msds and hoprocker hit it on the head. In this field, I think the best way to learn is to still go in and work with an expert and get your hands dirty.

That said, an introductory book that the local community college just recently started using (before that, there really was no book, just blueprints and notes because so much information came from the instructors) is the Precision Machining Technology [0].

Unfortunately, like many textbooks, it's not cheap. But it's a nice introductory book("I don't have a clue, but I'm interested in the topic")

[0]http://www.amazon.com/Precision-Machining-Technology-Peter-H...