Offset Non Planar(3D) Circular Curve

How to offset 3d polyline accurately.I am not able to achieve it using Offset Curve & OffsetLoose??

As the offset is not simply a copy, some segments get longer and some get shorter.

True, an offset is not a copy. Use Copy command to copy a curve and Offset to, well, offset a curve. Offset has expected behavior. That’s how offset works.

// Rolf