What is the role of SPINE in swept command in NX-cad

I don't use NX, but catia has the exact same thing. When you have a swept surface, you use a profile curve for the ouotside shape of the surface. A spine is a curve such that the profile is always on a plane perpendicular to the spine. The spine helps guide the profile curve to create the surface you want. An example would be a pipe. A circle would be the profile curve, and the spine would pass through the center of the circle and would be in the shape of the pipe.

Use a spine curve to control the orientation of the section strings and to avoid distortions caused by the uneven distribution of the parameters on the guides. A spine string works best when it is normal to the section strings.

1. Constructs section planes that are perpendicular to the spine and intersect the guide strings.

2. Aligns the isoparametric curves on which the sweep is based, to these planes.

To make it more easier a spine curve works like your spinal cord.

In this tutorial when i select the spine curve, the whole section or the boundary of the section aligns to the spine curve just like when creating a datum plane on path the plane orients normal to the path.
see the tutorial...........

if u give two guide lines and select one guide line as a spine which is most deviated ,the shape will under go with that guide in opposite direction also

Also the Spine curve controls the length of the resultant surface.

Hi there, what's the difference between a Spine and a Guide curve?