Original Part:

The original part was the right temple for my favorite pair of sunglasses. I did not want to throw them out, so I decided to design a replacement.

Failure Description:

More than likely caused by normal wear-and-tear, and maybe a manufacturing defect, the right temple split between the two screws holding it onto the sunglasses. Considering the lack of material cross-section in that area, it’s reasonable to assume there were multiple stress concentrations that likely facilitated the initial fracturing.

Replacement Part Design:

The main interfaces I wanted to preserve were the screw holes and the curved, organic shape that fit my head so nicely. The screw holes were easy to measure, as were the screws themselves to make sure I had adequate clearance. The curve was harder, but with some clever CAD work I think I was able to capture it.

Failure Mitigation:

I added slightly more material than existed originally, so the new design should last longer based on that alone. PETG is also nominally more flexible than injection-molded ABS, and is less reactive to UV radiation, so the new design might actually last a while.