What is the difference of a crown gear or a worm gear?

A crown gear has teeth that engage with other bevel gears. The teeth stick out at right angles to the face of the wheel. A worm gear is a screw that attaches to a wheel by engaging teeth along the wheel. As the screw turns, the wheel also moves and the drive reduces rotational speed and allows for higher torque. Worm gears are used when a project requires large gear reductions.