algorithmic modeling for Rhino

Hello everybody,

I try to design a simple spiral stair : a central post and steps turning progressively around the post.

But after long hours I have no idea how to design the steps of the stair.

How to tell to GH that each step sould have a different angle around the central post without making a box for eah step.


If someone have an idea he will save me from this deadend

Thank you?

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Maybe a start?

What are you holding in your hands in your avatar?




Thank you Chris,


the result is fully controlable, it is exactly what I need.

This picture is an Armadillo and a nice GH model to built !


Have a nice day


Not realising Chris had already answered this I created something to show you, some what redundant now but here it is anyway. You can see the slight differences for yourself, and I mean slight.

Thank you very much,


this tow solutions are really nice and usefull.

Have a nice day



This script could be more useful if the minimal restictions and considerations as can you walk inbetween two steps have been scripted as well. Im adapting the script now and will let you soon know the model for a minimal stair acording to the size of the human and local restrictions by law ( variable input per country )

Good beginning btw


I have an also basic question about this spiral stairs. 

How can i create a spline through the midpoints of the step outer edge, just like in the image below. 

I have to use it for a supportive metal plate construction instead of a core stud.

As you can see I can extract the points by dividing the curve to 2 pieces. But confused to pick a way on how to choose the midpoints with a combination of step by step. Tried to apply listing options but failed to suit a proper way for my data tree.

I used the following step for creating the stairs;

Thanks in advance. 

Okay, i can manage to draw the line with data tree but to the wrong side. I want to draw the int. curve to the outer side of the stairs.

Is there any quick way to do this and also choose only the curve in the middle out of 3 single curves ?






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