I suspect "hone in" is from "honing a craft" so hone in is like improving something. I would rather "home in" being for things like getting closer to being correct and "hone in" being for getting better at something.
"Hone" is from honing a blade, which is what you do to keep its edge. To "home in" on something is the process of locating where something is positioned (its "home.") That something could be "the answer" or a submarine. A homing signal is a signal you broadcast to assist others with homing in on your location.
"Honing" is more metaphorically akin to polishing. To hone a skill means to practice at it.
"Honing" is more metaphorically akin to polishing. To hone a skill means to practice at it.