Deadbolts

Deadbolts - Overview of the deadbolt

- by Andrew Reed

The deadbolt is the most widespread style of bolt lock for a very good reason: it works. The principle is simple enough. With one hinged component – the door – and one immovable one – the framing wall – the best way to keep them together is to connect them with a strong shaft that penetrates from one into the center of the other. There are two aspects of the shaft – length and strength – that make a big difference to the efficacy of the lock. The length of the shaft allows it to penetrate farther into the immovable frame, and its strength makes it more or less possible to cut through. Much of the value of a long shaft has to do with physics.

The pressure necessary to push the shaft of the deadbolt through the frame increases in proportion to the depth it’s embedded in the frame. I’m not a physicist, and the way geometric progressions work is something like a foreign language to me, so I won’t even try to explain them. What’s important to know is that if the shaft pushes one inch past the strike-plate into the frame, it takes far more pressure to break through the frame than if it penetrates only one-half inch, for the simple reason that there’s a lot more frame material – usually a wood or aluminum stud, but sometimes a steel door jamb – that has to be pushed through. As for strength, deadbolt shafts are made of many materials, the most common of which are steel and steel alloys. Steel can be manufactured in a variety of ways that strengthen and harden it. Tempering Steel is made of iron ore, and its properties have been known for nearly two thousand years. Unlike wrought iron, which is relatively soft and workable, steel is iron ore smelted with carbon. The carbon is usually a very small component, from .4 or .5 percent to just over one percent, but it’s essential to make the ore workable and subject to hardening.

The greater the amount of carbon, the harder the steel can become if it’s treated properly. Thus the term “carbon steel.” Iron carbide found in or added to iron ore mixes uniformly with the iron molecules when the metal is heated above a critical temperature, and it cools into a crystalline structure. If the molten metal cools slowly (anneals), the crystalline structure of the iron carbide is relatively soft, but if it’s cooled quickly – by being dipped into water, for example – the crystalline structure is extremely hard. But the harder the steel after cooling, the more brittle it is, as well. In order to remove the brittleness, it must be reheated (to anywhere between 450 and 1,350 degrees), and the proper procedure allows it to be reheated without losing its strength. The reheated metal can be worked into all sorts of useful objects like deadbolt shafts that, when cooled again, are far harder than nontempered metal. Other materials can also be introduced into the steel during the smelting process to add to the strength provided by the iron carbide. Zinc, chromium, manganese, titanium, and nickel are among those frequently found in steel alloys. A third factor that impacts the level of security offered by a deadbolt has little to do with the bolt itself.

That factor is how the strike-plate is attached to the immovable frame. Since the strike-plate adds great strength to the frame (it’s a lot easier to splinter wood than to bend steel and steel alloys), it’s crucial that the strike-plate is strongly attached to the wall stud itself, not just the door-jamb that frames the doorway. That means using long screws, generally at least three inches, to bolt the strike-plate into the building stud. Most deadbolts slide horizontally from the door into the frame, but for many homes with sliding glass or double French doors, a different application is needed. Vertical sliding shackle bolt locks pin the door into its frame at the top and bottom. For sliding doors, they can keep either door from moving; for French doors, if one of the two movable doors is solidly bolted into the frame, it functions as a frame itself to keep the other from being pushed in. Depending on the design of the doors and the bolt you choose, the shackle bolt can go directly into the framing timber or into a metal shackle attached to the top frame. A bottom shackle bolt can go directly into the floor joists or sub-floor. Whatever your house or apartment design, you should make sure that every exterior door has some kind of deadbolt. The experts at Mr. Locks, Inc. will be glad to provide your house and your doors with the security your family deserves.