Spent several hours trying to get join to work. Join factory kept doing endless "calculating" on incorrect, or incomplete, object lists...

Then starting going through Michaels many scripts, looking for non-interactive examples.

Amazingly, the SpurGearProfile script has all of the information and examples to do the join!

The time was not all wasted, as I can now, at least partly, understand the SpurGearProfile script.
Copied/borrowed/modified, some of the code.

The airfoil join now will non-interactively combine a curve, a mirror, a conic, and an arc, into one selection, ready for a users sweep.

The SpurGearProfile also has a "shorthand" function to create differrent types of factories, which would reduce the number of lines of code.
Did not utilize the function, so as to perhaps better demonstrate the various factories used.

Will post update file soon. (Still have to do cleanup, and update for changes...)

It is a little bit confusing whether a curve is a curve, or an object list, or a geometric object, or ...
(The old "trim" posts help a lot.)