Lock Failure???

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winstonknives

Joined
Apr 24, 2001
Messages
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There have been numerous threads on BF about linerlock failure. For someone to say that a lock "failed" is not valid to me unless they explain what they were doing or how they were using the knife when the failure occured. The very nature of liner lock construction demands that the more pressure applied to the cutting edge, the tighter the lock-up should become. This should hold true for any folding knife. Even slip-joints. Metal does not easily compress "end-ways", even thin pieces. I will not argue that given enough pressure on the back of the blade that a lock leaf could be caused to disengage. In what kind of situation can this pressure be caused? Why would someone beat on something with the back of a knife blade?

I have had a slip joint close on my fingers. I do not remember why, I just remember that it was 50 years ago and I was doing something stupid.

Maybe I am missing something here. Are there uses out there for knives other than as cutting instruments?
 
1: Brand new knife, after approximately 60 openings the liner slid past the blade wedging against the opposite side handle. A previous example of the knife did the exact same thing.

2: Large liner lock would close if I let it fall 1 inch onto my palm (edge up).

3: Expensive framelock. using moderate hand pressure against the back of the blade I could see the lock bar slide backward. Using a bit more pressure would likely cause to unlock completly.
 
winstonknives said:
I will not argue that given enough pressure on the back of the blade that a lock leaf could be caused to disengage. In what kind of situation can this pressure be caused? Why would someone beat on something with the back of a knife blade?

Maybe I am missing something here. Are there uses out there for knives other than as cutting instruments?
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David, I agree that a knife is for cutting. But your view of what that implies is very limited, if you think that the only kind of cutting that applies is cutting where all forces are easily controlled. Or, to put it another way, if you say that a particular knife is useful only as a gentleman's folder, opening mail, trimming nails, and other light uses where the cutting forces can be precisely controlled, then you have a point. But if a knife is meant for anything other than light use, not every force can be controlled all the time. Knives do bind up in materials and get torqued out. If a knife is meant for defensive use, that's a situation where specifically it's impossible to control the forces on the knife. I feel it's very unsatisfying for the response to lock failures to be: "if you were using the knife properly [meaning perfectly controlled edge-to-spine cutting] the lock wouldn't fail". Well sure, okay, then advertise the knives as light use only ... anything other than that, torquing, spine-to-edge type pressures, white knuckling, etc., will come into play, and the consumer absolutely should have an expectation that his lock will hold. The fact that one particular lock format has trouble with some of these things shouldn't mean they are "improper use", especially for a medium-duty or hard-duty or defensive folder. This kind of use is what the knives are being advertised to do!

I won't go through the past many years of stories. Some were doing remarkably pedestrian jobs, e.g., doing some pruning, knife binds in a stem, liner lock releases as knife is pulled out. The number of real-world failures has led to testing. As you probably know, we've figured out that liner locks are particularly susceptible to spine impacts as well, besides torquing and white knuckling. Spine impacts have always been a controversial subject here. I personally feel it's a perfectly reasonable test of basic lock geometry, and doesn't need to be done hard. There are real-world stories of people getting impacts to their blade spine, so it's not completely artificial in any case. But I don't want us to get off track here from the main point: I feel that any argument that labels as "improper" any knife use that isn't perfectly controlled, is out of whack with how knives are really used.

Joe
 
The linerlock that failed on me (CRKT Red Dog) had a wimpy liner, .5cm worth of vertical blade play, and a smooth contact surface. The liner slipped unlocked under rather minimal pressure, jimmying it out of a cardboard box I was cutting. 3 stitches and nerve damage.

Of course, I wouldn't have done the same thing with a slipjoint, but it was my naive assumption at the time that a locked knife would stay locked.
 
It happen to me with a CRKT/Hammond Grey Ghost Mirage (a liner-lock of course).
I was using the knife to remove dirt from the tread of my boots.
Using the spine of the blade I tapped the bottom of my boot to loosen up the mud and dirt (I've did this thousands of times with my old Schrade LB7) and "snap"! The lock failed, the blade folded on to my hand, and I started bleeding.
At first I thought that maybe I did'nt have the blade fully locked.
So after treating my cut, I examined the knife very carefully.
Nothing seemed out of order and when I snapped open the blade, the lock seemed 100% bank-vault secure.
Until I gave it a light spine whack!
Then it folded with the greatest of ease.
That was the truely amazing thing about the failure--the lock seemed so secure but it took so very little effort to make it fail.

Another "lock failure" I had was the Spyderco Vesuvius (a Compression-lock folder).
Now the lock did'nt really fail in respect to holding the blade open, it failed to hold the blade closed.
I was walking up a mountain trail while wearing rather loose shorts, the Vesuvius clipped inside the front right pocket. When I reached inside my pocket to get a piece of hard candy, the blade was half open inside my pocket. I managed to not get cut that time.
Later I experimented with the Vesuvius and discovered that it did'nt take much effort for the blade to open.
I can clip it in my pocket and do a few jumping-jacks and the blade will come open if the pocket is loose enough.

I might be willing to try another Compression-lock folder by Spyderco since the Vesuvius was one of their first models with that lock.
But I will not buy another liner-lock folder--I have heard way too many stories of them failing to feel safe using them.

Now some folks will say that if you use your knife for only cutting, and if you cut with the proper technique, your liner-lock will not fail.
To that I say, then why buy a locking knife at all?
If I wanted a knife that will close on modest spine pressure I would have bought a slip-joint in the first place.

Good luck,
Allen.
 
Thanks for all your comments. It certainly was not my intent to ruffle anyone. My post has had the desired affect. To get some feedback on what was going on when the failure occured. I suppose all mechanical devices can fail under the right conditions. Since the liner lock is otherwise very user friendly as far as one hand operation goes, maybe someone smarter that I will eventually cure some of these problems. Thanks again for your comments and hopefully we will get more.
 
Winstonknives,
Somebody already did cure the liner-lock problem to a great degree.

CRKT now has the LAWKS (Lake And Walker Knife Safety, I think).
It is like a safety lock for their liner-locks. While it's engaged the liner-lock cannot easily fail.

I still think liner-locks are not that great but the LAWKS does seem to work.

Good luck,
Allen.
 
Let's just put it this way. Any folding kinfe can be destroyed. there are some out there who insist on abusing knives and reporting on it. Any locking folder can be broken, its just common sense. I undertsand what you are saying. there are many young people into the "tatical knife" craze that has now been going on for the last 15+ years now. Many of them want an "indestructible" folder. A folder under most all normal condtions will last a long time, if not perhaps for a life time.

Personally, I have never thought of knives as a "tactical" weapon. Even when I was active duty in the AF for 8 years and in desert shield/storm our F/U's were almost never used in defense, or as weapons.

the knives (walker locks, SJ's, fixed baldes) I have made, I make sure it is known that they are for using and not to be abused. They will stand up to normal use, but are not made for prying, throwing, or puching holes through old junk yard car doors.
 
Allen, I go back and forth on the LAWKS. On the one hand, as you point out, it does work. On the other hand ... it seems silly that my lock itself needs another lock. Why not just start out with a lock that works the first time?

In the end, the LAWKS lets me consider buying a liner lock, when I don't buy liner locks from any other company or maker.

Dave, I wasn't ruffled ... I do admit to having a bit of a sensitive spot to the "use the knife correctly and the lock won't fail" argument :) I think the liner lock is just damn hard to get right. I can tell you about liner locks from very high-end makers that I can get to fail, easily. These guys are supposed to be the best and brightest, but when we're talking about a mechanical design that's this tricky to get right, no one will nail it all the time.
 
Hi Joe,

I tested my liner lock by whacking the spine on my palm, is that sufficient for light to moderate duty use? or do I have to do something more drastic?

Thanks very much in advance.
 
Ratcoon said:
Hi Joe,

I tested my liner lock by whacking the spine on my palm, is that sufficient for light to moderate duty use? or do I have to do something more drastic?

Thanks very much in advance.
Click to expand...

The "spine-whack" test is just fine for testing it for blows the to spine, but that is it.

As Joe indicated, there can be many forces at play on a blade depending on how it is used. If you really want to test it, get a kevlar glove and do some real hard work with it, if that is your intended or perceived need. I have had two handmade (custom) liner lock knives fail when just opening some really basic packages, so it just depends on how the forces are applied - these designs can fail, even when doing really simple chores.
 
Architect said:
- these designs can fail, even when doing really simple chores.
Click to expand...

I am sure this is true. But if failures were so widespread, would knife companies continue selling them? I doubt it. Is it true that there have been some liner lock failures but they are nevertheless rare?
 
AT Barr and I wrote a Liner Lock Test FAQ which has some of the tests. I really should change it to just Lock Test FAQ, since I use it to test just about all locks.

Here are the things that worry me most:
1. First, take the knife in your hand. Squeeze it pretty hard. Does the flesh of your fingers squeeze between the scales and engage the lock at all? Can you feel the lock move at all when you do this? If so, that's a huge red flag. Note that with a properly-done framelock, this movement actually reinforces the lockup rather than compromises it.

2. One of the top reasons for failure is torquing. In utility use, this usually happens because the knife binds up in some material or other, and without thinking you try to twist it out. In defensive use, I'm sure you can imagine all kinds of ways this could happen. To test this, I like to immobilize the blade, and twist and torque the handle. Twist it all different directions, and make sure you're squeezing the handle hard while doing it. Feel for any signal the lockup is changing.

3. I like to do a light-to-medium whippy spinewhack on a tabletop rather than my palm. Doing it in your palm gets the worst ones, but it is conceiveable that something strike the spine, and it's not asking too much for the lock to hold. You should hold the knife as if you're expecting the lock to fail (that is, keep your hand out of the path of the blade if it closes), and just flick your wrist to do a whippy snap on the spine.

The other reason people get injured with liner locks (this problem is shared with frame locks) is because there's no spring pressure holding the blade in. A good ball detent will apply some pressure, but often the ball detent is done badly. I like to shake the knife a bit to make sure it won't come open in my pocket, particularly if it's tip-up.

Joe
 
cognitivefun said:
I am sure this is true. But if failures were so widespread, would knife companies continue selling them? I doubt it. Is it true that there have been some liner lock failures but they are nevertheless rare?
Click to expand...

cf: On the other hand, what do most people do with their knives? Pretty light work. Anything can do light work. I've also see that the majority of lock failure stories do not result in injury. Certainly, when I had a lock failure, I "felt" it, and managed to take pressure off the knife before the blade contacting my fingers.

I think a pretty high percentage of us here at bf have seen at least one failure -- and hopefully no more, since we start testing after that. I do know that liner lock failures are not rare in testing, probably much more rare in real life though.
 
Just to add my 2 cents worth, I still have and most likely will buy liner locks or frame locks. Mostly because in the designs currently available which I like, liner/frame locks are all that is available. That being said, I consider them light to maybe medium duty knives. When I use them, I use them as if they were a slip joint. I like them better than traditional slip joints because they are easier to open and close one handed. For example, I received a BM 690 for Christmas, and so far like it. I have done the spine whack on a table and it has held up fine. However, even though it is built like a medium duty knife, I will still consider it a easy opening slip joint. If I really need a solid knife, I will always try to use a fixed blade, even though they are less convienient.
 
If you whack the spine on something hard enough I would think that the end of the lock leaf would be permanently deformed (shortened). This should result in over-travel of the lock behind the blade. Not good IMO.
 
cognitivefun said:
For testing a knife's liner lock...is an occasional spine whack good enough, do you think?
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Well... it depends.

I test my locks on any folding knife within the context in which I will use it.

For me, that includes:

- spine pressure: trying to close the knife against the lock (this emulates what happens if the blade is hung up in something dense and I'm trying to pull it up and out)

- light, whippy spine whacks onto hard material such as a book (emulating a knock on the back of the spine, say, if I had accidentally tapped it against the wall or a construction stud)

- harder, deep pressure whacks onto hard material like a box or a bed frame (emulating the same as above, but with more of a "mistake", or perhaps for passing in a SD situation.)

In the three above cases, linerlock failure modes seem to be individually exclusive -- a lock that fails in one of those situations does not necessarily fail in the other two.

I also test torquing the blade in dense material for curiosity, but I try very hard not to do that in real use.

Edit >> By the way, now that I read his post, I think all the tests I do were taken^H^H^H^H^Hinspired by Joe Talmadge's most awesome lock FAQ. :)

-j
 
winstonknives said:
If you whack the spine on something hard enough I would think that the end of the lock leaf would be permanently deformed (shortened). This should result in over-travel of the lock behind the blade. Not good IMO.
Click to expand...
I'm not sure "hard enough" is something I can actually physically manage.

For a couple of linerlocks that I've used, I've tried full-arm swings (yeah, curiosity) onto hard material with no apparent short or long-term damage to the lock.

I'm not using artifical leverage though...

I see considerably more wear from the actual open/close cycles of the lock... it always unnerved me to see all the black powder left on the blade tang mate face area after opening/closing a thin-liner Ti linerlock 10 times (and some framelocks, also.)

-j
 
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