Hi Alex, so you can probably get the missing one by using Edit > Separate on the polyline and then selecting the 2 separate individual lines there as the input to Fillet.

When fillet is given 2 separate curves that's when there isn't an angle limit used.

The fillet piece will be very small though when the the lines get close to colinear.

- Michael

Thanks Michael - the information provided has been very insightful into the process of converting these 3d spline curves back into usable polylines for tube bending process and understanding the limits ill post some pictures of bent pipe once we begin just been sorting files.

All the best
Alex.