I had a fling with Shrinky Dinks when I was little, but that passed... Until the last year, when I rediscovered just how versatile it is as a medium. Shrink plastic is easy to come by (and inexpensive if you know where to look), fabulous for decorative projects, and surprisingly handy for prototyping. I've made fun shapes that light up, jewelry, motorized mechanisms, and even working gears.
In this Instructable, I'll show you how to make light-up 3-dimensional shrink plastic shapes.
Step 1: Materials
Shrink plastic is a particular type of plastic called polystyrene, and you can find it in a lot of take-out food containers (like clear salad containers), cups, and anything labeled #6 plastic. It's also in styrofoam, which is indeed shrinkable and worth the experimentation, though I won't cover it here. These sources work fine for a lot of projects, are obviously less expensive, and have the bonus of being reused.
You can also buy sheets of shrink plastic in craft stores and online. They're made specifically for this purpose and shrink fairly evenly in a way that reused #6 plastic doesn't; if you cut out a circle and shrink it, it's likely to still be a circle at the end of the process. Reused #6 containers might give you a bit of an oval. These sheets also tend to be more expensive, though you can find decent prices with a little online hunting. (I use Grafix Shrink Film, which is $20 for a pack of 50 sheets - although not everyone uses that much shrink plastic!) If you're looking to do something that requires a precise shape at the end (like gears), specially-made sheets are more reliable.
You'll draw and cut a shape from the thin plastic, pop it in an oven or toaster oven, and watch it shrink down until it's a fraction of the original size, thicker, and hard. Normally it would be more difficult to shape a piece of hard plastic, but this way you can custom make any piece you like.
Step 2: Making the Pieces
Use permanent markers (like Sharpies) to draw the design you want on a piece of shrink plastic, remembering to make it 2-3 times larger than you want it to be after shrinking, and cut it out. (I drew thick black lines on my pieces to make them easier to see)
The front piece will be what you attach the LED to, and usually has the most decoration.
The back piece can be whatever shape you like, often it's the same size and shape as the front piece. Punch or cut a hole (about an inch in diameter) in the center to make room for the LED legs. If you prefer power tools (or if you forget to make a hole beforehand), you can drill a hole after you shrink the back piece.
The side pieces can be designed however you like, I've created them to be just the size to fit a 10mm LED. If you cut three 1.5-1.75" squares, they will shrink to about the right size.
Pop em on a tray into an oven or toaster oven (a microwave won't work) and watch them shrink. Wait til they have stopped curling, have flattened out and stopped shrinking, then carefully pull out the tray, letting them cool for a couple minutes before removing them.
The curling that happens during the shrinking process will usually fix itself, so wait for it. On larger pieces, there's more of a risk that the sides will stick together. If this happens, working quickly, pull the tray out and use pliers to gently separate the stuck edges, then pop it back in the oven until it flattens.
Step 3: Respect the Hot Glue Gun
Re: Hot glue guns - As you might gather, they're very hot. Be careful. You can find hi-temp, lo-temp, and dual-temp versions. High temperature settings are best for making more solid connections on heavier weight materials (like wood, plastic, metal, ceramics, etc), and as a result of the heat, the glue gets much more melty. Low temperatures melt the glue enough to adhere, but not enough for it to flow all over the place. Instead it makes a nice sticky glob that is more supportive when you first attach lightweight items. I prefer to use low temp settings for this project, but it's not absolutely necessary.
"Low temp" doesn't mean it's not hot; the setting can get up to 250 degrees Fahrenheit, and you can still give yourself a decent burn.
Something you might not know is how awesome hot glue is as a diffuser of light. So when you use it to attach your LED, the light will spread and appear to come from a wider source. You can apply more or less hot glue to play with this.
A safety tip: if you do nip yourself with the tip of a hot glue gun or some heated glue, your should immediately remove the hot glue from your skin. This isn't always obvious in the moment, your hand just wants to get away from the source, but taking the super hot adhesive off your skin makes a huge difference.
Step 4: Assembly
(Having said all that about how dangerous hot glue is, you'll notice that my photos have my fingers very close to the hot stuff. I'd advise being smarter than me and using pliers to hold the pieces or just assembling it on a table.)
Once you have all of the pieces, it's time to assemble them.
Apply a glob of hot glue to the front piece, and press in the end of your LED til it's cooled enough to hold it. The other small side pieces are glued at points around the LED. For the back, run a line of glue along the top of the side pieces, slide the LED legs through the hole and press it together. Tada! You have a 3d shrink plastic shape! See what other kinds of shapes you can make.
Step 5: It's Aliiive! (Adding Power)
At this point, you can simply slide a coin cell battery between the legs of the LED and tape it in place, or you can build a slot to hold the battery. See the photos for my method of making a battery pocket. I used pliers to bend the LED's negative leg underneath and its positive on top of a gap for the battery. Since I needed for the positive leg to get to the top without touching the bottom of the battery and shorting the circuit, I used a bit of hot glue to insulate that part of the leg. The pocket is completed by glueing on a small strip of unshrunk plastic to keep the battery in place. Pop the battery in to turn it on, push it back out to turn it off. If you come up with another method, please share in the comments, or in your own instructable.
You can attach this to a pin and wear it as a brooch, or string it as a necklace, or hang it from the ceiling.
Another idea is to create a string of these, chain the LED legs together (positive to negative), and power it all from one battery pack. It can be room decor, or jewelry, or part of a Halloween costume. Go nuts!