Spine Whack Myth ?

I think that a spine whack is a very useful test to determine if a liner or framelock was made correctly. I do agree, you don't need to, nor should you beat the knife into submission on a hard surface, all that is needed really is a firm hit into the heel/palm of your hand. Let me say this very clearly, if you hit the spine into the heel of your hand, and the lock gives, you have a defective knife that may very well one day take a finger or 2.

What the spine whack is actually testing IMO, is whether the angles of the lock and tang faces are correct. What allows a lock to slip and ultimately fail is not a stretching or a vibration, it is the angles the lock and tang were cut at. If those angles are off, then closing pressure, which can either be accomplished by exerting increasing closing pressure on the blade, or a spine whack, will cause the lock to slip to the left and ultimately out of engagement. If a lock fails a moderate spine whack, then it will also likely fail when you simply exert closing pressure on the blade, whether it be intentional, or accidental, and after all, what is a lock for, if not to resist closing?

A firm spine whack on your hand will tell you if your lock is made correctly, and if the angles of the lock face and tang face are correct, if they aren't, the lock will fail when closing pressure is applied to the blade in whatever form, a spine whack is really just a quick, easy way to see if the lock will fail under closing pressure, and if your lock can't resist closing pressure, then it isn't doing it's job, is it.
 
When I first read about these failures, I went and played with the two liner locks that I own. One would not fail, even under conditions that approached abuse. What was interesting was that the other one(brand new) would fail under a very narrow range of conditions. It had to be tapped just right, fairly softly, against a firm, but not hard, surface - the wrist pad in front of my keyboard was perfect. Hard whacks on a wood block or metal filing cabinet produced no failures. I just hauled it out again after a year or so of use and could not get it to fail under any conditions. I suspect that the mate between the blade and the locking bar has worn in a bit. I believe, based on a poor memory, that the lock bar is now farther to the right than it was when it was new. I feel better about this knife, but I'm still a little leery about liner locks, I'm kind of in the camp that you need to be more careful with a liner lock than a slipjoint, since they don't have a backspring. I'm not planning any more liner lock purchases.

Gordon
 
I just do a firm tap on my hand, nothing more. That said, though, overall I am not a fan of spine whack testing. For a linerlock or something that appears borderline, I will do it just to see how fragile the lock-blade interface is, but with most knives, I don't waste my time.

Why?

Because nearly every knife will pass, and those that pass the whack test may fail another test very easily. My Schrade cliphanger passes spinewhacks, but the blade will unlock in a firm grip. A knife a friend of mine built from a kit will pass the spinewhack test, but the lock fails if the blade is so much as tapped from the side.
 
Sword and Shield said:
My Schrade cliphanger passes spinewhacks, but the blade will unlock in a firm grip.
Click to expand...

Yes, this is why you need to do more than one check for stability/strength, the liner lock FAQ covers several.

-Cliff
 
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