Hi bisenberger - actually your mesh there is all welded up, meaning that it is "watertight" with no actual holes in it. Every vertex of the mesh will be joined to another vertex.

For some description of how a mesh that looks like that is actually all welded, please see these previous posts that have some illustrations:
http://moi3d.com/forum/index.php?webtag=MOI&msg=1536.30
http://moi3d.com/forum/index.php?webtag=MOI&msg=2102.45


So the issue is that you are getting n-gon polygons in some areas. That happens because the surfaces that are adjacent to one another are of different lengths and shapes, for example you can see just by eyeballing it that this surface here:



is longer than the one below it here:




By the time the mesher gets these surfaces, it does not know anything about them originally coming from the same sweep, the mesher only handles individual surfaces and processes things purely by the shapes of the surfaces. So things that are of different shapes and lengths can easily have different mesh structures created for them.

When you have some other kinds of surfaces like a surface of revolution, that ends up having a consistent curvature in the revolve direction for each piece, so that makes things like that able to have alignment because the shaping in that direction is actually the same. That's not the case here though.


Why is it that you are concerned about having the vertical mesh edges aligned at export time in particular? You should be able to render the model fine with its current structure. Again - your mesh is actually fully welded with no holes in it, all the n-gons have aligned points between them.

- Michael