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Framelock security "throw down"...

Z

zdp189

Joined
Feb 14, 2007
Messages
274
While out chopping wood the other day (with an axe, not a knife..) I thought it would be "fun" to throw my Sage 2 tip first into the chopping block, and see how deep it would stick. So I'm just standing next to the chopping block (an old stump I use), and I throw with moderate force so as to be careful it actually hits tip first into it. No problem, an easy trick for most of us I suspect.

Now here's the rub... Whenever the knife stuck at a perfect 90 degree angle with the ground (i.e. straight up), it was fine. But if it was even 10-15 degrees less than 90 (towards the open part of the frame side), it would stick in the wood just fine BUT the frame lock would disengage! I repeated this over again several times, 100% consistently. Handling the Sage 2 I can find absolutely no "lock rock" or play in any direction, and I can't manually cause it to disengage by pushing hard on the blade. In other words, there's nothing about the lockup (frame engages tange at about 40% of the way in, pretty optimal as far as leaving room for wear) in "normal" usage that would indicate it would fail like that.

But there's more... I repeated with exactly with a brand new ZT 566. (I also remember this happening years ago with a Benchmade CQC7 that I had, albeit it was the liner lock failing. I think it even bent/deformed after that particular test)

This shakes my faith in frame locks a bit! And it makes me wonder if there are any physicists who can calculate the forces involved from a moderate "throw down" of a folding framelock knife into a chopping block and compare that to the sort of force that would be applied to the lock in more "normal" usage, like when using the knife for chopping, etc.

ps. I'm gonna try this test with all of my framelocks to see if it affects my 561 or 550 as well. I may also try it with my lock backs.

Cheers
 
Yes, test your whole collection in this manner. Let us know how it works out.
Matt
 
That's it, I'm never going to buy another knife again. If the locks fail under ridiculous tests (read: abuse) which they were never designed to withstand how can I tell that they won't just up and close on my hands for no good reason at any time??? What is this world coming to if I can't even trust my knives not to close when I'm throwing them, this is a totally real world use test right here. I mean, what if I need to silently deanimate some sentries or something from 50 yards away...surely my liner or frame lock pocket knife should be able to handle this kind of stress without the lock failing. Failures of this type are OUTRAGEOUS! I'm going to upgrade my membership to platinum level and sell all of my knives on the exchange, just in case.
 
Shock loads act differently than static loads. Hard to tell exactly what is happening, but your results are interesting.
 
I am not a physicist, but the levels of force required to disengage a liner/frame lock would vary greatly among knives.

The Liner/frame-lock design (it doesn't matter which) is generally not designed to endure such use. Keep in mind how the lock functions: spring-tension force an arm sideways beneath the tang (which is often radiused) and directs compression-force from the tang at an angle along the spring's length into the liner of the handle. Since the compression force from the tang is directed at an angle, that means that some of the force is pushing outward on the spring in the direction of disengagement. A radiused tang, while it increases wear-life, also increases this sideways force. The lock-bar wants to disengage. Spring-tension on the bar is often quite low to make it easy for users to both deploy the blade (against the detent pressure) and also intentionally disengage. This low tension means that it is also easy to accidentally disengage if force vectors are in the appropriate direction... which they are. This is why Lion Steel uses the roto-lock, CRKT uses LAWKS - secondary lock-mechanisms that prevent the lock-bar from disengaging.

Again, this does not mean that EVERY liner-lock design without a secondary lock will fail with the same level of ease, it all depends on the specific design, but this type of disengagement is a feature of the design. Now you know.
Axis, Triad (and more basic back-locks), compression, virobloc, button-lock - these designs are not so constructed. Does that make them safer or more reliable? In this type of use, yes.

Ignore the haters.
 
Its an odd lock strength test. How far away was your release point to the block did the blade have to travel.
 
Don't damage all your frame locks to find out. Ive seen axis locks, compression lock, tri ad , plunge and Framelocks all pass. It is clearly worse on a frame lock or liner lock because of the load. But if your knife is like new and not even broken in. You might damage it for no reason before the lock gets a good grab after it has worn in a bit.

At work last year anything could happen at lunch time. Such as some of the interesting employees throwing their knives at a tree. Ive seen every lock pass. And every lock fail. How do you gauge it perfectly?
 
Mind as well do a spine what test while your at it :rolleyes:

Neither will really prove anything it's outside what those knives are designed to do. And it won't tell you how strong a lock is under real world use.
 
Two reasons (from a BASIC physics standpoint).

1. When the knife is at 90 degrees, all forces acting downwards are counteracted by equal linear forces. When the knife is NOT at 90 degrees, there is a torque applied by the moment couple of the momentum of the back end of the knife and the tip of the knife being held static. This torque can not be counteracted by the pivot pin or the stop pin, so all of the load is placed on the lock interface.

2. The linear forces on the lock interface act perpendicular to the lock bar when the knife is at 90 degrees. When the knife is at another angle, the action of the linear forces is oblique to the plane of the lock interface. Without going into mechanics, this means that the lock bar will be more susceptible to buckling.

Here's a little drawing, hope this helps.

Sage_Forces.jpg


ETA: It's a little hard to see, the lines represent the forces drawn acting in the Y direction.
 
It seems pretty simple why this happened. The lock area is angled downward for wear, so when there is shock force pushing the tang against the lock bar it naturally pushes the lock bar outward. Don't throw folding knives. Of all folding knives, don't fold a frame lock. They are designed to not disengage because your hand is around the lock.
 
Well said Bpeezer. And a nice drawing as well. It is like a spine whack from heck. It has the force of heavy negative pressure on the lock and a spine smacking at the same time. Ouch. So when it comes to throwing or hanging from a liner or frame lock , it is not a good idea.
 
BellaBlades said:
Well said Bpeezer. And a nice drawing as well. It is like a spine whack from heck. It has the force of heavy negative pressure on the lock and a spine smacking at the same time. Ouch. So when it comes to throwing or hanging from a liner or frame lock , it is not a good idea.
Click to expand...

That description is surprisingly accurate :) glad I could help.
 
I call BS. This is clearly a post to push people's buttons.

Been here for 7 years and doesn't known not to throw a stainless steel folding knife? Right...
 
Holy crap, I can't believe people consider throwing a knife on a wood block blade first as "abuse". Wow. You gentlemen need to get out and use your blades more. If you have a blade that you "use" and not keeping super safe and sparkly for collecting purposes then you'd realize how ridiculous your comments are. Unless you are just framelock fanboys.

OP, I don't trust framelocks for this exact reason. I use them very cautiously. I didn't think this was such an unknown event in the knife world. Many companies use secondary measures due to this issue. It's not knew. ALL my use blades are fixed.....except my leatherman wave...that gets a pass.
 
Cryptyc said:
Holy crap, I can't believe people consider dropping a knife on a wood block blade first as "abuse". Wow. You gentlemen need to get out and use your blades more. If you have a blade that you "use" and not keeping super safe and sparkly for collecting purposes then you'd realize how ridiculous your comments are. Unless you are just framelock fanboys.

OP, I don't trust framelocks for this exact reason. I use them very cautiously. I didn't think this was such an unknown event in the knife world. Many companies use secondary measures due to this issue. It's not knew. ALL my use blades are fixed.....except my leatherman wave...that gets a pass.
Click to expand...

If you want to throw knives, buy throwing knives. Folders are not throwing knives. One difference besides the lock is that throwing knives have a very low hardness. That way they bend but don't break.
 
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