Hi Val, thanks for reporting the problem!

It does look like it is probably a bug, but I'm not sure if there is much possibility to get a good result from that exact situation.

If you hide these 2 pieces here:



You can see that the center part is not a solid, it is an open surface:



If you actually select that open surface and run Construct / Planar to cap it off to be a solid, then you can get a proper union between it and the other piece like this:



When it is an open solid, the union is basically creating a sort of "squished together" slit in the objects rather than being able to separate them into different volumes.

In general the booleans are oriented mostly around working with volumes, so you may get some slightly unpredictable behavior similar to this when doing volume operations on non-closed objects that do not define a full volume.

If you solidify that open object first, you can avoid this problem.


> It would be nice to have some simple rigging tools. Like one parts rotates the
> other moves with it but is kept with respect to x direction, etc..

Unfortunately a rigging system is pretty difficult to add, even a simple one would require a substantial amount of UI - it is really something that is normally part of an animation system. The amount of work involved will probably make it prohibitively expensive to get that into MoI anytime soon I'm afraid...

- Michael