gald, .stl files are the "preffered format" for 3d printing. If you have a CNC, i'd say it's safe to assume you have some sort of CAD software. If yours can import an .stl, open it up (remember, most things are in mm not inches) and you should be able to lay down a good wireframe over it. Many CAD packages have a function to create 2d lines on the edges of 3D objects.