Use a razor knife and a straight edge.
- Mount the straight edge to your popsicle stick so that it creates a hard edge right down the center. You can simply tape it to a metal ruler.
- Now set the razor knife on the stick and pull it lengthwise down the stick, maintaining a straight line, by keeping it tight to the ruler. You don't need to press hard. Just push it down enough to score the surface.
- Go back over the scored line a few times, lightly pressing the razor knife (scalpel, exacto knife). Eventually it will work it's way through the wood in a very straight, smooth, and controlled manner.