Took minutes to model these coil springs in Inventor, using helix option. Unlike wire springs it is easy to add a torus top and bottom to make more stable to print. On second attempt I added some thin stiffeners in 4 angular positions to stop spring moving during print. These are easy to pick out with a fine file after the print is complete and results in less stalactites on underside of coil. Springs are a bit soft - if you print at 80% scale you get a 0.5" dia x 1" long spring.