Grooming a help desk supervisor

I hired my second help desk tech six months ago. He has learned a lot since and is well-liked by our 200-plus employees. I added a third tech three months ago and have left his training in the hands of number two, with oversight by me.

I’m about to offer number two a raise and a supervisory position at the help desk, but I’m concerned that I lay out my expectations about training number three (and number four in the spring) plainly and concisely so that I don’t have to come back in 60 days and pick up the pieces.

Any suggestions about grooming a bright up-and-coming tech for supervisory duties would be appreciated.