The attached file shows a set of curves to make a transition-piece for a staircase handrail. The green rectangles and circles outline an obround handrail section. I’m trying to sweep or otherwise construct this handrail such that it maintains constant section along its entire length. I’m not bothered whether that happens to be the rectangle or the circles - I can create the obround once I’ve managed to get Rhino to give me a constant section. And that appears to be something of a challenge in this case.
The magenta curve (1) is pulled off the top of the balustrade. The handrail has to sit on top of that, so it makes sense to use it as a rail to guide the form of the handrail. But no matter how I try - Sweep1, Sweep2, Pipe, Ribbon, Extrude along curve - I can’t get a method that maintains either constant height (for the rectangle) or constant radius (for the circle). I drew lines from the ends of (1) to the centres of the circles, used Sweep 2 using the two short (green) radial lines as rails and (1) as the section curve, then duplicated the edge of the resulting surface to give me a centreline for Pipe. I matched the curve ends for tangency to the two green lines coming form the circle centres before using Pipe, which gets close but offers no control over the location of the surface seam, and in any case it doesn’t give me a tube with ends that are perpendicular to the pipe curve for some reason, despite the fact that I used CircleAroundCrv to make the green circles, picking the end points of the magenta curve (2) as centres. (3) & (4) are isocurves pulled from a Sweep1 using the circles as beginning and end sections. Curve deviation shows that they aren’t parallel.
Am I missing something obvious here? The curves in the file are simple, clean and perpendicular or tangential where they need to be. Intersecting the green circles with the green rectangles gives me clean, singular contact points. Everything seems straight and true. Why can’t I get a constant section shape? This should be easy. I’m sounding like a newbie…
Sweep or Pipe.3dm (82.6 KB)