You Can’t Scare Me!

Over winter break 2017, my older daughter asked if she could make something. Before I even knew what it was, I was pretty excited. Finally after all these years of trying to show my kids that they can make things, I see a spark of interest. Here’s her idea in her own words:

“I want to build something that people can attach to their glasses so they can see who or what is behind them.”

So, we set to work on the design. I had her draw up her initial thinking on paper, and we took it from there. She decided that for the prototype, a clip would be the easiest way to attach the unit to her glasses

I wasn’t sure what we could use for the actual mirror part, but I remembered seeing mirrored acrylic somewhere, so we searched for mirrored acrylic sheets. We ordered the parts and set to work on designing the bracket that would hold everything together.

We decided that 3D printing the bracket would be the most efficient way to prototype it, and that turned out to be true.

Her first idea was a ball joint because it would allow the wearer to adjust the mirror’s position precisely. So, we found a ball joint on thingiverse and scaled it to the size we needed. The print didn’t work at all, and the joint wouldn’t fit together. Getting this joint to work for us would require a lot more engineering.

Discouraged but not hopeless, I decided I’d show her how to use OpenSCAD to design our own part. I mean, how hard could it be? We’d just create a static bracket for our first try and see what needed to be adjusted.

Using OpenSCAD was a great way to incorporate some of the math she’d been learning in school that year. We had to measure the dimensions of the clip with the vernier caliper and then calculate dimensions of the bracket based on those dimensions. She seemed to really enjoy the challenge.

Second design
The very first design connected the mirror mount at the edge of the mirror. After testing, she found this was too close to the eye and decided to move the mirror away from the eye a bit, resulting in this layout.

The next step was to put all the pieces together for the first prototype.

We had some hot glue available to us, and that worked… for a few hours. The failure of the hot glue would later clue us in to a design flaw.

Despite that, the first prototype achieved its goal. She decided that the mirror was too close to the glasses, so we should move the mirror outward a bit. We fired up OpenSCAD and adjusted the dimensions and printed again.

First Prototype
The First prototype had the mirror closer to the eye, which turned out to limit the visibility too much.

This time, we used Loctite silicone to bond the clip to the bracket. That joint lasted a bit longer, but still failed after about a day. As a remedy, we decided to use Gorilla super glue.

After gluing the parts together, one part of the joint failed again.

I decided I wanted to figure out why the glue joints were failing. I inspected the action of the clip and showed it to my daughter. We hadn’t taken into account that the clip’s spring expands past the clip’s edge when the clip is actuated. The slight expansion was causing the glue joint to flex and eventually break.

She also noticed that she couldn’t see that much around her and we discussed concave and convex mirrors.  So, we iterated on the design and came up with a curved mirror mount.

Curved Mirror Mount
This mount allows the wearer to see more of what’s around them.

By this time, we were running out of time, so we weren’t able to make more prototypes before school started back up.  We had a lot of fun doing this, though!

Issues for Further Development:
– how to make the fastener more generic to fit more types of glasses?
– carve out a small slot to accommodate the spring expansion.