Hi Barrie, well there's several things that will make that difficult to fillet, one of the biggest is that the leading edge has a quite sharp valley in a very small area where it comes together rather than being smooth:





That's pretty unlikely that the edge-based filleter could make any sense of that type of juncture between fillet pieces.

One other approach you could try would be to trim away some area to make both a larger hole and to cut back the blade to open up some space and then put in a Blend surface:





The other thing that could potentially give you some fillet surfaces to work with would be to do some surface/surface filleting. That's where you use Edit > Separate to break out pieces into individual unconnected surfaces, then pick 2 surfaces (whole surfaces instead of edges) and then run Fillet. That can create some fillet surfaces that you might be able to use parts of where the edge-based filleter won't have any chance.

The other thing that's difficult about these kinds of fillets are figuring out what should be done on the trailing sharp edge.

Another thing that you could try would be to use either blend or surface/surface fillet as described above to build some initial connecting surfaces, and then use Construct > Curve > Iso to extract some isocurves from them to give you some cross section curves to use in network or sweep to build your connecting piece although it won't be completely smooth.

- Michael