40mmFanGuard for 24mm hub

This is the so-called "jet style" fan guard. Other similar things have a struts beside the feathers of the fan, so the wind noise is large. I suppressed the sound by making it an aerodynamic shape.

"D_cut" means that this part has been cut to avoid hitting to other parts.
"Plus" has an experimental shape for utilizing the surface flow of the fan's planar part.

I am using this on Geeetech i3 Pro B.