Spine wack (Spelling ?)

H

Hawkings

Joined
Mar 31, 2006
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I've seen alot of post about/with the concept of spine wacking.
It seems to be a test of a folding blade with a lock on it.
It goes something like you hold the folder and then hits the spine of the blade.

Did I get that right ?

If I did, then why would one do such a test? It seems to me that there is no real world situation,that would make this happen while using a knife.
What info do you get from this?.
If the blade stayes open,then good.
If the blade closes, well it does not really matter because you would never use a knife in this way anyway.
If its to see how good the lock is, would it not make more sense to apply pressure to the spine instead of wacking it?
 
If the knife is just being used for general cutting, then it does not really matter. If you are doing heavy cutting, or worst case, you actually have to use the knife against another person it could be very important.

You do not want the blade to close on your hand. I've had it happen, and it's not fun. Thankfully, I only got a minor cut from it.

As far as the test itself, you are correct in that you will never in real life whack the spine against something. It's only for the test itself, to make sure the locking mechanism is strong enough.
 
your right, its not something you do with your folder in regular use or even extreme use. A spine wack test is a shock test, as opposed to pressure test. I know I wouldn't carry a knife if it did not do well in these tests.
 
Locking folders have had lock failures and closed on peoples hands. This is reality.

A spinewack is a way to test the security of the lock.

No, you will not be using the spine of your knife to hammer nails, but even during normal cutting things can happen that put force on the spine of the knife.

A common occurance is that while using the knife, it is accidently hit on something.

Even a sawing motion can make a knife want to close.

For very light cutting, no it doesn't matter if the knife can pass a spine wack. That is why slipjoints are fine for light cutting.

But if your folder locks, you want it to be a stronger lock than a slipjoint.

Passing a moderate spinewack is a decent way to test lock security. If it fails, it doesn't mean the knife is trash, but it means the knife should only be used for very light cutting. If it is a heavy duty knife, that means it is basically defective and should be fixed or returned.

I have owned cheapo knives that cannot pass a spinewack. They were not safe to use for almost any cutting chore. Even less safe than a slipjoint since a slipjoint at least has the spring to keep it open while a very poor liner lock (or any other lock) can slip with much less force and then the blade is basically on a hinge with nothing stopping it.
 
Spine whacking, if done often to show how great a lock is, will peen the liner over a bit and loosen the lock. It's something that's done, but really ought not be if you want the knife to work well.

Gene
 
Gene Martin said:
Spine whacking, if done often to show how great a lock is, will peen the liner over a bit and loosen the lock. It's something that's done, but really ought not be if you want the knife to work well.

Gene
Click to expand...

So its only a test for linerlockers. or does it apply to other lock allso , like axis locks ?
 
Hawkings said:
So its only a test for linerlockers. or does it apply to other lock allso , like axis locks ?
Click to expand...

It was origionated by A. T. Barr (knifemaker) for a security check on liner locking folders as those types of locks are prone to failure of that type.

Hair said:
No, you will not be using the spine of your knife to hammer nails, but even during normal cutting things can happen that put force on the spine of the knife.
Click to expand...

That is the problem. There is a misconception that since you don't load the spine directly there is no load on the spine and this is false. If the knife is wedged in cardboard and you pull up on the blade to remove it, then this acts very similar to a load directly on the spine.

Hawkings said:
If I did, then why would one do such a test?
Click to expand...

Because people who have done it a lot have noticed that locks which pass that test are more stable in actual use than locks which don't.

If its to see how good the lock is, would it not make more sense to apply pressure to the spine instead of wacking it?
Click to expand...

That is done as well, usually before you do an impact.

-Cliff
 
I have never whacked a spine on one of my knives, but I have pressed on the blade to see if the lock moves at all. I only have one locking knife that has failed that test. I still carry it, but recognize it's limitations when involved in the heavy use I give it (liberating letters, field dressing apples, defending myself from rabid cardboard boxs, ect). In other words to me it is an academic exercise. Steven
 
I had a Gerber "bolt action lock" close on my hand in moderate use. 8 internal stitches and 10 external stitches on my index finger. I personally believe that the traditonal buck style lock back has the most reliable lock from the mechanical standpoint. In order for the knife to accidentally close, the locking tab must fracture. Pretty unlikely. A good lockback should pass a whack test easily, and probably with no damage to the knife.
 
Hawkings said:
So its only a test for linerlockers. or does it apply to other lock allso , like axis locks ?
Click to expand...

Any lock. It's just that liner locks, due to their very tricky design, and disproprortionately prone to fail.

Hawkings said:
If I did, then why would one do such a test? It seems to me that there is no real world situation,that would make this happen while using a knife.
Click to expand...

Au contraire, there have been reports of knives getting stuck and, upon extraction, being struck on the spine and folding. In addition, for those who carry for defensive use, impact forces shuld be considered not just possible or probable. Besides, a light spine whack tests basic tang-liner geometry -- in my experience, a knife that fails this easy test is more likely to fail a torque test as well.

Gene said:
Spine whacking, if done often to show how great a lock is, will peen the liner over a bit and loosen the lock. It's something that's done, but really ought not be if you want the knife to work well.
Click to expand...

I've had liner locks that I've spine whacked for years with no ill-effect. However, if you're right about the peening effect, that's just another reason not to buy liner locks -- simple lockbacks, axis locks, etc. can go through really rough treatment without this kind of worry. Add to that the fact that only liner locks fail this test in such great numbers, I don't see why I'd pick a lock that's so fragile, for a working knife.

Note that I feel the spine whack is a very useful test of basic lock geometry, but I do it with a light whippy snap; there's really no excuse if that damages anything. Some folks do hammer type blows, which is another story.
 
Okay, here is why the spine whack became important to me.

I was in a Magnolia tree getting a particularly nice blossom for my wife. The stem on Magnolia flowers is fairly thick and woody. I needed to do a little chopping to get it as the knife I was carrying at the time was a Boker green Gemini(3 1/4" blade). I started chopping and on one of my whacks, the spine hit a branch above the flower and the relatively minor force caused the knife's lock to fail and the blade closed on my index finger and drew blood.

That knife would not even pass a spine tap, much less a spine whack.
 
Joe T knows what he's talking about! I have figured out what I believe to be a completely non-abusive, and easy way to spine-whack ("spine-bump" would be more akin to what I do) my folding knives and determine which ones can handle mild shock to the spine of the blade without failing.

I sit on a chair, extend my right leg out in front of me, and point my boot (with a rubber-type sole) straight up. I hold the knife from the back side (so as to avoid having my fingers in the path of the blade) and I make sure to keep my fingers away from the locking mechanism (back-lock types). I hold the knife out in front of me, and with a sharp, snap-like motion, strike the spine of the blade (about half-way up the spine) against the tip of my boot's rubber sole.

Now, I am talking about a whack of moderate speed & strength, not a slamming, high-speed whack as seen in the videos put out by a certain company. The rubber sole of my boot should not cause any harm to the knife, and is much less likely to be deemed "abuse" than whacking the spine on a hard object like a piece of wood, also as seen in a certain company's videos.

I've had very good experience conducting this test, and have actually been quite surprised by the results.


Regards,
3G
 
My comment about the spine whack test referred specifically to titanium liner locks. There are other tests that will do the job on lock up, whereas the spine whack invites abuse. About 4, maybe 5 years ago at a show, I watched a vendor, not a maker, showing evryone who stopped how strong his liner locks were. In 2 days he did over 200 spine whacks, really good, sloid ones.

That invited every purchaser to show off similarly to his/her friends about how strong the liner lock worked. I decided then to be very careful about ever making them. I stand behind all my work, but there isn't much point in inviting abuse.

I started talking to other makers about the effects of spine whacking and had a uniform response that it's abusive. I decided to stick with slipjoints and lockbacks. Ultimately I want to do multiblade folders.

I knew my comments would generate discussion. I appreciate the fact that there are a lot of informed users on this forum, users who don't set out to abuse a good knife. Sadly, there are a lot of uninformed users in the knife world who want to be as macho as possible with their knives, even if it includes unintentional but real destructive testing while showing off. I enjoy the former and worry about the latter.

Just my 2 cents worth.

Gene
 
Gene,

Thanks for your response, always good to have a maker's viewpoint. There are definitely makers out there who don't find spine whacks abusive. I'm not sure there are any who necessarily feel that treating a knife like a hammer is warranted, but a light spinewhack from time to time to check basic lock geometry seems a lot less controversial.
 
I must admit that I was of the mindset that a spine whack was abuse. I believe I even thought it was not a real world test of the blade lock up but have since learned a lot about that. It is a possibility in real world use to tap the spine. I do think repeatedly whacking the knife on a table top is abusive if you have proven that the lock up stood up to your test. Continuing on after its already proven its worth until the umteenth whack when a handle scale breaks seems a bit much to me.

With that said I do agree that liner locks in general seem to be the ones more prone to various lock defeats. They seem to be guilty of wear problems resulting in vertical blade play a lot also. I know I sure see enough in any given year for adjustments. With lockbacks you usually adjust them once when they are made if you even have to do it then and thats it.

What finally ended my love affair with liner locks was the realization one day that I've never had one last all that long before it needed some kind of attention. Even the best ones had locks that eventually travelled all the way across the tang of the blade at the interface. The shear number I get into my shop for work that are fairly new knives was no help either though.

To give a pespective. I have lockbacks I've owned personally and carried and literally beat up in my youth that are over 35 years old. One is a Buck 112 I remember throwing and sticking into trees when I was young. These still function and work fine. I venture to say that all but the one I threw into a tree are still pretty much the same lock up as when bought new, and even the one I threw is still 90% or better. Only a mint condition never used liner lock will ever be able to claim its still functioning like new or even close when it hits 35 years old.

As for the spine whack. I guess I don't believe so much in whacks as taps. I think it is necessary to find out if you can trust your fingers to the blade or not. I don't know about you but I need my fingers too much to risk them to a faulty lock.

STR
 
i dont think its too hard on the knife unless ya really whack it hard which imho isnt neccesary anyway, i use a LIGHT tap on either my hand or on the floor, ya just wanna make sure the liner is engaging right/isnt slipping.

now if ya wack it on a steel work bench as hard as possible thats another story of course.
 
Just had a Gerber Chameleon fail the spine whack----can't complain though---only paid $9 for it on Walmart clearance---so no big deal.
 
Gene- Since a folding knife is generally not designed to be used as a hammer (using the spine as the hammer head), I understand why a hard spinewack can be seen as abusive. But I think we are just talking about a single moderate spinewack to make sure the lock isn't prone to slipping.

This does cause at least a tiny bit of wear of the knife, but I think it is worth it to make sure the lock is at least secure enough for basic use.
 
I've used the ole' spine whack test a few times. I'm like the above poster Hair, in that a single moderate strike on a padded surface will usually put my mind at ease about the lock. Another test I use is to apply pressure to the spine, relax, apply pressure, relax, and do this several times and in a timely manner to see if that walks the liner over to the unlocked position. I was surprised when I did this to a fairly high dollar knife and saw the liner progress to the left until it became disengaged.
 
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