This is a working model of a spring. I printed this with 100% infill, although you don't need to (higher infill = stiffer spring). Printed with supports (not possible without them). 

Disclaimer: You need to keep in mind that you are printing with supports and removing them is quite difficult in this case (took around 1.5 hour). And after removing the supports the spring will have really rough finish. I think its possible to sand, but it will take a long time.

But after all you have a 3d printed spring. 

Don’t forget to check out my other models too.