Parameterized printable spring

It is a proof of concept of a kind of printable spring. Initially I designed it for using in my Prusa Mendel, because the z axis springs were very difficult to find for me. Then I generalized the idea and parameterized the spring.
These springs conceptually consist of a strip of plastic that is bended. The outer cross section of the spring can be square, hexagonal or octogonal.
The spring parameters are:
fid (fold inner diameter)
folds: Number of folds
th: strip thickness
Drill: Drill diameter
Diameter of the outer cross section
Here there is a video of the proof of concept:http://www.youtube.com/watch?v=dbjiXFEyg_E



Instructions
1.- Download the spring.scad file. Change the spring parameters and generate the STL
2.- Optionally you can just print the 3 springs given as examples
3.- I have used slic3r for slicing it. If the spring is small, it is quite difficult to print it. The easier springs to print are the ones with a square cross section.
4.- Print it!
5.- Before using it I had to file and clean the spring