There are a multitude of possibilities that fit your criteria. Try using an arc of radius 55mm. Make it tangent to both circles.
How accurate is your statement?
Do you really need the curve to be tangent to those two circles, or do you just need a smooth curve that passes through the points (-60,0) and (0,59.8)?
If you really need tangent, that may be tricky. If you really just need to hit those points, you can use an archimedean spiral. How math are you? Is that enough to get you in the right direction, or do you need someone to do the whole thing for you?
Before you create an equation here's 3 (easier?) options..
Conic / Ellipse / Spiral.. It's quite hard to discern the difference, so it depends how critical it is
conic-ellipse-spiral.SLDPRT.zip 50.9 KB
Thank you guys for your effort!
I think that Rob got roght for my case.
Still a greeny in SW...