How to fit a mortise lock

Trying to fit a mortise lock? We've got you covered, take a look at our easy to follow guide.

A mortise lock fits into a recess that's carved into the edge of the door. They're common in older buildings and are well known for their security properties. Fitting a mortise lock is a job for a keen DIY enthusiast.

Mortise locks comprise of four main components:

  1. Lock body

  2. Lever mechanism – this is housed in the lock body

  3. Lock trim

  4. Strike plate

If you are replacing an existing mortise lock, make sure it has the same dimensions as the previous one and that the holes for the handle spindle and key are in the same positions.

Fitting a lock body

1. Mark up

Using the body of the lock as a template, mark where it will be positioned on the door.

2. Make the recess

Use a drill to remove as much waste wood as possible before using a bevel-edged chisel to remove the rest. Square the edges of the hole so the lock sits flush.

3. Mark the keyhole

Using the body of the lock as a template, mark the keyhole position and drill it through. Hold a block of waste wood on the other side of the door to prevent splintering.

4. Cut the keyhole

Use a keyhole saw to cut out the shape for the keyhole to fit. Once the main locking mechanism has been fitted and screwed into its recess, check that it operates properly.

Fitting a lock trim

The lock trim is the decorative metal part that sits over the door, including the handles.

1. Mark the screw holes

Insert the handle spindle into the hole in the door and place the lock trim over it. Mark the position of the screw holes onto the door. Do the same on the other side of the door.

2. Drill

Drill pilot holes for the screws. Do the same on the other side of the door.

3. Attach the trim and handles

Put the trim on and attach the handles to the spindle. Screw into place.

Fitting a strike plate

The strike plate is the piece of metal that sits on the door frame and receives the bolt and latch when the door is closed.

1. Mark up

Push the door until almost closed and mark the position of the strike plate on the doorframe. Mark the position of the bolt on the frame.

2. Measure

Measure the distance between the front face of the latch and the edge of the door. Transfer this measurement onto the doorframe to ensure that the strike plate aligns correctly with the latch. Using the strike plate as a template, draw around it and mark the position of the bolt and screw holes.

3. Make the recess

Use a drill and chisel to hollow out the hole for the bolt and to cut out a recess to the depth of the strike plate.

4. Fit the strike plate

Drill the holes and screw the strike plate in place.

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