How To Fit A Mortice Lock To An External Door？

Fitting a mortice lock is a classic carpentry skill that enhances the security of your home. While it might seem daunting, with the right tools and a bit of patience, it's a project most DIY enthusiasts can tackle. Installing a mortice lock properly ensures your external doors are secure and function smoothly.

This guide will provide a clear, step-by-step process for fitting a mortice lock into a wooden door. We'll cover everything from the tools you'll need to marking out, chiseling, and final installation. By the end, you'll have the confidence and knowledge to add a professional level of security to your home.

Understanding the mortice lock

Before we begin, let's clarify what a mortice lock is. Unlike a cylinder rim lock (or Yale lock), which is mounted onto the surface of a door, a mortice lock is fitted into a pocket—the mortice—cut into the edge of the door. This makes it more secure and less visible.

There are two main types of mortice locks:

1. Mortice Deadlock: This lock features a single bolt that is operated by a key. It offers a solid, secure locking point.

2. Mortice Sashlock: This type includes both a key-operated deadbolt and a latch, which is operated by a door handle. It's common on back doors and internal doors that require locking.

For external doors, a 5-lever mortice deadlock is often the standard recommended by insurance companies because it offers a higher level of security against picking and drilling.

Tools and materials you'll need

Gathering your tools before you start will make the process much smoother. Here’s what you’ll need:

Tools:

• A sharp pencil

• Measuring tape

• Combination square or try square

• Drill (cordless or corded)

• A selection of flat wood drill bits

• A set of sharp wood chisels (e.g., 1/2-inch and 1-inch)

• A wooden mallet or hammer

• Screwdriver

• Utility knife

Materials:

• Your chosen mortice lock (including the lock body, strike plate, and screws)

• Masking tape

Safety First: Always wear safety glasses when drilling or chiseling to protect your eyes from wood chips and dust. Sharp chisels are essential for a clean job, but handle them with care.

Step 1: Marking the door

Accurate marking is the most critical part of this job. Take your time to get it right, as all subsequent steps depend on it.

Mark the lock position

First, decide on the height for your lock. A comfortable height for the keyhole is typically around one meter (about 39 inches) from the floor. This also aligns well with standard door handle heights if you're fitting a sashlock.

Once you've chosen the height, use your tape measure and combination square to draw a horizontal line across the face of the door and around onto the door edge. This line represents the center of the keyhole.

Mark the mortice pocket

Now, place the lock body against the edge of the door. Align the keyhole on the lock with the horizontal line you just drew. Use your pencil to mark the top and bottom of the lock body on the door edge.

Next, find the center of the door's thickness. You can do this by measuring the door's thickness and dividing by two. Use your combination square to scribe a line down the center of the door edge, between your top and bottom marks. This centered line will guide your drilling and chiseling.

Step 2: Cutting the mortice pocket

With your markings complete, you can now create the pocket for the lock.

Drill out the waste wood

Select a flat wood drill bit that is slightly narrower than the thickness of your lock body. This ensures you don't accidentally make the mortice too wide.

Wrap a piece of masking tape around your drill bit to mark the depth you need to drill. To find this depth, hold the drill bit against the side of the lock body. The tape should align with the end of the lock's faceplate.

Start drilling a series of holes along the centerline you marked on the door edge. Drill between the top and bottom marks for the lock body. Keep the drill as straight and level as possible. Overlapping the holes slightly will make it easier to remove the remaining wood.

Chisel the mortice

Once you've drilled out the bulk of the wood, it's time to clean up the mortice with a chisel.

Using a sharp chisel and a mallet, carefully remove the remaining wood between the drilled holes. Work from both sides towards the middle. Keep your chisel perpendicular to the door edge to ensure the sides of the mortice are straight.

Periodically check the fit of the lock body. The goal is a snug fit—not so tight that you have to force it in, but not so loose that it rattles. Continue to pare away small amounts of wood until the lock slides in smoothly.

Step 3: Marking and cutting for the faceplate

Once the lock body fits perfectly, insert it into the mortice. The faceplate should now be sitting against the edge of the door.

Use a utility knife to carefully score around the edges of the faceplate. This creates a clean outline for the recess.

Remove the lock and use your chisel to carefully cut out the shallow recess for the faceplate. The depth should be equal to the thickness of the faceplate, allowing it to sit perfectly flush with the door edge. Take your time with this step, removing thin shavings of wood until the plate fits flush.

Step 4: Drilling the holes for the keyhole and spindle

With the lock body back in the mortice, you need to mark the positions for the keyhole and, if you're fitting a sashlock, the handle spindle.

Use a pencil or a sharp tool to mark the center of the keyhole through the lock body onto the face of the door. Do this on both sides. If you have a spindle hole, mark that as well.

Remove the lock. You now have the precise locations for your holes. Drill a pilot hole through the door from one side. Then, using a larger bit that matches the size of the keyhole escutcheon, drill halfway through from one side, then complete the hole from the other side. This prevents the wood from splintering out.

Repeat the process for the spindle hole if you're fitting a sashlock.

Step 5: Fitting the lock and strike plate

Now you can permanently install the lock.

Secure the lock

Slide the lock body into the mortice. Ensure the faceplate is flush. Drill pilot holes for the faceplate screws and then drive the screws in to secure the lock in place. Install the keyhole escutcheons on both sides of the door.

Mark and fit the strike plate

The final step is to fit the strike plate on the door frame. Close the door and, with the lock's bolt extended, mark where the top and bottom of the bolt meet the frame.

Open the door and use your combination square to transfer these marks onto the inside face of the door frame.

Hold the strike plate against the frame, aligning it with your marks. Draw around the strike plate and the inner hole for the bolt.

Drill and chisel out the recess for the bolt in the door frame. Then, chisel a shallow recess for the strike plate itself so it sits flush with the frame. Screw the strike plate into position.

Test the lock. The bolt should move smoothly into the strike plate without catching. If it's stiff, you may need to adjust the position of the strike plate or slightly enlarge the hole in the frame.

A secure finish

Fitting a mortice lock is a rewarding DIY task that significantly boosts your home's security. By following these steps carefully and working with precision, you can achieve a professional result. Remember that sharp tools and accurate measurements are your best friends in this project. With your new lock installed, you can have peace of mind knowing your door is properly secured.

mortice lock

External Door lock

Interior Door lock