Fan Grid Concentric Holes Generator

Sometimes, during the design of a device, you have to add one or more cooling fans.
Because the fans should be able to blow air to / from the external environment, you need to drill holes on the surface of the case that you are going to draw.
There are normally two options:
1- Drill a trivial circular hole of diameter slightly less than that of the fan impeller, providing the necessary lateral holes to hook a protection grid
2- Drill a set of many, small holes or slits (for the passa