4 Replies Latest reply on Nov 7, 2012 2:52 PM by Tim Cochrane

    Offset Surface = Shell?

    Tim Cochrane

      I'm working on a file that has some poorly constructed geometry. Of course...some other parts are already built in reference to the shape. I'm curious if I can test one surface by just trying to offset it? Its takes quite a while to get everything in the tree in this part correct and ready to shell as a whole.


      Any other advice for a surface/solid that will not shell??





        • Re: Offset Surface = Shell?
          Jerry Steiger



          Yes, offsetting a surface is usually a good way to see if that surface would shell correctly. (I say usually because that has been my experience, but it is always possible that I haven't seen the particular cases where that isn't true.)


          If a solid won't shell, I try offseting all of the faces and then cut out faces until it will offset, narrowing it down to the "bad" faces. I'll then try offsetting the bad faces one at a time to see if they will offset a smaller amount. This often gives you clues as to where the problems lie. If I have the freedom to change the faces, I will try to fix them so that they will shell. If, for whatever reason, I can't fix them, then I will try doing the largest offset that I can, then try offsetting the offset to get the final offset or a closer offset until I eventually get to the final offset. If that doesn't work, I will try splitting the face so that I can offset part of it, then use a Fill Surface to fill in the gap. Sometimes you just have to fill in a large gap with a Fill Surface with guide curves or one or more Boundary Surfaces, using 3D Splines to approximate the shape you need. 


          Jerry S.

          • Re: Offset Surface = Shell?
            Alin Vargatu

            The Shell command has a great debugger for revealing all the faces that could be offset.


            Read this article for more information:



            • Re: Offset Surface = Shell?
              Charles Culp

              As Alin mentioned, some parts will shell, but won't offset, due to some advanced error correcting tools in shell that don't exist in offset. That means that if it offsets, it will probably shell; but not nessisarily the other way around. Also keep in mind that it can also be the transition between two surfaces that causes a problem with offset/shell, so make sure to offset all the surrounding surfaces as well.


              Another good option for troubleshooting shell is to use the split command to split the model into multiple bodies, and then only use the shell command on one of those bodies.

              • Re: Offset Surface = Shell?
                Tim Cochrane

                Thanks a bunch for the insight.


                I'll read through the advice and see what we can do.