Hexgrid lofting

Hi everyone,

I have a question about Rhino/ Grasshopper, that I just could not figure out yet. 

So, I am designing this hexagonal tower of 8m hight in a timber construction. It will be a look out, but also work as bee hive. The way I designed it, led me to work on a staircase that wraps around an inner core. The whole facade/wall of the inner and outer layer will be with a hexgrid, out of which the steps will seamlessly emerge.

see picture of staircase

I have projected a hex grid onto a double curved vertical plane, that marks the middle of the staircase (see the pink plane in the middle). This is to have the right size for the steps, that wind upwards and therefore narrow down towards the inner wall and broaden towards the outer wall.

So far so good. My problem starts here. I need to project this hexgrid, that the middle plane contains, onto the inner and outer plane in order to start modeling the facade. In the picture above I did it by hand, as I could neither find the right command in Grasshopper or Rhino. What I am looking for is a way to project the grid from the centerline of the hexagon (pink) towards the outside. So the hexagon hight maintains (and therefore the stair hight) but the width changes (so I can create a spiral stair case).

see picture of example step

I couldn’t find anything in Rhino (tapered extrusion, sweep, 1dscale, loft, project, etc.), nor Grasshopper, where I tried the following (connecting points from the hexgrid and centered attractor line with the closest point command):

see screenshot of rhino/gh

It just seem so easy to project something on a surface from a center which in my case is a line and not a point. But I just couldn’t find anything. Thank you very much!