What use of knife would cause lock failure?

[mdarby]

I have read with interest about the merits of different knife lock approaches.

I am curious, however, what type of activity / cutting motion would actually apply the forces which might risk a lock failure. It seems simply push cuts (like taking the bark of a branch) wouldn't stress the lock. Is the concern the blade gets stuck and the lock is stressed while trying to remove the blade?

Thanks for any help.

 

[Esav Benyamin]

As long as the cutting edge is moving forward, you're fine. It's only if you try to withdraw the blade that a weak or defective lock might be a problem. Especially if you withdraw the blade while twisting the handle, say, in trying to work it out of a jam. You could also accidentally release a lock if you were drilling the tip into something resistent. (This is why screwdrivers on multitools need locks even more than their knife blades do.)

 

[Joe Talmadge]

There are a number of ways a lock could disengage (I assume by "failure" you mean accidental disengagement here). Here are a couple:

- The blade is in a hard material that binds it up, and you need to squeeze the handle hard to get a good grip to withdraw it. The skin of your fingers or palm sinks in and engages the lock, weakening the lock-up. Liner locks can be susceptible to this, in particular. So can lockbacks.

- The blade binds in a material, and must be torqued or wiggled out. The stress changes the lock-up geometry and the blade gives.

- Spine pressure: The blade binds in a material and is pulled straight out. This puts stress directly in the opposite direction of "normal" cutting.

- Spine impact: less common, but you could, for example, have a blade that binds, and when you pull it out, it releases and the spine smacks on something. My first-ever lock failure was a sort-of spine impact -- I stabbed the knife straight down into something, but the angle wasn't perfect so some of the impact was spine pressure. At the same time, I believe my palm flesh had slightly interfered with the lockup (it was a linerlock with the lock a tad too high). Between the two, the lock failed. Any time you stab into something hard, if your entry isn't perfect, some component of the initial impact will come in from the spine down.

- Some combination of all of the above, at the same time. If your blade is so bound up that you have to torque it out, you're probably squeezing the handles pretty good too, right?

Joe