paralell spline btw two

 From:  Mike K4ICY (MAJIKMIKE)
5189.3 In reply to 5189.1 
Hi Andras!

So you have two curves (either closed or open paths), and you want a version that is a "mix" or approximation between the original curves.
In a 2D vector program like CorelDRAW, they call this feature a "Blend".

Do this and you should be happy.

1) Center each curve shape in a 2D ortho view.
2) Go to another 2D view where they look like flat lines and move one of the curves away from the other.
3) Loft the two together until you have a new 3D lofted shape.
4) Draw a straight line across the loft shape that best approximates what you need. (halfway?, angled?)
5) Use Project to cast that line across the lofted shape.

Now you have a new curve that is an amalgam of the two original curves.

I hope this helps.