The Ultimate iPod Touch Stylus -- The Prototyping Phase

It takes a great deal of wisdom to know when to stop conceptualizing and ideating, and to finally begin prototyping. As any long-time industrial designer will attest, there rarely is an "ultimate" design to anything...even though I've claimed such with the title to this blog entry for my most recent stylus design. Design is a fluid, evolutionary, and iterative process. And there is usually more than one solution for any given design problem. Which is good for us designers. It keeps us in a job.
At any rate, as I've found though an endless number of design projects, once you've laid out a good potential design on paper, it's time to drop the pencil and make it real. Since I like to revel in the creativity of the design process itself, it's sometimes hard to pin my ideas down to one actionable end. Creativity can be an insatiable beast...so sometimes I've got to cut it off, close the bar, and roll away the buffet (so to speak)--whatever it takes to just nail down a design so the prototyping and "real-world" problem solving can begin. Without "pulling the trigger" and building your design, the conceptualization zone may be the only place that you play in...and it's not necessarily the best place to be. I really prefer to see something completed so that I can touch it, heft it, use it, rather than just dream about what it might be. Pretty sketches and computer renderings can only go so far. So, after a boatload of sketching and conceptualizing, I've locked myself into a final design direction for my iPod stylus.
To get everything planned out and ready to fabricate the stylus, I determined all the dimensions I needed to build the stylus by modeling up my favorite sketch of the device in SolidWorks. Once I was convinced that things were going to work in the "virtual" world, I took my design to the shop, with shop drawings in hand, determined to cut some metal, assemble the stylus, and verify its real function. I had designed the stylus to be turned on a machine lathe using 6061 aluminum (for its corrosion resistance and ease of machining), with a tungsten core (from a TIG welding electrode) for good weight distribution (see the photo below). There's nothing like having a pen with the proper weight to it--and the mass of the tungsten seemed to fit the bill well, especially given the small size I was shooting for with this design. To verify the fit and sizing of all the pieces, I made sure to have my trusty calipers handy (also seen in the photo below). I used to swear by the old-school dial calipers, but have recently "upgraded" to the digital flavor...which seems to work alright. Before I get going too far in my explanation of this project, though, I should probably mention here that I'm not actually a bonafide machinist. I learned a few things in industrial design school, but never had all the specific instruction to make me a real, certified machinist. I've dabbled in the art of machining for a few years now, but have never really needed to understand all the ins-and-outs of machining that are paramount to somebody using a lathe or mill on a day-to-day basis. As a designer, all you really have to know is what a machine can or can't do in a manufacturing setting--simply so you can design appropriately for the processes used to manufacture your products. As a result of my lack of expertise, some of the processes shown here may not be 100% up-to-par by machinist standards, but they still helped me get my design 100% done with (at least) 98% of the quality that my perfectionist tendencies were looking for--and that's good enough for me. So that's my disclaimer.

To do all the dirty work of turning, I used one of the finest Chinese-made pieces of equipment that our state-funded shop could provide (see below). It's definitely not the "tightest" of machines (as bits and pieces keep falling off of it), but if you use it correctly, it can still produce good results--heck, with my critical dimensions, I was able to stay within +/- .002"...not bad for a non-machinist! I always fall back on the wisdom that it's the craftsman, not just the machine, that makes a work of art--which helps me feel better about not having the nicest equipment all the time. And since students can be some of the harshest users of tools, these lathes tend to perform well enough for what we do here.

To get started, I took some aluminum rod stock and put it in the headstock of the machine...

...and then tightened the rod in place with the chuck key, making sure the rod was centered correctly in the jaws of the chuck during tightening. When doing this yourself, ALWAYS REMOVE THE CHUCK KEY WHEN YOU'RE DONE. I've seen a lot of dented machines and holes in walls from a chuck key flying off at Mach-9 as the lathe was thoughtlessly turned on before removing it. Also, if your material extends out of the chuck, it's good to not extend it any more than two times the diameter without support at the other end--this will keep it from deforming or bending during various turning operations.

Next, I used a cutter to smooth out the end of the rod (called "facing") in preparation for upcoming machining  steps. In machining, irregularly-shaped material can cause all kinds of hazards, so it's usually best to clean up the shape of your stock material first.

Once the end of the rod is smooth, a center-drill (placed in the tail stock of the lathe) will put a nice little hole in the end for additional drilling or support by a live center.

This particular stylus design has a hollow center so that the tungsten weight can be added inside. To hollow it out, I drilled into the end just as deep as the inside hole needed to be.

I then extended the aluminum stock further out of the chuck and moved the live center in place into the drilled hole so it would support the stock as I performed the next cutting operations.

I measured out the length that I needed for the part (plus a little bit at the left end for support) and started in with the parting tool.

The parting tool is made to cut your completed part off of the rotating rod, but it can remove a lot of material at once. For that reason it works very well for rough-cutting material and getting it close to the shape you'd like. I took the parting tool and dialed it into the rod in several successive plunges until the rod was near the diameter that I wanted.

I then switched to the cutting tool to help smooth out the surface of my part. I frequently measured the part with the calipers to ensure that I was maintaining proper dimensions:

Since I wanted my stylus to be more "shapely" than straight, I worked the X and Y dials on the machine until the cutting tool had shaved away everything that I didn't want:

When it comes to complex contouring on the lathe, unless you've got a good CNC lathe, the part will need to be smoothed out quite a bit. To get all the "chunkiness" out of the surface, I used a course-toothed file (which won't load up with aluminum the way a fine-toothed file will) to dial-in the shape. This step is very similar to the final shaping steps commonly done on a wood lathe.

I used progressive grits of sandpaper (from 100-grit all the way to 500-grit, in 100-grit increments) to further smooth out the surface:

Once completed, I used a hacksaw to cut off the part...

...and the results looked pretty good. Just a little clean up on the hacksaw-cut end (which was quickly addressed with some sandpaper) was all that was needed to complete this part of the stylus.

I went through the same procedure to fabricate all the remaining parts for the stylus (shown below).

The completed set of parts looked like this (below). All that was left to do was cut the rubber grip to fit the barrel of the stylus, and then to insert the tungsten weight and stylus tip. Since the stylus needs electrical conductivity through the tip and into the fingers of the user, a band of aluminum from the barrel extends into the middle of the grip. With this aluminum contact strip and my fat fingers, it's almost impossible for me to hold the stylus without contacting aluminum at least somewhere on the device.

Although it's insanely hard (and will easily scratch glass), tungsten is a bit brittle. Thin tungsten rod, like this TIG welding electrode, can be broken with relative ease, just as if it were made of ceramic. (There are actually different alloys of tungsten that have varying degrees of increased toughness, but this wasn't one of them.) I broke the rod to the right length for insertion into the barrel of the stylus...

...and then checked it for fit in the stylus (see below). I did additional trimming of the tungsten using a stone-wheel bench grinder.

Next, I trimmed the rubber grip to size with an X-Acto knife.

I then assembled all the stylus parts together, along with the grip.

For the stylus tip, I used a bit of eraser (from a Pentel Clic Eraser)...

...cutting the eraser to size so it would snuggly fit inside the stylus' tip:

I pushed a piece of carbon fiber cloth (as in my "homebrew" stylus demo) into the tip, followed by the eraser tip, and then screwed those onto the body of the stylus.

Finally, I could verify whether or not this stylus was a good, functioning design. And, yes, it worked just as planned! A well-functioning product is always a good follow up for a lengthy build! But a product that functions well and looks good, well that's something worth posting!

In total, I racked up about eight hours of machining and fabrication time for this little tiny project...mostly because I could only work in one to two hours sessions (just fitting it in between all my other teaching, advising, and service responsibilities)--which always requires more time for setup and cleanup in this shop that is used by so many others. Projects seem to go much faster when there is a good, dedicated chunk of time to do things in. But we do what we can.
Now that I've got a new, proven stylus, I can move on to bigger and crazier projects...and I can now design them (at least in part) on my cute little iPod Touch. Design is fun. Keep rockin'.