3M Filter Exhaust Assembly

**WIP:** I have not yet fully-assembled this, as I am still waiting on some parts. The dimensions should be sound, but it may need some refinement.

This is an exhaust/fume-extractor assembly intended for 3D printer enclosures. It uses a 40mm fan and 3M 60926 respirator filters.

Many existing exhaust/fume-extractor setups use, at best, a HEPA + charcoal filter. This may make the exhaust air smell better, but does nothing to protect against some of the more-hazardous fumes from 3D printing, especially with ABS, Nylon, PETG, etc.

File names (colors correspond to cover image):
* `3M_Filter_Assembly_v1.stl` - All the parts in a single file
* `3FA_-_Wall_Flange_Inner_v1.stl` - Connector from filter to wall (green)
* `3FA_-_Wall_Flange_Outer_v1.stl` - Connector from wall to fan housing (yellow)
* `3FA_-_Fan_Bracket_Inner_v1.stl` - Fan housing, inlet side (blue)
* `3FA_-_Fan_Bracket_Outer_v1.stl` - Fan housing, exhaust side (red)


I recommend using fans designed for applicati