Boolean Union troubles

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 From:  Jacob
3930.1 
Hello all,

Can anyone tell me what's wrong with these four objects selected on the attached image?



You can see same four objects positioned inside the pen well, to be used as grips.

Whenever I try using boolean union (and difference) most of my "base" object is deleted, leaving only a bit of one of those objects.

They were constructed by a network using several copies of two curves - at first I tried to build them using a sweep, but it was giving me extremely wild results.

Scaling up didn't help.

Any pointers? I don't mind reworking them, just I like their shape.

Thanks!
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 From:  Michael T. (MICTU_UTCIM)
3930.2 In reply to 3930.1 
Hi Jacob,

Something wierd is happening. I've seen this before, but I do not have a good solution. I have attached a copy of your tablet file with the features joined to the tablet as one solid. I had to use a combination of boolean dif, union and intersect to achieve the final result. Michael G. might have better insite as to the cause of this.

Michael T.
Michael Tuttle a.k.a. mictu http://www.coroflot.com/DesignsByTuttle
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 From:  Jacob
3930.3 In reply to 3930.1 
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.

Thank you!
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 From:  Jacob
3930.4 In reply to 3930.2 
This is very useful, thank you!
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 From:  Paolo (PAOLOLOBBIA)
3930.5 In reply to 3930.4 
Hi Jacob,

Select the objects and use the separate command.
Eliminate the upper and lower flat surfaces.
Join the surfaces and finally use the planar command.
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 From:  Jacob
3930.6 In reply to 3930.5 
Interesting... I used Planar with edges Network produced to get original ones, since Network produced edges that were visibly different from original curves.

Thinking about it, I just realized I should have scaled *these bits* up and then re-work them after I have found that I can't boolean them in!

Thank you.
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 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
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 From:  BurrMan
3930.8 In reply to 3930.7 
This particular model can be fixed by running seperate/Flip on these three objects...



First select the large face and choose seperate. Then hit the tab key and type Flip. Then run join on the 3 seperate surface structures to get a solid again... Then select the 2 little cutting solids on this side and run seperate/Flip/Join on them also.. The model will now bool as you expect..

If you look at the 2 solids off to the side here away from the model, these 2 have reversed normals, though "history" is on and the 2 solids opposite them seem to be a mirror result, and the normals on those are pointing in the correct direction..

Possibly this mirror creation method has created the normal bug where it wont get pointed in the correct direction with a proper join??? Because it seems to be in the large piece as well as the small cutting objects

Was this model created in MoI??

EDITED: 19 Jun 2012 by BURRMAN

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 From:  Jacob
3930.9 
Thanks for all your tips!

Yes, this is 100% MoI. I think that Mirror actually *repaired* normals.. but on the second try only, when I mirrored both original and first copy.

Despite all these little snags, MoI is a joy to use. Perhaps even a little bit too easy to use - I can't seem to stop! :-)

Here is a little WIP scene that I created the tablet for; the chair, table, glass and that weird green thingy are from stock Modo content:




Cheers,

Jacob.
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