Spyderco byte September 2022: Folding Knife Locks and Ease of Use

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RamZar
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Spyderco byte September 2022: Folding Knife Locks and Ease of Use

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Post by RamZar »

Nice rundown on the various folder lock mechanisms in the September 2022 edition of Spyderco byte (there are also articles on MANIX™ 2 LIGHTWEIGHT and the Transition from H-1 to H-2).


Folding Knife Locks and Ease of Use

Choosing the “perfect” folding knife is a very subjective process. And while many knife enthusiasts obsess over blade shapes, grinds, steels, handle materials, and stylistic details, one of the most critical elements of a usable folder is its lock.

In simplest terms, lock mechanisms secure the blade of a knife in the open position so it can be used safely and without fear of unintentionally closing on the user. However, they also do a lot more than that. Because they form the heart of the knife’s mechanical operation, they also determine how smoothly and easily it opens and closes, the strength of its detent or self-close function, and the force necessary to operate the knife.

For casual knife users, these factors help subjectively define the overall user friendliness of a knife. For those who suffer from physical ailments like arthritis or diminished hand strength, this aspect of knife design can make the difference between having a usable tool and one that cannot be operated safely and reliably. To serious users who may have to deploy their knives in defensive or duty-bound scenarios, the stakes are even higher.

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“Spring” Into Action

Regardless of the specific lock you choose, it will typically include some type of spring element as part of the mechanism. Whether it’s a coil, flat, or compression spring or the integral split-liner leaf spring of a LinerLock, Compression Lock®, or Reeve Integral Lock (R.I.L.), that spring typically does two things. First and foremost, it provides movement and pressure to engage and secure the lock. However, just as importantly, it also provides spring pressure to the knife’s detent or self-close mechanism to keep the blade in the closed position when not in use. This latter function is critical, as it ensures the blade stays safely closed when the knife is carried in the pocket. It also has a significant effect on the amount of force necessary to open the blade—and the user’s ability to operate the knife smoothly and easily.

From a mechanical standpoint, the spring pressure applied to the blade to keep it in the closed position can be applied in one of two ways: in the plane of the blade or laterally against the side of the blade. Spring pressure applied in the plane of the blade is typically more intense and often creates a true “self-close” function. When the blade is almost closed, the spring gains mechanical advantage and actually snaps it closed authoritatively. This focused spring pressure also keeps the blade closed with greater leverage, which makes opening the knife a more deliberate effort.

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The best example of spring pressure in the plane of the blade is the tried-and-true back lock mechanism. Its stout leaf spring pushes upward on the tail end of the knife’s lock bar. In turn, that force causes the front end of the lock bar—with the locking lug—to press downward onto the tang of the blade. When the blade is opened, this pressure drives the lug down into blade’s locking notch to secure the lock. When the knife is closed, the flat bottom of the locking lug contacts a flat portion of the blade tang known as the “kick.” This portion of the tang is the forwardmost section of the ricasso (the unbeveled section of the tang closest to the handle) and is located adjacent to the “heel” of the edge.

In traditional folding knives, the kick usually extends downward to prevent the edge of the closed blade from contacting the inside of the handle. During manufacturing, careful grinding of the kick would adjust the seating of the blade in the closed position to ensure the lock bar sat flush with the handle back. Unfortunately, applying pressure to the closed blade or closing it too briskly could still allow the edge to hit the inside of the handle, causing a dull spot.

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Spyderco knives, however, have always used a unique kick design that contacts the inside of the locking bar directly above its pivot point. This design stops the blade authoritatively in the closed position to protect the edge more reliably. It also enhances the locking bar’s leverage on the blade to ensure a strong self-close action.

In a back lock mechanism, the bottom of the locking bar also contacts the radius of the outside of the tang during the blade’s entire opening arc. Because of this constant pressure, the shape of the tang’s outer radius also affects the force necessary to open the blade. In some knives, like the Delica® 4 and Endura® 4, the tang radius decreases toward the end of the blade’s opening arc, making the action feel lighter. Others, like the Native® 5 and Native Chief™, have a tang profile that is concentric to the pivot pin. This consistent radius maintains unwavering pressure throughout the opening arc, but supports the knife’s enhanced back lock geometry and sturdy lock-up.

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Other examples of lock mechanisms that apply spring pressure in the plane of the blade include the Stop Lock™ and Ball Bearing Lock™. Both these mechanisms also maintain constant contact and pressure on the blade tang during the blade’s opening arc, but that pressure is significantly lighter than in a back lock. In the Ball Bearing Lock, the pressure is also applied in a forward direction instead of downward toward the blade’s pivot pin. Together, these factors make knives with these lock mechanisms smoother and easier to open than most back locks. Like back locks, however, these locks still offer efficient self-close functions and, because of their symmetrical design, are completely ambidextrous and lefty friendly. With that said, all lock mechanisms with in-line springs also tend to require a bit more hand strength to release the lock.

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Going Sideways

Lock mechanisms that apply lateral pressure to the side of the blade are again typified by the LinerLock, Compression Lock, and Reeve Integral Lock (R.I.L.). Generally, the lock bars of these knives include detents, most often in the form of a steel or ceramic ball bearing seated partially into the surface of the bar. A portion of the ball bearing is allowed to protrude from the lock bar surface so when the knife’s blade is closed, the bearing can index on a hole in the tang of the blade. Ideally, the bearing doesn’t seat completely into the hole. Instead, its alignment is purposely off-center so it contacts the edge of the hole and applies constant pressure to keep the blade closed.

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Because of the small contact area of the ball bearing and the fact that the spring pressure is applied laterally to the blade, the amount of force necessary to overcome the detent is significantly less than that required for in-line lock mechanisms. Once the ball bearing is out of the hole, the only drag the spring applies to the blade is the top of that bearing sliding across the tang of the blade as it opens. This force is minimal, so after the initial resistance of the detent is overcome, the rest of the opening arc is typically extremely smooth.

If you encounter significant drag when opening a knife with a ball bearing detent, it is possible the ball bearing is “galling” or sticking to the tang surface. To alleviate this problem, apply a small drop of oil or, even better, grease to the top of the detent ball.

Also, if your knife has a R.I.L., pay careful attention to where you place your fingers when you initiate a one-handed opening. If you grip the handle tightly and your fingers press on the exposed lock bar, they will literally drive the ball bearing into the detent hole. That pressure will keep the blade closed at the exact moment you’re trying hard to open it and can be extremely frustrating. Adjust your opening grip of the knife to eliminate the problem.

Locks that apply lateral spring pressure to the blade generally require less force to release than mechanisms with in-line springs—especially if the handle includes a generous cutout to allow easy access to the lock bar. For users with limited hand strength or finger dexterity, designs like the Military™ Model, Tenacious™, Persistence™, Resilience™, and Ambitious™ will be more easily operated than the Bradley Folder™ 2, which is purpose designed to require a deliberate closing effort.

Choosing a knife that works best for you is just as much a matter of mechanics as it is size, style, and ergonomics. Hopefully the insights in this article will help you better understand this aspect of knife design and ensure that your next knife purchase is the right one for your needs.
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