how do you do the liner lock "whack" test?

M

mykem

Joined
Feb 23, 2001
Messages
294
hi,

i keep reading about the liner lock "whack" test.

how do you do it? and it doesn't sound gentle. can the knife be damaged? is there a safe way to do it?

thanks,

mike
 
I whack it against my palm as strong as I dare, because it can be painful. Following which I hit my desk with the spine of the blade. Just a few light pops. If the lock works, it is more than adequate for my purposes. If the knife folds or suffers damage, it doesn't worth a dime anyway, so I send it back to the vendor or simply throw it out. I've only seen one knife which failed this way, but there are several dents in my desk, so it's time to send that piece of furniture back to it's dealer.:p

I think a decent quality folder can't be damaged by this method, except if you hit an anvil with it repeatedly with full arm strenght.
 
Better question is why you want to do this test? Another question is to which knife [knives] do you want to test?
 
nelson,

just got a new kershaw talon and i read a few posts where people said the liner locks on these were sometimes questionable.

so i want to test it, but i don't want to damage it.

i have a line on several of these and have already bought two.

mike
 
GarageBoy said:
Someone damaged a ReKat this way. It was working perfectly fine til he did it
Click to expand...

Well I have to say that depends very much on how hard he did it, but if he did it with resonable force it wasn't working perfectly fine if it got damaged.

The real problem is to manage the force in this test. Every decent lock/knife that was made for hard use should withstand spine-whacking within limits. The problem is how to control and measure the force of the whack. If you get carried away with it, you can easily destroy any folding knife with sufficiently hard blows. It is really not that difficult.

After having though on this for a while after having had a knife folding on me, I would tap it only lightly on something very hard, like a steel surface. To me this test is not about lock strength but about lock security. All you want to see is whether you can make the lock "bounce" in to a position in which it might disengage. On the knife that failed, the lock did not engage very deeply so a light, but sharp whack would lift the lockbar enough that the lock would slip out of engagement (the knife was replaced and the replacement is rock-solid). So "whacking" it on a palm doesn't seem to make much sense to me since the palm absorbs most of the shock and the sharpness of the blow is reduced. Clobbering it with a piece of wood is more a lockstrength test that has value if you want to know how well the knife holds up to batoning or in general, for example when Cliff pushes a knife to the limit, but it is not exactly the right test to see whether the lock is functioning properly. So I tap it lightly on a steel surface (e.g. a sledge hammer head) and see if I can "jostle" the lock out of engagement, or have it move to a position that I deem questionable. To see how it holds up under loads I prefer white-knuckling.
 
mykem said:
nelson,

just got a new kershaw talon and i read a few posts where people said the liner locks on these were sometimes questionable.

so i want to test it, but i don't want to damage it.

i have a line on several of these and have already bought two.

mike
Click to expand...

You could take it down and put more of a bend on the liner to help it engage tighter. I've done this to a few Bucks, Kershaws, and CRKT knives, seems to help a lot. Experiment on it, especially if you can get more of them, sacrifice one. Just remember to post pictures of your results ;)
 
As has been reported here numerous times. Liner locks can pass a spine whack test repeatedly and then suddenly fail, or they can fail on the first whack and then never fail again. It sounds to me after reading a lot on the subject that perhaps the whack is not the best test to perform on one but a tap or spine pressure to test the security of it is not something to ignore.

I'd sure be cautious using any knife unless you knew the lock was backing the blade properly at the interface with a liner lock with enough thickness and that it did not back off the blade from pressure or light taps. If you elect to do heavy whacks with it you can indent the lock enough to make it move in behind the blade more and at times even seat the lock better and eliminate the defeat problem though. I had a Superknife that the lock only barely came out on and could easily be defeated by simple pressure on the spine and whacking it actually fixed it and now the lock travels in farther and its just much better. At other times you just cause vertical play in it if the lock has already travelled pretty far across the blade and is worn from use anyway.

On some integral lock knives the angle of the grind on the interface is so steep that its just an accident waiting to happen. I generally ignore those.

Oh yeah. You simply grab the knife so as to make sure your fingers are out of the way in the event that the blade closes, and tap the spine of the open blade on a board or some other surface making contact on the board more with tip than the middle or back of the blade. Use something you don't mind putting marks on, not the kitchen table in other words :-)

STR
 
GarageBoy said:
Someone damaged a ReKat this way. It was working perfectly fine til he did it
Click to expand...

the "lock of the 21st century" the rolling lock by rekat was easily damaged by virtually anything imho if there was any knife i would wanna make sure was locking right it would be a rekat, though they can lock right one moment and not lock the next so i do suppose on them its a mute point lol.


i do the spine whack test much as described by redguy, either on my palm or on a carpeted floor, and LIGHTLY whack it to determine if the lock is functioning correctly, i dont think this is in any way shape or form abusive ,at least not to any quality knife as long as ya dont go nutz whacking it on a steel table/etc, i mean if i wanna break something i'll do it every time.
 
I was checking the integrity by lightly whacking on a leather covered steering wheel - and a lock failed. I sure didn't hit it hard enough to cut the leather. The replacement got whacked a lot harder on formica covered work benches - and failed.

IMHO short, thin liners with steep engagement ramps fail, which is exactly the wrong way to build them. Somewhere between paper and production the reason for a long, straight liner leaf is not communicated and we get value engineered technology.

Do I see this as an explicitly American marketed problem? Is the god of "Low Price Gaurantee" mocking us?
 
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