A month ago, I broke my nose. I won't go into extreme detail, but it would be safe to say that my face had a brief and painful encounter with an icy ski run in Vermont. The silver lining of nose injuries is that they heal pretty quickly; I was mostly functional again after about two weeks of rest and relaxation. However, functional doesn't mean structurally sound. Noses (as any other bone) take about six weeks to heal when broken. For this four week period, I was in a precarious state: healthy enough to be active, but also unable to take any physical contact to the nose. This means no contact sports (soccer for me) or any risky activities. To protect fragile noses from incidental contact, many companies sell pricey polycarbonate face-guards. I decided to print my own.
My face mask has two real requirements: ensuring nothing touches my actual nose and being as un-intrusive as possible. Preventing any contact on my nose boils down force distribution - physics states that force directed at the face has to be applied somewhere. The key is controlling where it's applied. On a successful mask, the plastic is stiff and impact resistant, immediately distributing all the force to facial contact pads on my cheekbones and forehead. The printed part of the mask should not touch my face directly, as Onyx alone would be uncomfortable. In addition to being safe while playing, I want the mask to interfere with my ability to play soccer as little as possible. Therefore, the mask must be light, fit snugly, and not impair vision in addition to being impact resistant.
When designing this mask, I had no empirical face dimensions to base my CAD on. So, I measured critical dimensions of my face with calipers and based the general shape of the mask off of the CAT scan cross sections that I had of my nose. After a couple of iterations, I settled on a facial contour that fit well while giving 5mm of clearance from my nose. By varying the radii of the top and bottom profiles, I ensured that the support material prints on the bed (instead on top of the part itself. I cut out two large eye slots, making sure to leave enough material to fully cover the inside bridge of my nose.
After thinking about what materials to print the mask with, I settled on Onyx and Kevlar. Kevlar is a specialized fiber that exhibits excellent impact resistance with nearly no risk of failing catastrophically. Though carbon fiber is stiffer and stronger, I found that a Kevlar reinforced mask would outperform the polycarbonate mask while being less likely to fail catastrophically than one reinforced with Continuous Carbon Fiber. In order to decrease the odds of the mask snapping along layer lines, I also refrained from adding fiber along the bridge of my nose. This increased its layer adhesion strength without seriously compromising any other physical aspects of the mask.
To hold the mask on my face, I purchased two cheap elastic Velcro straps and fit them onto the mask mid-print. They hold the mask tightly on my face without being uncomfortable. Using Loctite 401, I adhered foam pads to the corner of the mask.
So far, I've played with the mask twice. During that time, I've been hit a couple times in and around my face without any problems. I'm able to function mostly normally - with two exceptions: the mask prevents me from using peripheral vision to look downwards and the mask compacts the muscles in my cheeks enough that it's a little difficult for my eyes to focus. Neither of these are serious issues (though it does make it more difficult to dribble a soccer ball) and I plan to wear it until I'm cleared for full contact exercises.