3D CAD models are created by CAD drafting services that specialize in 3D Modeling. These companies more times than most are in the mechanical drawing field because they deal with mechanical parts that must be 3D modeled with special software. Architect's are now starting to use CAD software that is extremely similar in quite a few ways. For instance, you can create 3D walls and door's by selecting which dimensions you want and inserting them into the CAD drafting software. It will instantly create a wall with an exact width, length, and height.
Technology is really starting to catch on when it comes to design and designing 3D CAD models. You can actually design something on CAD like a gear for instance. Send the drawing file to a special shop that has CNC machines made specifically for machine parts, and have it created in an instant. This could be used for any number of things like parts on the space shuttle, or what about a bicycle frame. The limitations to 3D CAD models are basically limitless. Anything the mind can imagine, can be designed with this CAD drafting tool, and nothing is out of reach. The only thing holding someone back from designing any 3D CAD model they want is their imagination.
3D CAD modeling has taken over the days of the ordinary draftsmen and his drafting table. With an array of tools at the fingertips of the CAD drafter the drafting board doesn't have a chance. Believe me though I'm not extremely excited or anything, I actually grew up using one of these and that's the reason why I'm in the drafting field now. Technology with 3D CAD models is just going to get more advanced, and user friendly as time goes on. More sophisticated designs will be produced, and the software will make the job easier for draftsmen.