Lateral Stresses on a Folding Knife

Cynic2701

Cynic2701

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Mar 31, 2009
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In an effort to stop keep this thread from becoming a flame war over brands, I want to start off by saying that my question has absolutely nothing to do with the strength of the locking system on a folder.

Nothing whatsoever.

What I am after, instead, is this: when a knife is placed under enough lateral force to cause failure, what happens to the knife?

Does the knife blade snap? Does the pivot screw strip? How much force would it take to actually cause a knife to fail? Has anyone had a knife fail in this manner in hand?
 
i understand that my opinion is probably a bit odd in a hinderer, strider etc perspective but imo if your knife breaks due to lateral stress you failled, not the knife.
 
I can certainly understand that perspective.

What I'm asking is something like this: I place the blade in a vise, and then purposefully exert pressure until the knife fails. What I'm wondering is, does the blade always snap? Or does the pivot fail in some manner?

I am aware that some knives are ground out of thicker stock than others.
 
To be honest, I'm kind of tempted to do such a test with a BM 940, since I can always get a replacement blade.
 
Based on threads I've seen on broken knives, the blades tend to snap before anything else. That may vary depending on the model, but just about all broken knives I've seen that have taken abusive-level lateral stress have snapped at the blade. One factor leading to this might have to do with the fact that folders tend to use stainless steels and the designs aren't as concerned with being able to take such stresses. My understanding is that large chopping fixed blades would tend to be able to take these stresses much better than your average folder steel. But that's more about the blades snapping rather than bending and not so much about the blades failing rather than the pivots. I think it's just easier to make a stronger pivot than a usable blade to take lateral stress at the abuse level.
 
Also, blades with opening holes seem to lose a lot more lateral strength than those without them, all other things being equal.
 
Kaizen1 said:
that's more about the blades snapping rather than bending and not so much about the blades failing rather than the pivots. I think it's just easier to make a stronger pivot than a usable blade to take lateral stress at the abuse level.
Click to expand...

sorry cynic i didn't answer your question but i agree with kaizen even if i've yet to break a single folder in use.
 
Kaizen, that makes sense. I was thinking that was what would be the most likely scenario. There is a reason that larger fixed blade knives are made out of "softer" steels; they are more dependent on being tough enough to withstand impacts (including lateral ones) in order to be useful in their purpose.

Folders generally have blades around 60 HRC, so they are harder, but more brittle.
 
IF the blade cannot snap(it is fully inserted in material, or very has very strong design), you will get bended liners and broken pivot pin and maybe broken scales.
 
Idaho, you wouldn't happen to have pics of a knife with a broken pivot pin/broken scales due to lateral stress?
 
Too many designs and too many variables for this to be answered meaningfully. Just to illustrate the point - a small slipjoint with weak pins will behave very differently to a decent tactical with a large screw pivot and a solid handle
 
One other addition to the mix - the current trend towards one-sided Ti frame-locks, a la the Benchmade 755 and Boker Haddock I recently acquired. I can see the warping of the glass-epoxy G10, which started life as electronic circuit board material, flexing before the upgrade metal blades snap at the pivot hole. Knives like my recent ZT-301, with it's steel liner on the G10 side, are probably much less likely to fail on the non-Ti framelock size. How it would fail will remain a mystery to me... unless the youtube 'Michelin-man' has already recorded such.

It's an academic exercise for most - especially if you started with slippies. Such regular use develops an appreciation of the folding sharp device as a strict slicer/cutter. As one of the gurus of MI fb knifemaking, Mike Stewart, would say - folders start out as broken knives! Let's be careful...

Stainz
 
Usually the blades snap from what I have seen over the years.
 
Also consider if you're "shearing" the scales or not. A bent, fatigued screw is much easier to pull apart than a virgin one.


Demko stomps on some Cold steel production folder with no failure.

Since AUS8 is a relatively tough steel, not a hard one, it's interesting to see where the damage goes. If I recall correctly, the folder was an American Lawman, which has no nested liners in the G10.

I can never bring myself to like CS, but that's a different story..
 
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