Thankyou Michael.

I'll have to try mapping a circular spiral set of treads, from its vertical post to a slanted post.

- Brian

The rise of each tread will be constant.
Tread length is roughly left to right shaft opening less post diameter less say 3 inches.

The left to right slant distance of the slanted post is roughly tread length plus 3 inches.

Edit: Will try out Barry's node.

Agree with Grendel. 6ft 5inch headroom is one code.
Grand arc of stairs from movies much preferred.

The geometry is interesting though.