A door lock is more than just the few visible pieces you frequently come into contact with. The locking mechanism is an intricate series of springs, pins, cylinders and shafts that work together to secure the door. What is seen besides the handle is the deadbolt knob, the inner and outer panels, the key entry, the bolt plate and the bolt itself. First the visible parts need a brief explanation then the mechanism itself will be looked at.
Visible Parts of a Door Lock
Lock installation usually involves one of two types of door lock: a key lock in a doorknob or a deadbolt security lock. The first type has the mechanism inside the handle, thus all that is visible is that. A deadbolt, on the other hand, has several outside parts.
- Deadbolt knob: the small handle that is turned to activate the deadbolt
- Inner and outer panels: depending on the door lock type, it could be a plate of various sizes to which the deadbolt handle attaches on the inside and the key inserts on the outside
- Key entry assembly: the keying mechanism into which the key inserts from the outside
- Bolt plate: the plate that attaches to the edge of the door that holds the deadbolt in place
- Deadbolt: the solid metal cylinder known as the tang that secures the door when extended
Door Locking Mechanism
The parts of the door lock that are not visible but that function to keep the lock working are known as the door lock mechanism. Inside the lock cylinder–the housing containing both the key entry assembly and the deadbolt knob – are pins, springs, a cam, and the tang. To lock the deadbolt, when the right key enters the lock, it allows the cylinder to turn, which turns the cam. This releases a spring which pushes the tang partially out of the cylinder and into the door jam. It is the opposite action which locks the door.
More specifically, inside the cylinder are upper pins and lower pins in pairs and of different lengths. Small springs hold each pin in their place. The upper pin of each pair is partially in the cylinder and partially in the door, securing it from opening when the door is locked by ensuring the cylinder cannot rotate. A key has notches that push each pin to an appropriate height when it is inserted. The right key for a lock, when it is inserted, pushes each of the upper pins completely out of the cylinder, freeing it and allowing it to rotate, unlocking the door. The reverse action brings the pins partially back into the cylinder and pushes the tang into the door jam and the wall, locking the door once again.
As you can see, a door lock mechanism is quite complicated, yet most of its working parts are concealed from sight. Learning how a door lock functions is helpful if you ever need to replace or change the door locks in your home.