I work for a large aerospace and aircraft manufacturing company. We had a want-to-be machinist that was a PITA. He didn't know what a face plate and a lathe dog was... He never could hold a tolerance anyway. A lathe dog is what I was trained on in my first Jr College machining class. When one turns on "centers" you can remove your work and put it back in and continue to machine on the piece where you left off.