MakerGear M2 80mm Bed Fan mount and duct.

grabcad

I wanted a larger bed fan that would run slower to reduce noise. Here's how I did it. I used a generic 80mmx15 24V fan mounted to this duct. The small grill goes over the standard 40mm fan for the extruder. I printed everything from PLA. The fan grills press into the flanges. I put a small drop of CA Superglue to bond them together. The 40mm flange glues into the duct. I used JB Weld for that. CA might work as well.