One rail sweep, getting distortion

3rd ave handrail.3dm (481.9 KB)

Under curvature analysis your sweep rail has all kinds of problems. There are breaks in tangency and overall lack of smoothness. The end result is your sweep gets built as a polysurface which is the tip off that there is something really wrong with the curves. The super close together knot intervals is another indicator when the surface isocurves are shown. I rebuilt your curve to fix the tangency, smoothed it and used setpt to align the points that needed to be. The end result is a smooth surface sweep.

Copy your red rail VERTICALLY to meet the midpoint of the bottom of your cross section (1)
Project your cross section on vertical plane (2)
Sweep line (2) along 2 rails: your red and (1)
Attached file where I have done it. Looks better, I think (blue surface)

3rd ave handrail sweep2.3dm (819.1 KB)

Thankyou for your time, however as the railing twists through the helix, it is distorted as is seems to flatten and profile changes. Any solutions for this?

Thank you for the adjustments, looks much better. I’m very new to rhino and don’t really fully understand what you did. Could you go into maybe more of a step by step sequence and also send the corrected rhino file. thanks BH

You are right, the profile flattens and this is not acceptable. Attached better solution.

3rd ave handrail sweep2 corected.3dm (683.9 KB)