Hi,
the intent is that there's no minimum damage, but all weapons can theoretically deal enough dmg to bypass armour if you roll enough sixes on your mighty blow.
I know that's pretty brutal, but I wanted an armour system that was "realistic" and "unfair" in the sense that if you only have a dagger and you're facing someone in full plate, you should probably reconsider the situation rather than trying to stab them.