Mortice locks are ideal as second locks on a front door and for back or side doors, which are not used as final exit doors. The lock body is fitted into the edge of the door, and the heavy-duty bolt locks into the door frame when the key is turned. You will need to know the width of your door edge when buying a mortice lock.

1. Measure the width of the door edge at a couple of places and join the halfway points to make a vertical line to ensure you fit the lock in the centre. Hold the lock casing (attached to the faceplate) against the edge of the door where you plan to fit the lock, and mark around the casing so that you know where to make the recess.
2. Choose a drill bit that is as close as possible to the width of the casing of the mortice lock, and drill a series of overlapping holes slightly deeper than the depth of the casing along the centre line to remove most of the waste wood. Wrap masking tape around the drill bit to act as a depth stop.
3. Use a chisel to square the edges of the recess until the lock fits. Mark around the faceplate of the lock and chisel a shallow recess so the lock is flush with the door edge.
4. Remove the body of the lock from the recess and hold it against one side of the door. Mark the position of the keyhole.
5. Drill through the recess to the other side of the door (refer to the instructions on the packaging for the size of drill bit to use - usually around 10 mm (3/8 in). To stop the drill bit splintering the wood, clamp a block of scrap wood against the other side of the door. You will need to make two drill holes, one below the other, to allow the key to work smoothly.
6. Put the body of the lock back into the recess and screw in place. Fit the escutcheon (display) plates over the keyhole, using the tiny brass screws provided.
7. Close the door and turn the key ...