Hi Jim,
> Doh! OK at least part of the problem in my experiment
> was that I was only using 2 curves.
Yeah if you have 2 curves selected, then Blend will try to build a curve blend which is a smooth curve connecting between the endpoints of the 2 open curves you have selected.
If you have 2 closed curves like 2 circles, then there aren't any open endpoints to connect between them so nothing is generated in that case.
So yes if you want to generate a surface blend result then you'll need to be doing the blend between 2 surface edges and not between 2 curves.
Here are a couple of recent posts on this subject:
http://moi3d.com/forum/index.php?webtag=MOI&msg=3968.4
http://moi3d.com/forum/index.php?webtag=MOI&msg=3981.7
> I presume that the objects being joined need to actually
> be surfaces first, or at least one does.
Yeah actually they will both need to be surface edges in order to generate a surface blend result.
It's also a good idea to delete any connecting faces (like for example the end cap of a cylinder) so that the blend surface has one clear orientation to come off from that edge. If you try to blend to an edge that is a joined edge where 2 surfaces meet, it will just pick one of those 2 surfaces to make the blend smooth to.
Then also like Steve mentions above, you have to pick the edge object and if you have some construction curves still hanging around those can pretty easily be overlapping the surface edges and get in the way, so hide or delete any of the original curve objects that were used to construct the surface to get them out of the way.
> So maybe all that's left is making sure that the curve
> points are equivalent?
You mean the number of control points in the curves? That's actually one thing that you don't have to worry about - there can be any number of control points in those edges, including a different number for each one.
The way NURBS surfacing works in general (for a variety off stuff including Loft, blend, etc...) it can make a result that follows the shape of your input curves and doesn't necessarily just try to connect one control point to another control point.
- Michael
