff in the meantime, your best bet is still transparent aluminum. We do still wonder if there’s a way to eliminate the need for epoxy, too.
[prubeš] shows that parts printed with carbon fiber filament are as strong, or at least as stiff, as you’d expect. He then shows that his method for producing carbon fiber parts with a mixture of traditional lay-up and 3D printing is even stronger and lighter.
[prubeš] appears to be into the OpenR/C project and quadcopters. These things require light and strong parts for maximum performance. He managed to get strength with carbon fiber fill filament, but the parts weren’t light enough. Then he saw [RichMac]’s work on Thingiverse. [RichMac] designed parts with pre-planned grooves in which he ran regular carbon fiber tow with epoxy. This produced some incredibly strong parts. There’s a section in his example video, viewable after the break, where he tests a T joint. Even though the plastic starts to fail underneath the carbon fiber, the joint is still strong enough that the aluminum tube inside of it fails first.
[prubeš] innovation on [RichMac]’s method is to remove as much of the plastic from the method as possible. He designs only the connection points of the part, and then designs a 3D printable frame to hold them in place. After he has those in hand, he winds the tow around the parts in a sometimes predetermined path. The epoxy cures onto the 3D print creating a strong mounting location and the woven carbon fiber provides the strength.
His final parts are stronger than 100% infill carbon fill prints, but weighs 8g instead of 12g. For a quadcopter this kind of saving can add up fast.
The carbon fiber look is a pretty hot design element for things these days. Even things that have no need for the strength and flexibility of carbon fiber, from phone cases to motorcycle fenders, are sporting that beautiful glossy black texture. Some of it only looks like the real stuff, though, so it’s refreshing to see actual carbon fiber used in a project, like this custom headphone rack.
True, this is one of those uses of carbon fiber that doesn’t really need it – it just looks cool. But more importantly, [quada03]’s build log takes us through the whole process, from design to mold construction to laying up the fiber mats and finishing, and shows us how specialized equipment is not needed to achieve a great result. A homemade CNC router carves the two-piece mold out of Styrofoam, which is then glued up and smoothed over with automotive body filler. The epoxy-soaked carbon fiber mats are layered into the mold with careful attention paid to the orientation of the fibers, and the mold goes into one of those clothes-packing vacuum bags for 24 hours of curing. A little trimming and sanding later and the finished bracket looks pretty snazzy.
We’ve discussed the basics of carbon fiber fabrication before, but what we like about [quada03]’s build is that it shows how approachable carbon fiber builds can be. Once you hone your skills, maybe you’ll be ready to tackle a carbon fiber violin.