Hello,
I've been having a bit of an e-mail dialogue with stjames for the past week. At this point, I'm still trying to puzzle some aspects out, but these are my feelings after popping a non-Sebenza integral lock using the above torque test. Joe, I'd most certainly love further comments from you as I see you as a "lock guru" of sorts.
A common point of liner-lock defeat happens with the "white knuckle" grip. Here, a knife is held in the forward grip, and the index finger contacts the liner-lock bar. If the grip is increased to a "white-knuckle" grip, the pressure of the index finger on the lock may be enough to cause the liner to slip, defeating the lock.
Another point of defeat is with a similar test, one that I call the "foos-ball torque test." Here, the handle is held in the forward grip, with the index finger contacting the liner-lock bar. The blade is immoblized in a rigid material (ie: several layers of cardboard). For a right-handed person using a right-handed knife, the knife handle is then torqued counter-clockwise. Again, pressure on the lock-bar by the index finger causes the liner to slip, defeating the lock.
The important thing to realise is the above two tests are not the same. The non-recessed linerlock is susceptible to defeat in both tests. The integral lock, by it's very design is immune to the "white-knuckle" test. However, since the lock-bar is still exposed to the index finger, there is a possibility of "foos-ball torque" defeat.
Here's how I think it works. Please feel free to poke holes at will.
There are three forces holding a right-handed integral lock closed.
1.
The friction between the integral lock bar and the angled ramp of the blade tang.
2.
The tensioned force of the lock-bar causing it to spring over to the right (and locked) side.
3.
The force of the index finger pushing the lock to the right (and locked) side.
In the white knuckle test, none of these forces are opposed, so there are no forces acting to unlock the knife. You will not see an integral lock fail this test. Ever.
This is not so in the torque test. I've done it before.
In the torque test, as the knife handle is being rotated, there is a second force imparted by the index finger. This force is pressing on the exposed inner surface of the integral lock-bar and is trying to disengage the lock.
Now, it's a competition to see whether the forces trying to keep the lock engaged are stronger than the torquing force trying to release the lock. If it isn't, the lock defeats and the knife closes. If it's close, the lock bar moves slightly but the knife stays locked open.
The torquing force is generated by your arms, while the grip force is generated by the index finger. Since my arm muscles are stronger than my index finger muscles, I do NOT expect a strong grip reinforcing the lock-up to protect against defeat in the torque test.
The above thread listed by stjames was an attempt to solicit tests from Sebenza owners, to see whether the above theory works in practice.
stjames has been testing out the hypothesis that this lock theory goes a whole lot deeper than just whether your arm muscles are stronger than your index finger muscles.
The length of the integral lock bar also seems to play a role in determining the leverage the torquing force can exert in unlocking the knife.
As well, it is important to consider the size, and location of the exposed surface of the lock-bar, and therefore the contact point between the index finger and the lock bar. This contact point, at the time of torquing, will determine the angle and direction of the unlocking force generated by the torque. And that ultimately determines whether the lock holds or releases.
Unfortunately, since each user has different sized hands, it's ultimately possible, if not extremely likely, that some users will pass this test while others will fail. Each person should test their own locks.
What are your thoughts?
Ian
