folder strengh: What I want to know is...

D

David Rock

Joined
Oct 3, 1998
Messages
883
Everyone likes to talk about how much weight a folding knife should be able to support. The common test seems to be that of clamping the blade in a vise and applying weight to the handle, to see how much force is required to collapse the blade into the handle.

A more interesting question for me is, how much force can a knife withstand in the other direction. In other words, rather than (or in addition to) trying to close the knife against the lock, why not clamp the *handle* in a vise and apply pressure upwards against the edge? Does anyone besides me want to know how hard I can lean into a knife when actually cutting something?

Assuming the knife in question has a stop pin, is the stop pin likely to endure more than the lock? In addition to the usual chin-ups-while-hanging-on-the-handle test, perhaps the Navy Seals knife testers (or Cliff Stamp) should do some elbow dips as well.

Maybe I'm crazy, but I worry less about cutting myself due to lock collapse than I do about breaking my knife when actually cutting stuff. (Bear in mind, I'm not talking about accidental lock release, but rather, structural failure.) Would a guy have to be King Kong to break a typial "tactical" folder in the manner I am describing--applying pressure upwards against the edge?

Maybe we can persuade Frank aka Rage to break some more knives.
smile.gif


David Rock

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AKTI Member # A000846
Stop when you get to bone.

[This message has been edited by David Rock (edited 04-05-2000).]
 
The locking bar on a Pakistani folder broke in half on me once, but I have never heard of a knife that cost more than $5 failing that way. Surely everybody presses very hard trying to cut something at least occasionally, especially when the knife is dull. If knives could fail that way we would know it.

I don't mean that $5 limit as a hard-and-fast rule ... it's probably worth testing any cheap knife. It's easy enough to test; should only take a minute.... You don't need a vise, just press hard on a piece of scrap wood.

-Cougar :{)
 
Yeah, that's probably only a serious problem with the ultra-cheap folders. Heavy duty chopping type stuff could probably put enough force in that direction to cause structural damage, but you'd have to try really hard to hurt the knife. I love reading about breaking knives though, and it wouldn't hurt to try breaking a few the other way!

Speaking of ultra-cheap knives, those Spyderco rip-offs from China fare very poorly in this kind of test. When you push down hard on the edge, the spine of the blade will actually jam underneath the locking bar. That can't be good!
redface.gif


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Cerulean

"Just because some folks think you make great kydex sheaths doesn't make you into some sort of mind reading psychologist." -Paracelsus
 
I have to eat my words -- I have now heard of a knife costing more than $5 failing that way, a Gerber EZ-Out: http://www.bladeforums.com/ubb/Forum54/HTML/000297.html

Sheesh ... that statement wasn't true for long, was it.... I will rephrase that to: I have never heard of a knife that wasn't &#$^*&* junk that doesn't even deserve to be called a knife failing that way. I think that'll be true for more than a few minutes ... I think that statement is pretty safe.

-Cougar :{)
 
The old Italian pick lock switchblades commonly failed backwards if used to chop on a solid object. It is a feasible failure mode for lockbacks. Just think about how much stress you can apply to the junction of blade and the lockback end if you take a full force chop at a tree limb. If the face of the lockback and the mating face on the back of the knife don't mate just right the lockback will start to creep up under high stress. Once it gets above the cut in the back of the blade you just lever the lockback to permanent failure. Strong backsprings tend to resist this. Switchblades had light backsprings and failed more than the equivalent pick lock design in the non-automatic stilletos.
 
In the case of liner locks or Axis locks, I suppose this sort of failure would have to involve either bending/shearing the stop pin, or tearing the stop pin out through the handle material (depending on how the stop pin is attached). The latter is probably not easy to do, especially if there are metal liners under the scales. I'm pretty sure I would have a hard time generating that kind of leverage with my merely human strength. Can an average person apply much more than his own weight to the knife (cutting downward in the normal fashion) without his wrist giving out or simply tearing the knife out of his hand? Even chopping doesn't seem like it would generate enough force to break even a moderately strong stop pin or handle, since you can't get much leverage with a blade 4" or less in length. I guess the ultimate test by any means practical would be to insert the blade into some appropriate nook or cranny, with the edge oriented upwards, and do chin-ups on the handle. I think this would generate more leverage against the stop pin than one could ever generate in normal cutting, because in normal cutting you would be applying force closer to the pivot point, or even on the blade itself.

Has anyone read the Allister MacLain novel "Where Eagles Dare"? There's a scene where the guys are climbing on the steep roof of a building and they have to stab their knives (not liner lock folders, of course) into the icy roof to hold on. Naturally I've never had to do that with a pocket knife. It's nice to know what's possible, though, right? In my experience the hardest I've ever pushed on a knife was when cutting through lumps of beeswax. My very light weight Al Mar Falcon Ultralight--a lockback with unlined Micarta handle--was able to do this with no damage whatsoever. I think I was pushing on the blade spine as much as on the handle.

David Rock

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AKTI Member # A000846
Stop when you get to bone.
 
Doing chin-ups will test the strength pretty well, but what about a chop instead of a slice?

<font size="-1">
just for the sake of the previous statement:
- A slice would be putting the blade against the material and then start pushing.
- A chop would be holding the blade in the air and starting the cutting motion and then hitting into the material. </font>


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"If the only tool you have is a hammer, everything looks like a nail"
Such a funny quote, true or not.
-ediconu
 
David :

A more interesting question for me is, how much force can a knife withstand in the other direction.
Click to expand...

Probably the primary reason it is usually done the other way is that failure in that direction is a more serious danger. There is no reason however you cannot look at it in the other direction as you describe.

break a typial "tactical" folder in the manner I am describing--applying pressure upwards against the edge?
Click to expand...

I was cutting hardwood with my Spyderco Calypso Jr. and leaning into it fairly heavily and noticed the handle seperating. I stopped then and took the blade in one hand (wrapped) and the grip in the other and by rotating my wrists popped it apart.

-Cliff
 
Cliff,

Your experience with the Calypso Jr. is interesting, as that is one of the knives whose strength I have been specifically curious about in this respect. Was your Calypso Jr. Micarta, steel, or Zytel? I used my Micarta Calypso Jr. to cut beeswax as described above, and I concluded that this knife was a lot tougher than I had thought. Now I'm afraid I don't remember exactly how hard I was pushing it. I was probably putting a significant amount of pressure on the blade spine in an effort not to overstress the handle (or the pins, actually). If you apply most of the downward pressure against the blade spine, I suppose you can push about as hard as you want (a ton or more of pressure?--certainly more than is humanly possible) without fear of breaking the knife. You might crush the edge, but that's about it.

I think I'm going to post a note over at the Spyderco Forum. Maybe Sal or Vince can tell us to what extent they test knives in this manner.

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AKTI Member # A000846
Stop when you get to bone.
 
Don't know much about the strength of locking folders. Just trusting the insghts gleaned from the forum and carrying a BM 720 axis lock daily.

Do know about "Where Eagles Dare." Which happens to be my favorite WWII-style movie. In the movie, they use climbing gear ice-picks. Guess they decided the knife thing didn't look right or something.

Brad
 
They probably tried it and found that it didn't work. I doubt it would.

Or maybe I may have forgotten the details of the novel. It's been twenty years or more since I read it. That icy roof-clinging scene must have made quite an impression on me.

David Rock

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AKTI Member # A000846
Stop when you get to bone.
 
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