Hello Brian, Hello Wayne,

it's difficult to say what happens. I think that internally a transformation matrix is used for this operation/factory. To create one, you need additional informations like the rotational information that are not given by two lines and certainly not when they are parallel. I had the same problem for the getCrvSFrame. The only info you have here is the direction/tangent of the curve. To create a frame/local coordinate system I used the dominant directions of the main coordinate system. That leads to some weired effects while changing the curves geometry -> flipping axes. Another method would be to use also the center of a soothing circle, but that would fail for straight lines. And yes - it is similar to the gimbal lock. A possible workarround is to add tiny values for the display of the vector - that helps the factory to calculate the orientation.

Maybe Michael can tell us what's going on under the bonnet.

A nice day to all
Karsten