The Cut-Rite pool cue tip shaper/cutter is a very handy tool.  It performs two main jobs.  When you put the tip of your pool cue into one side, a surgical steel blade cuts away the mushroom edge of the tip and makes it flush with the ferrule.  Put your cue into the other side, and the blade perfectly trims your cue tip into the curved shape you need. Fits tips up to 13mm in diameter.