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Installing Mortice Locks

The key measurements you need to match to replace a mortice lock are:

Backset: distance from the edge of the lock to the centre of the key hole

Case height: length of the case from top to bottom.

Forend Length: distance from top to bottom of face plate

The most important measurement is the backset as this is the position of the existing key hole cut into the door. If you can match this measurement then you will not need to adjust the position of the key hole in the door

1. Placement

Remove the lock from its box and hold it to the door to decide on a suitable location to fit it.

2. Marking

Position the lock body against the door and mark the top and bottom of the case with pencil. Mark the centre of the door and draw a line between the points. This will give you the position to drill.

3. Drill Hole

Using a 19mm flat wood bit drill along the pencil line in the centre of the door to the depth of the entire lock case.

4. Clean Hole

Using a sharp chisel (19mm wide if possible) clean out the mortice hole. Cut out the excess wood and adjust the width of the mortice to allow the lock case to slide into the hole smoothly.

5. Forend Hole

With the lock case located in the mortice make sure the forend is vertical and straight and mark around it with a sharp pencil. Remove the lock case and chisel out the forend depth. Try not to chisel out to much wood here as this will mean the lock will sit too far in the door and not have a neat finish.

6. Mark Key Holes

Align the lock to the edge of the door with the top of the face plate level with the top of the mortice you have cut into the face edge of the door. Holding it in position poke a thin braddle through the key hole to mark the centre of the key hole. Repeat process for other side key hole.

7. Drill Key Holes

With a 10mm flat wood drill bit drill the hole marked for the key hole. Drill another 10mm hole directly underneath the first hole. This will give you the entire length of the key hole. Clean out the hole of any wood splinters and repeat for the other side key hole. Place the lock into the mortice and check that the key holes are in line and large enough to accept the keys.

8. Escutheons

Mark up the escutcheon plates by inserting the key through the escutcheon and into the lock. Level up the escutcheon plate and mark the 2 screw holes. Drill a small pilot hole for the screws and screw the plates to the door. Repeat the process for the other side.

9. Faceplate

Throw the bolt of the lock and place the faceplate onto the bolt. Drill a pilot hole for the screws and screw the plate into the door. Try to throw the bolt and make sure the key is easy to turn.

10. Mark Door Frame

With the lock fitted into the door you can now fit the strike plate onto the frame. Start by throwing the bolt and gently closing the door. Mark the position of the top and bottom of the bolt on the frame.

Measure the distance between the inside edge of the door and the strike plate. Mark this measurement on the door frame. Align the bolt hole in the strike plate with the marks made onto the frame. Once this is lined up mark the top and bottom of the box onto the frame. Mark the centre line of the frame and mark from the top to the bottom of the box marks you made earlier.

11. Drill Frame

With a 19mm flat wood drill bit drill along the pencil line marked onto the frame. Clear out the hole with a chisel widening the side ever so slightly. Keep adjusting the hole according so that the box strike plate fits into the recess.

12. Strike Plate

With the box strike located into the hole mark around the plate of the strike. Remove the strike plate and chisel out the frame to allow the plate to sit flush into the frame.

13. Adjustments

Once the striking plate has been fitted into the frame close the door and check that the bolt easily locks into the frame. If you meet resistance then you will need to remove the strike and adjust its position by chiselling out the frame to locate the strike plate in the correct position.

14. Fix Strike Plate

Drill the pilot holes for the screws and fix the strike plate into the frame. Now make sure the lock works from both sides of the door and you are finished.