Velocity stack for Noctua 40mm fan NF-A4x10

I upgraded the fans on my Monoprice select mini from the cheap 30mm units to 40mm Noctua. I found a particularly nice design for a velocity stack for 40mm fans that I was going to print out, but discovered that it had a larger center hub cover than the relatively small 17mm motor hub on the Noctua fan. Several folks had asked for a Noctua fan version, but the designer didn't post it. I downloaded the STL and used MeshMixer to resize the center hub to 17mm, and once I had printed it out and discovered it worked, I tried to post a remix, but discovered that the original design had a "No Derivatives" license. I commented on the original thing that I had a modified version for the Noctua and I could supply it, but no interest from the original designer.

I was recently contacted by someone who was interested in my modified STL, so I sent it to them, but then started wondering if I could completely redesign the item from scratch in Fusion 360. I've been constantly trying to improve my skills in Fusion 360 and it looked like it could be a good challenge. So, here is what I came up with, and the results look pretty good.

Since this is designed from scratch and takes inspiration from several sources, it's not a remix and thus isn't in conflict with the no derivatives license of the first one that I printed.

Note that there's no math behind this design, I just went with elliptical curves and measurements that looked cool. Does it actually increase airflow? No idea, but it looks cool.

Also, since I drew one support leg and then patterned that, I realized I could skip the pattern and have a minimal single-leg design, which again - looks cool. That design has provision in the back for a 3mm pin, but I am using it with only one screw and simple friction holds it in alignment. I also printed out a twin-leg design. Obviously the four-leg design is the most secure, but I can't imagine that four M3 bolts to hold one little 40mm fan in place are absolutely necessary.

I've also included versions with a 22mm and 25mm center hub to work with fans with larger motor hubs. Only posted those in the four-arm design, contact me if you'd like a single or twin-arm design or need a different hub diameter.

Thanks to Joshua Bentley for suggesting to omit the center supports altogether and make the motor nose thingy separate. Had to remodel the basic shape from scratch but those are posted as well.

Print instructions

Should print as-is with no supports. Can print with a fine layer height for a better look and smoother walls but it probably wouldn't make much difference.