Hi Robert, also it seems that you're using version 2 - you should probably use the current v3 beta instead which you can get from here: http://moi3d.com/beta.htm

If you would have done the same steps including boolean union in v3 it actually works ok - there's been a bug fixed in v3 that deals with combining overlapping closed edge curves, and a whole lot of other fixes and improvements too so it's just generally better to use v3 instead of v2.

Usually though it does tend to be better to use Edit > Join to glue together 2 surfaces at common edges that already meet up, because Join _only_ glues together edges and does not try to slice up objects with one another. Boolean union can work for this too, but really the booleans are overall more focused on intersecting objects with one another and removing some chunks. If you know that there is not any cutting involved using Join can just be more reliable since it's more targeted in only doing that particular job.

And if your object has planar openings, you can just select the whole object as the input into Construct > Planar and it will look for edges that form a closed planar opening and automatically create the planar cap and join it into place all for you, so that's a shortcut for this kind of thing too.


Anyway in this particular case you were running into a bug that's been fixed a ways back in v3, the bug made your bottom edge fragmented into pieces.


- Michael