this is designed to use bearings for the teeth so that the resistance created on the face is very very small.

I also did this using 2 slightly offset grooves and 2 bearings per so that one bearing was in contact with one face and the other bearing was in contact with the face on the other side, I did that so that I could make it a zero back-lash setup.

This one also works well both ways, that is turn the larger gear and it turns the smaller one or turn the smaller one and it turns the larger one, even at some steep angles