[EricH]

For a mill and lathe, you could probably train the basics of both of them in a couple of weeks. More advanced stuff would take longer, of course.

In terms of safety, as long as proper precautions are taken (safety glasses, etc.), you could probably, depending on site insurance of course, allow students to use the machines under supervision. Supervision doesn't have to be leaning-over-your-shoulder; it could easily be, "I'm going to be in this area keeping an eye on you; you never know when I'll show up right next to you."

CNC mills and lathes are probably a little bit too much at this point; I'd go for a manual that can be converted over later, if needed.