Creating a Helix with a custom profile

Hi, I’m relatively new to rhino.

I’m trying to generate a railing for a staircase.

I have created this before using the helix tool, generating a curve and then extracting it.

However, I can’t use this function this time because it is more of a square with curved corners (see pictures).

The railing will be a wall and follow the internal spiral of the stair…
Does anyone have any ideas how to do this?


What is the end use? Are you planning on getting this actually made, or does it just need to look right?
A quick way would be to use the interpolatecrv command and trace the profile of the risers as they go up. Then extrude the resulting curve vertically by desired amount.
On a side note, generally you’d do this sort of stair with basically straight risers and then winders at the corners, at least in my area.

Thanks for the reply.

The stairs are modelled from an existing staircase, from a survey. And we will be replacing the balustrade.

I tried tracing the profile of the risers to generate the curve and then extruding vertically, but the result wasn’t great.

Is there a way to smooth the curve?

See below:

can you post the actual rhino file for people to have a play with? It looks like you’ve used the standard polyline command, you need to use interpcrv

Sure thing.

(I’ll try now with the interpcrv)

Apologies, the file is a bit messy:

StantonRd_Stairs_Small.3dm (175.6 KB)

Hmm yeah that looks a bit tricky because the stairs are pretty free form. I’ve had to do something similar in the past, started with interpcrv (played around with the setting to try get a better ‘fit’ to the plan), then extrude to approximate height, then turn points on for the surface and manually pull points up and down using the gumball to get a pleasing line.

If someone has a better method, I’d love to hear it also!

A quick screen grab of interp crv below. This version deviates from the stair in plan a bit too much though, would need work.


I thought about turning points on, and manually pulling them into place.

The shape you have looks a lot cleaner than mine.

Another thought I had was to extrude the centre profile, and use this to wind a curve up (offset from the pitch).