SketchUp Speed Modelling: A Simple Spiral Staircase [updated]

I supposed spiral staircase is one of the most popular subject in 3D modelling tutorials, however, for all the models I've done, spiral staircase is not in the list.

This is a simple spiral staircase -- with chequered plate treads welded to tees, which in turn are welded to a circular hollow section post. Balusters and railing are of circular hollow sections, too. I supposed the post should be mounted on a base plate that is bolted to a solid base.

The principle modelling process took less then 30 minutes to complete. The model of this staircase can be found in 3D Warehouse, as below.

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Updates: I made an animation with this model, on this page.