Unwanted geometry

Making the preview RC creates unwanted geometry. If I make a larger box, it creates a larger geometry. How can I avoid it? Filtering large triangles makes a hole in the piece. Any suggestions. I saw two post with this problem but no solution. Thanks

Hi IDIT_IberoPuebla,

go to Scene 3D tab/Tools/Mesh Model/Advanced and choose Select marginal triangles. Then in Scene 3D tab/Tools/Mesh Model/Advanced use Filter selection tool

I must be doing something wrong. I already filter selection on both positions of my piece but when I put toghether both positions that I worked separatly this new geometry appears, if I change orientation of the figure the geometry appears on the back, or on the bottom side of the pieceĀ 

What do you mean by both positions? After filtering those triangles it is possible that there will be a hole, but there is also tool Close holes for closing that holes.

Have you filtered just marginal triangles or have you select by yourself the unwanted triangles?