I know that Jay Leno uses 3D printers to make parts for his cars but he has expensive 3D printers, not desktop 3D printers. Sometimes, he uses 3D printers to make parts that are to be made another way such as casting. He has 3D scanners and 3D modeling software. For example, the only part for a car was broken and there are no good parts. He scans the part into 3D modeling software, clean up and fix the part, and prints the part. He also uses CNC machines for making new parts.

Look at videos at https://www.google.com/search?q=jay+...hrome&ie=UTF-8