Boolean Union troubles

 From:  Michael Gibson
3930.7 In reply to 3930.3 
Hi Jacob, I've taken a quick look at your original file and I haven't yet been able to see what is wrong with it, but it could be a bug in MoI - if the mechanism that determines which direction is supposed to be the "outside" of the object gets confused it could lead to something like this where the meaning of union and difference gets transposed. I'll need to investigate that some more.

Your other question:

> Another question about the above model:
> Is there a method to "split" a surface without dicing up the
> solid? I would like to split the tablet's upper surface into
> "bezel" and "screen" areas to make it a bit easier to work
> with in modo but I'd rather keep it smooth, rather than
> beveled/extruded/inset/grooved/whatever.

You can use the Edit > Trim command to slice up just the surface skin of an object, which will split it up into different surface areas. Those will be separate objects but unlike a boolean they won't be totally separate volumes (they won't have inner side walls and stuff like that), they will be different surfaces and you can then follow that immediately with an Edit > Join to glue it back together into a solid which will then have things split up where you did the trim cut.

To do this, when you're in the Trim command at the point where it asks you to pick which fragments of the object to discard you instead just push "Done" or right-click at that spot instead of picking anything and that will cut up the object and leave all the pieces behind.

Let me know if you need more info on doing this part.

It's also possible to use Trim followed by Join to work around the boolean problem, since Trim does not work by volume, it isn't messed up if the inside/outside of the object's volume is not correct.

Also another thing you can try if a Boolean is seeming to give the wrong pieces of objects back is to use Edit>Separate to break the objects into individual surfaces, followed by an Edit>Join to glue it back into a solid again. That will force the inside/outside-ness of the object be recalculated and can fix an object that had it wrong. That actually seems to do the trick in your case here - if you select the 4 little grip pieces that are positioned inside the main object and then run Edit>Separate on it then followed by Edit>Join then they do seem to get fixed up and the boolean union behaves as expected after that.

- Michael