CompFab Press-Fit Butterfly Ear Cuff

Back in January, I made a set of aluminum-wire ear cuffs shaped like swallowtail butterfly wings so that I could wear earrings without piercing my ears. I chose this specific design because I needed some sort of structure from which to hang the earrings, and I wanted the cuff itself to look interesting so I wouldn't have to worry about concealing it. Swallowtail wings have a curve that seemed like it would match the curve of an ear, and the "tail" that sticks off the end seemed like it would make a good hook for the earrings.

The set I ended up making was a lot simpler than the design I sketched and, though they fit and looked pretty cool, definitely weren't all that robust. For this assignment, I tried to adapt that design to a 3D-printed set of parts that would be more structurally sound. My approach was to separate the decorative part of the cuff- the wing- from the structural part- the part that attaches to the ear- into a "face" piece and a set of hooks. This way, if the kit fits together as intended and the hooks hold the cuff to my ear properly, I can design different "faces" and swap them out with the same hooks to have a variety of ear cuffs. Designing the faces for a 3D printer also makes it a lot easier to do more complex designs, and scale them to different fits.

Fusion 360

3D printer

Like I mentioned before, I made the original set out of aluminum wire months ago. I started by making a bunch of sketches off a reference picture. (A couple of those sketches are shown along with the reference in the introductory image!) My goal was to make the V2 design out of wire, but that turned out to be harder that I expected. Aluminum wire is nice to work with because it's pretty soft compared to other types of wire, but that also means it's not particularly strong. It warps really easily, which made it tricky to create a complex continuous shape without occasionally bending the parts I'd already shaped out of place. It also starts to break apart after a fairly low amount of stress, so it's hard to undo any sharp bends that have been placed in the wire without weakening it significantly. After breaking the wire a couple times, I ended up simplifying the design by just including the main structural "veins".

The final set of ear cuffs is shown in the second picture- there are small hooks at the top, middle, and bottom of the innermost edge to attach it to my ear. As the third picture shows, they do stay on and look pretty good, but usually after I spent a good few minutes reshaping the hooks to fit. Over time, those hooks will probably break off, since they constantly have to be bent when the ear cuffs are put on or taken off.

I wanted to get an idea of how good the fit would be for my specific printer if I just printed out a set of matching parts at the scale I wanted to print the ear cuffs at, so I downloaded Professor Jacobs' sample fit test and modified the parameters so that the largest peg was a little smaller than a quarter of an inch. The exact parameters I used are shown in the first screenshot.

The second picture above shows the two separate parts of the fit test, and the third picture shows them fit together. On my first print, the piece with the hole fit perfectly on the first peg, so I was satisfied that the printer would be able to print the fittings for the ear cuff at the relatively small scale I was aiming for.

The "face" piece is the piece that's going to be shaped like the butterfly wing, and it needs to have some parts that some pegs will fit into to attach it to the ear.

I was inspired by Jayleen's Instructable from last week (https://www.instructables.com/Geometric-Turtle-Stamp/) to start the design from an image, so I imported a screenshot of my old V2 sketch into the Fusion 360 as a canvas. I then traced the pattern using fit-point splines, which I offset by 0.02in and closed to form surfaces that I then extruded to a height of 0.15in. I tried to follow the design pretty closely for the upper half of the wing, but I wasn't sure how cleanly it would print with all the details, so I decided to make the bottom half much simpler so I could compare the two. I then scaled it so the inner contour would be between 2 and 3 inches tall. One thing I had noticed with my original wire design was that it was a little shorter than my actual ear, so I wanted to try scaling this one up a bit. I don't actually have a ruler though, so I had to estimate the amount I scaled it up by. The first 3 images show the process of creating the decorative part of the face.

Then, I made the fittings by creating a 0.5inx0.5in rectangle with a circle of 0.25in diameter cut out of the middle, extruded to a height of 0.15in. I duplicated this body to create 2 fittings, then intersected them with the wing at the top edge and outer corner of the center. These will be the points where the hooks are connected. I chose the outer corner of the center, rather than the inner corner as I had on the wire versions, because I wanted to make sure I would be able to clip the hook onto the outside edge of my ear, but looking back it might not fit as well as it would've if I'd been able to attach it to the inner edge of the cuff instead.

One other thing that I hadn't realized was that I had made the face thicker when I scaled it up, so in the end it turned out to be about 0.3in compared to the 0.15in-thick fittings. I think it should work out fine as long as the fittings and the pegs match up, and it might also help keep the fittings a little less visible.

The final face piece with the fittings is shown in the last image.

Since it's a completely flat shape, I decided to print it with no build plate adhesion (and definitely no supports). Printing a single wing takes a little over 5 hours.

I wanted to create a single hook design that could be used at both attachment points, so I could easily reuse the hooks and not have to distinguish between them. In the future, however, it might actually make more sense to have different hook shapes, since they're going to attach to very different parts of the ear.

I started making the hooks by creating the peg that would go into the fittings on the face. I created a circle of 0.25in diameter extruded to a height of .17in, to ensure they would definitely fit and hold. I then drew the profile of the hook itself- it has a flat section behind the peg, so that it will be flush with the face piece, and then a small stopper in the back to hopefully provide some grip. I based this loosely off of the shapes that tended to work well for the wire hooks, although I'm not entirely sure how comfortable they'll actually be.

Once the face finishes printing, I'll be able to print 2 of these off (with supports) and finally test how they fit on my ear!

Things went a little awry pretty early into printing the face piece, as shown in the first picture. I realized that the build plate had become really un-leveled, so the top half of the wing was missing material, and the bottom half wasn't adhering to the plate very well. I actually thought it looked sort of interesting, with the organic-looking upper half and the geometric lower half, so I decided to just continue the run after a few adjustments. I paused the printer and leveled the bed a little better, and added more glue to stick the existing print to the bed. After continuing the print, it actually went on perfectly fine and the odd leveling and missing contours were covered up after a few layers. The second picture shows the final result of the face piece! I was able to print off the hooks without any issue, shown in the next two pics.

Finally, I was able to assemble the pieces. The pegs on the hooks didn't print perfectly round, since I didn't use a raft, so part of them was resting on the buildplate during the print. After a bit of shaving, however, the parts all fit together fine. The hook was also shaped pretty well to fit over my ear. However, as I had thought, it turned out that it would have been a much better idea to put the fittings on the inner curve of the ear cuff, because it hangs way too low with the fittings on the outside. The last picture shows how it would ideally sit on the ear.

If/when I print this design again, I'd move the fittings to the inner curve and also flatten the face piece since it printed much thicker than necessary. Overall, though, I'm happy with how the details on the face turned out, and I think the hooks themselves are functional and reusable.