ResMed S9 to 3M bayonet filter adapter

thingiverse

This adapter snaps into the back of the ResMed C9 in place of the built-in filter retainer, and allows you to attach a respirator filter compatible with the standard 3M bayonet cartridge mount. I had the idea for this last summer, when we had historically bad air quality due to nearby wildfires. I was wearing my 3M respirator mask (even inside the house) most of the day due to the smoke, but I sleep with a CPAP, and the CPAP's built-in filter is minimal at best. The two STL files differ in the amount of clearance between the lugs on the filter adapter and the mating surface, (the parameter is the total height of the connector, not the clearance under the lugs). The 7mm version requires an inhalation port gasket (3M part number 6895) to seal properly with the filter cartridges I've tried. The 5mm version works without a gasket with the N100 filters I have (3M p/n 2091), but does NOT work with the multi-gas vapor cartridge (3M p/n 60926), which is made of harder plastic and is less forgiving of tolerances being off. I've also included an STL with test versions of the adapter with different clearance values, which may be useful if you need to tweak the fit for your specific filter cartridges. I designed this from scratch in OpenSCAD. I've included the .scad file, which is reasonably well-commented and modular. The connector() module, in particular, may be useful if you need to make something that can accept 3M bayonet filters.