Hi Jacobo & Josu - I've spent some time looking at this bug that you sent, that you showed here: http://moi3d.com/forum/index.php?webtag=MOI&msg=656.11

It appears to be a bug in Join. This model has some really tiny edges in it. Like there is a large surface, and some of the edges of the large surface are little lines around 0.005 units in length.

This is causing problems in the joining procedure, those little lines are getting flipped around and compressed and that produces some problems in the trimming boundaries of the joined object. Then these problems in the trimming boundaries (they are almost like small loops), are messing up the mesh export.

Unfortunately it is going to be difficult to fix this right now. It's kind of a delicate area, if I try to mess around with it, it is likely that I will mess up other things. So it might be a while before this particular one gets better.

One thing you can do is if you have any control over how these models are being exported to you, ask if you can receive the IGES data as IGES type 186 ("Manifold solid") entities instead of individual surfaces. That will maintain the joined-edge information in the IGES file, so when you read it into MoI it will come in as a joined solid already and that should work better.

- Michael