Disc Tumbler Lock

The classical Abloy design consists of a notched semi-cylindrical key and a lock with detainer discs with holes ranging from a semicircle (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 obstruct 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 in 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.