We believe key locks keep our homes and belongings safe, but most people know very little about how key locks work. Because the key lock mechanism is hidden, we can only imagine what happens when we insert and turn the key. There are many types of key locks that work in different ways, but the most common is the marble key lock. Most doors use this type of key lock.
Door handle latch key lock and key lock tongue: two common types of marble key locks
In modern homes, entrances are often equipped with door handles or lever latches key locks, and/or key lock tongues. These two types of key locks provide different levels of security.
A simple latch key lock keeps the door closed when you turn the knob or handle while allowing it to open easily. However, a house with only a doorknob key lock is relatively easy to break into. Due to the small angle of the latch key lock, an intruder may be able to pry open the latch key lock with a credit card. Additionally, an intruder may break a doorknob or handle with a stone or hammer and then remove the key lock mechanism in this manner.
A dead key lock provides more security. For one, it works by inserting square bolts into adjacent door frames. The square shape prevents anyone from using a credit card or other tool to pry the bolts off the frame. Another benefit of the key lock tongue is that it fits directly on the door rather than inside a knob or handle. Therefore, breaking the key lock tongue by force is much more difficult.
Despite the differences, door handle latch key lock and door latch are both examples of pin key lock and pin key lock. Both types of key locks require a key correctly aligned with a series of pins to key lock or unlock the door.
Parts of marble key lock
Even among key locks that work in the same way, there are differences in design. However, all marble key locks contain the following parts.
Key Slot: When you look at the door key lock from the outside, you will see a keyhole, also known as a key slot, cut into the center of the circular metal part.
Cylinder: This metal part is called a plug or cylinder, and what you see on the outside is one end of a long cylinder that slopes back 90 degrees.
Housing: The plug is in the center of a larger, circular part called the housing.
Shaft: Inside the housing, a series of posts or shafts run front to back above the keyway.
Springs and Pins: Each shaft is fitted with a spring and at least two cylindrical pins of different lengths called drive pins and key pins.
Bolts: The bolts are perpendicular to the keyway, and when the door key lock is on, the bolts fit into the square holes framed by the metal bumper plate.
How the Pin-Tumbler mechanism works
When there is no key in the key lock, all lower (key) pins are placed on the floor of the key slot. Part or all of the drive pin (on top of the key pin) is below the top of the cylinder but partially extends into the shaft. These pins prevent the cylinder from turning.
The grooves or teeth on the edge of the keys are designed according to the height of each pin. When the key is inserted, the key pin rests on the key, causing all drive pins to move up into the shaft and all key pins to end at the top of the cylinder. The top of the cylinder, where the axis begins, is called the shear line. When the key pin and drive pin meet exactly at the shear line, the cylinder can turn freely. The rotation of the cylinder activates the bolt, sliding it in or out of its box.
Changes in marble key lock
The above key lock is a linear tumbler key lock because the pins are arranged from the front to the rear of the keyway. The pins can also be arranged in a circle, a design called a tubular key lock.
However, not all marble key locks use pins. Wafer marble key locks use spring-loaded wafers with parts that protrude below or above the cylinder to prevent it from turning. As the key passes through the center of each wafer, a notch in the key raises or lowers each wafer into place, allowing the cylinder to rotate. Car ignitions and filing cabinets often use this type of key lock.
Another type of pinball key lock is called a disc pin or disc key lock. In a disc key lock, the keyway goes into the center of a row of vertically notched discs separated by washers. A thin metal strip on top of a row of discs keeps the cylinder from turning. However, when the notches on the disc are properly aligned, they create a space for the rod to fall into. This type of key lock provides a high level of security.
Other types of key locks
In addition to marble key locks, there are two types of key locks that most people are familiar with: password key locks and electronic key locks. None of these types require a key.
You may have used a combination key lock for a school key lock or bicycle chain. As you turn the dial to each digit of the key lock combination, the internal cam rotates to align the three slotted discs. When the grooves on the disc line up, the internal assembly can rotate and release the key lock that holds the curved metal strip in place.
Electronic key locks are triggered to open by some type of data, such as a password embedded in a magnetic strip or biometric data from a fingerprint or retina scan. Since biometric data cannot be replicated, it is becoming more and more popular in the field of information security.