Thanks pbacot, the Export for SU button worked.
Workflow answer. I am an architect. Stairs show in the floor plans that they connect, so need to be able to print on a plan, showing stair from floor above, the other from the floor below. I model stairs in 3d, so I know they work, use components for treads so I can add/ adjust details... As landing on it, and a stair above going to the next floor as a section cut through a wall yields good results. A cut through a stair is not good, one riser is in section others light linework, and hard to get stairs from two floors to show at the same time. So I have two layers for a stair, one that is 3d for model shots, perspectives, and or elevations. The other, for plan view, is a 2d graphic that represents the stair, with a break line. The 2d graphic shows stairs coming from above, and from below.
Is there a better way to show a stair in plan?