How Your Home Locks Work (Nov, 1946)
How Your Home Locks Work
PSM photos by W. W. MORRIS
1. The simplest, most common door lock is the single-tumbler type, the workings of which are exposed here in an oversized model. The slots in its key are called wards. They are mated with projections inside the lock to permit the key to turn. This type of lock gives little protection since an ordinary skeleton key will usually open it.
2. Inside a one-tumbler lock. The semicircular projection (arrow) just inside the keyhole fits a notch in the rear edge of the key and prevents a strange key from turning.
3. As the key turns, the notch or bitting in its bottom edge permits it to pass along the back of the irregular tumbler (arrow) fixed to the bolt. Without this notch the key would be stopped.
4. The turning key hits a projection (arrow) that throws the bolt forward. The rear-edge ward now rides the semicircular track again and the key can swing around to its starting point.
5. The pin tumbler lock, invented by Linus Yale, Jr., in 1864, was a big step forward. Five small pins, divided at varying points along their shafts, must have these division points lined up perfectly before the key can turn. This cutaway model of a lock, several times actual size, clearly shows that before the key is inserted the pins are held at irregular levels, keeping the cylinder from turning.
6. Insertion of the key lines up the division points of the pins. The lower sections of the pins vary in length so that when each finds its proper notch in the edge of the key it will be lined up. Sloping edges of notches permit the key to enter, forcing each pin up against its individual spring.
7. Here is how the whole lock looks before the key is turned. The cylinder containing the pin tumblers is in the upper right-hand corner. The lever on the end of the cylinder throws the bolt.
8. As the key turns, the pins divide along the edge of the cylinder, permitting it to revolve. The lever that, throws the bolt, screwed to the end of the cylinder, is beginning its turn.
9. Here the lever on the end of the cylinder is partly turned, engaging the bolt.
10. The key has turned the cylinder far enough to push the bolt forward and lock the door. The cylinder can now finish its circuit. When the key is withdrawn the pins will fall out of line again, freezing the cylinder into place.