I'm working on a few iterations of spiral staircases in scale, and I created a simple version to test before venturing on to more complicated projects.
This version is in 1:24 scale. Sixteen treads are required to complete a 360 degree revolution. The rise is 9".
I have some landing options I plan to upload in the near future.
As formatted, the STLs create a Left-Up staircase. Mirror files if you desire a Right-Up version.
Print as many treads as you require, plus a base. Treads are designed to thread onto a bamboo kabob skewer, or other rod 3mm or less in diameter, but this is not required. Snap treads into one another - the snaps are offset to maintain correct spacing between treads. Use acetone for permanency, though the pieces hold together well without an adhesive.