Trouble with a helix made from a rectangle

[ctbritt]

I’m trying to create a helix 2 feet high from a rectangle swept around a central spiral. (See here: Shapr3D Webviewer). I’m trying to select the outer face of the rectangle and lift it up 24 inches to get a smooth spiral all the way down. But when I do, I get very strange distortions like so:

At a bit of a loss. How would I do this?

Thanks,
Chris

[TigerMike]

Do a ‘conical spiral’ search on this forum. Many examples can be found.