Worm gear
it is used to change directions
In worm gears, an axle or shafts has a screw that connects with another gear. This system is used when you need to change the direction of motion and reduce speed
A worm drive.
Even slower
gear box or speed reducer.
A worm or machine can be geared with worm gear to give it higher torque or to reduce rotational speed in the machine.
A hobbing machine is used for cutting gear teeth in gear blanks and for cutting worm, spur, or helical gears.
linear distance moved by the gear(worm,screw jack) for one rotation of the gear(worm,screw jack)
Sand mullers break up sand after it has been used in molds to facilitate sandcasting. By effectively breaking up the sand, it can be reused. The worm on a motor or on the "driven" side of the device will engage with a worm gear. The worm rotates continuously, and the spiral cut gears "worm" their way "along" the axis of the gear. The worm gear (or spur gear) engages with the worm and rotates continuously as well. Also, the worm gear will translate the rotary motion of the worm by 90 degrees. It is fairly easy to see how the unit works if you look at some pictures or drawings. Hey, how about some animation or video? Got a couple of links.
yes you can reverse worm and gear. A worm gear can rotate the worm, its based on the lead angle, pressure angle and co.efficient of friction between the pairs.
The worm-gear design involves one helical gear, the teeth of which form segments of a helix, and another component that resembles a screw. The screw-like component is known as a worm, and its threads typically form a complete helix. This worm is typically used to drive the gear, which can provide a great deal of torque. In most cases, attempting to use the gear to turn the worm will result in the teeth locking. Both of these basics of worm gear-design can be exploited in the tuning knobs of stringed instruments, which provide the torque necessary to pull the strings taught and then automatically lock in place to keep them that way