In the drawing area, click to select a center point for the spiral.
Click a start point.
Click an end point to complete the spiral.
Completed spiral staircase
The spiral is limited to fewer than 360 degrees. If you overlap spiral runs, a warning is displayed; the stringers and railings are not placed accurately.
Click (Finish Edit Mode).
Tip: To create a spiral staircase to multiple levels, on the Properties palette, under Constraints, specify the top level for the Multistory Top Level parameter.