Meshmixer: use commands 'flip normals' and 'combine' to create a hollow object

[lopezsaa]

Hi,

I'm using the commands 'flip normals' and 'combine' to subtract a complex mesh from a cylinder in order to have a hollow object (see figure below).  The operation is successful for having internal cavities inside the cylinder. However, this procedure yields an uneven finish across the external surface of the cylinder and thus, creates conflict for 3D printing. 

I tried using 'Boolean difference but using it doesn't allow me to have open holes at the cylinder's surface.

I would appreciate any suggestion.

Many thanks,

Sebastian

[Anonymous · Accepted solution]

Combining shells(flipped or not) to one object doesn't change the geometries. The flipping and combining thing only works if the interior surface is included totally by the exterior shell.

Those pale pink areas on the visible surface are regions of the interior surface intersecting the exterior one.

Your cylinder (before Combine) simply was too small to include the flipped surface totally.

If you want holes where the inside intersections happen BooleanDifference  is the only way. Don't flip the "inside" surface in this case.

Two reasons why this tools might fail:

- Too different mesh densities of both objects. Most likely the cylinder is too low res. Use SELECT/Edit/Remesh to get a denser mesh , almost equal to the inside object. Hit W to see the wireframe.

- Too many intersections of both meshes. To solve this might be over MM's ability at the default SearchDepth of 2 (= 3 tries at 3 levels). You can increase the SearchDepth to allow further tries (> longer computation time).

[lopezsaa]

Hi,

Thanks a lot for your help! You have helped better understand these
operations.

Unfortunately, using 'Boolean difference' directly has not worked for this
complex geometry. I will try using a shape like this
[image: image.png]
to first subtract the extra portion of the complex mesh, and then use
'Boolean difference' between a cylinder an the remaining complex mesh. I am
not sure if this will work but I can't think of a better procedure.

Thanks again,
Sebastian

[Anonymous · Accepted solution]

Unfortunately I can't see the image you refer to.