Here is what I think happens: When two groups share a common edge, the points along that edge get automatically duplicated. They cannot be separate groups and both share a point in common. Therefore a weld command does nothing. The program must have two points with identical co-ord. each belonging to a group. What you probably need to do: open the CR2 and go to the third section Find the weld statements Tell 2nd sectionR to weld to central Tell 2nd sectionL to weld to central Tell 3nd sectionR to weld to 2dR Tell 3nd sectionL to weld to 2dL This should keep them together. These welds are more like glue than turning two points into one.