In the last year I’ve had two of the rear fan blades damaged (as can be seen on the damaged fan used in the assembly photo), once when I stupidly touched it while adjusting the filament guide, and the latest when the head lead was pushed into it while printing something large.......so I decided to design a grille to sit over each fan on the inside of the cabinet.
I printed it in ABS to withstand the heat and not warp.
The lower inner fixing bolt should be reversed so that the nut is attached from the rear of the printer housing.
Edit......I’ve just realised that with the original grille that I posted, being 5mm thick, required the lower inner fixing hole to be countersunk to move the fixing bolt away from the vertical back plate of the heated bed.......if not done the bed will not raise high enough.
So taking this into account, I have revised the grille and have added a new stl file for a slimmer, 4mm grille.
Print with the flat surface (inside facing surface) face down on the bed.