Hi Jops, thanks for posting your model file.

So kind of the basic problem that you're running into here is that you seem to be modeling this more by drawing a whole lot of separate 3D curves and then trying to create a lot of separate individual surfaces one piece at a time.

By working that way, you're basically trying to use the most advanced and more difficult to learn modeling style right off the bat, rather than leveraging solids modeling and 2D curve drawing techniques which is where NURBS modeling is actually the strongest and easiest at.

Have you watched the video tutorials available from here:
http://moi3d.com/2.0/docs/tutorials.htm

notice in those tutorials that I try to keep pieces as a solid and carve pieces off of that solid with 2D curves instead of building an entire 3D curve structure that gets filled in which is how I think you're trying to work.

I guess part of that has to do with your particular model shape that you've picked to create though.

Which tool have you been primarily using to build the surfaces, is it Network? If so then you're probably running into the issue described here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=3939.2

This is fixed in the v3 betas right now, but in the current v2 demo version network uses a looser tolerance than most other things in order to try and make lighter weight surfaces but that can cause it to not be within join tolerance. That particular problem can be solved by scaling your current model down by 1/10 in size and then doing the join - it will then join into a solid.

But it looks like you have some other surface defects in your model as well, which are caused by using a couple of surface techniques that are not well advised - the particular problem is the top and bottom surfaces which look like they have 2D silhouette but instead of actually using a 2D curve to cut with, they appear to be surfaced between 2 3D curves that touch each other at their ends. I'm referring to this bottom surface here:



If I turn on control points for that surface you can see they look like this:



At first glance that might seem like it's all ok - and in fact is ok in these areas where the points are fairly far apart from each other here:



Where it's not ok is in the very tip area where the points have collapsed down on top of one another:



It's very easy when points get collapsed down like that for them to be in a somewhat jumbled mess right in that collapsed region - if your input curves curved evenly slightly inwards where they met it will form a self-intersecting surface that overlaps back on top of itself right in that small area. Such self-intersecting surfaces will cause numerous problems with surface/surface intersection calculations.

In this case, it seems that the area on the right-hand side of the bottom surface is the one that has that kind of jumbling/self-overlapping in it.

See this previous post for some additional description of this kind of folding and self-intersection shape:
http://moi3d.com/forum/index.php?webtag=MOI&msg=1127.4


If you have a top or bottom piece of something that has a 2D silhouette to it, it's much better to build things to be taller and then do a cut with a 2D curve to form the top and bottom surfaces instead of trying to surface them directly between 3D curves like that. When you cut with a 2D curve, the surface that is generated will be an extruded surface which will have no control point pinching in it at all, and it will have trims on it that trim off the excess area.

Trying to build everything directly to 3D curves is basically the problem - you need to try to leverage more simple surface structures that get trimmed instead of trying to build every single surface directly to its final edges.

It tends to take a while to get the hang of using extended surfaces and trims.

Really you're kind of jumping immediately into somewhat advanced territory with what you're trying to do - that's why you're experiencing frustration.

Try to think more about building some basic block-form of your shape initially and then cut that block to form your final shape rather than focusing so much on getting a complete scaffolding of 3D curves to start with.


Some previous discussions with examples of stuff like that:

http://moi3d.com/forum/index.php?webtag=MOI&msg=4657.11
http://moi3d.com/forum/index.php?webtag=MOI&msg=3795.2
http://moi3d.com/forum/index.php?webtag=MOI&msg=4298.4
http://moi3d.com/forum/index.php?webtag=MOI&msg=4163.1
http://moi3d.com/forum/index.php?webtag=MOI&msg=2282.2


Basically for this style of surface modeling you need to consider trimming as one of the basic tools that you'll use in combination with the surfacing.

Don't try to force a surface to go through an irregular outline or get mashed or smooshed up when you are directly creating it - if you're trying to do that, it's usually a sign that you actually need to create a more simple big extended sheet surface that then gets trimmed to produce the final surface result.

Hope these tips help!

- Michael