Folding Knife Locking Mechanisms
Estimated reading time 4:20 minutes
Pocket Folding Knife Locking Mechanisms
The first pocket knives in history were used in ancient Rome, but they did not have any locking mechanisms and were held open solely by the friction on the inside of the handle halves. Today, these simple knives are known as friction folders. In order to make the operation of pocket knives safer, numerous mechanisms have been developed over the centuries with which the unfolded blades can be locked. We would like to briefly explain the functions of the most common designs today.
FRAMELOCK
This blade lock was invented by Chris Reeve, who originally coined the term Integral Lock for it. The mechanism is based on a locking spring that is part of the handle frame, which is usually made of titanium or aluminum. The locking spring is a latch cut lengthwise into one of the two handle halves, which is pre-tensioned. When the blade is unfolded, this latch snaps under the blade root and blocks it. To be able to fold the blade back in again, the locking spring is pushed to the side. When closed, a ball pressed into the locking spring (detent ball) snaps into a tiny recess in the blade root and prevents the blade from opening accidentally. The relatively simple construction allows framelock folders to be very flat. To reduce wear, some manufacturers have started to mount a replaceable steel plate at the contact point between the aluminum or titanium spring and the blade root, which prevents direct friction between the softer materials and the steel blade root. In addition, some framelock models have an over-stretch protection: a small disc screwed onto the handle prevents the spring from being pushed too far outwards when unlocking. This disc can also take on the function of an additional locking of the locking spring.
BACKLOCK
The backlock is a tried and tested mechanism that originated in the 19th century. The design consists of two components: A locking lever is kept under tension by a spring anchored at the rear end of the handle. At the front end, the lever with a hammer-shaped head engages in a correspondingly shaped groove in the blade root. To release the lock, the lever is pressed down against the pressure of the spring. There is usually a crescent-shaped recess at the rear end of the handle that allows the lever to be pressed down. However, there is also a variant in which the pusher is attached in the middle of the back of the handle (mid-backlock). Even when the blade is folded, the locking lever presses on an edge of the blade root to prevent the blade from opening accidentally. Due to the symmetrical design, backlock folders are suitable for both right- and left-handed people.
SLIPJOINT
Around the middle of the 17th century, English knife makers invented the back spring. The spring mounted between the handle scales presses on a stepped recess in the blade root and thus prevents the blade from folding in. This mechanism, known as a slipjoint, is not a locking system in the strictest sense because the blade does not have to be unlocked before the knife is closed. When folding in, the blade only has to overcome the resistance of the back spring. The spring tension also prevents the blade from accidentally folding out. Slipjoint knives are particularly popular in Germany because they are not prohibited under current law. One disadvantage of this type of pocket knife, however, is that the blade can fold in accidentally if used carelessly. To make operation safer, some slipjoint models have a so-called half stop: when the blade is closed, it clicks into place at the 90-degree position, which is noticeable, so that the fingers are protected.
LINERLOCK
The liner lock mechanism, perfected by the American knife maker Michael Walker, is often used in pocket knives whose handles are made up of metal plates and handle scales attached to them. Similar to the frame lock, a locking spring ensures that the blade is locked in the open position. In contrast to the frame lock, however, the locking spring is part of the plate and is therefore much thinner. In handle designs without plates, the spring can also be inserted into the handle scale as a separate component. When the knife is opened, the spring slides under the usually beveled stop of the blade root. If the spring is pushed to the side, the blade can be folded in again. A detent ball holds the closed blade in the handle. Even if the locking spring is usually much thinner than in the frame lock, the liner lock is a very reliable locking mechanism. A disadvantage of both systems, however, is that they are usually only designed for right-handed use. Only a few manufacturers offer special left-handed models.
BUTTONLOCK / PUSH BUTTON
The design of the push button lock, also known as a button lock, consists of a locking bolt mounted on a spiral spring that can be pushed down through a hole in the handle. When the blade is unfolded, the blade root slides over the widened base of the bolt and pushes it down. The widened base snaps exactly into a corresponding recess in the blade root and thus locks the blade. If the bolt is pushed down using the push button, the part of the bolt with the smaller diameter releases the blade root again. When the blade is folded in, the spiral spring pushes the bolt into another groove that is shaped so that the blade is reliably held back in the handle.
HIDDEN LOCK
Technically not a different lock system, but we would also like to point at hidden locks. Due to governments worldwide trying to restrict peoples ability to defend themselves, all kinds of knife restriction laws have been made. Automatic opening knives often fall victim to these laws. So knife makers in the past were creative in making knives look like non-automatic opening knives. Nowadays hidden locks are becoming in style again. In the knife shown below, the (slide) button is hidden in the bolster.
