Consequences of spine wack tests?

[Lurp]

I was thinking of doing some spine wack tests on some of my knives and would like to know if doing them will damage the lock. Does the sudden impact of the spine wack cause any kind of damage that would weaken the lock even if it didnt initially fail?

 

[orthogonal1]

Knife locks are a mechanical device, therefore anytime you stress them wear/damage occurs. Usualy it is of negligible import.

However, should the lock be stressed to the point of failure, the lock is more likely to fail at a lesser stress the next time.

That being (badly) stated, I generally recommend stressing a knife's lock under controlled, safe conditions so you know it'll hold. If it fails, you at least have an idea under what stress it took to fail. Then, appropriate considerations can be taken when you use it. I do it to my knives now, and suffer less un-intended blood loss as a result.

There have been various discussions on this (contraversial) topic, with some of the forums "bigger" names chiming in. Search them out.

 

[SIFU1A]

do a search lots about this topic,

imho a LIGHT tap on the back of the blade wont hurt anything and will tell ya if its locking correctly, notice i said light, ya dont have to go nutz with it.

 

[cognitivefun]

Don't you think any knife you own should be stress tested to some degree? I'm not talking about doing anything extraordinary in a double vice with pliers, but I am speaking of spine whacks (watch those fingers) lateral whacks on any new knife, as well as hard twisting and generally trying to get the lock to fail. If I don't do this, I can't be confident in that particular knife.

 

[DGG]

I was thinking of doing some spine wack tests on some of my knives and would like to know if doing them will damage the lock. Does the sudden impact of the spine wack cause any kind of damage that would weaken the lock even if it didnt initially fail?

I think you already know the answer. If you have any doubts ask yourself, "What was this knife designed to do?" Also read the manufacturers warranty information.

If were mine I wouldn't whack it! I could hold the blade with my fingers and see if there is excessive movement in any direction and check the lock allignment.

 

[Blop]

I would consider a spine WHACK to general testing reviews and would look for some other non - stressing tests at home.

I have had used a Puma lockback for over eight years, which developed blade play in any direction but never was failing. I ruined it in a minute after five whacks on wood, like i did with the Benchmade 550. The Puma lost its back spring all of a sudden.

So: As said before but only considered to lockbacks, after the spine whack you may know how strong the lock was until the test. Consider linerlocks i wouldn´t expect it failing after that because of the spinewhack. An axis is hardly to destroy by a spine whack but it won´t do it any good.

Is there a situation, where repeated sudden impacts are in sight? If so: Check the warranty and decide if to do or not.

In any other case: Strong pressure or light repeated knocks on the spine, as mentioned above, are the way to go.

The mechanics are made of steel, not porcelane. So don´t take this wrong. But i only saw a folder failing because of a spine whack.

If it is for SD, why not taking the knife to trainings and see.

 

[Cliff Stamp]

Does the sudden impact of the spine wack cause any kind of damage that would weaken the lock even if it didnt initially fail?

It can, it depends on the knife and what it was made to do, some of the heavier use folders are promoted for this type of use, some are not. I have seen very cheap and very light built folders (Kershaw Vapor) take hundreds of spine whacks hard enough to put a mm+ dent in hardwood birch flooring and have no effect on the lock, so it isn't unreasonable to expect folders to be able to take it.

-Cliff

 

[yam]

Unless you really want/need to do this, it sound a lot like testing the bumber on your car by bumping it into a concrete pole.

 

[SIFU1A]

i want & need to know if mine are locking up right.

 

[puukkoman]

I have seen very cheap and very light built folders (Kershaw Vapor) take hundreds of spine whacks hard enough to put a mm+ dent in hardwood birch flooring and have no effect on the lock

...bet you got in trouble with a female for putting dents in the floor...

 

[Cliff Stamp]

No, that is well eclipsed by cutting up the concrete step to the front door.

-Cliff

 

[Joe Talmadge]

I wouldn't carry a knife I didn't spinewhack. And if a spinewhack caused damage to a knife, I'd get a better knife. I have knives I've spinewhacked for years with no ill effects, including relatively inexpensive ones. If you believe a spinewhack is important to assure basic lock geometry quality, do it. The main thing you'll need to think about is how hard to spine whack your knife. There are very few times I feel the need to go beyond a light/medium whippy snap.

Note that there are arguments that a spinewhack can make your knife MORE safe. It is a frequent observation -- it's happened to me personally plenty of times -- that a knife fails its first spinewhack, and never fails again. A knifemaker who I can't remember (maybe AT Barr or Kit Carson) explained this as the force of the spinewhack "setting" the lock. Sal Glesser has stated he doesn't believe in this effect, and that if the knife fails once, he thinks it's unsafe. However, my observations differ from Sal's: I've seen it happen a bunch of times that a knife fails that first spine whack and then seems to be immune from spinewhacks thereafter.


Joe

 

[Cliff Stamp]

I think it is possible for both things to happen, I have seen knives that get progressively worse with even light impacts and in a short period get to the point that you can just tap them off your hand and they fail. Inertial openings can also seat locks, but there are makers and users who will also claim abuse there as well, just like with spine impacts. White knuckling is pretty much accepted now, but that once used to be complained about as well. Torques are another aspect for which some thing is abuse and others don't. If it is important to you then just buy from a maker/manufacturer who has a similar viewpoint.

-Cliff

 

[STR]

I see nothing wrong with inspecting your knife to make sure it passes the tests you decide on to make sure you are at peace in your own mind with the security and strength of the lock, blade and grip on it. I personally don't believe in spine whacks but as Joe said the difference is in how much force is applied to the whack. I prefer, as he stated, light to medium force taps verses really whacking it to where it dents a table top. To me that is pushing the envelope toward gross abuse there.

Personally once a knife fails in my hands I never feel the same way about it again and probably will not grow to love it and carry is as much once that happens. I don't think I believe the setting the lock theory but it is the first I've heard of it. There may be something to it but we are talking about hardened steel here. How does hardened steel seat or set against another piece of hardnened steel? It isn't like they dent and form fit into each other so I have a little trouble buying into that theory. In my mind if it failed once it would always make me double cautious when using it from then on. Just my .02 worth on that.

STR

 

[Joe Talmadge]

STR, regarding the lock seating theory, I think there are a few things that could be happening -- all theoretically, of course. First, it's often a titanium lock face against a steel blade, so the titanium could somehow gouge or conform to the steel in some what. Perhaps more importantly may be what's going on around the lock: is there any shift in the frame geometry or pivot?

I'm not 100% bought into this lock-seating theory, but have seen it seem to work a number of times. I've also seen, as Cliff describes, progressive degeneration. Again, possibly explained by changes in the lock geometry as the test is done.

 

[Cliff Stamp]

How does hardened steel seat or set against another piece of hardnened steel?

This is usually noted with liner locks. Often initially they are just barely engaged, only a fraction of the liner actually makes contact with the tang and this can cause the lock to fail almost any check, I have even see them fail to engage when opened. However if subjected to some kind of impact the liner wears, moves to the right and gets far more secure.

-Cliff

 

[STR]

I guess when I was typing that I was thinking lock backs for some reason but with titanium liner and frame locks I can see the softer ti indenting a little if it was not used much yet. I should have thought of that because I've seen it in my own folders that I had to tighten the locks up on after they were carried for a few years.

This seems to be alleviated to some extent with an oxidized layer three light layers deep minimum though.

I've seen many frame locks that barely engage the blade and it has always puzzled me as to what benefit the thicker stronger lock is supposed to provide if no more of it engages the blade than a standard .040 thick liner lock would. I recall one review Cliff did on a #880 Buck Strider where the lock sheared from something like that where not enough of the lock was engaging the blade and what little was sheared right off in a spark fest. With that little bit of lock on the blade a spine whack is almost a recipe for a broken lock face.

I guess over time the lock can work its way in more as it progressively degenerates but truthfully I've recently owned two Sebbies that were older used knives when I got them and their locks still only half way engaged the blade. In other words not much had changed in how much of the lock engaged the blade after they were used and carried for a few years time. I also note that my own Kershaw Vapor's lock that has seen much use still does not really engage the blade fully but only about 5/8 of the lock thickness ever at any one time is on the blade to secure it.

I've never really made a frame lock (yet) but I have approached it in some of my recent hand made liner locks using .100 thick titanium for the locks. I try to make them engage the blade fully before I'm happy with them but maybe I'm advancing wear on them by moving it along that much. I may need to rethink that but it just seems to me to be more secure with the whole lock on the blade tang.

Thanks for the feedback.

STR

 

[Cliff Stamp]

I've seen many frame locks that barely engage the blade and it has always puzzled me as to what benefit the thicker stronger lock is supposed to provide if no more of it engages the blade than a standard .040 thick liner lock would.

It is less based on what I have seen because I have never actually cracked or broken a full liner, even the thin ones are really strong, see the work Nemo and Fred did with a Military for example where they viced it. The only real issue is compression of the mating faces which can lead to vertical play.

-Cliff

 

[bubinga]

Unless you really want/need to do this, it sound a lot like testing the bumber on your car by bumping it into a concrete pole.

What he said. Why on Earth would want to do this to the kind of quality product that might withstand it? What extraordinary experience do you think you might have that your knife might have to withstand such abuse?

I know some of you are thinking, "Obviously, this guy has never considered the possibility of a meteorite striking him at a particular angle..."

 

[STR]

I know some of you are thinking, "Obviously, this guy has never considered the possibility of a meteorite striking him at a particular angle..."

I don't think that. I follow what you are saying exactly and agree. I've been saying the same thing for quite a while. It goes with the theory that if it walks like a duck and quacks like a duck and looks like a duck it is probably a duck. Meaning if the knife feels quality, passes the basic user simple tests for fit, function and finish it is probably going to be pretty much identical to the ones that were tested. With the precision CNC machining being used today it is even easier these days to expect each one to be so similar that they can be easily confused one with the other.

In other words: Just because my Jeep has bumpers that can stand up to a 10mph hour crash without damage to them as proven in a video or promotion by Chrysler Motors, doesn't mean I have a free license to now go out and pick a brick wall to hit just to test them to see if it is true. I ask you, who in their right mind is going to even expect Jeep to honor a warranty repair when I pull in and tell them, "I saw the video and your bumpers are faulty because I hit a brick wall at exactly 10mph and they didn't hold up?"