Fillet and Blend fails - simple warped surfaces

This thread is about basic problems with FilletSrf, FilletEdge, BlendSrf and BlendEdge when the angle between adjoining surfaces switches sign along the coincident edge. The attached example is very basic and was created to demonstrate the problems. This thread is not about how to work around the problems using other methods to create a fillet and blend between the surfaces.

The starting geometry is two very simple warped surfaces of degree one and two control points in each direction. The angle between the surfaces reverses along the conicident edge with the surfaces tangent at the mid-point of the edge.
Transitions 02.3dm (122.1 KB)

FilletEdge creates the correct fillet along half of the edge, but the fillet for the other side is completely off the surfaces

The results of FilletSrf depends on where the surfaces are selected. Selecting the surfaces near the middle of the edge results in only one surface being visible, and two zero size trimmed surfaces. Selecting the surfaces near one end of the edge results in the correct fillet along that half of the edge. A repeat use of the command selecting the surfaces near the other end of the edge results in only a partial fillet.

BlendEdge creates the correct blend surface along half the edge, but the blend surface for the other edge is completely off the surface.

BlendSrf fails. I was not able to obtain any results using it. Update: BlendSrf appears to want a gap between the surfaces.

The problems appear to originate with angle between the two surfaces reversing.

I know you don’t want to talk about other methods so I’ll refrain on that front. One command you didn’t mention though that also can’t account for this case in v5 does however now work in the WIP for v6. VariableFilletSrf produces the result below but you do have to use it twice.

Would that work for you?

I see the issues with FilletEdge and BlendEdge are still with us for this case and believe we’d need to be able to make two surfaces instead of the one for it to work. I found this exact case filed already as do you want to move it from Trunk to v6?

Thanks for the report.