Artist's Comments: Here's a new twist on an old trick, and a newer one as well.

The spiral on the left is created from a standard Strata lathe with horizontal and vertical scale, and vertical sweep. I converted it to Bezier surface, ungrouped the result, and deleted the end cap Bezier regions.

I simplified the remaining Bezier surface, and converted it to polygon mesh. I selected the center edge loop ( a simple loop selection) in the second image, and then selected inverse, which meant every edge except the highlighted one was selected. Then I hit option-delete leaving only that edge remaining. I selected the remaining edges, shown in the center below. While they were still selected, I set the extrude option to not break edges. I held the shift-C keys, and extruded vertically, to get the step shown.

Then I ran thickness to get the fifth object below. When I apply subdivision to the last one, I will have a smooth spiral.

We’ve done similar things recently, but I wasn’t sure that the disembodied edges would extrude as nicely as they did here.