A friction gear is a group of one or more gears where the motion of the gear is created by the friction of two surfaces. The two surfaces travel in a rolling motion against one another when they come into contact with each other. Friction gears are most commonly seen in mechanical engineering products and automobiles, and may be found in the transmissions of cars and many other types of machinery that are both simple and complex. Although all friction gears operate in roughly the same manner, there are many different types of friction gears that can be used in the construction of mechanical equipment.
One type of friction gear that is commonly used is the flat faced gear. This type of gear consists of two of more wheels. These wheels are normally covered in leather or rubber.
The covering in a flat faced gear allows the gear to produce more friction as the wheels come into contact with one another. Frictional engagement can also be increased by adjusting the wheels. Making adjustments and moving one wheel toward the other will increase frictional engagement. Making adjustments and moving one wheel away from the other will decrease frictional engagement.
Another type of friction gear that is commonly used is the grooved gear. Grooves on the surface of the wheel increase the bearing of the surface. When the wheels come together, the grooves catch on one another to move the gears in a rolling motion. This is probably one of the most commonly seen examples of a friction gear.
When using the grooved gear, it is generally best to have the two wheels only slightly engaged with one another or just barely touching. Doing so allows the gear to roll continuously with little to no friction. When moved too close together, the grooved friction gear will actually lock up or take a long time to rotate because of the increased amount of friction.
The last type of friction gear commonly used is the beveled friction gear. This type of friction gear uses two cone shaped frustums instead of wheels to move. The cones are set up adjacent to one another at right angles.
In the beveled gear, as movement occurs, motion is then transferred from one shaft to the other. The closer together these cones are placed the more friction exists and thus less motion. The farther apart the cones are from one another the less friction there is, which increases the motion.