Man am I happy with my new UP! 3D printer (from 3dprintingsystems.com)
I designed my propeller using SolidWorks in pieces so I could dismantle them and to make each part the right size for my printer.
You will see that the blades have a rim on the top and bottom of their mounting that slips into the corresponding channels/recesses in the nose cone and base. I have put a spline on the bottom of the nose cone shaft to provide alignment for everything and to give a positive drive when used. Unfortunately it makes the keyed hole for the drive shaft rather small.
The blades are able to slip in this housing if they hit something but unfortunately they might also slip if there is too much drive power. Next time I would run the spline down the whole shaft and put them on it too.