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how does a mortise lock work - how does a mortise lock work

How Does a Mortise Lock Work? A Complete Guide

Mortise locks are a popular choice for both residential and commercial properties due to their durability and security. At Trinity and Sons Locksmith in Charlotte, NC, we often get asked, How does a mortise lock work? Understanding the mechanics of a mortise lock can help you appreciate its benefits and make an informed decision about your security needs. In this article, we will delve into the workings of a mortise lock, its components, and why it is a preferred choice for many.

What is a Mortise Lock?

A mortise lock is a type of lock that is installed into a pocket (or mortise) cut into the edge of a door. This type of lock is known for its strength and reliability, making it a popular choice for exterior doors and high-security applications.

Components of a Mortise Lock

Lock Body

The lock body is the main component and is housed within the mortise cut into the door. It contains the locking mechanism and interacts with the other parts to secure the door.

Lock Cylinder

The lock cylinder is where the key is inserted. It turns to engage the locking mechanism inside the lock body.


The spindle is a metal rod that connects the door handle to the lock mechanism. When the handle is turned, the spindle rotates to operate the lock.

Strike Plate

The strike plate is mounted on the door frame and aligns with the lock body. It receives the latch or bolt to secure the door when it is closed.

Latch and Deadbolt

The latch is a spring-loaded bolt that holds the door closed. The deadbolt is a solid piece of metal that provides additional security when engaged.

How Does a Mortise Lock Work?

Engaging the Lock

When you insert and turn the key in the lock cylinder, it rotates the lock mechanism inside the lock body. This action can either extend or retract the deadbolt, depending on whether you are locking or unlocking the door.

Operating the Handle

Turning the door handle rotates the spindle, which moves the latch inside the lock body. This allows you to open or close the door. When the door is closed, the latch automatically engages with the strike plate to keep the door shut.

Advantages of Mortise Locks

  • Durability: Mortise locks are built to withstand heavy use and are often made of robust materials.
  • Security: The combination of a latch and deadbolt provides enhanced security.
  • Versatility: Mortise locks can be used with various door styles and are suitable for both residential and commercial properties.
  • Aesthetic Appeal: These locks are often more aesthetically pleasing and can be customized to match the door design.

Table: Comparison of Mortise Locks and Cylinder Locks

Feature Mortise Locks Cylinder Locks
Durability High Moderate
Security Enhanced (latch + deadbolt) Basic (single bolt)
Installation Complex Simple
Aesthetic Options Customizable Limited
Cost Higher Lower

How to Install a Mortise Lock

  1. Measure and Mark: Measure the lock and mark the door where the mortise pocket will be cut.
  2. Cut the Mortise: Use a chisel or router to cut the mortise pocket to the appropriate size.
  3. Install the Lock Body: Insert the lock body into the mortise and secure it with screws.
  4. Attach the Lock Cylinder: Insert and secure the lock cylinder.
  5. Install the Strike Plate: Align and secure the strike plate on the door frame.
  6. Test the Lock: Ensure the lock operates smoothly by testing the key and handle functions.

Common Issues with Mortise Locks and How to Fix Them

Key Sticking

  • Cause: Dirt or debris in the lock cylinder.
  • Solution: Clean the lock cylinder with compressed air or a lock cleaner.

Handle Difficulty

  • Cause: Misalignment of the spindle or internal components.
  • Solution: Check and adjust the alignment of the spindle and internal parts.

Deadbolt Not Engaging

  • Cause: Misaligned strike plate or door frame.
  • Solution: Realign the strike plate and ensure the door frame is properly aligned.


1. What is a mortise lock?

A mortise lock is a type of lock installed into a pocket cut into the edge of a door. It is known for its strength and security, making it ideal for exterior doors.

2. How does a mortise lock differ from a cylinder lock?

Mortise locks are more durable and secure, with both a latch and deadbolt. Cylinder locks are simpler and easier to install but offer basic security with a single bolt.

3. Can I install a mortise lock myself?

Yes, but it requires precise measurements and cutting. Professional installation ensures proper alignment and functionality.

4. Why should I choose a mortise lock?

Mortise locks offer enhanced security, durability, and aesthetic appeal. They are suitable for high-security applications and can be customized to match your door.

5. What are common problems with mortise locks?

Common issues include key sticking, handle difficulty, and deadbolt not engaging. Regular maintenance and proper installation can prevent these problems.

6. How can I maintain my mortise lock?

Regularly clean the lock cylinder, check for proper alignment, and lubricate moving parts to ensure smooth operation and longevity.


Understanding how a mortise lock works can help you appreciate its advantages and make an informed decision for your security needs. At Trinity and Sons Locksmith in Charlotte, NC, we specialize in installing and maintaining high-quality mortise locks. If you’re looking for reliable locksmith services, contact us today for professional assistance.

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