Thank you for that!
I am going to make a link to your comment from the forum post in question:
https://community.carbide3d.com/t/knapp-joint-with-cnc/19723 (scroll all the way to the bottom)
and will hopefully be able to translate that into Open(Python)SCAD code so as to make a generalized solution for my current project:
Hey you made my day, I can now say that I contributed to a CAD project. Had never heard of a "knapp joint" before!
OK so your bottom circles are identical, so the y-position of the center of the top circle is easy as pie.
What does your code need to do?