How does a Combination Lock work?

During most of my teen years, I used a combination lock at school to open up my locker. Before making this video, I really didn’t understand how it worked. So I did some research, looked at a few patents, and then opened one up to see what’s on the inside. Let me show you what I learned. (bright music) Here’s the case that holds all of our parts. This metal curved bar is called the shackle. It won’t come out until the right combination is put in. Then, it pops right open. This piece is called the lever. It slides right onto the bar here. The lever can rotate counterclockwise. This piece of metal wants to flex outward. Once it’s bent inside of here, the tension makes the latch want to spring back to its original position. Normally, the latch would just keep going, but the rotation will be stopped by this tiny bump. The lever also has a tiny latch here that is spring loaded from the inside. The shackle comes down, pushes the latch in, and then the latch fits right into the groove, and we are locked. When the shackle is pulled out, the latch is forced to rotate to allow the shackle to come all the way out. Then, the lever springs back into place. Let’s watch that again. The shackle can’t come all the way out because of the shackle collar. It guides the shackle as it slides along here. But it stops us once we hit the very top. Okay, the reason that the locking mechanism works is that, if the latch can’t rotate, then the shackle won’t come out. This is where the three cams come into play. Let me show you. The back place has a bar sticking out. It holds the three cams, washers in between, and a spring at the end. The spring ensures that the three cams and the washers are all pressed together. Cam two and three can spin freely. But cam number one is actually attached to the dial. So when the dial spins, this cam spins too. This is what it looks like al put together. Each cam has an indentation in them. The lock will open when all three of them are lined up. You can see how the lever can now rotate, which allows the shackle to open. When these three indentations are not lined up, the lever can’t rotate, which means the shackle can’t come out. So how do we line up the cams by only turning this dial? Let’s look a little closer. Each cam has at least one of these teeth sticking off of it. You can see them better from this point of view. If we turn cam one far enough, the tooth on cam one will contact the tooth on cam two. And then if we keep turning, all three cams move together. In fact, this is the first step to opening up the lock. Let’s walk through this process on the inside. This time we’re looking at it from the front, so all three cams will need to line up here. We turn the dial clockwise three times to clear it. All three cam teeth are in contact with each other and move as one. Now let’s keep turning the dial until we hit the first number in the combination, which in this case is 21. Notice how cam three is now lined up right where it should be. Now let’s work on the second number in the combination. This time we turn counterclockwise one full rotation. Watch as the teeth from cam one come in contact with came two on the other side. Notice how this doesn’t touch cam three, which is still right where it should be. Now we keep spinning the dial until we hit the second number, which is 34. Now cam two and cam three are lined up. For the last number in the combination, just rotate the dial clockwise until it lines up with the third number. And there we go. All three cams are lined up, the lever rotates, allowing the shackle to come out. As the shackle is pushed back in, it comes down with a bit of a jolt, which is usually enough to nudge the cams out of alignment. This means the lock won’t open a second time for free; you’ll need to use the correct combination once again.