Knife lock testing

  • Thread starter Thread starter -
  • Start date Start date

I have heard several instances of people 'whacking the spine of the knife' to test the lock. Let me get this straight...open the knife and hit the top of the locked blade against a hard surface to try to get the lock to fail?????

Why would anyone try this potentially damaging test on a knife? And how do you know if a sufficient impulse (force) has been applied? And the results of this test (at least for liner locks) might depend on the adjustment of the liner lock. This testing sounds highly suspect.

This type of testing should be performed by the factory. Maybe we could encourage manufacturer to conduct a standard test could be devised to determine maximum load/moment (in foot pounds) on the blade prior to lock failure. I'll bet those specs would put the liner lock in its place.

Then again, I've bought all the folders I need...moving on to fixed blades.

Rick
 
You raise some very good questions. The fact of the matter is that numerous users have reported on a variety of failure modes of just about every type of folder and that has led to both an increase in interest in testing by individuals and a wider variety of locks to choose from. I see both of those developments as positive and necessary for the betterment of knife design.

I've had liner locks fail under some surprisingly simple normal conditions. Evidently, so have lots of other people. Noted knifemaker AT Barr came out with a series of non-abusive tests so simple that one could easily perform them at any knifeshow prior to purchase. Joe Talmadge tried (and arguably perfected) these techniques to a level that often shows maladjustment and/or early failure rates of a far higher number of liner locks than most manufacturers have caught. That's really the problem in a nutshell. Relying on manufacturers to spot potential real world problems has not proven effective in a highly competitive marketplace. A good many manufacturers have proven time and again that they'd rather market lots of products than market good products.

The idea that something as simple as a mere folding knife must be in perfect adjustment to merely lock open begs the question of why consumers accept such obviously dubious reasoning. For most folks, the only time a mere knife is going to be adjusted is prior to purchase, and that's just clearly not happening and doesn't speak well of the long term durability of a good many knives. Rhetorically, I ask why is it that a good many folks will expect something mechanically complex like a lawnmower to last 10 years or more, but will forgive something as simple as a folding knife if it fails within months?

Suggesting that customers should rely solely on factory provided tests would basically mean that customers revert back to the old school of swallowing any and every bit of offal that various factories and manufacturers deem fit to spew. Let's face it, all knives produced can't all be "the best", or the strongest or any adjective that can be dreamt up. The bottomline is that what is really needed is a reliable, repeatable, meaningful independent assesment of the merits of various knives. Personally, I'm not holding my breath waiting for that event.

Where I do very much like and agree with you is the whole issue of what constitutes a meaningful test. Believe it or not, I've spent quite literally months and years agonizing over that very question. In one weird way, I almost think that knives are too personal and too simple to be completely objectively tested in any meaningful manner. In another light, I think that giving such non-answers, answers nothing and contributes nothing to any meaningful dialogue about the relative merits of various model knives.

So I ask you, what, to you, would constitute a meaningful knife test? I really want to know.

mps
 
Foregoe all the tests to make liner locks fail. Just buy a Sebenza!
wink.gif


Also, I assume this "testing" is done on ones OWN knife and not that of a dealer....
frown.gif




------------------
"Walk softly and carry a big stick"...TR

 
Rick, simple answer to why should it be done, it that there are knives that can handle it easily so what is the advantage in having one that does not. That is the basic reasoning for any test.

As for letting the factory do it - if you want to depend on them that's cool - I definately will not. As MPS stated "here be Dragons".

-Cliff
 
Rick,
After hearing about so many lock failures on models from well-known makers, I've recently made it a practice to test all of my folders, regardless of locking mechanism. Could it potentially damage the knife? Yup. I've been lucky so far but, FWIW, I'd much rather have a lock fail when I am prepared for it than when I'm putting a folder to hard use.

------------------
--+Brian+--
 
To some extent, testing *is* a personal thing. If someone decides the whack-the-spine test doesn't apply to them, so be it. It's their fingers, after all.

That some set of tests is worth doing should be beyond question. There are way too many stories of people getting very badly cut with folders to ignore them. In particular, in the martial arts community, and among people who really use their folders hard at work or doing chores, there's a frightening amount of very bad stories. Typical failures in the martial arts community are when thrusting into something, or white-knuckling the knife. In the utility community, sticking the knife into something and then torquing it, or white knuckling often cause failures.

Any doing any kind of hard use might white-knuckle their knife at some time, and so I feel this is a test that you should always do, with your hand in a variety of positions.

Anyone doing any kind of hard use might end up putting relatively-slow pressure onto the spine, so progressive spine pressure tests are a must. So are torquing tests.

Steady pressure on the lock is very different from impulse-pressure on the lock. VERY. The spine-impulse tests (whack the spine tests) are a little further out there, and I leave it up to the user to decide if those tests are for him. I worry much less about this test for my little gent's folders. For both hard utility and defensive use, I've decided that I do feel my knives should pass these tests, partially because I've heard of knives that pass the steady-pressure tests, but still end up failing in hard use, and we find out later that knife only fails the impulse tests. And since, as Cliff Stamp pointed out, there are plenty of knives which DO pass these tests, I see no reason to make up excuses for the ones that don't.

Exactly what kind of damage do you think you're doing when you do a whack-the-spine test, BTW? In point of fact, this test very often FIXES the locks in question!!! A moderate whack-the-spine can "set" a lock that had been slipping before. Anyone who has done a lot of testing (and I qualify) can tell you many stories about knives failing the tests, and then after one moderate whack-the-spine, the knives stop failing and the locks hold. A.T. Barr and others have specifically mentioned this effect.

If you don't like this test, hey, they're your fingers. Most knife users don't use their knives all that hard anyway, and it's very likely you'll never run into the kind of spine pressure failure that whack-the-spine warns you about. On the other hand, there's so many people who have used their knives hard enough, and who have paid for it with grave finger damage, that I think it's dangerous to ignore this test.

Joe
jat@cup.hp.com
 
Here're some q's for you all:
What constitutes an effective but not necessarily damaging test of lockbacks?

Unlike liner locks, there is some significant danger of simply destroying an otherwise good knife by whacking a lockback hard enough on the spine to cause lock failure. Primary failure points aren't limited to just the lock tooth and notch, but also to the rocker bar and rocker bar pivot pin.

I've thought a bit about how I use a lockback, and I can't really envision too awfully many scenarios where the lock would fail for reasons other than dirt in the lock or inadvertant hand pressure on the release mechanism. Both have happened to me in real life working conditions which is one reason why I'm very curious about other lock mechanisms that seek to address those two failure modes.

Unfortunately, even with some of the newer >$100US knives with supposedly newer and better locks, I can't envision much protection against dirt in the lock mechanism.

Still, getting back to lockbacks, what is a reasonable amount of force that you all would expect the lock to take in both impulse and sustained modes, both forwards and backwards? What's realistic and what's just abusive and pointless?

mps
 
For a hard-using knife, here's the way I've been testing. I don't claim this is the universally correct test, but it's what satisfies me.

Constant-pressure test: I believe a knife should be able to take a lot of constant pressure. I hold the handle in one hand, with my fingers tucked out of the way. I put my palm on the other. Then I try with a lot of force to close the knife. This test must be performed hard -- after all, there are plenty of realistic situations which can put a lot of force slowly on the blade spine. For example, you stick your knife into something and can't get it out, so you start wiggling and torquing it. Numerous people have told me about bad cuts they've gotten this way.

Impulse test: For this, I use moderate pressure at most. I think there's sometimes a misconception that I slam the knife down hard, like I'm using it as a hammer. I tend to do a high-speed but very low-torque whack-the-spine test. I flick my wrist so the knife comes around fast, but put very little real muscle pressure behind it. If I do this against a wooden desk, I usually won't even dent the wood. The reason I sometimes can fail a knife that other people can't, is because they do a hard-pressure whack, and I do a lower-pressure high-speed version. Then sometimes I'll do a moderate-pressure whack to just make sure things are okay, but so far no knife that has passed my high-speed low-presssure test has ever failed any other test.

Joe
jat@cup.hp.com
 
You must log in or register to reply here.
Back
Top