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Issue:

Shelling a Boolean Union inward doesn’t create the result I expect. It adds a wall or a gap between the bodies.

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Applies to:

  • Shell
  • Implicit modeling

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Cause:

A wall or a gap can appear between the two implicit bodies due to the fields of the bodies. When the two shapes are Boolean Unioned together, it adds their fields together. Therefore, when the Implicit Bodies are shelled inward, it follows the contour of the field, creating either a wall or a gap depending on the fields of the original bodies. If we use the Shell block on this Boolean Union of two boxes, the result lines up with the shape of the contours, depending on what Direction we choose Outward, Inward, and Center. Therefore, if we shell it inward, it adds a wall between the two objects. The image below shows the field of two neighboring boxes that have been combined and shelled. Despite the boxes being merged into a single body and then shelled, the field shows a wall between the boxes. Two neighboring boxes that have been combined and shelled.

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Solution:

To shell inward without a wall or a gap, you need to make sure the boolean union objects are overlapping slightly, then you convert the Boolean Union into a mesh and then back into an implicit. When you do this, it won’t have a wall or gap between the two shapes because it won’t recognize the individual fields of the shapes from before they were unioned together. Two cubes that are overlapping are merged using a Boolean Union block. The single body is then meshed and then converted back into an implicit body. The field view of the body shows a single box with no wall dividing them. If you want to learn more about implicit vs boundary representations, check out this blog.

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More on this topic:

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Keywords:

boolean implicit Shelling shell between question fields field driven design wall inward