This exhaust cover was created to keep snow and bugs from getting into my laser's air system. Also, it helps me keep the lab insulated so I don't waste energy heating up cold air blowing in through the laser in the winter, or cooling down hot air in the summer.
To make the design, you'll need some 1/16" (1.5mm) steel rod (I used welding filler rod), one copy of the baffle frame, and three copies of the blades. You'll also need some metal tape to make sure the blades stay in even when the weather gets rough, and some more tape or caulk to seal up the frame.
Start by cutting three lengths of rod that are between 118 and 120mm. Feed a piece of rod through each of the holes on your baffle blades until an equal length is sticking out of each side of the blade (~4mm). This can take a decent amount of force depending on your printer's settings. I fixed the rods into a vice one by one and pushed the blades on to them while twisting the blade. After they were almost all the way through, I used a hammer to tap them home and then even out both sides.
After that, install your baffle frame on to your exhaust. This was designed to fit over a 3in exhaust flange without having to disassemble or modify the flange itself. I experimented with both metal tape and silicone caulk for adhering the frame, and both seem to work well.
Finally, attach the blades by sliding them into the slots on the frame. Be careful not to drop your blades as you're sliding them in. After that, run a strip of tape along either side of the frame to cover up the slots and prevent the blades from jumping out during a storm.
Turn your exhaust on and give the system a test. The blades should swing freely and allow plenty of airflow. If they don't move freely, chances are one of your rods is bent a little. In that case, you can take the sluggish blade out, use some pliers to straighten the rod, and reattach.