August 02, 2006

Blades : Linerlock

When picking a folding knife, a big concern should be the existence and quality of a locking mechanism. No fear is more common among new knife owners than that of chopping their fingers off by closing the knife wrong. A good lock will prevent that from occurring in any circumstance. Note that some areas do regulate the carry of locking folder knives, as they may be considered straight knives (such as in the United Kingdom).

The most common type of true locking blades I see today is the 'linerlock'. It's not quite as simple as the lockback or as secure as a framelock, but it is fairly inexpensive and reliable. And, unlike the ubiquitous slipjoint, a well designed linerlock is secure enough to be used without risk of removing digits.

A linerlock knife snaps open a piece of the liner (the metal care the knife normal rests in), usually through spring or metal memory action, to lock the tang and shoulder of the blade in place. The linerlock is then shut back by pressing the liner back in place by the frame and applying pressure to the knife. This can be done fairly easily one-handed, although for safety's sake, I suggest doing so very carefully until you've mastered it.

How do you look over a linerlock?

First, ask if the knife's current owner would mind. It's just polite : you don't handle someone else's property without permission.

Second, look the knife over. The blade should open smoothly, with no grainy spots or strange points of higher resistance. Linerlocks should make an audible click sound when opened - this is not just a safety feature to tell you the knife is or isn't locked, but also a sign that the lock is opening instantly. When closing, it should make a similar sounding, if softer, click. The blade should not show any lateral movement no matter the position, and when locked, should not move at all. If any of the above are not true - it doesn't "walk and talk", or it has significant play in the joint - put it down and walk away.

Next, grab the knife between the thumb and forefinger of your non-dominant hand (as if it were a pen) with the blade pointed upwards and the joint right next to your thumb. Carefully open the blade with your dominant hand, and lock it open. Keep the path of the blade, were it to close, clear. Press gently but firmly against the spine of the knife, and watch the linerlock for any deformation. You shouldn't see anything significant, even in beat knives.

Finally, after you're sure the knife is satisfactory otherwise, lock it open. If possible, find a magazine or pull out your wallet, if not, the arm works. Continue holding the blade by its sides, and keep your fingers outside of the blade's path if it were to shut. Gently rap the spine of the blade with your magazine or wallet, or against the back of your arm. Don't hit anything hard: a bad linerlock will either fail with a small amount of pressure, or you'll be fine with it until you're reaching forces where the metal is about to break (at which point the knife's condition is not going to be at the top of your list, compared to the condition of your fingers). This is called the "spine whack test", usually attributed to a Joe Talmadge.

For the last two tests, be gentle. A lot of force there can be very hard on your blade even when it survives them - the majority of folding knives are not intended for use as hammers. For all normal situations, you do not need to know the strength of a lock, only that the knife's lock is reliable. A knife that will pass the above tests won't close on your hand when a bad slip causes your hand to hit a wall or board, and won't slam back on you should you need to thrust with the blade. It even mirrors a majority of the typical counters to a folding knife, such as a koppo stick to the spine.

A good knife doesn't have to be expensive, nor can you assume that an expensive knife will be good. Only by testing can you feel secure.


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