This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
As all the parts except the face-plate are hidden in the mortise, there is no use in ornamental work. The exposed face is usually plain brass or bronze; the case is generally cast iron or pressed steel, which should be heavy enough to hold its shape firmly, without springing or cracking if for any reason the mortise for which it is intended is not of the proper shape or size, which it rarely is.
After the question as to the use of a rim or a mortise lock is settled, another, covering just what is wanted of each lock, should be carefully considered, so that appliances will not be installed which are never to be used. Practically all locks contain a latch - that is, the part which is operated by the knobs and which holds the door closed under ordinary conditions. As the latch is the part subject to most frequent use, it is very desirable that its mechanism be as simple as possible and that all moving parts be of brass or bronze. The use of iron, except in the casing, should be avoided.
Fig. 27. Rim Lock.
LIVING ROOM IN RESIDENCE AT KENOSHA, WIS.
It is often observed, in finished work, that the latch is not easily pushed back when the door is shut, making it necessary to turn the knob or to give more than an ordinary slam to latch the door. This is caused by badly fitting parts, poor springs, and the shape of the latch-face. If the latter is a simple line as illustrated in Fig. 29, it will probably cause constant annoyance. If, however, the latch-face is carefully shaped after the manner shown in Fig. 30, there will be less, if any, trouble.
The latch should be heavy. It receives hard usage, and the heavier it is, the more evenly it responds to pressure. There are various anti-friction devices on the market, but they are rarely any improvement over the well-designed and well-manufactured latch-face. Should the selection, however, be unfortunate, and the operation of the latch unsatisfactory, conditions can be remedied to a certain extent by occasionally oiling the face of the strike with a heavy oil which will not readily disappear.
Fig. 28. Mortise Lock.
Fig. 29. Unsatisfactory Outline for Latch Face.
Fig. 30. Better Outline for Latch Face.
In a large majority of cases, this latch (Fig. 28) will perform all the necessary functions of the lock and latch for outside doors if it is arranged with stopwork on the face. By pushing in one button, it can be operated from the outside only by means of a key; by reversing the button, it becomes a latch operated by knobs from both sides. Under the former condition it is as secure a lock as is the dead bolt operated by a key independent of the latch - a device which, while often considered a necessity for outside doors, is rarely used.
Inside doors rarely require a lock; and where they are not really needed, it is not wise to arrange for a possible future need, since in most cases, if such need arises, the keys will either have been lost or have become hopelessly mixed.
In selecting door locks, the first and most important consideration should be given to the latch lock. A type with the heaviest mechanism and best materials in the smallest case, should be selected; and that type, in one of its various forms, should be used throughout to the exclusion of all other forms, unless unusual conditions require other appliances - as, for example, where doors are to be locked from both sides, in which case the dead bolt is necessary, which can be operated only by key from either side. With this, as with all hardware, the simplest form is the best. Locks which have peculiar combinations, such as turning the key in a certain way to operate one bolt, and further in the same way or in an opposite direction to operate the second bolt, are to be avoided. They afford no additional protection, and are often confusing in the extreme to the owner. The distance between the center of the knob and the face of the lock should never be less than 2¾ inches, and it is better to be 3 inches. If less, the fingers of the operator will be pinched between the knob and the doorframe.
Fig. 31. Latch-Key of Flat-Key Type.
Fig. 32. Common Type of Bit Key.
The key is an important item, and selection of the style of key should always be with strict reference to the use of the lock. The latch-key will be in daily use and carried by several persons, and should be of the smallest flat-key type (Fig. 31), with a distinctively shaped hand end so that it can readily be distinguished at all times from desk or drawer keys on the same ring.
If a dead bolt is used, its key should be of the larger type of bit key (Fig. 32). This is inconvenient to carry away, is not easily lost, and can generally be found at the rare intervals when it is needed.
All keys should be strong, whether flat or bit. Delicate keys are often twisted off when the lock "sticks" a trifle, or - which happens more frequently - when they are not inserted quite far enough before an impatient wrench is given them. Once bent, they are useless. They should be well finished and nickel-plated. Otherwise they will rapidly wear the pocket, and become rusted; and a rusty key will rarely work satisfactorily.