Hi Richard, this seems to be the "Clipping issue". One reason for this is too large (kilometres or miles) geometry OR any geometry being this far from the origin. You can import cad files two ways; preserving the drawing origin or not preserving it. Before importing, check out the "Options" (in the file browser window) and uncheck this option so SU will place your model to the SU origin. BTW here you can also set the original drawing units so you may spare that scaling, too. Sometimes there are some stray edges or any geometry far away from the model (often drafters add this to the origin) which can still cause this effect. In this case, Zoom extents (Shift+Z) then select all (Ctrl+A) to see if anything suspicious is also selected somewhere far away from your model. Delete that bit of geometry and move everything to the origin.