The locks used in house doors fall into two main classes: mortise locks and rim locks. A mortise lock is housed in a mortise or hole cut in the door on its closing edge and is quite concealed on both sides when the door is shut. A rim lock is designed for fixing to one face of the door, to which it is held by three large screws on the face, and two smaller screws through a tongue at right-angles to the front of the lock and bedded in the edge of the door.
Mortise locks give greater security than rim locks, as they cannot be got at until the door is opened; whereas a rim lock is accessible on one side, and removal of the box staple into which the bolt shoots renders the lock useless. Moreover, the box-staple can be forced off with comparative case from the other side of the door. Mortise locks cannot, however, be fitted to doors made of thin stuff.
The trouble which most often overtakes a lock is the breakage of the spring, or one of the springs, controlling the mechanism. Where only a single spring is used, the snapping of it will cause the handle latch to remain in the lock, though the locking mechanism may not be affected. Again, a lock with two or more levers may refuse to work if one of the spring levers breaks.
Removing a lock of either kind begins with taking off the knobs and the square spindle over the ends of which they pass-If grub screws are used in the knobs, one of these must be unscrewed. Where the knobs are attached to their roses, one rose must be unscrewed, after making marks to ensure the holes in it being respectively opposite to the same screw-holes in the wood when the knob is replaced.
A rim lock has simply to be unscrewed to be released. Most mortise locks have a false front, held to the lock itself by two short screws. The front must be taken off to get at the carpenters screws holding the lock in place. When these have been drawn, the bolt is shot and used to pull the lock out of the mortise.
In a rim lock a removable plate forms the inner side. Two screws hold it in place. Some mortise locks have a casing split down the middle, one half being removable; while others have a removable side. When opening up the lock be careful to disarrange the mechanism as little as possible, and before taking any part out of place, no to its position and in which direction it faces.
Locks are of so many designs that it is impossible to describe them in detail. A single spring presses at one end against the tail of the lock lever and at the other against the tail of the latch. The follower, when turned in either direction by the knob spindle, moves the latch backwards through the medium of a plato from which two studs project behind the arms c-f the follower. The ends of the last are stepped, to fit holes in the locks sides, which prevent it shifting. When the key is turned, the lever is lifted, as the keys tip enters a notch in the bolt, until the narrow part – called the gate – in the opening in the lever is level with a stud projecting from the bolt. The lock can then be moved forward by the key.
By the time it is full out the key allows the lever to fall, with the notch behind the gate embracing the stud and rendering the bolt immovable. Should the lever be raised too far or not far enough by a wrong key, the gate will not register with the stud, and the bolt will refuse to move. A lock with several levers has a narrow spring to each lever, fixed into the back end of the lever and turned over to press against the inside of the top of the lock.
In many locks the latch is reversible, so as to suit either left-hand or right-hand closing. So care must be taken to replace it, if removed, the same side up.
A broken spring is easily matched at the ironmongers if the part of it are available as a pattern; so keep a sharp lookout for them. An over-long spring can easily be shortened by nicking ft across with a file and breaking off the surplus with pliers.
While the lock is open, see whether the follower has become worn at the ends of the barrel. If it has, replace it if possible. Also clean out dirt and dust, and oil the mechanism well. A lock lasts much longer if lubricated periodically.
Do not necessarily condemn a lock because it is old and out of order. A small expenditure may restore it to good condition. This remark applies especially to old locks of superior make, many of which are of excellent materials and workmanship.
Filling a Door Lock
When buying a mortise or rim lock make sure that it is of the correct hand, that is, will shoot the bolt hi the required direction when right way up. If of the wrong hand, it will have to be turned upside down.
The flange is first sunk into the cdgo of the door. Then mark and bore for all holding screws, and screw on the lock temporarily. The next step is to mark the wood for the knob spindle and keyhole with a sharp metal point pushed through the lock. Remove lock and bore from the lock side, taking great care to centre the bit correctly and keep it quite square to the door in all directions. As soon as the tip of the bit appears, finish the boring from the other side, to avoid splintering. Two or three small holes will be needed for the keyhole, the wood between them being removed with a padsaw or chisel.
The more correctly the keyhole is made, the better will it guide the key into the lock. In any case it must allow the key to enter easily. Replace lock, fix the handles, and the rose and keyhole escutcheon (a small brass plate surrounding the keyhole) on the non-lock side.
Finish by screwing on the box staple at such a height that there is plenty of room above and below the bolt and catch.