Since many new watches have the plugged end cannon pinions it has probably occurred to many just how to tighten them. That was my worry a few months ago. Here is my solution.
Grasp the cannon pinion in a pair of cutting pliers with the pinion well over to one side of the jaws. Place a tapered broach next to the pinion, toward the inside of the jaws but not beyond the center. Give the broach as much freedom as you would were it through the center of the pinion and clamp the pliers. Try on center pinion, if not tight repeat operation. I have also found it necessary, in cleaning a watch by machine, to put a very little oil on the center pinion or the cannon pinion is apt to freeze.