Clearance in a Vacuum: The plot thickens. 

I like your style of working through minor mistakes. I did not learn anything new but you explained a lot of reasons why things work. Thank you.

Your videos are so well produced and thought out. I'm always left feeling inspired. Modeling something like this "every day object" is particularly exciting to me because I can see practical use-cases for these skills and tools. Now to finally buy a 3D printer...

When I worked in Maya (and I believe also in Alias Studio) a "shell" referred to a connected set of geometry. If you created a bottle and a separate stopper for it, the bottle would be one shell, and the stopper would be the other shell. So I appreciate that FreeCAD doesn't call thickening a surface a "shell."

Watching you resolve the tangent vs equal constraint issue probably saved me time and frustration in the future. Had the referenced geometry been a complete circle instead of an open arc, I'll bet the default constraint would have been equals. Too lazy to prove it! Update: thanks for doing the test! I will definitely encounter this issue at some point as this is my workflow so you definitely saved me future time.

17:10 freecad at its finest

I'm very new to solid modeling, and I'm a bit confused. If you have two "separate" solid shapes, which overlap in 3D space, does that confuse a slicer for 3D printing? Do you need to overlap and join those shapes together, or does the CAM process (in my case a slicer) ignore the boundaries which are entirely inside both solids? What if you have coincident faces which define the ends of the shapes, and there is zero clearance between them? I'm assuming that would be considered as separate, but this is a new world for me. Thanks for any help you can give.