Theory Behind SolidWorks Shell Errors
I want to explain a little theory about what happens and makes you face these ugly errors. Do not skip this part, because it’s important to understand it to improve your design strategy.
Understanding the Geometry Limitation
Consider this happy circle for instance:
If I try to draw an offset inside of it, the center point is a limit and we can’t draw the offset with a distance equal to or more than the radius of this circle. If I extrude this circle into a cylinder and try to create a shell from inside, the same scenario rules the situation. You can’t have a pipe with a thickness greater than its radius. Every inner shell is like an offset surface normal to the original reference at each point and filled as a solid feature. So, if the thickness value is greater than the radius of some point somewhere on the object, it’s not possible to have such geometry.
Why Inner Shells Fail
In some cases, the inner shell contains surfaces that cross each other and there is something I call “Negative Volume”. This is CAD and not quantum physics, so we can’t have such hypothetical concepts either.
Negative Volume Problem
When the inner offset surfaces intersect, they create invalid geometry that SolidWorks cannot resolve into a valid solid body.
Solutions for Shell Errors
When the error occurs, use the check tools in the “Error Diagnostics” section to understand what is wrong with your geometry and determine what you are dealing with.
1. Use Error Diagnostics Tools
SolidWorks provides diagnostic tools to identify the exact faces and edges causing the shell failure.
2. Reduce Shell Thickness
If a little less thickness is not crucial and does the job, that’s an option to give it a try.
3. Divide and Conquer
Another solution is to divide the part into separated sections, create separated shells, and combine them again. This approach was used in the X-1 Pulsar UAV concept design where the complex blended wing body geometry required section-by-section shelling.
4. Exclude Problematic Areas
In some cases, you can exclude the area that caused the error by dividing it, doing the shell, and combining it back to the model.
5. Surface Offset Alternative
If the shell doesn’t work, but the offsetting surface is possible, you can create the surface offset and try to give it a thickness.
Anything we discussed here could happen when you try to shell outward as well and the solutions are more or less the same. If you have any questions or if there is something I should know, comment down below, or join us on our community on Reddit.
