Making hemp rope/string after harvesting your plants?

Good cannabis plants grown for resin are not going to be very fiberous. If you want to try, though, you should look at traditional methods of harvesting and utilizing. I believe it involves soaking fresh stalks in water (and maybe lime?) to soften them, and then rolling and/or pounding them to separate the fiber strands.

You'll then need to weave these strands into cord of your desired size, I think this can be done with a reel of some sort.

Its a fairly ambitious project, good luck!