Fillet fail at ends

[chodson54AH5]

Trying to add a fillet to this threaded feature, and it fails at the end. I know that it is failing cause at the end of the edge, it is physically not big enough to add the fillet. I tried to create a variable fillet with the ends being zero, and it still failed. When I created the primary geometry for the thread I added fillets in the sketch to make it easier so possibly part of the issue?

I get this error: Error: The fillet/chamfer could not be created at the requested size. This might be occurring at the ends of the selected edges.
Try adjusting the size or using multiple separate operations. Check that the selected edge chain ends at a sensible position, and if not try selecting more edges.

I have tried searching several ways and not able to find an exact solution for fillet failing at the end of an edge.  

Thanks in advance for your help!

[KristianLaholm]

Using a coil as the sweep path has the drawback of creating multiple faces along the thread, which can interfere with operations like fillets.
In my file, I used an alternative workflow that results in a single continuous face along the thread, making fillets work more reliably.

[chodson54AH5]

Thanks for your help much apprecated I was able to follow your model and solve the issue. 

For future reference, are there solutions for filets with that error other than developing a better model? In this scenario, I understand that a better modeling method was best, but just in case a similar issue arises in the future. 

[KristianLaholm]

As far as I know, the most common cause of fillet failures is "bad" geometry—especially small or narrow faces, tiny edges, or overlapping/intersecting features. These often trip up the fillet algorithm and cause it to fail.