How does one DO a "spine whack test"?

[peacefuljeffrey]

I've read so much about them, but never heard how they are performed. My mental image is of taking an open knife and slamming the SPINE of the blade against something like a table or workbench, to see if it overwhelms the lock's ability to keep the blade open.

Is this what people do? If so, how does one hold the knife so that IF the lock fails, the fingers are not injured? Do you hold the handle in the manner in which some close an Axis-lock (i.e. thumb on one scale, tips of fingers on the other, nothing in the path of the blade)? That seems like a pretty insecure way to hold a knife that's being whacked against something.

This test seems questionable to me. When performing any test on a specimen that will then be used in its normal capacity afterward, one has to wonder if the test itself may have caused a fault that will not be discovered until the item is placed under stress again, and fails.

That is why I question the utility of a spine whack test on an individual's knife. On a prototype or test knife at a factory, yes, you could measure stresses and see what it took to make a design fail, and then you can assume that additional specimens manufactured to the same design standards would hold up similarly. That's different from testing your own carry knife. If you get it to fail at a certain point, do you throw it out? Do you still carry it, with the assumption that the test stresses were well above those the knife will face under normal use? How do you know that the fact that you pushed the knife to failure does not mean the next time it will be weaker, and fail sooner??

---Jeffrey

 

[Cliff Stamp]

The spine whack test is done in two fairly broad ways :

1) As a test of security. This has the knife held in a pinch and lightly hits the tip of the blade in a fast snap against something hard. The force isn't high enough to damage anything (as the blade isn't held rigid), however the impact is fast enough to cause some locks to unseat. This method can be used to actually fix sloppy locks.

2) As a test of strength. The blade is hit very hard against something rigid, in extreme it can be taped to a pole or similar. This is likely to damage many locks to the extent of making them fly apart, or even grossly damage blade parts. This is what most people argue against calling the test abusive, however it isn't the origional intended test, but can be relevant for some knives.

Any test, or any useage in general, can damage a knife (or anything else), you prevent (or at least) minimize failure with regular inspection. Just like you check the break pads on your car which wear with every application, take the knife apart and look for signs of impaction, loosening, cracks and so on.

-Cliff

 

[DaveH]

I once had a knife that if I held it 1.5 inches from the table and let it fall by it's own weight only, the blade would close. That's a pretty light tap.

I returned it to the manufacturer, if it only fails a strong whack I'd probably keep using it.

 

[HJK]

Most people just turn the knife upside down and whack the blade on a table [covered by a cloth or cardboard, I presume] holding the knife by the sides so the fingers don't get chopped off. It isn't difficult.
I do a practice, short, sharp, backslash [or snap] with my fingers out of the way, to duplicate one of the movements I would actually use and need the knife to withstand.
You could also throw the knife, if you know how. That would pop most locks.
Another idea is to use a hammer and whack the spine. You could hold the knife in your other hand or get a friend to hold it, but a vise would also work.
If you have a large truck, you could make a little ramp and build a small support for the handle of your knife, leaving the back of the blade exposed. You would then drive the truck over the blade so that the rear of the front tire is perched on the tip of the blade exerting maximum weight and torque on the blade and the lock. Your truck positioning would be critical, of course, but I'm sure most of us here would have no trouble. In the alternative, I'm sure an appropriate laser/gps positioning device with the requisite precision and remote projection monitor is available on ebay for a reasonable price. You never know when you'll be run over by a truck or a car with only your folder for protection.

Similarly, how many times have you seen train tracks with gaps suddenly develop in them? Derailments are no laughing matter. You could insert your folder, and your lock absolutely must hold - lives depend on it. Think of all the positive publicity for the knife community and the image of knives in general! What, you never watched Superman?

So you see, it isn't true that the spine whack test is unrealistic. There are many other uses that will require the lock to withstand such pressures. Too numerous to mention. Mixing cement. That's one. Any other ideas?

 

[Danbo]

A person with a brain wouldn't do this to a knife. A knife is meant for cutting and slicing.

 

[Keith Montgomery]

I have occasionally given the spine of a folder a good solid whack into the palm of my hand. That is as far as I will go when doing a spine whack test.

 

[Keith Montgomery]

Originally posted by peacefuljeffrey
When performing any test on a specimen that will then be used in its normal capacity afterward, one has to wonder if the test itself may have caused a fault that will not be discovered until the item is placed under stress again, and fails.

This most defintely can happen. It is one of the chances you take when you do a spine whack test.

 

[Cliff Stamp]

Danbo :

A person with a brain wouldn't do this to a knife.

This test was actually started by a fairly well respected knifemaker. It has been somewhat distorted since then, I don't think he (Barr), used the pole slamming technique that I think Steve Harvey originated for tactical folders.

-Cliff

 

[allenC]

I think the spine whack test is something that must be done with every locking folder, especially LINER-LOCKS.

But I don't condone using a hammer or taping the knife to a long pole and slamming the spine on a hard surface.
All you need to do is hold the handle so that your fingers are not in the closing blade's path and give a couple of firm taps to the spine of the blade. I do three steady firm taps.
The "spine whack (or tap) test" does NOT test the actual strength of the steel locking-liner so much as the angle of the liner to the tang's ramp. It's kinda hard to explain, but you will be amazed when you come across a lock that fails.
I have one knife, a CRKT Gray Ghost Mirage, that fails the spine-tap every time. When you deploy the blade it locks in place with a nice crisp authoritive snap. It seems perfectly strong and reliable with virtually no blade play at all. And then I do a light spine-tap and it folds with amazing ease, like it did'nt even have a lock.

I discovered that the lock was bad while using the spine to tap mud from the tread of my shoes. It folded and cut the back of my hand bad enough to leave a small 1/2" scar.
I still have the knife and it's always fun to demonstrate the failure to my friends or non-believers.

Dismiss the "spine whack test" if you like, but don't say I did'nt warn you.

Good luck,
Allen.

 

[brownie0486]

Danbo:

A knife must also be readily capable of stabbing something.

Brownie

 

[Joe Talmadge]

Originally posted by peacefuljeffrey
This test seems questionable to me. When performing any test on a specimen that will then be used in its normal capacity afterward, one has to wonder if the test itself may have caused a fault that will not be discovered until the item is placed under stress again, and fails.

If one or two moderate taps to the spine will cause a material fault that causes a lock failure, don't you think that particular knife had a problem in the first place? All these "tactical" liner locks that are easily failing the spine whack test -- the makers are claiming you can take these knives to hell and back, but it can't take a bit of a thwack to the spine? Don't you think there's a problem in the reasoning here? You can pick an axis lock at random from my collection and give it a good spine whack -- hell, give it a hundred. Won't matter, it will hold up fine. In my view there is absolutely no excuse for a few moderate whacks to the spine to cause any kind of damage. If it does, re-label the knife as a gents' folder suitable only for cleaning nails and opening mail and slap a "fragile: handle with care" sticker on it, and be done with it. There's just too many knives out there that can pass spine whack after spine whack without failure to make excuses for the knives that don't pass the test.

Joe

 

[rdangerer]

You can impart a good bit of force to a folder's spine without hurting the blade or lock. I've only discovered one folder that wouldn't pass a modest spine whack... an Al Mar Sere 2000 liner lock. Shame, I liked the design fairly well.

I whack the spine on a keyboard palm-of-your-hand pad (ergo hand support for typing)... it is about 1" thick foam, has enough firmness to test, but is resilient so as not to hurt anything. It imparts a good bit of "rebound" force to the knife blade when you whack it, and seems even better than a hard surface at confusing a poorly made lock and coaxing it into unlocking. This based on the Sere 2000 experience.

If a knife passes 2-3 whacks, I'm done testing that one.

It's not like I sit here in front of the computer and whack it repeatedly ... despite what others may have told you.

 

[VampyreWolf]

I just grab it as it comes out, and thumbs open, fingers out of the path, thumb clear, but a firm enough grip that it's not going flying, and give it tap about 5lbs or so on a solid object... be that a table, chair, counter, stairs, shelf... haven't had any fail yet.

 

[Sundsvall]

Hold the knife edge down by your fingers and turn your whole hand until the blade edge is facing up. Wack the spine into an unfinished pine 2x4. Pine is pretty soft so you will not scratch or hurt the knife. Whack the spine into the 2x4 so that the indents are 2 or 3 mms deep. That should be enough force to determine if the knife will fail under moderate to heavy use.

I don't think any folding knife can survive high stress test. Liner locks and frame locks are obviously weaker than lockbacks. However, sufficient downward force will force any of them open.

The lower lock strength of linerlocks and framelocks is the price you pay for the one handed convenience.

 

[Nathan S]

I don't think hard spine whacking is appropriate. On the other hand, I feel that a light - to - moderate tap on the palm of my hand is a very useful measure of the stresses a liner lock should be able to withstand. This in no way constitues "abuse", and is a sterner measure of the lock's validity than you might think: my SERE 2000 failed repeatedly when subjected to this test.

 

[HJK]

Liner locks and frame locks are obviously weaker than lockbacks.....

The lower lock strength of linerlocks and framelocks is the price you pay for the one handed convenience.

I don't think that's right. The opposite is true, I thought. Comments?

 

[rdangerer]

Originally posted by Sundsvall
Liner locks and frame locks are obviously weaker than lockbacks.
The lower lock strength of linerlocks and framelocks is the price you pay for the one handed convenience.

In fact, in my experience, I have found that the most true generalization I can make is exactly the opposite. I.e., especially when it comes to production knives, integral locks are the stoutest as a class, followed by liner locks, followed by lockbacks.

There are exceptions, but most production lockbacks range from cheap to mid-range price/quality knives. Exceptions, that serve to illustrate proof of this rule, are few and far between. SOG Tomcat/Sidewinder/Stingray are very stout lockbacks, so is the Spyderco Keating Chinook. These are, however, not cheap lockbacks, they are mid to moderately expensive.
http://www.spyderco.com/dealer_prod...1020&mscssid=FM6DVCMB211R9KMBJ837B7C0V2SNBAP9
http://www.sogknives.com/tomcat.htm
http://www.sogknives.com/sogwind.htm
http://www.sogknives.com/stingray.htm

There are legions of cheap lockbacks that are relatively insecure locking mechanisms, partly from thickness of lock material, partly from fit/finish of lock and tang notch, partly from flexy handle materials that compromise the lock under stressful use.

Generally, many linerlocks are more expensive than say their same manufacturer's lockbacks/rocker locks. Many have a good lockup, but when cheaply made, or when QC is poor, linerlocks ARE less reliable than lockbacks. Companies that routinely have done a good job with linerlocks are about all I continue to own, a selection process: Benchmade, Spyderco, Microtech.

Most integral locks surpass lockbacks and liner locks in stoutness. There are the cheapie integrals, e.g. Kershaw Vapor, but even this one has a decent lockup (spring tension is a bit weak), IF you sort through the inventory and find a "good" one. They are $20 retail at WalMart afterall.

Most integral locks are stout... the originator Chris Reeve Sebenza is still a "best" example, Darrel Ralph, JW Smith, Elishewitz, host of others, all good locks.

What I would observe from my own use is that liner locks, when designed poorly, are more likely to be accidentally disengaged by your index finger than are lockbacks... force in the wrong place, on the lock, rather than excessive pressure on locking mechanism.

Poor design of linerlock... what do I mean?... I mean the index finger can put excessive pressure on the liner lock in normal use in normal grip position. Especially when twisting the knife in a counter-clockwise direction. Poor design can be inadequate lock tension, inadequate liner width (skinny liner), inadequate liner length (makes lock swing too far past 1/2 way on tang), a blade tang angle that is too shallow or too steep, improper radius angle of liner swing, soft liner lock face (wear), etc.

Bottom Line: Beware the cheap or poorly designed folder used in demanding ways.

 

[Nathan S]

Liner locks and frame locks are obviously weaker than lockbacks.

Nope, I don't agree with this at all. I should first point out that I'm a big fan of lockbacks. The lock on my SOG Tomcat, for example, is bombproof. That said, however, I think a well - executed framelock (and here I'm thinking CRK) is a step up with regard to the lockback. The framelock becomes more secure when you grip your knife hard, the lockback does not. Plus, framelocks are easier to clean and maintain than lockbacks: you can more easily see and remove lint or crud (which may otherwise cause the lock to fail) from a framelock than you can from a lockback.

I won't address the question of liner locks, though. I got rid of the ones I had, and don't plan on acquiring any more of them.

 

[HJK]

There's a thread here about the relative strengths of different locks
http://www.bladeforums.com/forums/showthread.php?s=&threadid=267767

 

[Joe Talmadge]

Originally posted by HJK

I don't think that's right. The opposite is true, I thought. Comments?

Sometimes when people are talking about lock reliability, they incorrectly put it in terms of strength (or weakness). Just look at the various current threads on locks and testing them, and see how many times someone has used the word "strength" when the meant to use the word "reliable". Perhaps this is what Sundsvall did?

Joe