How Does a Mortise Lock Work?

Steve Smith

A mortise lock fits into a door itself, as opposed to the door knob and lock or cylindrical lock, which is installed through a hole drilled into the door. A mortise lock requires a section of the door to be skillfully gouged out with a router. Then the lock knob and hardware is installed into this section.

The second part of the design is the bolt chamber, which is also fitted into the structure, but this is installed inside the door frame. The lock uses a strike plate, face plate and lock assembly (door knob, dead bolt and handle) just like other door handles.



A mortise lock requires the use of a latch and handle system. Some also have a sliding bolt mechanism. Any type of knob and latch can be used with a mortise lock. The latch is the handle or door knob that one pulls to slide the bolt back and open the door. This uses a series of tumblers and key to lock into place. Otherwise, the latch will slide back whenever the handle is pulled or turned. To set the dead bolt, most mortise locks require a simple twist of a knob inside. A cylindrical tumbler and key can be used to slide the bolt back from the outside.


It requires a little more skill to install a mortise lock because the lock is set into the frame and door itself. A locksmith or woodworker may have acquired the skills to install mortise lock. In some cases a mortising bit and router can be used to drill out the channel for the lock. This can also be done by drilling into the door frame with a large drill bit several times and then straightening the slot. The mortise lock is then inserted into the door, and the face plate installed over it. The strike plate is inserted into the door frame in the same way, level with the bolt. A hole is drilled right through the door itself for the key hole. The key inserted right through this hole, without any hardware showing on the outside of the door. There is very little hardware showing that would indicate any lock is installed at all.