Combination locks -- the keyless lock on your gym locker or the more complex ones found on safes -- are a very effective way of securing your belongings without the risk of losing a key. You turn the dial this way and that way, and eventually the lock opens. Wouldn't you like to know what's happening inside the lock? Take this quiz to learn more about how combination locks work.
The modern combination lock is based on a wheel pack mechanism that has been around for about 100 years.
The combination dial is the numbered wheel that you turn to input the numbers of the combination.
A wheel pack is the collection of gears inside a combination lock. These gears are set to a particular combination, and work together to allow a combination lock to open.
The spindle is a thin metal tube that extends from the dial, through the center of each gear in the wheel pack. When you turn the dial, the spindle rotates, and with it any gears that have been activated.
Each time you change directions to input a number into the lock, you activate a different wheel in the pack. There will be as many wheels as there are numbers in the combination.
Each gear wheel, or cam, will have a tab known as a drive pin, which extends outward toward the face of the combination dial.
As a gear turns, its drive pin will eventually latch onto a similar tab known as a wheel fly, which extends backward from the adjacent gear. When the drive pin latches unto the wheel fly, the adjacent gear joins the other rotating gears.
Along the perimeter of each wheel is a small notch, appropriately called a wheel notch. When the correct combination has been entered, the notches line up to create a gap.
Large combination locks, like those you might find in a safe, have a component known as a fence. The fence keeps the mechanism locked by blocking the safe's bolt.
When a combination has been correctly entered, the fence will fall under it's own weight into the slot created by the lined-up wheel notches.