How would you build the top rail for a handrail of a spiral stairs

[Joe Carrick]

Joe,

The reason that the rail is segmented is because when you edit the 3D molding line by changing it's End Z value, you really are not forming part of a spiral, you are just rotating the arc in one plane.
Try the same thing with a nearly completed circle and you will see that the arc stays coplanar and just rotates in the one plane.

You can't actually define different start and end heights for a 3D polyline arc - they always default to coplanar.

Glenn,

Take a good look at the 3D PLine dbx (Selected Arc Tab). The Start and End Coordinates (x,y,z) can be edited.