This is a simple operation well within the capabilities of any handyman. As in all aspects of carpentry though, special care should be taken in marking out, and only the correct tools for the job used. First work out where the lock is to go. In most cases it should be fitted midway up the door, which allows space further up for the addition of a rimlock or safety chain. If another lock is already fitted at this point, it can easily be unscrewed and located higher up. Mark out the position of the lock and its area, by holding it against the door at the correct location.
Remember to allow for the thickness of the face plate and mark in the correct position of the keyhole. Now, using a mortise gauge, calculate the width and height of the mortise and mark out these measurements on the edge of the door. Particular care should be taken to centre the mortise in the door so that it is the same distance from both surfaces. Most of the mortise can be cut out by boring with a brace fitted with a bit exactly the same width as the lock. To assist in boring accurately, a centre line is drawn down the area to be cut away and the centres of the holes marked in. This is best done by carefully marking out with the aid of a 45 degrees combination square or adjustable bevel gauge as follows.
Lay the bevel edge against the side of the door, and adjust its position so that one edge of the rule meets one corner of the area to be cut away. Draw a line from this point to meet the opposite side, then reverse the square and, using the same technique, draw in another line from the point where the first line crossed the edge of the mortise housing. Repeat this procedure along the whole length of the area to be cut away, then mark in the points where the diagonal lines cross the centre line to give the bore centres. Fit the bit with a depth stop so that the depth of each bored hole can be gauged correctly.
If you do not possess this fixture, an alternative is to tie a piece of tape to the bit at the correct point. Bore out each hole to the required depth, ensuring that the bit is held at right angles to the door edge. A simple way of checking that the bit is held horizontally is to place a large washer over the bit. If the washer moves towards you as you drill, the bit is held too low; if the washer moves towards the door, the bit is held too high. The bit is horizontal when the washer does not move. When you have bored the mortise out, clear the hole with a chisel. Keep to the marked lines and don’t try to remove too much waste wood at once. Instead, chisel out a little at a time and keep testing for size by fitting the lock into the mortise.
The lock should just fit with no play. Alter checking that the previously marked locations of the keyholes are correct, remove the lock and bore them out with a bit slightly larger than the diameter of the keyhole on the escutcheon. Do not bore right through the door from one side; reverse the direction of boring before the bit emerges through the wood. Clean up the keyholes and, if necessary, cut them to shape with a coping saw. Now insert the mortise lock in position and test the action of the key in the lock. If it turns smoothly, fit the escutcheons in position over the keyholes. Secure the lock in the mortise by fixing screws through the holes on the face plate. Cutting the face plate rebate insert the lock into the mortise so that the face plate is flush against the edge of the door.
Mark out the extent of the rebate by marking round the face plate with a handyman’s knife to the required depth. Take a chisel with a blade exactly the same width as the rebate and make a series of cuts down the length of the rebate. This allows the rebate to be cut out in small sections. Hold the chisel at a flat angle against the door and remove each section with very light blows from a mallet. When the rebate has been cut to the required depth, clean up the edges and insert the lock but do not secure it with screws.
Fitting the striker plates
The striker plate is recessed in the door frame in exactly the same way as the lock. To mark the correct position, first turn the key to extend or ‘shoot’ the bolt, pull the door to and mark out round the bolt (and the latch if the lock is fitted with this feature). Following the same procedures that were used to mark and cut the mortise for the lock, cut out the recesses for the bolt and the striker plate and screw this piece into place. The fitting is now complete and the lock ready for use.
Maintenance
Like any other fixture with moving parts, the lock should be lubricated at least twice a year. A light oil or powdered graphite inserted into the mechanism through the keyhole should ensure the smooth operation of the lock.