What is needed to get FilletSrf to follow round a bend?

My filletSrfs dont go round bends, is there a prerequisite to enable them to do so ?
In the attached example firstly both objects blue and magenta are extrusions of closed curves.
I am able to pick the blue surface but it wont let me pick the magenta…why ?

I had to clone the magenta then give it a purple layer, then explode it and join the relevant surfaces.
Try again and it was pickable BUT only one surface became selected and the fillet formed, it ignored the fact they were joined.

The fillet stopped where the purple surface stopped.

Why would it not honour both extruded surfaces and then ignore the joined surface.

How do I get one fillet to do the entire route A to B ?
FilletSrf around bends.3dm (485.2 KB)



Hi Steve- - make another fillet - it goes surface pair by surface pair. I’d set Extend=No.


How can I find out from properties the radius used on a fillet ?
I have for the moment continued with a lesser radius but doing it pair by pair there is an area it wont fillet, whilst if it took the entire route I see no reason why it would have stopped there., and started beyond.
The blue surface is already joined so its not as if I am selecting a blue surface too small to work with.
I had extend=no and trim=no.
see attached.
FilletSrf around bends.3dm (568.8 KB)


Hi Steve - probably easiest here to just build your own little transition surface there - I’d DupEdge the neighboring fillet edges, rebuild these to degree 5/6 points, Loft and then MatchSrf for tangency.