I liked this. Very human and not pretentious at all. I built one of these myself for fine dust extraction. I have pretty much built it the way you did. Funny about the spade bit. Liked it. Also subscribe.
I really love that you used the cone drill, it was epic! I was like, oh he's making a tapered hole... nope, going all the way through, okay, cool, whatever works.
It cost me nothing since I already had the fan and wood. I hardly use the thing now though, since I can't even reach the window to put the fan up with all the clutter around the garage doors. When I was building it I was mostly wanting something that was discreet and not permanent.
When I was a kid, 10 years old or something, my grandad was throwing a pair out. He used them when he was cleaning factory roofs. I gave the matching one to a friend and he lost it a day later (his parents probably threw it out!). I'm glad I held onto it because they're expensive new. Although I use a cheap half-face respirator now because it's way more comfortable. If I was desperate for a full face respirator now i'd probably have a look at military surplus on ebay. You can get S-10s for £20, and as far as I know they take standard 40mm screw in filters.