35. Common-Grade Rim and Mortise Locks. The rim lock, as illustrated in [Fig. 36], is generally used for buildings of the cheapest class, such as tenements and small houses. As cheapness is the controlling factor in such goods, especially the goods made for speculative building purposes, the quality diminishes with the price. For cheap work, rim locks are used on account of their low cost and because they are easily applied. They also require no trim, such as escutcheon plates, etc., and are complete when the spindle and the knob are furnished with them. Rim locks are made in various sizes and either square or rectangular in shape, the long dimension being placed either horizontal or upright. They may also be obtained with either iron or brass bolts, and are furnished with iron, tinned, or nickel-plated keys. The cheapest grades of rim locks are made with two bolts and one tumbler, while the better grades have an additional stop and a slide bolt with three tumblers.
Rim locks are generally constructed of cast-iron, and in selecting them, a careful inspection should be made of the internal mechanism, choosing only those rim locks in which the bolts and the tumblers are constructed of steel or brass. Rim locks, however, are also made of all steel, and these are coming into general use. They present a somewhat better appearance than cast-iron locks, as may be seen from [Fig. 37].
The cast-iron rim lock may also be obtained with an ornamental case. These cast-iron cases, as a rule, are finished in imitation of bronze. Such rim locks, however, are not in general use on account of their somewhat higher cost, and from the fact that their appearance is not greatly improved by the ornamentation.
Fig. 38
Cheap mortise locks, or sets, are also largely used for the more common grades of work. They are sold in sets, that is, with escutcheon plates, etc. of steel or cast-iron, both in plain and ornamental designs, as illustrated in [Fig. 38]. The cheapest lock sets are fitted with pottery knobs, and the better grade, with metal knobs. All of these locks described are of poor construction, as quality is a secondary consideration.
Fig. 39
36. Medium-Grade Mortise Locks.—The locks grouped under the term “medium-grade” hardware have been greatly improved in recent years and are adapted to a large range of uses, but they are especially made for residence work. In dwellings of the better class, the best types of rim locks are used for doors in attics and basements, and for closet doors, but for all other doors, the medium-grade mortise locks are used. These locks are provided with cast- or wrought-bronze lock fronts, are made with from one to three lever tumblers, and have drop-forge steel cases. The locks are constructed with easy springs, which allow the latch bolt to retreat within the case on one light spring when the door is closed, and when the knob is turned, to operate the latch, both springs act jointly in order to overcome the friction of the knob and to throw the bolt back to central position. The mechanism of an easy-spring, mortise knob lock is illustrated in [Fig. 39].
