Hi Lee - there are a couple of different things there that give the filleter problems.
One is that there is a kind of crease where your 2 halves meet - that causes the edge filleter to have to try and fill in a corner in that area which is harder to do than if they were smooth:
Also this back end comes to a quite sharp point, that is not a very simple edge structure there, that will tend to make it hard for it to calculate as well:
Basically this edge structure is just not really simple and distinct enough for the edge-based filleter to handle. Combining that with a fair amount of bending and tight curvature to some portions of the surfaces and that is quite a difficult situation.
It is possible to fillet it though by using a surface/surface fillet calculation instead of an edge-based one.
To do that, I untrimmed your surfaces to get rid of the sort of sharp pointy end at the back:
Then select those 2 individual surfaces and run fillet. This will do a surface/surface style fillet instead, which can create fillets in places where the edge-based one will not work:
I took that resulting fillet and copy/pasted it back into the main model, trimmed the surfaces, and that resulted in the attached version 2_filleted.3dm .
It is a lot more difficult to use the surface/surface filleter because you have to do more "low level" type operations like surface trimming, but it can do the job in situations like this where you do not have a very simple edge structure.
Basically if you wanted the edge filleter to work you would need to simplify the shapes there, have the halves meeting more smoothly with each other, not have a sharp edge at the back, just have a generally more simple structure there in several aspects.
Unfortunately the fillet calculations are pretty finicky, the more wiggly bits, tight bends, sharp corners, not quite smooth things you have it can easily cause problems for it.
- Michael
