Great respons here! Thank you for the insightful answers.

I'm actually trying to join 3d helices - the trimmed circle solution might be a good bet.
Just wanted to make sure, that it was a correct behaviour I was seeing.

In the end I need to make a kind of tool to turn springs with changing diameters,
but with fewer turns than the attached screencap and more than one change in diameter.
I just need a good method for making a clean geometry. I'll post results when I have tested the arc method.

Thanks!