liner lock failure

liner lock or frame lock strength all comes down to a properly built lock. It isn't as simple as just cutting the lock to fit the tang. Where the lock actually engages the on the tang face, how much of the lock actually makes contact on the tang face, is the lock face and the tang face polished, how close to the pivot is the engagement point for the lock, angle the of the tang face. There are some more, but the point comes down to quality of the lock.

I have never had a properly build liner lock fail, even doing a spine whack. I don't generally do a spine whack on a folder, all I have found the need to do is put good pressure on the spine of the knife and see if the blade pulls away from the stop pin at all. I might throw in a spine whack against the palm of my hand. I have found more than a few poorly built locks doing this. I can then return the knife to the maker or company and have no qualms about telling them I didn't abuse the knife.
 
Just exactly how does the spine get whacked when you are holding the knife in your hand in a using grip? Isn't the hand covering the spine of the blade, sorta prttecting the spine?
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Actually, I lhold my folders in a hammer grip most of the time.
This leaves the blade spine exposed.

The spine whack is a valid test, as long as you don't damage the lock face when performing it, I can indicate if a liner lock is properly set up from the maker or not and whether it may have a prediliction towards failure.

Almost all frame locks laugh at the spine whack test due to the added thickness of the lock face and better lock/tang surface area ratio.
 
I agree with Anthony.

I do believe that the spine whack test is a valid test for a knife that is carried for defensive purposes. The odds of a knive's spine getting struck is significant enough to validate this test, IMHO.

Also I have noticed that some of my blades that pass the spine whack test, don't pass the spine "tap" test. A light tap on the spine will ocassionally unlock one of my folders, that a more agressive whack will not. I would think this is a more serious problem.
 
shane45-1911:

Thats a very interesting/good observation and one that should be expounded on by others here.

Very interesting. What have been your observations as to why there is this difference? Any conclusions drawn from this by your own testing?

Inquiring minds, ya know? I think thats more serious as well. I need to know more now as that difference could definately be relevant.

Brownie
 
Originally posted by brownie0486
Very interesting. What have been your observations as to why there is this difference? Any conclusions drawn from this by your own testing?
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I don't know why I have experienced spine whack vs. spine tap failures. Perhaps others have noticed the same phenomenon?

Initially, I am inclined to believe that it is a harmonic vibration/frequency thing - some light taps seem to induce just the right amount of vibration between the locking liner and the blade tang, that allows it to break contact for just the right amount of time to allow disengagment. I'm certainly not a physicist or a metalurgist, but I would suspect that different lengths of liners, and different material properties would lead to vibration anomolies.

So...is it possible that a lighter tap would cause a different frequency of vibration that would allow unlocking, that a stronger "whack" would not??? Wish I knew....but it is certainly a repeatable phenomenon with one or two of my folders.
 
Shane, I have seen this on a couple folders. From what I could deduce on those folders came down to where the lock face engaged the tang. It was close enough to the correct spot, that a sudden impact would be enough to have the lock bend and the lock would then engage the tang in the correct spot. With a light tap, there wasn't enough force for the lock to bend and enage in the correct spot, so it would then slip from the incorrect enagagment point. This was about the time I figured a full power spine whack was no longer needed.
 
Originally posted by Dirk
liner lock or frame lock strength all comes down to a properly built lock. It isn't as simple as just cutting the lock to fit the tang. Where the lock actually engages the on the tang face, how much of the lock actually makes contact on the tang face, is the lock face and the tang face polished, how close to the pivot is the engagement point for the lock, angle the of the tang face. There are some more, but the point comes down to quality of the lock.
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Exactly my point.

posted by Dirk:
I don't generally do a spine whack on a folder, all I have found the need to do is put good pressure on the spine of the knife and see if the blade pulls away from the stop pin at all.
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This is how I test my blades, and it has served me well. As I stated earlier, I've owned high end production linerlocks for several years, and none of them have even hinted to me that they'd fold up during hard use.

This is a great discussion, and I've enjoyed the varying opinions without a flame war!
 
The knife needs to resist closing pressures. The whack is one way to test this, but not exhaustive.

Joe Talmadge often points out the pressure from a palm gently pushing on the spine can make the lock fail, somewhat similar to a tap test. I've had some LLs fail in cardboard cutting from this sort of pressure on the withdrawal. AFCK, Mini AFCK, various CRKTs and such.

Each of these failing knives subsequently also failed the spine whack test.

I've torqued a few to failure in use too.

I believe the LL has it's uses, but not for working/defense knives.

Phil
 
Originally posted by phatch


I believe the LL has it's uses, but not for working/defense knives.
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Phil, I felt the same way until I got my Spyderco Millie. Still, outside of this knife I haven't found a linerlock I really like.
 
Originally posted by CODE 3
I really don't trust the spine whack test as a valid testing procedure, and will NEVER perform it on one of my knives.
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The "spine whack test" has ruined way more knifes then any other test i know of, without saving anyone's fingers as far as i know. It doesn't prove a thing IMO, not the same as using a knife for sure, bad test and i hope some day i will not hear about it anymore, i will thank the gods if that day ever comes!

James
 
Originally posted by brownie0486
Steve Harvey:

You know people who have lost fingers on linerlocks through inadvertently whacking the spine of the knife? If you can, ask them to explain how the spine was whacked under use and get back to us....
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Please do not restate my message incorrectly. Nobody said anything about lost fingers. Nor have I ever damaged a knife in testing the lock.

A search will turn up the threads. I've seen all I need to see, read all I need to read. I could not care less if anyone's mind is changed or not.

I'm tired of this discussion, and the way some people like to make it sound like you are a fool for wanting to have the highest level of confidence possible that a locking folder is going to stay locked unless it breaks.

The fact is, some knives can take it, and far too many liner locks cannot. I choose to limit my consideration of a knife for serious work to those that can.

For those who want to be sure, test your knives however you see fit. They are your fingers. For those who are willing to simply believe that liner locks are reliable the way that some people believe that god will protect them from rattle snake bites, may the odds be with you.
 
Common sense, mine anyways, easily shows that the spine-whack test (SWT) is relevant.

With all due respect, brownie0486 is quite mistaken in his strong rejection of the SWT. His reasoning is quite flawed.

No elaboration. This subject, the spine-whack test and those who love it and those that hate it, has been done to death already. Do a search on Bladeforums.

If I had a brane I'd be
 
Steve Harvey: from your thread sir "The people that have had their fingers cut by collapsing liner locks have done some unfortunately all too realistic testing. They probably would have preferred something less realistic."

You did state cut, not lost fingers. I stand corrected. Please point me to these people who have cut themsleves when the locked failed due to a spine whack and not related to another issue with the knife.

You are certainly no fool to heed others advice if they have actually experienced failure in use by whacking the spine inadvertently. I haven't met anyone of those people in my travels as an instructor/trainee and most carry linerlocks.

I'm sure someone out there knows someone directly involved with this happening, however, the numbers of users who carry them and the number of actual cases of spine whack failure is so negligable as to be of no concern to me when carrying mine.

All of the 50 or so linerlocks I have had from various makers, custom and production, have been reliable and never failed when used. I'm sure that some would fail the spine whack test as well and theres the rub, they may fail that "test" but it has not affected their use in my hands for 15+ years.

It's a test that's irrelevant and has no direct relationship to how well the knife performs in the field. I can get any knife to fail by beating on it enough. Where I don't beat on mine in normal use I see no need to beat on them for tests. On the other hand, if you plan on beating the knife up then perhaps it is relevant.

Brownie
 
______________________________________________________________________
Originally posted by brownie0486
Steve Harvey:
Just exactly how does the spine get whacked when you are holding the knife in your hand in a using grip? Isn't the hand covering the spine of the blade, sorta prttecting the spine?
Brownie
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______________________________________________________________________

Brownie,
I've experienced this problem before.I was working as a loader on a
cargo plane.As we were loading a pallet on the plane,the cargo net
covering the pallet got caught under one of the locks that holds the
pallet in place once it's in position.I had to climb over the pallet
and try to cut the net so that we could slide it the few inches left
to activate the locks.

I wasn't able to get the nylon rope cut all the way through before
the blade slipped causing the back of the blade to contact the
aluminum track.The lock failed with this sort of light tap.Thankfully
I was wearing leather gloves and I lost no flesh,but it did cut the
leather through to the finger.:eek:
Marauder:D

(I guess I should clarify that the whack to the back of the blade
spine was right at the point where the blade pivots in the handle)
 
Marauder:

Understood. Good thing for the gloves.

I had one fail in slashing tests as well with gloves on. It wasn't a spine whack but a worn pivot area which allowed the blade to go further than the stop pin and disengage the liner. Had it fixed and would depend on it again [ this was a custom high end knife from a known maker ].

I'm more apt to change my thinking with actual case history like yours. Murphy follows us bladesmen everywhere we go and if it can happen it will eventually I suppose.

If the angles aren't right [like the recent Emersons I have seen once the customer got it ] on the liners of course they will fail easily. I give mine the strength test to see if they will collpase but I'm no whacker.

Stabbing test performed should give enough shock to collapse a poorly designed linelock which I perform on various blades at the website for all to see. Haven't had one [ even on the thin liners like the CRKT and Cuda EDC ]collapse yet under heaving stabbing into wood.

Brownie
 
I think the best thing about "spine-whack validity" threads is that it feels so good when they're over :)

Sal Glesser once mentioned the following possibility: user is cutting something, the blade gets wedged in, the user pulls the knife out, it gives suddenly and the spine hits something during the ensuing uncontrolled release. I was a bit skeptical at the time, but there are plenty of stories like maurauder's or sph3ric's. Well, maybe not "plenty", but enough to show that it's a reasonable concern. Thus, I believe that's proof enough for the validity of a light-to-moderate spine-whack test.

More philosophically, I think we all agree that pressing a palm to the blade spine to see if there's any movement or release is a perfectly reasonable test. The only difference between that and a light spine whack is the speed in which the energy is dumped into the lock -- certainly the light spine whack doesn't use anywhere near as much force as a typical palm-to-spine test. I'm just not willing to bet my fingers that my knife will never see this type of quick application of force. From the accidental uncontrolled release that maurauder stated, to a hard upwards thrust suddenly hitting a bone in a defensive situation, it's not that hard to postulate why fast application of force to a blade spine is reasonable to worry about. I believe the spine whack shows a fundamental geometry problem in the lock, simple as that.

I also don't buy the "spine whack damages the lock" argument. Spine whacks don't seem to cause problems to any other lock format in the universe except liner locks. If liner locks, and only liner locks, are truly damaged by a light whack to the spine, liner lock fans have even more to worry about -- why is this particular lock format so fragile? shouldn't I consider any other lock format which doesn't have a similar problem and isn't damaged by such a light force? Now of course, there's not the slightest bit of evidence that a light spine whack really "damages" anything except maybe the owner's ego when his high-$$ folder fails.

Lastly, I concur with everyone who has found a light, whippy spine whack can cause more failures than the hard hammer-blow type spine whacks that many people use.

For me, a liner lock is a perfectly acceptable format for a gentleman's knife, where it's light-use duty and the liner lock's smooth action really fits in. For any harder use, pick a lock format that isn't so difficult to consistently build in a reliable manner.

Joe
 
I must say that I agree with Joe on the "test" and its value/effects.

Perhaps I can share another point of view. We feel that it is the manufacturers responsibility to make sure that their locks on folding knives are safe. We have established lock strength standards that constantly tested (broken). Spinewhack test is a required procedure done at the manufacturing level on every knife at the end of assembly and at QC. There should be no reason why an ELU should be concerned about a light tap just to see if the integrity of the lock is there (as Joe mentioned) or even to see if there might be some lint or other material lodged in a location that might make the folder unsafe. I lightly tap the tip spine on a regular basis as a quick test.

This is not "destruction testing", every lock has its limits. Get your hand out of the way of the blade edge and give the tip of the spine a light tap on something hard. Keep in mind that the tip may damage the object being hit, so furniture, etc is not the place. If the knife easily closes as a result of a light tap, then you have probably saved yourself a cut. Clean it to make sure debri is not obstructing the lock and try the test again. If it fails again, put it away, send it back or whatever. A modern very sharp folding knife with a bad lock is a potentially dangerous tool.

On the other hand, custom makers do not have the opportunity and equipment to do constant testing, so it really depends on what you are going to do with the knife. A beautiful custom is a work of art. You would not test art....toss the Mona Lisa like a frisbee to test the strength of the canvas. If a custom maker says he makes his knives for using, then he's more than likely spine whacked the knife numberous times himself and wouldn't might a "light test tap".
On a very expensive art knife that is not going to be used, there is no need to test at all.

Just some thoughts to share.

sal
 
I had a CRKT S-2 that failed and cut me on the index finger once. I just cleaned, lubed and sharpened it and was giving it a little test to see if there was any vertical play just put a small amount of pressure on it and it poped off the lockbar, I got poked pretty good. Im off liner/framelocks, I dont like the idea of the slight angle on the end of the lockbar, there is always a outward force trying to push the bar off the tang...not good. Lockbacks and Axis locks especially, have a nice 90 degree angle between the lockup mechanisms which would seem to make them much more resistant to failure due to slick stuff.
 
Having mulled over the few who have had problems and related such here with unlocking linerlocks by pressure applied to the spine of the knife, I'm going to incorporate the following procedure into my testing of tacticals on www.folders-r-us.org

I already perform stab tests and ripping the knife out laterally for strength of the lock and tip. I'm going to also attempt to draw the knife stuck in the wood backwards against the spine to see if it will release.

I wear gloves and dull the edge in other tests before performing the stab tests for obvious reasons.

Brownie
 
has anyone around here tried putting oil on the lock bar of a a high end framelock/linerlock and tried a strength test?
 
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