Boolean Difference

[Anonymous]

Hi, I am attempting a project where I have laser scanned an object to create STL1 of the object. I have then used modelling clay to fill recesses in the object and re-scanned it to create STL2. I have then aligned the two and pulled them into Meshmixer. I made each of them a solid and used the inspector tool to autocorrect any issues. I then ran a Boolean difference function and every time it fails. Even though there are no problems with the meshes when I begin, running the boolean difference seems to create them. I have accounted for co-planarity and still battling. Any suggestions would be most welcome! Thanks

[MagWeb]

Booleans on objects owning (as you use scans: almost) redundant surfaces is a hard job as there a tons of microscopic intersections. Maybe you can get a result increasing the SearchDepth (more solving iterations) but expect loooong computation time.

Handling Co-Planarity is meant for planar surfaces (e.g. two cubes sharing a common plane).

What you might try instead:

SelectAll of your STL1 (the one without added clay) and run Edit/FlipNormals.

Now Combine both objects to one.

Run MakeSolid, set a high SolidAccuracy and MeshDensity (You can set values over the slider's range by clicking on the parameter's number and typing) and hit Accept.

This is some kind of boolean difference via voxelisation...

If you're going to 3Dprint such a difference I'd go another way:

Use STL1 as a subtractive modifier object for STL2 and do the boolean in the slicing process...

[MagWeb]

Arghh no way to edit.

I meant "and hit Update" instead of "and hit Accept"

[Anonymous]

Thank you so much. I am intending to 3D print the difference. The original STL is converted from a CT scan - another option would be to do the moulding using the sculpting tools on Meshmixer rather than manually with modelling clay. Would that simplify the issue? That way the sections that are the same are literally identical since they'll have been from the same starting STL? When you say "Use STL1 as a subtractive modifier object for STL2 and do the boolean in the slicing process", what exactly do you mean by that? Thank you again - this is a great help.

[MagWeb]

If you'd duplicate your STL1 (without added clay) to STL1 and STL1(copy) and you'd do the modelling on STL1(copy) the same issue: redundant surfaces.

But if you'd create STL1(copy) with a small negative offset (e.g. selectAll of STL1 and run Edit/Extract offset with a small negative Offset and Direction to Normal and after that Separate) and model on this while keeping STL1 visible, so  only your clay intersects the surface of STL1, BooleanDifference (STL1(copy) minus STL1) should work.

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@ doing this via slicer software for 3D printing:

Each outer perimeter of a slice is basically a 2D polygon. Boolean operations in 2D are much easier...