Hi joe,

re:
> The parameters of this fillet can no longer be enlarged,

MoI is not a parametric modeling program so it does not have a function for altering the fillet parameters after it has been constructed. For that kind of functionality take a look at parametric MCAD software like OnShape, SolidWorks, Alibre, etc...

> and why are these two lines in the crossing?

Fillet pieces between surfaces will only match up with each other directly if the surfaces are smooth to each other. Since your surfaces are not smooth to each other here:



that will mean that the fillets will be of slightly different lengths where they come together so it will have to make a fill in piece there.

It sort of looks like you're constructing things in a "patch by patch" manner by building separate network surfaces between a framework of 3D curves. That kind of method can be problematic since it easily leads to creases between the separate patches. It is instead generally better to build larger and extended regular surfaces and then remove some areas by booleans or intersections rather than building surfaces directly to a 3D curve framework.

If you're coming from a polygon modeling background, see here for some tips:
http://moi3d.com/forum/index.php?webtag=MOI&msg=4865.2

- Michael