DIY iPod Touch Docking Station -- Prototyping With Acrylic Plastic

So, let’s say you’ve got an idea for a sweet design—a design that needs to be lightweight, weather resistant, inexpensive, and easily fabricated. Maybe it even needs to be clear, which would suddenly make this design a tall order to fill. Well, if you look at traditional materials to fit the bill, then you'll find that wood is lightweight and easy to work with in the shop, but it’s not all that weather resistant, and it sure ain’t clear. Metal is a durable, useful option, but it can require some expensive tools to fabricate parts with, especially if welded joints are required. On top of that, metal isn't transparent (unless you have some great top-secret leads on alien technology), and it can be heavy and have limited weather resistance, depending on the particular metal you select. But, If you want a prototyping material that fits all of these requirements at the same time, you might look into the "magical" world of wonderful substances we commonly refer to as “plastics”. 
In modern life, we use plastics more frequently and extensively than most people even recognize, but they are often already formed into products and can be difficult to reuse or reappropriate for our own specific use—unless you know about thermoplastic sheet materials...like acrylic. Acrylic plastic (or polymethylmethylacrylate--PMMA--for those of you who want to use the long name to lay down the nerd card at your next Jeopardy party) is one of the most easily obtained and usable thermoplastics and is also sold under the trade names of Plexiglas and Lucite. Like many traditional building materials, acrylic has the benefit of being solid at room temperature and easily worked using common shop tools. But, unlike typical materials, acrylic can be quickly and easily formed with inexpensive heating tools--which opens up a world of shaping possibilities that other materials simply don't possess.  
Acrylic plastics can be purchased in a couple of different forms, but for quick prototyping purposes using power and hand tools, it tends to be easiest to use in its common sheet form. Compared with traditional materials, it can be somewhat expensive in thick sections, or when large sheets are required, but is relatively cheap when procured in pre-cut sizes or as scrap. This can be helpful for the do-it-yourselfer who may be working on a small prototype or project, since these smaller scrap sizes are generally easier to transport, manage, and work with anyway. Acrylic sheet plastic is also available in many colors (either opaque or transparent), and can be easily painted using common automotive paints. One caution on using acrylic plastic, however, is that it doesn't have the same impact resistance as the plastics typically found in mass-manufactured consumer goods, like ABS, polycarbonate, or polypropylene. Therefore, take care to avoid dropping, overstressing, or overloading acrylic plastics since they can chip or fracture without much effort.
To demonstrate the ease of working with acrylic sheet, this blog posting will walk through the steps needed to fabricate a custom iPod Touch docking station (shown below). Although this docking station has a rather simple design, the methods shown here illustrate some of the common cutting, finishing, and forming steps that could be used to produce just about any prototype that would benefit from acrylic's useful material properties.

As a bit of background, I first started working with acrylic sheet when I was in a shop class in middle school--and I have to admit that I became totally enamored by the stuff. As I recall, the first project I made was a cheesy little 80's unicorn clock for one of my sisters. But I couldn't just stop there--the fabrication possibilities provided by acrylic were beckoning me to do even more. At the time, I was way into writing and illustrating comic books and started buying large pieces of acrylic plastic from my shop teacher so that I could make full-body suits of armor like the characters in my stories had. Luckily, I never had to go into battle with any of that plastic armor, but it sure helped me develop my skills in working with plastics at a young age.

When working with acrylic sheet, it's important to develop your design from the beginning so that it can be fabricated from flat stock. If you've got a design with all kinds of crazy compound curves and wacky form to it, you're going to be in for some serious headaches (although such shapes may still be possible with a lot of work--and assuming that you like the mental pain). However, if you intend for your design to rely on simple bends, flat pieces, or even modest glue joints, you should be able to make it without much trouble. Also, keep in mind that thicker plastics don't bend very well (or easily), so if your design has lots of tight bends in it, thinner plastic is advisable. Generally speaking, I shy away from plastic over 1/4" thick when I'm doing a lot of bending. Plastic that is around 1/8" thick works very well for most small projects like this.
To get started with this little demo project, I first created some quick sketches to explore a few shape and function possibilities for the docking station. I settled on a basic chair-like form that would proudly display the iPod while allowing for straightforward mounting of the stock Apple dock connector/USB cable to the finished acrylic base. Using these sketches, I cut and folded some paper to make a quick mock-up of the docking station so that I could be assured that the size and proportion was correct (see below).  

Once I was content with my design direction, I unfolded the paper mock-up to make the cutting pattern for the plastic. I also used a pen and ruler to mark the location of the bends so I could reference these later in the building process.

Next I traced the pattern onto the acrylic sheet. Acrylic typically comes with a backing of either paper or plastic film on it to minimize scratches. It's usually best to keep the backing on for as long as possible during the fabrication process to avoid the hassle of unnecessary buffing and polishing to scratched surfaces. I like to transfer the bend lines onto the acrylic backing film as well, because it comes in handy later on to remind me where I need to make all those bends.

Acrylic cuts very easily with a table saw, but I recommend special plastics cutting blades to keep the plastic from blowing out (or chipping) as the blade cuts through the sheet. These types of blades are pricey, so a fine-toothed carbide blade can work well instead. Remember to always use a push-stick (shown below) when cutting narrow pieces!...it helps keep those digits where they belong. Heck, that's why I've still got mine today.

For curved cuts, the bandsaw works well. If I need to make really tight-radius shapes, relief cuts in the plastic can help keep the blade from binding around the curves. If the shape I'm cutting is just too insane for the bandsaw, I move my project over to the scroll saw since it's actually made to handle intricate and curvy shapes.

A belt or disc sander can help shape up the edges very quickly. But avoid using fine-grit or old, grit-less sandpaper since these will generate a lot of heat and end up melting the plastic more than sanding it.

Sanding with power tools will leave some heavy grit scratches in the edges of the plastic (as seen below). Such scratches really detract from the overall appearance of the project, so I spend the extra time to demonstrate a respectable level of craftsmanship by smoothing these imperfections out.

To create pretty, smooth edges, I go with the standard lineup of sandpaper, utility knife blade, and polishing compounds (shown below). The sandpaper knocks down waves and nasty, chunky grooves on the surface of the edges. A fresh razor blade in a utility knife can quickly scrape the surface clean while avoiding lots of time with progressive grits of sandpaper. And lastly, the polishing compound takes the fine scratches out of the surface and leaves a respectable, sparkly surface that shows how much you really cared to make your project look spiffy. Our shop is outfitted with polish that is made specifically for plastics, but course to fine automotive polishes will work well also.

When sanding straight surfaces, I always use a sanding block to reinforce the sandpaper. This helps produce a uniform sanding surface that levels any peaks and valleys in the plastic very quickly. I'm using a 220-grit sandpaper in this picture because it's generally sufficient to get the 100-grit grooves out of the plastic that were left by the power sander.

After leveling the edges, I usually take a utility knife (with a brand-new blade in it) or straight razor blade over the edge to scrape along and take out the 220-grit scratches. This method is just as effective as using 320-grit and then 400-grit sandpapers on the edges, but it's a whole lot less time intensive; it usually only takes a few passes and a few seconds rather than the several minutes required to actually sand the edges.

To get the edge ready for final smoothing, I use a fine-grit sandpaper to get rid of any small grooves that may have been left over by the knife blade. For this final fine-grit smoothing, wet sanding works best, though with paper-backed acrylic sheet, the paper starts to dissolve a bit and becomes messy and difficult to remove when finished. Consequently, if you've got paper-backed acrylic, just dry sand the edges with 500-grit sandpaper

Finally, I'm ready to do the polishing. I start with the "heavy scratch remover" first, which has a grit to it that is similar to traditional toothpastes...though I don't think I'd try brushing with it. (It just doesn't smell like something that I'd like to put in my mouth in the first place.)

I apply some good rubbing pressure with the polish to work the scratches out...

...and then move up to the "fine scratch remover" to bring the shine up even more. The final super-slick and sparkly polishing step really produces a mirror finish in the plastic.

As you can see in this finished edge, the polishing steps really pump up the bling.

Next, the plastic needs to be bent using some simple heating methods. To mark the location of the bends, I use a white colored pencil or grease pencil to transfer the bend lines from the paper backing to the edge of the plastic. This is an important step because it's difficult to find where the bends need to be once the backing paper has been removed...and it has to be removed before heating and bending.

Once I've got everything ready to start the bending processes, I peel off the backing paper and try to avoid scratching the surfaces while I'm handling the plastic.

For simple, straight bends, a strip heater (shown below) is a super-duper-awesome tool. A heat gun will also work well, but it tends to produce a wider, less controlled zone of heat on the plastic. If I need to heat the whole piece of plastic at once, I simply put it into the shop's oven at about 375 degrees Fahrenheit for a few minutes until the plastic gets soft and pliable. Always make sure to use gloves when touching any heated sections of the plastic--it can get very toasty!

Once the strip heater is plugged in, turned on, and allowed to pre-heat, I place the acrylic piece over the gap in the top surface of the strip heater, making sure to line up the bend marks on the edge with the heating element (shown below).

I try to flip the acrylic over periodically to help promote even heating on both sides of the piece. This makes bending the plastic much easier. As you can see in the picture below, acrylic sheet has such a perfectly smooth surface that it produces mirror-like reflections from overhead lights...at least until it starts to heat up to its bending point. When it gets sufficiently warm, the plastic begins to soften and deform a bit, causing ripples and warps in the surface reflections. I use these warped reflections as a way of gauging when the plastic is getting ready for bending.

When the heated plastic loosens up (and before it starts to sag) then it is ready to bend. Never try to bend acrylic that has not heated all the way through its thickness; it can catastrophically fracture if it is too cool when forced into a bend. To control a straight bend on a straight-sided shape, a table top works well to keep things in line. It's best to hold the plastic in place until the bent area has cooled to the point that it is only warm to the touch.

After a couple more rounds on the heat strip, the base for the docking station is fully formed. All that's left is to use a rotary tool (like a Dremel) with a cut-off wheel to cut a hole in the bottom through which the standard dock connection/USB cable can be epoxied in place and the iPod can be securely docked.

And there you have it--plastic simplicity, with lots of possibilities mixed in. Since the students in my plastics class are currently working on their own acrylic projects, I'll show off some of their work in an upcoming blog entry once I've picked the most impressive of the bunch.
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