body{font-family: Geneva,Arial,Helvetica,sans-serif;font-size:9pt;background-color: #ffffff;color: black;}Just so happens that I was in an assembly drawing today, and saw the issue Gerry was describing firsthand. In my case there were 3 parts in a stack. Part A interfered with part B, and part B interfered with part C, but A & C had clearance. Part A was on top, but almost completely disappeared in the view due to the effect Gerry was talking about. The stranger thing was, part C was underneath all of them yet showed tangent lines through all the parts <odd>. One fix was to go to VIEW>EDGE DISPLAY and individually set the disappeared Part A edges to "wireframe". That made them reappear. The only remaining issue was the tangent lines from part C that were showing through that shouldn't have.PTC could do better, but like someone said, that would take way too much code and slow down the graphics horrendously.Regards, Jeff-- Jeff Sampson Engineering - This thread is inactive and closed by the PTC Community Management Team. If you would like to provide a reply and re-open this thread, please notify the moderator and reference the thread. You may also use "Start a topic" button to ask a new question. Please be sure to include what version of the PTC product you are using so another community member knowledgeable about your version may be able to assist.