Disc tumbler lock

Not to be confused with wafer tumbler lock

The underside of a disc tumbler lock

A disc tumbler lock is a lock composed of slotted rotating detainer discs. The lock was invented by Emil Henriksson (1886–1959) in 1907 and first manufactured under by the Abloy brand in 1918.^[1]

Design

Disc tumbler locks are composed of slotted rotating detainer discs. A specially cut key rotates these discs like the tumblers of a safe to align the slots, allowing the sidebar to drop into the slots, thus opening the lock. Unlike a wafer tumbler lock or a pin tumbler lock, this mechanism does not use springs. Because they do not contain springs, they are better suited for areas with harsh conditions and are often used at outdoor locations like railroad and public utility installations.^[2]

The classical Abloy design consists of a notched hemicylindrical key, and a lock with detainer discs with holes ranging from a hemicircle (180°) to a 3/4 circle (270°). The key is inserted and rotated 90 degrees. Notches, machined to an angle, correspond to complementary angles in the holes of the discs. Thus, the misalignment of the slots is "corrected" by a rotation to the correct angle. For example, if the hole is 270°, the key is 180°, and if the hole is 240° (270° minus 30°), the key is 150° (180° with 30° notch) of the circle. In addition, there is a notch in the perimeter of each disc. A sidebar inside an opening in the lock cylinder around the discs, and an edge in the casing obstructs the movement of the cylinder beyond the 90°.

When a correct key is inserted and turned, all the discs will rotate so that notches in the perimeters line up. This allows a sidebar to drop from the cylinder into the groove made by the lined-up notches in the disks, so that it does not obstruct the cylinder, allowing the cylinder to rotate and open the lock. If a key with one wrong notch is used, one disc will be rotated to an incorrect angle, thus its notch will not line up with the rest, and the lock cannot be unlocked.

The lock is locked again by rotating it into the other direction, sliding the sidebar back into the cylinder opening and allowing the straight edge of the key to return the discs to the scrambled "zero" position.

The mechanism makes it easy to construct locks that can be opened with multiple different keys: "blank" discs with a circular hole are used, and only notches shared by the keys are employed in the lock mechanism. This is commonly used for locks of common areas such as garages in apartment houses.

Lock picking

Disk tumblers tend to be more difficult to pick than competitively-priced pin tumbler locks, and are often sold as "high security" locks for that reason. Picking the lock is not impossible but typically requires dedicated, professionally-made tools. They may also require relatively more time to pick. The disc tumbler lock cannot be bumped. This level of difficulty tends to drive attention to alternative methods of gaining entry. More expensive locks have 'false gates' which are similar to security pins on pin tumbler locks; catching the sidebar making one think they have picked a disk but in fact they have not.^[3]

The locking mechanism can be disabled destructively by drilling into the lock to destroy the sidebar. Anti-drilling plates can be installed to prevent this.

Alternatively, for cheaper locks, the disks can be bypassed by inserting a screwdriver or similar torqueing device, causing the retainer to pop off and the inside 'guts' of the lock to spill out.^[3] The same effect can be created by turning a torque tool in the lock until the end-cap pops off.^[4] After this, cheap plastic locks can be turned by hand, pulled out with pliers, or deformed by heating – causing the lock to open, or completely fall apart. More expensive disk tumbler locks use metal parts that can defeat this technique or make it more difficult.

References

↑ Emil Vilhelm Henriksson was born in Helsinki, Finland on February 24, 1886. He became a mechanic specializing in office equipment. In 1907, he was repairing a mechanical cash register when he realized that its rotating cylindrical disks could be used as the basis of a lock. After two years, he had developed the first disc tumbler lock. In 1918 he applied for a patent, which was granted on February 15, 1919. Also in 1918, he formed the Ab Låsfabriken-Lukkotehdas Oy company (Ab Låsfabriken = Ltd. Lock Co. (in Swedish) and Lukkotehdas Oy = Lock Co. Ltd. (in Finnish)). (The name was subsequently shortened to "Ab Lukko Oy" and finally to "Abloy".) He died in Helsinki on December 19, 1959. See: History of the Abloy company.
↑ "Notes on Picking Pin Tumbler Locks". Retrieved 30 June 2011.
1 2 bosnianbill. "Defeat Chinese Disc Detainers by Expoliting their Design Defects". Lock Lab. bosnianbill. Retrieved 30 August 2016.
↑ bosnianbill. "Defeating Chinese Disc Detainer Locks Using Torque Tool". Lock Lab. bosnianbill. Retrieved 30 August 2016.

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