NanoHack Cloth Filter Holder

thingiverse

This is a super fast yet highly functional design to get one or two pieces of cloth into the modular filter cylinder of the stock NanoHack mask. You put the material over the inner ring and capture it with the outer ring. Then you trim the excess material. The fit in the cylinder is snug but not too tight, so it won't get stuck. Adding extra cloth can make a tighter seal. A small rubber band could also be used as an emergency fix to act like an O-ring. Fortunately, my printer has been accurate enough that the tolerances in the actual file are correct. The outer ring works with all filter holders. The inner ring comes in two sizes and two forms - one for single-ply fabric and another for double-ply. Both have offset or stand-off options to keep the ring from blocking any air intakes at the end of the cap. I've also included an O-ring design, which is actually a ring that's meant to be printed with flexible filament like TPU. This O-ring isn't necessary for using the filter holder, but it's an added convenience if you have TPU on hand. The FreeCAD source files are included along with the STL file in case anyone wants to modify the design. For instance, if you want to use three layers of thick material, you might need to open up the gap between the rings even more. For ideas and suggestions on which materials to use as a filter, check out this article that cites its scientific source material: https://smartairfilters.com/en/blog/best-materials-make-diy-face-mask-virus/. Important note: The "methodology" of the scientific paper upon which the article is based makes it clear that the cloth wasn't stretched tight. So when you capture the cloth, it's probably best to leave it a bit loose and avoid making it like a trampoline. I'm not a scientist, engineer, or medical professional, so I don't know if this design is functional or potentially hazardous. However, in an emergency situation, I'm providing it anyway. For single-ply holders, I'm using cotton and cotton blend materials. For the two-ply holder, I'm layering non-woven polypropylene from a re-usable shopping bag with 100% pure cotton as a backup filter. Since the polypropylene is of dubious quality, I'm relying on the cotton to provide a backup filter.