The best one I have found which is cheap(free) is the one from HAAS. I posted it a year or 2 ago and cant find it.
its the manual haas use's for there class's.
Take there class's they are free (at least my HFO)and well worth the time. few hours a day.

My wife took them she liked them and said they were easy.I have borrowed her book to look up some code also that I have forgotten.

Delw