It would be really hard to go through a typical day in the developed world without running across something made from ABS plastic. It’s literally all over the place, from toothbrush handles to refrigerator interiors to car dashboards to computer keyboards. Many houses are plumbed with pipes extruded from ABS, and it lives in rolls next to millions of 3D-printers, loved and hated by those who use and misuse it. And in the form of LEGO bricks, it lurks on carpets in the dark rooms of children around the world, ready to puncture the bare feet of their parents.
ABS is so ubiquitous that it makes sense to take a look at this material in terms of its chemistry and its properties. As we’ll see, ABS isn’t just a single plastic, but a mixture that takes the best properties of its components to create one of the most versatile plastics in the world.
If you’ve ever taken a coast-to-coast car trip across the United States, the one thing that’s sure to impress you is the mind-bogglingly immense amount of corn that we grow here. If you take the northern route — I’ve done it seven times, so I know it by heart — you’ll see almost nothing but corn from Ohio to Montana. The size of the fields is simply staggering, and you’re left wondering, “Do we really eat all this corn?”
The simple answer is no, we don’t. We grow way more corn than we can eat or, once turned into alcohol, drink. We do feed a lot to animals, many of which subsequently end up as burgers or pork chops. But even after all that, and after accounting for exports, we still have a heck of a lot of corn to put to work. There are lots of industrial uses for this surplus corn, though, and chances are pretty good you’ve got an ear or two worth coiled up next to your 3D-printer, in the form of polylactic acid, or PLA.
There’s a lot to be said in favor of getting kids involved in hacking as young as possible, but there is one thing about working in electronics that I believe is best left as a mystery until at least the teenage years — hide the shrink tube. Teach them to breadboard, have them learn resistor color codes and Ohm’s Law, and even teach them to solder. But don’t you dare let them near the heat shrink tubing. Foolishly reveal that magical stuff to kids, and if there’s a heat source anywhere nearby I guarantee they’ll blow through your entire stock of the expensive stuff the minute you turn your back. Ask me how I know.
I jest, but only partly. There really is something fun about applying heat shrink tubing, and there’s no denying how satisfying a termination can be when it’s hermetically sealed inside that little piece of inexplicably expensive tubing. But how does the stuff even work in the first place?
It’s the year 2260 and you’re being beamed from your starship to the planet below. Being a descendant of present day 3D printers, the transporter prints you out, slowly making one layer before moving on to the next, going from the ground up. The you-that-was hopes nothing spills out before you’re done. But what if you could print every atom in your body at the same time? If those transporters are descendant’s of Daqri’s holographic 3D printing technology then that’s just what will happen.
Daqri’s process is akin to SLA (stereolithography) and SLA/DLP (digital light processing). In SLA, a laser beam is shone onto a pool of resin, hardening the resin at the beam’s point. The laser scans across the resin’s surface, drawing one layer. More resin is added and then the next layer is drawn. In SLA/DLP, the light for an entire layer is projected onto the surface at once. While both methods involve stereolithography, the acronym SLA by itself is commonly used to refer to the laser approach.
Holograhically 3D printing a paperclip
Daqri’s process however, uses a holographic chip of their own making to project the light for all the layers at the same time into the material, a light-activated monomer. Their chip is a silicon wafer containing a grid of tunable crystals. Those crystals control the magnitude and phase of light reflected down into the monomer, creating a 3D volume of interference patterns. The brief description of the process says that a laser is used to shine light onto the crystals, so there’s probably still some scanning going on. However, in the video, all of the object being printed appears illuminated at the same time so the scanning is likely very fast, similar to how a laser in a light show seemingly paints what appears to be a 2D shape on the side of a building, even though it’s really just a rapidly moving point. There’s also the possibility that the beam’s point is large enough to encapsulate all of the chip at once. You can see a demonstration of it in the video below.
We are all used to Fused Deposition Modeling, or FDM, 3D printers. A nozzle squirts molten material under the control of a computer to make 3D objects. And even if they’re usually rather expensive we’re used to seeing printers that use Stereolithography (SLA), in which a light-catalysed liquid monomer is exposed layer-by layer to allow a 3D object to be drawn out. The real objects of desire though are unlikely to grace the average hackspace. Selective Laser Sintering 3D printers use a laser on a bed of powder to solidify a 3D object layer by layer.
The laser creating a ring.
While an SLS printer may be a little beyond most budgets, it turns out that it’s not impossible to experiment with the technology. [William Osman] has an 80 W laser cutter, and he’s been experimenting with it sintering beach sand to create 2D objects. His write-up gives a basic introduction to glassmaking and shows the difference between using sand alone, and using sodium carbonate to reduce the melting point. He produces a few brittle barely sintered tests without it, then an array of shapes including a Flying Spaghetti Monster with it.
The results are more decorative than useful at the moment, however it is entirely possible that the technique could be refined. After all, this is beach sand rather than a carefully selected material, and it is quite possible that a finer and more uniform sand could give better results. He says that he’ll be investigating its use for 3D work in the future.
We’ve put his video of the whole process below the break, complete with worrying faults in home-made laser wiring. It’s worth a watch.
A while back I looked at lubricants for the home shop, with an eye to the physics and chemistry behind lubrication. Talking about how to keep parts moving got me thinking about the other side of the equation – what’s the science behind sticking stuff together? Home shops have a lot of applications for adhesives, so it probably pays to know how they work so you can choose the right glue for the job. We’ll also take a look at a couple of broad classes of adhesives that are handy to have around the home shop. Continue reading “Glues You Can Use: Adhesives For The Home Shop”→
If your shop is anything like mine, you’ve got a large selection of colorful cans claiming to contain the best and absolutely only lubricant you’ll ever need. I’ve been sucked in by the marketing more times than I care to admit, hoping that the next product will really set itself apart from the others and magically unstick all the stuck stuff in my mechanical life. It never happens, though, and in the end I generally find myself reaching for the familiar blue and yellow can of WD-40 for just about every job.
