From:  Michael Gibson
865.3 In reply to 865.2 
No problem, it is certainly easiest when you answer your own question! :)

Just to clarify for others that might get stuck with Join - Join works to join together either curves or surfaces.

When you use it on surfaces, it will glue together surfaces along edges that overlap, but it will only glue edges that are not already attached to another surface.

What I mean is for example if you have 2 boxes that are touching one another, you can't use Join to fuse them together since all the edges of the box are shared between 2 surfaces already. For Join to work in this type of situation you need to delete the common face from each box first before joining.

When deleting the face, it creates what are called "naked" edges - those are edges of a surface that belong just to that one surface and are not shared between another surface as well. Naked (sometimes also called "lamina") edges are the ones that get joined to one another.

In this box touching box type situation, it is possible to use Boolean Union to merge them together though - the booleans in general will merge pieces together by doing intersections and throwing out pieces which Join will not do on its own.

The Boolean operations are actually a lot like a bundled up version of doing manual trimming or deleting followed by a Join.

The ability to Join can be helpful when you want to do more sort of "low level" surgery on an object. Like if you want to remodel a certain piece, sometimes it works well to select the faces you want to tweak, use Edit/Separate to break them apart from the main body of the object, then mess around with them and use Join to fuse them back to the main body again.

Here is a mini tutorial on using these kind of low-level tweaking techniques to fix up a model that had one component out of place: .

- Michael