There's not tutorial what I know. I can make one when time isn't flying by.
I'm restructuring the workshop at the moment so I'm pretty busy with that.
But lets say you have two polylines in parallel. If you use a tapered cutter (V-carving bit that is) the cutter will cut deep enought to touch both polylines at the same time. If the lines aren't parallel it means that the cutter will go deeper in one end than in the other, the toolpath will go deeper and deeper to keep double contact all the time. It works pretty good with polylines created with the Rhino Text command.
EDIT: have you ever played a flipper game where the ball jumps on a rail made out of to steel bars and rolls away to another place in the flipper board? That's exactly the same idea. if the ball is the cutter it touches both steel rails (or in this case, polylines) at the same time.