I am offering a fan blade "cage".
This protective cover is from a Hyper Wind fan, but it may work with your fan.
The diameter of the space for the fan blades is 19".
The depth is 4½".
The diameter of the rim is 19⅝".
The diameter of the hole in the back half is 3¾".
This hole must fit around a rim on the fan motor cover.
(Then you rotate a securing ring onto the fan-motor-cover-rim to hold on the cage.)
There are four small holes around big hole.
These four holes are to hold four pegs, to keep the cage from moving.
(Then you put the fan blades on.)
Lastly, you put on the front cage.