Boolean difference encountered fatal error

[yufanwu]

Hi all, 

I tried to do a boolean difference between the two files I attached: https://drive.google.com/drive/folders/1weCyobWeWMZ4IYkphndYJpZpRMxaIsbq?usp=sharing

I first created an offset of 0.2 mm on the true3.stl file to clear things off and then tried the boolean difference. However, meshmixer gave me a warning afterwards saying that "an unknown fatal error has occured", and parts of the resulting model has turned red. 

I tried a couple ways to trouble shoot, including remeshing on both models and extruding the true3.stl file instead of offsetting that. However, neither way worked. 

I'd appreciate any insights! 

Viola 

[hfcandrew]

Ya booleans are hard on big files. Fail all the time. Can you instead attach your .mix?

[yufanwu]

Sure! Attached is my .mix file. Thank you for taking a look! 

[Anonymous]

Your True object owns two surfaces where their normals point outwards for each. That's a no-go object. You might want to flip the normals of the inside shell to make True some kind of a tube or just use one of its shells?

Also: you might need to fill the open boundaries

Do you want to get Whole-True or True-Whole?

Eg: This is Whole-True(exterior):

[Anonymous]

This is True-Whole(exterior):

[yufanwu]

Hi, 

I wanted true - whole. I tried to use "offset" instead of "extrude" on true to get rid of the additional surface, and I also tried "edit - fill cracks" on both models. However I still encountered the fatal error warning. Could you help taking a look? Many thanks! 

[Anonymous · Accepted solution]

So if you need only one of the two surfaces in True:

1. Make True the active object
2. Run EDIT/SeparateShells 
3. Activate the shell you don't need and hit X to discard it

Now run ANALYSIS/Inspector on the remaining True object :

1. Use default settings of Inspector and hit AutoRepairAll to fill the open ends

Now you've got two watertight objects which a boolean operation can handle (MM handles booleans on objects with open boundaries only if the open boundaries do not hit the intersection loop of the objects)

Activate True as the first and Whole as the second object and run BooleanDifference (default settings should work).

Now there might be still some defects at the boolean result (small red marker dots).

Run Analysis/Inspector > AutoRepairAll to fix it.