your input is causing the trouble. The curve that doesn’t fillet has a very tiny radius like transition with radius of approx. 0.002mm…

Well yes, the RADIUS at the transition between these two curves is actually ZERO. Rhino created this tiny radius when it joined the curves. But keep in mind the same algorithm created all the other curves, most of which resulted in a FILLET.

Perhaps you could explain why this radius is important and how to join two curves at something approaching a right angle without this resulting micro curve. I am being forced to deal with issues that are not relevant to creating a fillet between two curves much like BLEND does, except a true tangential fillet. I dont need joined curves for that.

But this discussion is irrelevant. The curvature of the join between the two curves is no where near the tangency point resulting from the rolling ball. It just doesnt matter.

The problem is the underling algorithm is too simplistic or requires inputs that cause the problems it then baulks at.

These were originally TWO CURVES that were joined and to be able to feed into the module as ONE CURVE along with a t value of the location of the crease. It should expect this kind of input curve or accept TWO CURVES as an input.

The module that accepts two curves as input doesnt produce a resulting fillet on any of the 60+ curves. No idea why. Thats why I was forced to use this module.

I am again today faced with rewriting a fillet algo from first principals because the resulting surface doesnt follow the curves created, so the brep wont join and volume cant be calculated. Its frustrating.

In this case the fillet gradually fades out alone the length of the curves.

The algo must accommodate a change in the location of the vectors by which the curves are move to find their intersection. If the curves are curved, the error in vectors causes the rolling ball position to be calculated incorrectly.

Ill create a simple demo later and post it

ADDED

Another problem: It appears that my curves are not TWO single curves in places due to the way they were derived:

So before I do any surfacing, or filleting I must deal with curves that are posing as a single curve from the output of BREP/PLANE INTERSECTION. I assume FIT CURVE will generate a single curve? such that the original curve is matched at the project tolerance setting or CCX will fail further down the page

Then the next problem with the curves is that the direction varies depending on the surface they are derived from. so before creating surfaces, before filleting, before even working on these curves, back to the surfaces that they were derived from and thus back to the curves that made them. Basically scroll back to the top and start again.

The central problem appears to be overlapping at the intersection of some of the curves.

we are talking about .005 or so, but its enough to cause CCX to find 2 intersections between these two curves, and for JOIN to create something that all the FILLET modules baulk at.

Both these curves have been trimmed using the same XY plane, one set of curves above, the other below. They should all meet perfectly at the plane… but no.