Early Lock-up: knife-makers, fans, advocates please help me understand WHY??

[bhyde]

Thanks for the responses guys. I appreciate the explanations and photos and contributions in general



I like your style bro Hard to disagree with what the Godfather, Mr. Terzuola has to say about the topic! Thanks for those pics :thumbup: I feel like I'll have to dive into Terzuola's book sometime soon...




To answer your question I posted that pic as an example to contrast with the absurdly early lock up in the other pic that I posted.

Do I think that the lock I posted will NEVER slip in its current position? No, but I do believe it is secure, and like I said I trust it. I trust it because I have used this knife and intentionally applied heavy forces on it in various directions and ways in the attempt to stress the lock out of position and it has remained solid. Just for the purposes of testing it out and satisfying my curiosity, I have also spine-wacked it pretty hard with no failures. I have used it to chop, just to see what happens and the lock didn't move any noticeable amount after that...I don't regularly spine-wack or intentionally beat on the majority of my folders, but this knife conveyed such a sense of solidity upon first getting it that I felt the need to test it, stress it, and wail on it so as to see if it really was as solid as I initially believed it to be. Forgive me for not being able to present you with more scientific data in response to your questions - all I really have are my experiences and associated anecdotal evidence.

Basically up to this point the knife I pictured has satisfied all expectations (and then some!) and based on my knowledge of the knife maker (and assumptions about his level of skill) as well as my personal experiences with the knife, I will continue to trust it...

You weren't the one that I quoted and thus responded to. If I read your original post right, then you didn't buy the knife with the ridiculously low percentage of lockup.
The second knife you posted, I interpreted as yours and have no issues with the engagement of that lock.

 

[hookahhabib]

You weren't the one that I quoted and thus responded to. If I read your original post right, then you didn't buy the knife with the ridiculously low percentage of lockup.
The second knife you posted, I interpreted as yours and have no issues with the engagement of that lock.

Oops! Misunderstood your post...thought you were responding to us both! Multi-tasking between forums and studying for finals, sorry for the mix up


And yes, you read and interpreted correctly

 

[bpeezer]

I snipped the pics out..Not that they are not helpful, but no point in repetition.
You probably are misunderstanding the surface area that I am speaking of. It's the surface of the TANG that I want more engagement to, regardless of the geometry of the lockbar.

First, yes,. Depending on who the maker is, you are going to see varying geometries as well as contact point widths. Some have more engagement than others. The the pic the OP posted for example. Do you think that the lockbar itself will never slip in this position? If so, is it the faith that you have in the bend/spring force on the tang that gives you such faith? If this is the faith that you have,..what do you think about applying a force perpendicular to the axis of the blade, either intentional or unintentional? Something like a spine whack, or even batoning? Probably won't even take this much force depending on the pivot, the thickness of the ti and a few other factors. This is saying absolutely nothing about material fatigue or improper heat treats of the lockbar face.

And one last question; Ever wonder why Chris Reeve and a whole host of others target having the center of the tang as the optimum spot for the lockbar? If the center was causing them issues, either with returns or failures, do you think that they would have moved the position to a lower percentage of lockup?

Some things to think about..

My observations are not without experience, especially in the field of machining and tool making as well as design. I must be doing something right after 25yrs in this field. All my fingers are accounted for.. One poor decision is all it takes

Several things:

1. I do not think that the lock will never move. I have spent a bit of my free time studying tribology, enough to know that any liner/framelock cycled enough times will move to a higher lockup percentage. That movement rate may be imperceptibly slow, and it may change over time. This is evidenced by people having locks move from 30%-60%, and then "stopping" there.

2. Increased surface area contact could reduce pressure on the lock/tang face. This could reduce the possibility of plastic deformation of the lock face. From everything I have seen, the lock fails due to buckling rather than face deformation. If you have any examples/anecdotes pointing to the opposite, I would truly be interested in seeing them.

3. A framelock can be thought of as an end loaded column. Force applied to the ends of the column can lead to buckling. Further offset of the contact point from the bending point will require greater internal moments to counteract the load, and thus increased likelihood of buckling failure under the same load conditions. Here is an image that describes this.

4. Here's the interesting part...I think the difference would be negligible in any real scenario. I'm not trying to say that less lockup percentage is better. I'm trying to say that MORE lockup percentage is NOT better. I don't think it matters very much at all, as the movement is relatively slight and failure loading is normally high enough that I think both lockups would probably fail under the same real-world shock load. If someone has done enough testing on identical lock interfaces to show a strong correlation between lockup percentage and failure load with a high level of statistical confidence, I will gladly be open to their results. I would love to test it myself, but I don't exactly have the resources right now

5. My observations are not without experience either, as my degree is in Mechanical Engineering and I analyze tool failure on a frequent basis. More often than not, I find that failure is due to operator error (such as spine whacking )