# what's the spine wack test ?



## radu1976 (Jan 19, 2009)

I have read this : to test the reliability of the locker , you must do a spine wack test ...what does it means ?
This :
http://www.youtube.com/watch?v=v7PnQA7ZPwE ?


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## 65535 (Jan 19, 2009)

It's a bad idea and it hurts the knife. Like hundreds have said before, many people do every reasonable thing you would use a knife for without a lock at all. I would not use the spine whack or any lock abuse test to mean much about a knife.


The "test" just shows if the knife will fold from a sharp blow against the lock face.


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## Guy's Dropper (Jan 19, 2009)

Having a locking knife is not all that important to me. However, if it was, I don't see what would be wrong with performing the spine whack test. If the lock was good enough, there would be no damage. If it failed, well, better fail during the test than fail during real use. Damage would only result from a failed test.


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## Th232 (Jan 19, 2009)

The main problem (apart from damaging the lock) that I've seen with the spine whack test is that a spine whack is essentially a sharp blow that allows things to bounce about, which can get confused with a gentler but more constant pressure on the spine of the blade.

As 65535 said, it causes damage to the knife (a force analysis makes for some disturbing reading), and then the question you want to ask yourself is: "Will I be comfortable using a knife which I might have already damaged?". Of course, the extent of the damage is up for discussion.


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## chmsam (Jan 19, 2009)

A test like this should be performed by the maker only, to test the strength of the design. Good enough to know that the test (or other stress test) has been done at some point during the manufacturing and design process. Doing this to a knife you intend to use makes about as much sense as ramming your new car into a tree to see if the airbags work. Also, the video does not include information about how the knife had been used or abused prior to this stunt. It is good to consider how rare it is for a user to subject the knife to such a sudden impact to the spine of a knife in the locked open position. 

While it is smart to be aware that this could happen to a design of a lock, this specific test reminds me of a car safety test in which the car was driven on wet pavement and jerked from side to side repeatedly. Amazingly enough when the steering wheel was released the test group found that the car lost control. Who would have thought it possible!?! :shakehead Sheesh! 

A better indication of the strength of the lock is to simply look at the mechanism to see how much of the lock engages the lock spring or stop. I would not trust a lock that only engages on the edge or that has a significant amount of the lock overhanging the edge of the spring or lock stop. Better lock designs have beefier locks and engage at or near dead center of the spring or stop. It is a smart move to examine all locking knives to see if this is the case as an error in assembling the knife can cause the failure of an otherwise well designed and built knife. 

I also test the lock of each knife I handle by flexing the blade. There should be no up and down motion against the lock and hopefully little or no flex from side to side as that might possibly cause the lock to slide off the lock spring or stop.


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## RA40 (Jan 19, 2009)

This guy has no clue... 

This is not a typical force the knife will be subjected to in normal cutting use. The big thick side locks are more tolerant in wear because they have much more material to support the blade, this is still not an appropriate "test" of a folding knife. By doing this spine test, it takes many-many opening and closings off the lifespan of the Ti. Depending on harshness, I'm talking years of what would be normal lock engagement. Lock engagement and detent firmness is easily checked in a gentle manner and by ear. As far as what I experience, a lock is typically well seated at about 50-100 openings. May take more if not well cut initially.

Abuse like this is why we have lawsuits. Guys like this use a tool in the wrong way and when it fails resulting in injury they blame the object rather than their brain-dead use.

Like this: 
http://www.youtube.com/watch?v=ybXe4khkLP0


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## PG5768 (Jan 19, 2009)

I ran across a discussion on this topic a little while ago. Here is a link to a Spyderco Forum thread. Post #5 by STR is what you should take a look at.

http://www.spyderco.com/forums/showthread.php?t=29377

He's not a fan of the "whack", but does recommend testing locks.


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## cl0123 (Jan 20, 2009)

PG5768 said:


> I ran across a discussion on this topic a little while ago. Here is a link to a Spyderco Forum thread. Post #5 by STR is what you should take a look at.
> 
> http://www.spyderco.com/forums/showthread.php?t=29377
> 
> He's not a fan of the "whack", but does recommend testing locks.


PG5768, 

Good read! Thanks!

With Aloha, 

Clarence


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## PG5768 (Jan 20, 2009)

cl0123 said:


> PG5768,
> 
> Good read! Thanks!
> 
> ...



I'm still learning and more than happy to share what I find.

Mahalo.


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## Kiessling (Jan 20, 2009)

Good thread, thanx. 
bernie


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## Outdoors Fanatic (Jan 20, 2009)

A spine whack test will NOT damage a good-quality, well-made, strong lock at all. I'll quote Mr *Sal Glesser*:



> The question that you are asking is far deeper and more complicated than it might appear.
> 
> Regarding locks, reliabilty and strength are two very different questions.
> 
> ...


 :thumbsup:


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## Th232 (Jan 20, 2009)

OF, maybe my eyesight is going, but I don't see any reference in that quote (or in the thread it came from) to a spine whack not damaging a lock. Info regarding strength and reliability, yes, but not regarding a spine whack. Actually, I didn't see any mention of the words "spine whack" in that thread. 

If you push a material beyond its yield strength, it'll permanently deform, and with a spine whack, it's actually rather easy to put that much pressure on the material thanks to leverage and a very small contact area. Simple physics and material science. STR's post in the link above provides more info on this.


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## Outdoors Fanatic (Jan 20, 2009)

Th232 said:


> OF, maybe my eyesight is going, but I don't see any reference in that quote (or in the thread it came from) to a spine whack not damaging a lock. Info regarding strength and reliability, yes, but not regarding a spine whack. Actually, I didn't see any mention of the words "spine whack" in that thread.
> 
> If you push a material beyond its yield strength, it'll permanently deform, and with a spine whack, it's actually rather easy to put that much pressure on the material thanks to leverage and a very small contact area. Simple physics and material science. STR's post in the link above provides more info on this.


What I was trying to demonstrate is that a truly heavy-duty folder (As Spyderco classifies as being heavy-duty) cannot be damaged by a simple spine whack test according to that scale above. There is not enough force in such test to even "tickle" a strong lock.

If your folder is considered to be heavy-duty and a snipe whack test (whacked by a human, I mean. Not by an hydraulic machine...) manages to damage its lock or made it fail, then I am truly sorry, but you bought yourself a real piece of crap knife.

I've tried to brake a Native and I couldn't, and this knife is not even classified as being heavy-duty by Spyderco...


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## Th232 (Jan 20, 2009)

I can see what you're getting at, but I beg to differ. 

The numbers given by Sal say when the lock will _break_, not when the lock will be _damaged_. While the lock might fail at, say, 200 inch/lbs (when the weakest part reaches its ultimate tensile strength), it will most definitely be damaged before that point (0.2% yield strength as a general benchmark, but probably even less), almost definitely to the point where any sane person would retire it. From the materials and mechanics courses I've done, I also recall differences between gradually applied loads and suddenly applied loads, but I can't remember how different they were. Suddenly applied loads did cause a fair bit more damage though.

For an example, if a particular car will be completely destroyed if it crashes into a brick wall at 100 km/hr, we won't say that it's fine if it's only crashed at 60 km/hr, it might be repairable, and possibly drivable if you're lucky, but nobody would say that it's ok to crash the car at 60 km/hr, much less do it repeatedly or put the car back on the road without repairing it first. Damage will occur proportionally to the speed the car hits, not all suddenly appear once we exceed a given threshold. Same deal with knives, after the yield strength is passed, damage will occur according to the stress-strain relationship of that material, so it'll deform before it breaks.

I'd be interested in seeing a video of how much deformation takes place from 0 force to the breaking point of the knife. Only question is how quickly they'd add a load, since if it's done too fast the deformation might be too quick (or too small) to see.

I would also recommend looking over the post made by STR in the link above, he's got considerably more experience than me in knives that have been damaged in this way.


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## chmsam (Jan 20, 2009)

I'll stick to what I said in my original post. Tests by makers or manufacturers under situations to simulate actual use or to test the limits of a knife are one thing but the video of the spine whack "test" seems to me to be abuse and I can't easily imagine it being anything close to what would happen in a real world scenario. Better, far safer, and easier to just flex the blade while locked and also examine the locking mechanism to see how well made and designed it is.


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## jzmtl (Jan 21, 2009)

Outdoors Fanatic said:


> What I was trying to demonstrate is that a truly heavy-duty folder (As Spyderco classifies as being heavy-duty) cannot be damaged by a simple spine whack test according to that scale above. There is not enough force in such test to even "tickle" a strong lock.



From what I can tell spyderco's test is static load, not shock load like spine whack.


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## cl0123 (Jan 22, 2009)

PG5768 said:


> PG5768 said:
> 
> 
> > I ran across a discussion on this topic a little while ago. Here is a link to a Spyderco Forum thread. Post #5 by STR is what you should take a look at.
> ...



Not that I usually have a lot of hardcore cutting chores, but thanks to some of the generous wisdoms shared in CPF, I may have just avoided injuring myself or the church kids that sometimes share my tools. Here's my: 
Pseudo Slip Joint Knife​
Many years ago, the CRKT folding knife shown above was left inside my car after some _entrepreneur(s)_ decided to _acquire_ the stereo gears :thumbsdow. They were never apprehended but left that blade behind, which also matched the pry mark left on the lock outside the passenger door. This knife re-surfaced from the back of my kitchen drawer a few weeks ago, and I put a razor edge on it on waterstones. I don't know enough about the different steel types but this one sharpens really easliy. Anyway, knowing the vulnerability of the lock on this particular knife, I will be more careful in letting anyone uses it. 

:twothumbs to *PG5768* and *STR* :twothumbs

With Aloha, 

Clarence


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## asdalton (Jan 22, 2009)

jzmtl said:


> From what I can tell spyderco's test is static load, not shock load like spine whack.



This is an important distinction. "Whacking" and similar impact testing actually tests the tool's ability to absorb _kinetic energy_ without breaking. This capacity cannot be inferred from a static force test.


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## 2xTap (Jan 22, 2009)

I have been in numerous discussions of this type on many a forum, and here I will say what I have always said in regards to such "tests" and the use of folding knives with locks. A knife with a folding blade is just that, and should be used as such. Never trust a lock. You'd never point a loaded gun at a friend or family member if the safety was on, in the same token don't use a folding knife in a way any pressure could be put against the back of the blade that could cause the blade to close on your fingers! Don't trust it, regardless of the make.

I have carried slipjoint pocketknives since I was very young, I have never had one close on me and yet every single slipjoint I own would fail a spine-whack test every time.

I have never had any folding knife close on me in use, locking or other, if you use a knife as it was intended to be used no one would. If you use any folding knife in a way that puts undue pressure on the spine......THEN YOU ARE USING THE WRONG TOOL FOR THE JOB!

Knives are designed and intended to cut things, they are not pry bars, they are not hammers, and they are not screwdrivers......such chores are why we have Pry Bars, Hammers, and Screwdrivers.

2xTap


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## StriderSMF (Jan 22, 2009)

+1:thumbsup:Tottaly agree its a stupid test.you wont see me driving my car into a wall to see if the airbags work.


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## cyberspyder (Jan 22, 2009)

StriderSMF said:


> +1:thumbsup:Tottaly agree its a stupid test.you wont see me driving my car into a wall to see if the airbags work.



Best analogy...guys drop this. It has been rehashed many times, and it is a useless test. I wonder why most people even knifeworthy people don't do this. Reason? there isn't a need to because maybe one in a million knives will be subjected to this kind of force naturally. Drop this. 

EDIT:

Because of stupid retards on youtube, and the fact that youtube is taking over the internet, newbies will take that as an actual test and believe it. Do the right thing, spread the word around about how this is unsafe and stupid.


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## dano (Jan 22, 2009)

It's a complete load of crap that doesn't test anything that a folding *liner *lock style knife should endure during normal usage. Folding knives are not that strong, and it isn't too difficult to get ANY folding knife to fail by hitting the back of the blade, against the lock.

Smacking the back of a blade of a liner lock knife is supposed to "test" the geometry of the mating surfaces of the liner and the tang of the knife; the small area (and it's actually a very small area: a correctly designed and constructed Walker Linerlock should not have full contact with the lock face and tang) of the tang should be angled in such a way that it will not slip or fail when the back of the blade is smacked against a hard surface.

If the blade closes, the lock is considered a "failure" usually in the geometric angles of the mating surfaces. Yet, this same knife, when tested by a more logical test (the constant direct pressure on the back of the blade) may not fail. So, what's more realistic: hitting the back of the blade or applying constant pressure?

The internet mall ninjas will say that the knife user may, in some fantasy, may have the back of the blade hit in such a manner that the lock will fail. Therefore, this failure makes the knife in question unacceptable to use.

Applying constant pressure to the back of the blade will yield results that may indicate a truly defective or compromised lock, and it's a much more realistic "test" of a liner lock's strength.

The Spine Whack, as I remember has it's origins on the old Knifeforums.com (before the split when bladeforums.com was created). It might even go a bit farther back to the early days of Usenet's rec.knives, which would be 1995/96, about fours years after the introduction of the first tactical liner lock production knife: Spyderco's C15 (which was actually produced by Benchmade for Spyderco). The mid-90's saw an explosion of liner lock knives, some of which were crap, as not to many production knife companies understood how to manufacture a correct liner lock, thus someone (names with held) created the Spine Whack Test.

-dan


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## cfromc (Jan 23, 2009)

I will admit that several, several years ago I saw or heard about these "tests" and decided to test my collection. This may have been in the mid-90's, its been awhile and I don't think I still own any of those knives. What I found was that most or all of my liner-lock and cheap knives failed the test easily while many of the more expensive ones either did not fail or it took more effort to make them fail. I "learned" which lock type failed easiest. Due to the results of that "testing" and a few unintentional lock disengagements while I was using liner-lock knives, I decided to sell all of my liner lock knives and now all of my knives are axis-lock, lockback, or slipjoint. I liked the liner locks because of the quick opening and the large variety of knives that use that system but sometimes when I grip the knife and use it the lock disengages. I know many people use them without problem but for me the axis-lock offers the same benefits (although less variety) and you do not need to place your finger in the path of the blade when closing the knife.


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