Spine whack test?

billy blade

billy blade

Joined
Nov 11, 2005
Messages
562
I bought a new knife from a guy on line cheap! He claims in his listing it has a weak lock spring because it didn't pass his "spine whack test". What is a spine whack test? I'm having a hard time believing the new knife from a quality and beloved manufacture has a weak lock spring. I just want to hear from my fellow blade forum members about this so called test.
 
This is a test where you open the knife, and smack the back of the blade against a table (with your hands out of the path of the blade of course). If the lock fails and the blade closes, it has failed the test. This is considered a destructive test and many people agree should not be done, especially repeatedly.
 
If you go to YouTube and check out "nutnfancy" videos - I believe he has come up with a good way to test the strength of a lock. He duct tapes a folding knife to a broom handle and repeatedly jabs it into a 6"-7" thick stack of cardboard that is taped taped to a 100 lb punching bag.

I have never had a lock fail on me yet, and I have liners, axis, compression, frame and spine locks. I have tried the whack test on knives that are known to have weak locks and could not get them to fail. I guess I wasn't hitting them hard enough!!
 
I think its a valid test. If the lock fails it should fail towards the inside of the knife and not release the blade. If the blade releases and starts to fold up as in close, imho get rid of the knife or send it back if for repair. The whole idea behind locking liners is that if and when they fail it fail towards the inside of the knife and not unlock the blade itself. For instance I have a pretty nice MOD Tempest old school. Fails the spine whack test so I don't use it. Anybody wants to buy it cheap I'll oblige them but I ain't holding my breath. keepem sharp
 
billy blade said:
I bought a new knife from a guy on line cheap! He claims in his listing it has a weak lock spring because it didn't pass his "spine whack test".
Click to expand...
I hope you go it really cheap. IMO if a knife has failed the "spine whack test", either it was defective to begin with or the "tester" has broken it. In either case, I would not trust the locking mechanism on the knife any more, and treat it the same way you would a non-locking slip-joint. :thumbdn:
 
I saw the listing the OP was talking about. The knife was a back lock, not a liner lock. Unless the seller damaged it with his testing, the warranty will cover it IF there is a real problem.

I've done enough metal work over the years to have a pretty good idea what happens when you start beating small bits of precisely machined and fitted metal together. It IS destructive testing. If you need a lock that much, you shouldn't be considering a folding knife.
 
yablanowitz said:
I saw the listing the OP was talking about. The knife was a back lock, not a liner lock. Unless the seller damaged it with his testing, the warranty will cover it IF there is a real problem.

I've done enough metal work over the years to have a pretty good idea what happens when you start beating small bits of precisely machined and fitted metal together. It IS destructive testing. If you need a lock that much, you shouldn't be considering a folding knife.
Click to expand...

I agree. I've never had a lock fail, and have had only 1 mishap with a slippie. IMO, if a lock fails, it is more likely to be the fault of the user than the manufacturer.
 
Tell the manufacturer you spine whacked it and see how legit they think the test is.

STR
 
I feel it is a legit test- but I test it by smacking against my fingers. THis way you can see if a slight jar will make the lock give, but not giving a super strong smack, unless you have no nerves left in your fingers. A light tap should not be considered abuse in my book- usually it is less than would make a slipjoint close.

My opinion only of course.
 
I don't think it's a valid test because at what point during use are you going to beat something with the spine of the blade.

That said, a knife shouldn't fail that "test" and if it does, something isn't right. But beating the back of the blade on the table until it fails isn't testing, it's breaking. If you whack it once and it doesn't fail, it's not going to under normal use. But if you whack it 100 times and then it closes, it didn't fail, it broke and shouldn't be covered under any warranty.

I have never had a lock fail and I tend to use my knives pretty hard. But I don't pretend that the spine of the blade is a hammer.
 
Depends on how you "whack" it.

I lightly impact the palm of my hand with the back of the opened and locked blade.
I have never had a knife fail such a test.
I have never had a knife fail in use.

But then I don't use a knife for stabbing, only for cutting. YMMV.
 
why you would need to really whack the spine on anything like that, maybe a tap on your hand thats one thing but on a hard surface is just goofy. A folding knife is a folding knife it folds if thats really a concern in what your doing you should be using a sheath knife. If it folds it can fail, doesnt mean it will but it could.
the right tool for the right job and respecting the tools will guarantee a could long life and you just might keep all your digits:)
its an excessive and misguided test at best
ivan
 
It shouldn't take much more than the weight of a knife to test. It's hard to describe over the internets, but spine taps shouldn't be destructive at all, far less energy in involved compared to flicking a knife open for example.
 
I'm on board with a very light spine whack test, but not death by spine whack:eek:
 
Psychopomp said:
I don't think it's a valid test because at what point during use are you going to beat something with the spine of the blade.

That said, a knife shouldn't fail that "test" and if it does, something isn't right. But beating the back of the blade on the table until it fails isn't testing, it's breaking. If you whack it once and it doesn't fail, it's not going to under normal use. But if you whack it 100 times and then it closes, it didn't fail, it broke and shouldn't be covered under any warranty.

I have never had a lock fail and I tend to use my knives pretty hard. But I don't pretend that the spine of the blade is a hammer.
Click to expand...

Covers it pretty well IMO.

Some of you guys may be interested in reading my full opinion on it. Warning. Its a mouthful. Disagree all you want but this covers my thoughts and experiences on it pretty much start to finish. :D

http://www.bladeforums.com/forums/showpost.php?p=4848597&postcount=2

http://www.bladeforums.com/forums/showpost.php?p=4850235&postcount=6
 
Older microtech socoms were notorious for failing this test. You could probably make it fail by flicking the spine with a wooden pencil. They would fail consistently for 2 or 3 taps and then lock up solid as a rock for the remainder of their lifetime. Were you to find that out in real use you'd probably loose your fingers.

My old mini-socom had a very sticky lock, so much that sometimes I had to use a chopstick or screwdriver to pop the lock open again. When I heard about this I figured there was no way in hell that thing was ever going to fail. Well I used the nearest countertop and ever so gently tapped the spine against it. Folded right up, 3 times, then on the 4th tap didn't fold up. A couple of harder whacks later to reassure myself (the lock look any different at all) and I carried that knife for 3 years with no problems. I occasionally retested it and it never failed that test again. Also fixed that sticky lock it had, so not only did spine tapping fix the unreliability of the lock, it made it easier to use as well.

*edit: I don't think any amount of static load would have made that lock fold up like the spine tap did. While I didn't try lifting my body up with only the lock supporting me I did check by applying hand pressure to fold it, no go.
 
I test all of my folding knives by giving the two or three sharp raps on the edge of table....if the knife fails it either get's sold w/an appropriate warning to the purchaser or is doomed to collect dust.

I've had several folders from major quality manufacturers fail this test over the years.

I'm not trying to be "ninja" but my job sometimes dictates I might have to use my folder for some less than ideal utility tasks or as a last ditch weapon.
If your thrusting upward with your knife and you strike a bone or belt buckle you don't need it closing up on your fingers (another reason reverse edge methods kick-a$$).

If your strictly a collector and you don't want to "abuse" your knife by spinewhacking...then don't. If however you ever think your well being might depend on having a folding knife that won't exacerbate your already sh-tty situation by giving you midget digits....well you might want to test it.

Just my opinion.
 
yoda4561 said:
Older microtech socoms were notorious for failing this test. You could probably make it fail by flicking the spine with a wooden pencil. They would fail consistently for 2 or 3 taps and then lock up solid as a rock for the remainder of their lifetime. Were you to find that out in real use you'd probably loose your fingers.

My old mini-socom had a very sticky lock, so much that sometimes I had to use a chopstick or screwdriver to pop the lock open again. When I heard about this I figured there was no way in hell that thing was ever going to fail. Well I used the nearest countertop and ever so gently tapped the spine against it. Folded right up, 3 times, then on the 4th tap didn't fold up. A couple of harder whacks later to reassure myself (the lock look any different at all) and I carried that knife for 3 years with no problems. I occasionally retested it and it never failed that test again. Also fixed that sticky lock it had, so not only did spine tapping fix the unreliability of the lock, it made it easier to use as well.

*edit: I don't think any amount of static load would have made that lock fold up like the spine tap did. While I didn't try lifting my body up with only the lock supporting me I did check by applying hand pressure to fold it, no go.
Click to expand...


Cliff Stamp, Joe Talmadge, and his friend Steve all proved many times that the test was very bad at really telling you much of anything as to if the liner lock was a good or bad one. I recall reading that for all of them on occasion a liner lock would never fail at all and always work and then for no real identifiable reason at all one day it would defeat but never defeat again after that. What does a test like that tell you? I mean it was unpredictable and all of them reported it. Its happened to me as well. I tested knives Thomas W sent me and had a Junk Yard Dog here he sent me new before it ever was even known about or available to the public and first tap on the fence out back it defeated. Then later after using it in cutting trials and other things I ran the knives through testing 13C26 when it was new to Kershaw I literally whacked that thing so hard I could have driven nails, which wore the lock out to where in the end it was traveling all the way across the contact but it never defeated again or even came close. However when I took it apart later and looked it over the lock was obviously indented and marred up where it contacted the blade. The blade went off center after this test too and I could never get it to sit centered quite right again but it still worked even though it was effectively worn completely and had just a hint of vertical blade play.

I used to love liner lock type folders adamantly defending them, but based on what I learned on my own testing and from reading posts by Joe and Cliff on their findings I finally just reached the conclusion, slowly I admit, that it was apparent that spine whacking have no real conclusive findings with all liner locks because you may have one that you tested for five years and never see it fail only to test it one day that way and see it pop shut right off the bat. Frame locks too for that matter. Now on some of course the defeat is repeatable. On others its obvious testing can't continue like when I sheared a lock contact right off and fractured the rocker arm on a lockback. Again though the reasons are more speculation than anything definitive with trying to reach any conclusions. It was just one of many reasons I came to the conclusion that the test was really not that great at really telling you how the lock will work out for you in normal usage. Its seems that eventually if you do tap the blade spine long enough you will cause the lock to defeat one day when you cock your head just right as you do it or when you say the magic words for lack of a better explanation because when it happens you'll be standing there wondering why and what was different about that time than the 20 or 30 before that.

It seems to me after my own testing that the lock back designs and the thinner liner locks suffer the most from this type of test. Frame locks hold up much better based on what I've seen but even that is depending on several factors like how the lock contacts, the foot print of it as to how well its done and material its made of and it seems the axis does well for the most part against these forces but I've defeated axis locks doing this test too.
This link here shows damage from spine whacks in the form of indenting that led to overtravel of the lock and vertical play.

http://www.bladeforums.com/forums/attachment.php?attachmentid=95216&d=1208822756

STR
 
Spine whack is not ok, spine tap is fine. The problem is defining the limit of what's a "whack" and what's a "tap". I like Cuts Like A Kris' idea of just tapping it against your fingers because it naturally limits the amount of force you can use.

As a side note, I wonder why additional/secondary safety lock is not more common. I remember that certain models of Extrema Ratio folding knives have beefy secondary safeties. ER RAO even has an extra stop pin as secondary safety.
 
You must log in or register to reply here.
Back
Top