Disk Tumbler Locks

Combination or "puzzle" locks were invented to further improve security and the protection of valuables. The older safes and lockboxes were good security devices when they came into the market, but some people became curious and realized that these safe locks had inherent weaknesses. One of the main problems was that the disk tumblers were not mechanically isolated from the bolt that unlocks the safe door. In other words, you could feel and hear the tumblers while turning the dial by applying pressure on the handle of the bolt.

When that problem was recognized and solved, thieves started drilling through strategic places in the lock itself to open it. Knocking off hinges was an all-time favorite tactic as well. Then came punching out the dial shaft, blowtorching, and just plain blowing the door with explosives. Greed can breed great creativity.

The first problem, that of manipulating the tumblers open, was rectified by making use of the dial to operate the bolt upon completion of the dialing of the correct combination. This made it nearly impossible to feel or hear the tumblers. Drilling was deterred by laminating the safe door with hard steel and beryllium-copper plates. The beryllium-copper plates pull heat away from the drill tip quickly, and the bit just spins without effect; drilling can not take place without the generation of heat at the bit's cutting edges. Knocking off hinges was discouraged by using three or more bolts operated by a main linkage network. Punching out the dial shaft to let the tumblers fall out of the way of the bolt was corrected by beveling the shaft into the wall of the safe door.

Presently, safe locks are quite sophisticated. Picking them would require supernatural power. The older safes, however, are much easier and even fun to pick. Picking combination padlocks is a good way to start learning how to open safes, and we will get to them shortly. But first, let us discuss some basic prmciples of disk tumbler locks.

Disk tumbler locks work by the use of flat, round disks of metal or plastic with a notch and a peg on each disk. The notch is called the tumbler gate. The gate of each tumbler has to be lined up with the pawl of the bolt mechanism by usage of the linking capabilities of the pegs.

The first tumbler of the disk tumbler lock (also the last combination number dialed) is mechanically connected to the dial through the safe door. When the dial is turned, the first tumbler picks up the middle tumbler when their pegs connect. The middle tumbler in turn picks up the last tumbler for one more complete turn and the tumblers have been "cleared" - you are ready to dial the first combination number by aligning the last tumbler's gate to the pawl. After you have reached this number or position, rotate the dial in the opposite direction one complete turn (for three tumbler locks; two turns for four tumbler locks) to engage the middle tumbler and drive it to the second combination mlmber. By rotating the dial back into the opposite direction to the last combination number, the bolt can be operated to open the lock, or as in the case of newer safes, the dial will operate the bolt by turning it once again in the opposite direction.

One of the innovations that developed to deter sensual manipulation of combination locks was the use of serrated front tumblers (last combination number dialed). These were designed to foil listening and feeling of the tumblers' gates by burglars.

When the bolt encountered any one of these shallow gates, the safecracker could never be sure whether or not a tumbler was actually aligned with the pawl-bolt mechanism. Some burglars solved this problem by attaching high-speed drills to the dial knob to rotate and wear down the first tumbler's shallow false gates against the bolt, thereby eliminating them altogether, or at least minimizing their effects. Still, today the serrated tumbler is used as an effective deterrent to manipulation in combination padlocks where space is a factor.

Let us move on to combination padlocks. The most common and difficult to open of these small disk tumbler locks are the Master combination padlocks, and they are quite popular. I have had good luck in opening these locks with a wooden mallet or soft-faced hammer. The manipulation of Master combination padlocks is quite easy - I have done it thousands of times, and you can learn it, too. The newer the lock is, though, the more difficult it will be to open at first. If the lock has had a lot of use, such as that on a locker-room door where the shackle gets pulled down and encounters the tumblers while the combination is being dialed, the serrated front tumblers will become smoothed down, allowing easier sensing of the tumblers. So, until you have become good at opening these locks, practice extensively on an old one. Let's try to open one:

Opening A Combination Padlock

Step One

First, clear the tumblers by engaging all of them. This is done by turning the dial clockwise (sometimes these locks open more easily starting in the opposite direction) three to four times. Now bring your ear close to the lock and gently press the bottom back edge to the bony area just forward of your ear canal opening so that vibrations can be heard and felt. Slowly turn the dial in the opposite direction. As you turn, you will hear a very light click as each tumbler is picked up by the previous tumbler. This is the sound of the pickup pegs on each disk as they engage each other. Clear the tumblers again in a clockwise manner and proceed to step two.

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