Creating Stairs in Rhino

1. DupEdge the top edge of the step.
2. ArrayCrv, RoadLike, Top Cplane this curve on the spiral curve.
3. Open the Osnap toolbar and float it near where you are working.
4. Turn on Planar at the status bar.
5. Orient the original step with Copy=Yes, Scale=No snapping to the end of the edge at the spiral as the first point and the far end of the edge as the second.
6. Now for the target points, you will need to toggle Osnap projection so that each time you pick on the 'inner' end of a target line Project is off, and every time you pick on the 'outer' end Project is on. You can toggle these inside the Orient command so you can do it all in one go, but it is a lot of clicking.

- PascalRhino Newsgroup