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

[Glenn Woodward]

Hi Scott,
Here's my 360 degree spiral using an arc 3D Molding Pline. It is segmented but only 7.5 degrees per segment - it just the way the arc is converted to line segments by Chief. I'm not sure if there's a way to smooth it further but it's pretty good and ray traces well.

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.