Locks and Locksets

Control over unsupervised access into a building often relies on keys and locks, which have problems despite some technological advances. There are four major kinds of key-operated locks used on exterior doors: locksets, mortise locks, rim- or surface-mounting deadbolt locks, and cylinder deadbolt locks. Two other kinds, crossbar and brace locks, are more cumbersome and less attractive but offer even greater security.

Locksets for doors, also called cylindrical or key-in-knob locks, are manufactured assemblies of parts that make up complete locking systems. They include knobs, plates, and the locking mechanism itself. In a lockset, the entire mechanism is built into the doorknob. The outer knob has a key cylinder and the interior knob has a pushbutton or turn lever to operate a deadlatch. The deadlatch is a spring latch plus a deadbolt plunger that prevents opening the latch with a plastic card. A cylinder lock (Fig. 37-3) is housed within two holes bored into the door at right angles to each other, one through the lock stile of the door and the other through the door edge. Cylinder locks are relatively inexpensive and easy to install.

While very popular for their trim appearance, all but the most substantial and most expensive locksets offer only limited security. The outer handle containing the

Cylinder lock is housed in two holes at right angles to each other.

Figure 37-3 Cylinder lock.

key cylinder can be sheared off with a few blows from a sledgehammer, and the mechanism can then often be operated with a screwdriver. An exposed key cylinder should be protected with a guard plate if possible.

A door is held shut by a spring latch that moves when you turn the handle or that is pushed back when its slanted face hits the strike plate on the jamb. The strike is a plate with a recess for the deadbolt that is mounted on the doorframe. A door can be locked securely only by a bolt that extends at least one inch into a substantial strike plate. A deadbolt has no spring and is moved by turning a key or lever in a cylinder lock.

A mortise lock (Fig. 37-4) is housed within a mortise cut into a door edge so that the door covers the lock mechanism on both sides. The lock is concealed except for a faceplate on the door edge, the knobs or levers, a cylinder, and the operating trim. The spring latch is operated by a doorknob on both sides, or by a thumb lever above a fixed handle on the outside. Pushbuttons in the edge of the door can block operation of the latch from i Mortise is cut into door edge so that lock is covered on both sides



i Mortise is cut into door edge so that lock is covered on both sides



Figure 37-4 Mortise lock.

Figure 37-4 Mortise lock.

the outside. Security locking is provided by a separate deadbolt that is operated by a key from outside and a lever from inside. The pocket for a mortise lock can be a weak spot in the frame of a conventional wood door. Adding a reinforcing plate is a wise measure.

Unit and integral locks combine the security advantages of mortise locks with the economy of cylinder locks. Unit locks (Fig. 37-5) are housed within a rectangular notch cut into the edge of the door. An integral lock fits into a mortise cut into the door's edge.

A rim lock, also called a surface-mounting deadbolt, or night latch, fastens on the back side of a door stile and has a deadbolt that engages a strike mounted on the jamb. The rim lock is operated by a small knob (thumbturn) on the inside and by a key from the outside. The key cylinder extends through a hole in the door's stile. The deadbolt may move horizontally or vertically into the strike. A vertical bolt is more secure because it engages holes in the strike and cannot be popped out by prying the door away from the jamb. The strike should have an L shape that mounts with screws from two directions. Rim locks are easy to install and provide good security if bolted rather than screwed to the door, and if strike screws reach into the door studs.

A cylinder deadbolt lock is installed in the same manner as a cylinder lockset. A single-cylinder lock is operated with a key from the outside and a thumbturn from the inside. To open a double-cylinder lock from either the inside or the outside, you need to use a key. This prevents anyone from operating the lock after making a hole to reach inside. However, in an emergency anyone inside can be trapped unless the key is immediately available. For this reason, some communities ban double-cylinder locks in residences.

Cylinder deadbolt locks offer excellent security when they are properly mounted in a substantial door. Depending on the design of the lock and the thickness

of the door, some cylinders protrude on the outside. They must have tapered guard rings of casehardened steel to protect them from being gripped with a wrench or attacked with a hammer. A cylinder deadbolt or a rim lock is often used in addition to a mortise lock or a lockset for increased security.

A crossbar lock mounts on the back of the door, with a key cylinder in the center. Turning the key or an inside knob extends two hardened metal bars into metal braces bolted to the framing on either side, or above and below. A brace lock or so-called police lock mounts on the lock stile of the door, above the handle. A removable, heavy-duty metal rod fits into a socket on the floor to provide triangular bracing. A key from the outside and a lever from the inside operate the brace lock. Both kinds of lock offer substantial security, but they are very large and quite ugly.

Interior chain locks or door guards permit opening the door only partway, but offer no security. Surface-mounting sliding bolts offer various degrees of security depending on their size, design and materials. The same is true of padlocks in hasps, which may be suitable where appearance is not important.

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