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Fitting a deadlocking mortice lock

• Although a good deadlocking cylinder lock will secure your front door, your local Crime Prevention Officer would advise you to fit an additional mortice lock. This lock should be fitted well below the latch to add support to the door and help prevent a forced entry.
  
• A mortice lock should be a snug fit in the slot, or mortice, cut in the edge of the door. Only the face plate, which is set flush with the edge, is visible when the door is open. The lock can only be operated by a key from the inside or outside.
  
• Buy only good-quality strong locks that conform to BS 3621. This shows the lock meets with the current British Standards and carries the kite mark.
  
• Mortice locks are made in various sizes, but a typical lock body measures up to 100mm (4") deep, but 65mm (2.5") deep locks are available for narrow stiles. Measure the width of the door stile to make sure the lock will fit.
  
• A door stile needs to be at least 45mm (1 3/4") thick to take a mortice lock.
  
• The procedure for cutting the mortice is the same whether you are fitting the lock to a new or existing door.
  
• It is important to position the mortice lock well below the cylinder lock, while avoiding the cross-rail joint.
  
• The mortice must be cut accurately so that the lock fits snugly - an oversize mortice will weaken the door stile.
  
• Set a marking gauge to half the thickness of the stile and scribe a centre line for the mortice on the edge of the door.
  
• Holding the body of the lock against the edge of the door, mark a line at the top and bottom to indicate the length of the mortice.
  
• Select a drill that is the same diameter as the thickness of the lock body. Remove the waste between the marks on the door by making a series of overlapping holes down the centre line. Use either a hand brace and bit or a power drill and spade bit.
  
• Clean out the remainder of the waste with wood chisels to leave a neat rectangular slot for the lock body.
  
• Slide the lock into the mortice and carefully mark the faceplate with a knife.
  
• Cut a recess to set the faceplate flush with the edge of the door. Make a series of shallow cuts across the marked out area and, with the chisel held bevel down, pare out the waste. Take care not to split the wood as you trim the sides of the recess.
  
• Hold the lock against the face of the door with the face plate level with the recess. Mark the centre of the keyhole with a bradawl. Drill a hole through the door - clamp a block of scrap wood to the other side of the door to prevent splitting - then use a padsaw tp cut a keyhole on each side of the door.
  
• Fit the mortice lock and try the key from both sides. If all is well, screw the lock in place and attach the faceplate cover if required.
  
• Screw the escutcheon plates over the keyhole.
  
• Now fit the striker plate to the door frame. With the door open, shoot the bolt out and close the door against the door post. Mark the position of the bolt on the frame. Cut a small mortice and recess for the striker plate in the frame.
  
• As well as a lockable bolt, a mortice lock has a spring-loaded latch that is operated by a lever handle on both sides of the door. These are typically used for rear and/or side-entry doors.
  
• They are fitted like a standard mortice lock, but you have to drill one extra hole through the door for the lever-handle bar. Some locks are made to fit left hand or right hand opening doors, so check before you buy.
  
• Fit the lever handle - some are made with concealed screw or bolt fixings, others are face-mounted.