Modifying Safety Glasses to Combat ACD

Placeholder headline image: replace with picture of glasses with rev1 pieces attached

I recently bought an MSLA resin 3D printer, and before it'd came in the mail I already had the perfect project idea in mind. Nothing about this project was particularly difficult, but nonetheless it would serve to prove just how far you can push the SLA printing process. And it turned out to be a pretty fulfilling little endeavor.

A friend of mine has to use a certain type of bifocal(?) safety glasses for her work—ones that have magnified sections on the bottom. Her workplace provides several different kinds of safety glasses, but only one kind that has magnification, which she needs for inspecting finely detailed parts.

Her problem is that she experiences Allergic Contact Dermatitis in response to some plastics. The rubber nosepiece appears to be one of those plastics, as it causes her nose to break out in a rash if she wears them for too long.

Designing a Solution

Picture of unmodified glasses, zoomed to nose piece area, with pads in background

My friend had suggested the idea to me of 3D printing a replacement nosepiece which she could screw some metal nose pads onto—the kind you typically find on prescription or glasses. Knowing my FDM printers weren't up to the task of creating such small parts, I told her it sounded like a great project to test out my new MSLA printer. She lent me a pair of the safety glasses in question as well as a titanium nose pad kit she'd ordered online. And thus the brainstorming began.

My task was actually pretty straightforward, thanks to the construction of the glasses. The nose piece we needed to replace is a flexible rubbery part that slots onto two posts that are molded onto the glasses frame. I decided the easiest solution would be an adapter that attaches to those posts and then has a slot to screw on the titanium nose pad.

Because the adapter piece was going to be so small, I felt that any screwing, slot and groove, or clamping mechanisms weren’t going to be feasible; that left only two real options for fastening it to the plastic posts. The first being a press fit, relying on the part being sized just right so that once on the post friction would keep it from falling off. And the second option would be to superglue the adapter to the post, which of course means the adapters wouldn't be reusable. Considering how consumable safety glasses are, option two wasn't very appealing since it would mean I'd have to print quite a large batch of these nose piece adapters and then keep producing batches of them into the future. For reference, in some manufacturing environments it's not unheard of for workers to wear out a new pair of safety glasses every week.

Press fit it is then.

Picture of reading glasses, zoomed to nose piece area from behind, one nose piece on, one off

The next feature of the adapter would be how the titanium nose pads attached to it, and for that I took some inspiration from a simple pair of reading glasses. For each nose pad they have a box with one end open, then a hole through the top and bottom for a screw. The flange on the back of the nose pad slots into the box, then the screw runs through it all to lock everything in place while still letting the pad pivot some as it rests against the wearer's nose.

I figured I'd do the same; so in a simple sense all I needed was a tube with a box on it. Of course, this adapter will be visible right there on my friend's nose all day, so a design with a bit more elegance is prudent.

CAD pictures of rev0 design

Prototype pictures of rev0 parts

And that's what I came up with—a tube-shaped body to slide onto the shaft which expands on the bottom to fit the nose pad slot. The slot had two differently sized holes on it, one slightly larger to let the screw slide in easily, then a smaller second hole so that the screw would self-tap into the plastic. To avoid confusion during assembly, I embossed a tiny screw symbol onto the back of the adapter showing which way the screw needs to go in.

Picture of glasses with rev0 nose pieces attached

I went through a few different test pieces, mostly tweaking the hole dimensions and testing the repeatability of my resin printer. I wanted to make sure these parts could easily be made in batches in the future rather than each one being a one-off due to poor tolerances or inconsistent material properties. In that regard, the little machine did not disappoint. Even using some cheap Elegoo rapid prototyping resin I was achieving predictable size tolerances—within my acceptable margin of error.

Thankfully, it wasn't too difficult getting the press fit on the posts just tight enough to hold, but not so tight that the plastic would snap apart, as well as getting the screw holes sized just right. We all know just how small and finicky glasses screws are so it was important to me that the titanium flange would line up with the screw holes perfectly so that the screw would drop right into place ready to tighten with a tiny screw driver.

One thing I did notice in my prototyping is just how easy it was to strip out the threads when tightening the screws. I couldn't really do anything about this, but hoped it wouldn't be a problem.

Confident in my design, I printed a final pair of nose pieces off, gave them to my friend explaining how they worked, and she tested them out for a few days.

Iteration Required

While quite comfortable, she said before the end of the first day one of the screws had already broken lose letting a nose pad pop out and fall to the floor… I have no idea how she found it. She used some wire to thread through the screw hole and re-attach the nose pad.

With this knowledge I decided it was time to revise the design. This time, I took inspiration from my friend's quick fix. Why bother with screws and tiny fragile threads when I could just attach the nose pieces with some wire?

CAD pictures of rev1 design

Prototype pictures of rev1 parts (incl. WL emboss closeup)

I beefed up the plastic on the top and bottom of the nose pad slot, which gave me room to add some channels for wire to sit in. The idea was to thread some wire through the holes, run it through the channels, and the up to the top where it could be twisted together and the slack tucked into a small pocket to keep it from catching on anything and pulling loose.

The finished product looked quite smart, and I was even able to add a tiny bit of Will's Lab branding where the screw symbol was once embossed. A nice touch, though not visible unless you take off the glasses and really look for it.

Results

I'm sure you can tell from the macro shots of the adapters above how much individual pixels (voxels, to be precise) of detail mattered on the finished part. Without going much into how the MSLA printing process works, my printer produces voxels roughly 50x50x50µm in size, and some of the small features on this part were really pushing the boundary of what my printer can reliably render. Many people use resin 3D printers for creating beautifully detailed decorative parts such as board game pieces and miniatures, but producing very small functional parts where those details have to meet fairly tight tolerances, such as these glasses adapters, really shows where the boundaries are for consumer SLA printing. All that is to say, I've learned a lot about what I can, and can't, expect from my new printer. And I must say, I'm pretty satisfied.

I'm also happy to report my friend has been using this version of the nose pieces for a couple weeks now without complaint.