1Before you buy a lock measure the side rails of the door and make sure the lock will fit. If you are changing a lock bring the old lock with you to buy a new one, so you can be sure to get one that fits.
2Position your lock to match up with the strike plate of the previous lock. If working on a new door and frame your lock should be 900mm – 1m above the ground. Mark the top and bottom of the body of the lock on the door. Give yourself an extra 5mm leeway.
3Next ‘pencil in’ a vertical centre-line to aid drilling. Secure the door with a wedge before drilling.
4Mark the length of the lock body on the drill bit with a strip of tape. This will give you a rough guide as to how far you need to drill into the door. Add about 3mm to the length of the lock. Then make a series of drill holes along the centre-line.
5Use a chisel to smooth the sides of the mortice slot so that the lock body will slide neatly in to the door
6Sit the lock in and mark the edge of the lock plate.
7You must now make a recess in the edge of the door so that the front plate of the lock is flush with the door. Using a hammer and chisel make a series of cuts with the chisel down the length of the door where the plate will sit. Then ease out the indentations made by the chisel to give you your recess.
Top Tip: Always hold the chisel with the bevel side facing the area you are chiseling out and always chisel inside the line.
8Hold the lock in position against the face of the door, and with a pencil mark the centre point of the keyhole and the handle spindle (if there is one). Repeat on the other side of the door.
9Using a drill, make holes through the door the same diameter as the keyhole at the positions you have marked with the pencil. Drill in from both sides to avoid splitting the wood. Make the keyhole the correct size by stitching two holes together.
10Insert the lock body into the door. Gently tap with hammer, if required. Then insert screws to secure the lock, and screw cover plates over the keyholes to finish off the job. Finally if working on a new frame chisel out a recess for the strike plate on the frame of the door. If replacing a mortice lock, fit the new strike plate in the same position as the old one.