Hi Brian, do you have any older versions of this file that you could post? It might help me give you some more details about what stage had the problem.

It's a bit difficult to tell exactly what went wrong by looking just at the final result. Ideally I would watch you as you were constructing it, but of course that is difficult to do.

Here is some illustrations of the kind of thing that I'm talking about though.

Say for instance you have these 2 curves and you want to position them next to one another:




One way you might try to do it (this is the bad way) might be to grab just at some spot interior to the curve like this:



And then drag it upwards like this:



Continuing upwards until it looks like the ends are pretty close to each other, and then releasing it there:




That's the bad way - the position of these 2 objects are just "eyeballed", there wasn't any end-to-end snapping kicking in which would ensure that the ends are definitely locked together. They just look pretty close but looking close from a zoomed out position is not the same thing as locked together - it will cause things like gaps between surfaces that are constructed from these curves later on.

So instead of eyeballing it, you want to use snaps that target the specific points you want to lock together. So for example in this case, you want to snap end-to-end.

So when you start to drag the bottom curve, instead of grabbing it somewhere near the middle of the curve, grab it nearby the end, like this:



When you click down and start to drag from that position, you will see an "end" snap highlighted on the curve, like this:



That means that you grabbed a snap point and you are going to be specifically placing the end of the curve somewhere. Now you can move to the end of the other curve, and it will show an end snap there at the target location as well:



That's how you know you have placed 2 curves exactly snapped together precisely end-to-end with no gaps between them. Then when you create surfaces from those curves, those surfaces will touch precisely as well instead of having empty space between the surfaces.

- Michael