Curve formula

Hi guys,
Could anyone give me a curve formula for making a spring with two
axis. That's its shape in top view to be rectangle with two semi
circles at its two ends.

Thanks guys
Mohan S

 

I don't think you can create what you're looking for with a single
formula. However, you can see how to create an elliptical helix here,
http://www.synthx.com/tom/sy_tip_0504.htm

To create a rectangular or slot-shaped helix, you'll need to interset
a helical surface sweep and a slot-shaped surface. The link below is
for SolidWorks, but it should still apply.
http://www.cadjunky.com/watch/6385104

 

http://www.mcadcentral.com/proe/forum/forum_posts.asp?TID=25769
http://www.mcadcentral.com/proe/forum/forum_posts.asp?TID=29666

Maybe search for some more. Something might seed an epiphany.
There have been a few discussions on planar curves that might be
applicable if a z function is added. Trocoid and super ellipse
come to mind as possible search terms.