Here’s some blast gates I made. I cut up some of those black
plastic blast gates for the external fittings. The outside parts
are made out of 1/2” prefinished maple ply. The inside is 1/4”
markerboard, which I waxed. I’ve seen designs where the
builder used rubber gaskets but I wanted to keep it simple and
the rest of my ducting is far from airtight anyway.
The blast gates work really well and seal better than the
cheap plastic ones I made them from. Gates are accessible overhead
with a pull cord tied to each “ear”, I don’t have to walk around
my table saw to open the gate anymore. Also I can place
the gates closer to where the ducting makes a “Y” and thus
eliminate downstream leakage from having the gates at duct
drops at the ends of the ducting runs.