Spine test Question

[Marek]

What are your opinions on the "spine test"?
How valid is this test to everyday use?
I recently read an article in Blade magazine in which a maker states that the folding knife was never meant to be used that way and will not take that kind of "abuse". I have to admit he might have a point here. Is there another method to test the lock strength that might be better?

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Tough times don't last,tough people do.

 

[misque]

I was doing some cutting on some fairly thick cardboard one day when the knife slipped and did a 180 on me. Before I could stop, the blade went thru the cardboard at a bad angle and the knife handle slid around in my hand and was spine down on the table with a lot of my weight on it. It all happened so fast, I could not believe what had just happened. Fortunately, the lock did not fail and no damage was done. However, had the lock failed at this critical point, I could very well have severely cut or even lost a thumb. This incident convinced me that strange things can and do happen when using knives hard and one should look at all possible problems that might crop up when using a knife.
This is why I believe the spine whack is a valid test that should not be taken too lightly. Others will contest the validity of this particular test, but after this incident happened to me, I'm convinced that the Spine Whack has it's place in the realm of folder testing. One may go an entire lifetime of knife use without an accident, but all it takes is one time to change one's life forever. I'm a firm believer in "better safe than sorry".


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The individualist without strategy who takes opponents lightly will inevitably become the captive of others.
Sun Tzu

[This message has been edited by misque (edited 04-15-2000).]

 

[synergize]

How do you do a proper Spine wack, with cutting yourself? Do you let the knife fall free after
the wack or what?

 

[Marek]

synergize
Your questions are partially the reason for my post. As I understand it the knife is held so that the back of the blade can be struck against a surface with a downward motion. How hard is the blow?,where on the back of the blade is the force concentrated?,where is the handle gripped etc.. These variables would seem to have a great effect on the outcome of this test IMO.


misque, sounds like a close one and clearly illustrates the need for some type of lock strength test. This I agree with completely.
It's the variables outlined above that make this particular test questionable IMO. I would like to see set parameters and procedures for lock strength test that are not open to so many variables. What do you think?

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Tough times don't last,tough people do.

 

[synergize]

I agree with you, doing a spine wack sounds pretty fool-hearty to me, especially since a razor sharp blade has a way to alter flesh rather easily. I still don't see how all these spine wackers do it, they must be partially masochistic to attempt something so stupid. Unless, they have a good supply of sutures or bandaid strips around. I think you let the blade fall to the floor after the test, there is no other safe way to do this.

 

[satherton]

I have to admit that I have never performed a "spine whack test" and I really don't see the necessity of this test. To me, the locking mechanism is a backup to safe knife handling practices. It seems like many people don't pay enough attention to how the knife is being used. When I use a knife, I always subconsciously ask myself, "If this knife slips or get hung up, what will it do?". I want to make sure that I'm not going to lose a finger or get a nasty gash. I consider the locking mechanism just an extra measure of protection. It seems like too many people rely on the lock. A folder is not a fixed blade--you have to respect the compromise inherent in choosing a folder. Now, I don't use my knives for personal protection, so maybe there is some bizarre stress placed on a folder after it enters a body that affects the lock. In that context, there may be some reasoning for the "whack test". But for everyday use, I don't see the relevance. I could be wrong, these are just my personal observations. I have handled knives since I was just a boy and so has everyone else in my family and I've never seen a "whack test". But then again, I came from a small rural town in the midwest. It's just strange to read so many threads about something I've never heard of before. Sorry this was so winded.

 

[Cliff Stamp]

Marek :

I would like to see set parameters and procedures for lock strength test that are not open to so many variables. What do you think?

That it would stop reflecting actual field stress because that is not so precisely constrained and does contain many variables.

Synergize :

I think you let the blade fall to the floor after the test, there is no other safe way to do this.

You can grip the folder by the side of the handle slabs, wear protective gloves, grip the handle with a pipe, tape a protective barrier on the edge, etc.

-Cliff

 

[Rex]

The spine whack test reminds me of the guy who crashed his car into a tree to see if the seatbelt would hold.:rolleyes

 

[Marek]

Cliff,
After reading your reply I went to your site and read some of the reviews you had done on large folders. I think I understand that since the variables that might cause a knife lock to fail cannot be rigidly defined then testing for this also cannot be rigidly defined. This makes sense to me. Looking at the test from this perspective then we can say that the "spine whack" does supply some information on how a lock will perform if subjected to stresses it was not specifically designed for but may occur in the use of the knife.
Whether this test is called "abuse" or not,or "valid" or not then depends on the individual to decide to what standard a knife lock should be held.
I have to agree with synergise & satherton in that I don't think I would test my own knives this way but would be interested in the results of such tests. At the very least a knife lock that performs well in the Spine whack test would undoubtedly perform well under normal use,and we've all seen knives that don't even accomplish that. Thanks to all for the input.

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Tough times don't last,tough people do.

 

[misque]

One also has to keep in mind the fact that knives vary from speciman to speciman. Several times I've tested two or three of the same model of knife and some passed the Spine Whack and others did not. At least two runs of a very popular brand failed the SW time after time, so much so that the dealer told me he was giving up on this particular model and would no longer carry it. Lock strength on a folding knife is very important. It's the only thing keeping a sharpened sliver of steel from guillotining your fingers off in an accidental closure.
While the Spine Whack test is not an end all answer to the question of testing lock reliability, it does have it's place. I say this because I've bought a knife before and after I got it home and played with it an hour or so, I could disengage the lock simply by lightly tapping the thing against the palm of my hand. This is BAD NEWS. A slip joint had more "stay open" power than this knife. If I had to cut something and the knife edge deviated one way or the other during the cut, an accidental closure could have resulted. OWIE!

Satherton,
Sometimes out of neccessity demands are placed on a folding knife that are above and beyond it's intended performance parameters. Sometimes the folder has to do jobs that are meant for a fixed blade knife and circumstances have dictated that no fixed blade is readily available at the time for whatever reason and one must make do with the tool that one has available. This is why the Spine Whack test is relevant, IMO. Now, some folks can go an entire lifetime and their knives see only light to medium duty use as does their friends' and families' knives. The vast majority of my knife use is "light duty". But, there are those times when a heavier hand is needed to make a cut, for whatever reason. Or a mishap during a cut can occur. This is when the security of the lock is most important.
The SW is just a safety measure. No one wants to be caught unprepared.
Now, I agree that a lock is a safety measure, however, all of us who use lock blades rely on that lock to hold. If it fails, blood will likely be shed, and I'm like you and everybody else I know, I am highly allergic to getting cut.

So, I want to insure that my chosen tool is not going to fail me when I need it. I'll test my regular carry knives from time to time just to make sure they are holding up alright. Better safe than sorry. Stay Sharp!

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The individualist without strategy who takes opponents lightly will inevitably become the captive of others.
Sun Tzu

[This message has been edited by misque (edited 04-16-2000).]

 

[Cliff Stamp]

Marek :

I think I understand that since the variables that might cause a knife lock to fail cannot be rigidly defined then testing for this also cannot be rigidly defined.

What you need to do is set the parameters to ranges not specific values. The ranges should be extensive enough to cover the possible field stress that the knife will see. For example when I do spine whacks tests I hold the knife in a variety of positions and hit it multiple times along the back of the blade right up to the tip. I change speeds from light whippy hits to harder more deliberate impacts.


-Cliff

 

[Joe Talmadge]

What are your opinions on the "spine test"?
How valid is this test to everyday use?

I always tell people, if you're convinced the spine whack test isn't real world, that's fine with me, it's your fingers

This is one topic worth doing a search on, it's been discussed in depth in the past ...

I recently read an article in Blade magazine in which a maker states that the folding knife was never meant to be used that way and will not take that kind of "abuse". I have to admit he might have a point here.

I have no problem with that, provided the maker comes right out and says that his knives aren't suitable for hard use. In almost any kind of hard use, torquing, spine pressure, and even spine impact can and do happen. If this maker is making gents' folders designed to clean nails and open envelopes, and he says clearly that these are the limits of his knives, by all means don't spine-whack his knives. Any maker selling knives for "utility", "hard use", "tactical", etc., or who makes claims about the strength, reliability, and toughness of their folders, should expect to get called on it.

The main problem with the spine-whack test is that there are so many badly-done locks out there, that too many knives fail, especially liner locks, which are the hot lock format and everyone's bread-and-butter. Some makers and manufacturers respond by saying the test is invalid, while others respond by studying whatever problems their own locks had and fixing the lock geometry. The second kind are the ones I buy knives from.

I can fail many knives with just a moderate whippy-snap of a spine whack, nothing hard. These locks are not failing due to some kind of structural failure, they are failing due to bad lock geometry and execution, plain and simple. Almost any lock that fails this test will fail under a hard torquing test, too. The spine whack is the easiest way to test the lock geometry, and I claim its results are definitely real world. They're not real world if all you do is open envelopes, but otherwise, they are.

Is there another method to test the lock strength that might be better?

The spine whack test is absolutely not a test of lock strength, it is a test of lock reliability. The distinction is extremely important. There are definitely better ways than spine-whacking to test the lock strength. For reliability, the spine-whack is one of a group of tests I think should be done -- you can read the FAQ here on site to see the other tests (I co-wrote the FAQ with knifemaker A.T. Barr).

Joe
jat@cup.hp.com

 

[Joe Talmadge]

Your questions are partially the reason for my post. As I understand it the knife is held so that the back of the blade can be struck against a surface with a downward motion. How hard is the blow?,where on the back of the blade is the force concentrated?,where is the handle gripped etc.. These variables would seem to have a great effect on the outcome of this test IMO.

As Cliff stated, the knife can be held a number of ways so that the blade on a badly-done lock won't cut the fingers. The method I use is: Open the knife and hold it upside down, handle towards you. Between the thumb and forefinger, pinch-grip the back of the handle -- that keeps all parts of your hand out of the path of a closing blade. And, as Cliff does, I test the knife with a range of force of impacts, and a range of motions from whippy-snap to more hammer-like. I personally usually don't do this test ultra-hard, because if the lock geometry is bad, usually I can see it even with a moderate blow. But other guys like to do the test much harder.

misque, sounds like a close one and clearly illustrates the need for some type of lock strength test. This I agree with completely.

Except that this is a test of lock reliability, not strength. I'd do different tests to test the strength of the lock. Spine whacking is good to test the lock reliability, and you don't have to do it all that hard to expose problems.

Joe

 

[misque]

Excellent point Joe.
Lock reliability is what we are testing for with the Spine whack. Lock strength is tested differently and is mucho importante too.
Thanks for clearing that up Joe! Last thing I want to do is mislead someone with incorrect terminology on a topic this important.

BTW, Joe brings up another valid point in that it does not take a full strength whack to test a knive's reliability. I start light and work up to a light/medium whack walkng up and down the length of the spine to test my folders and that does, in fact, expose any underlying problem quite nicely.

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The individualist without strategy who takes opponents lightly will inevitably become the captive of others.
Sun Tzu

 

[Samurai6]

In the dinosaur days we used folding knives with no locks at all on them, and we were as careful as mice to only apply pressure to the blade in the cutting direction, or else.

Nowadays, as politically incorrect as it is (gasp - some knife magazine editors even shudder to mention it in print), some of us carry folding knives with self-defense in mind as part of the knife's purpose. We may want to do snap-backcuts with the tip of the blade, and we may not want the blade to chop half our fingers off if the spine gets whacked by a pool cue. That means liner locks and most lockbacks are obsolete (welcome to the new millenium minus one year), and to make sure knives are up to our expectations, we test them by whacking them with pool cues and the like.

 

[Marek]

Thanks to all who replied. As is usual when good questions are given good answers the issue seems much clearer now than before. After reading some of the other threads as Joe suggested and re-reading the replies here I have a much better understanding of the test and the conclusions drawn from it.
Thanks again for the help, you guys are great!

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Tough times don't last,tough people do.