I am know where near a prop expert, but i like to have mine sharp enough to cut paper. I hold a piece of paper on edge, pull it tight and swipe the blade across the edge of the paper. If it cuts clean i know its sharp, if it leaves ripped,fraid edges it isnt sharp enough yet.
This is the way i do it, others might want it sharper,or more dull than other people so its basicaly personal preference, or a yep thats good enough after youve spent any hour on it.lol.
Cleaning up the cast is the most important part.
Alden