Ceramic ball on Umnumzaan

pbubsy said:
What do you mean with Strider, I don't really know much about what you say...I don't doubt you, I just want to know more. I've never heard that. Do their locks not engage fully?
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They cut the lockbar face at an angle so only the very bottom contacts the tang. This equals very little metal to metal contact. They say its to get the knife locked up as strong it can be. I like the full contact my Sebbies and XM have, more contact makes me feel better about the lock. Chris and the gang know a lot more than I, so I do trust them. I also just wonder I guess. :o

I will see if I can find a pic, or make a pic of a Strider lock bar locked up.

Here is STR's take (Click me)

It is from this thread (Click me)

And Strider's own site talking about why they cut their lock face this way. (Click me)

I am not trolling here, so I am going to duck and run. I am a BIG fan of CRK, just wondering why they changed from full contact to little contact? :confused:
 
The ceramic ball imbedded in the lockbar is flattened where it contacts the blade tang, and it makes up about half of the surface area of the face of the lock bar. From what I can see, haven't been able to take it apart yet, it looks like the ceramic does not stick out from the lock bar, but I guess it does, and the distance it comes out is very, very small and my worn out eye's can't discern it. I can't really tell how the ceramic is secured in the titanium, but this is a bigger piece of ceramic than you would find in a typical detent ball. I am talking about a production model and not a prototype. When the takedown tool becomes available I will be able to tell a little bit more about it.
 
i have been carrying strider SNG's for years and i *hate hate hate* that concept of minimal lock-face interface. *EVERY* sng i've owned has developed blade wiggle prematurely because that minute area of lock face has worn. the sng would have greatly benefited from a full lock face mating, like they were in the 1st and i think 2nd generation.

still, i carry an sng daily (and have owned 7-8 of them over the past years) because i like the weight and size and blade shape and ergonomics and everything else about the knife... just i hate the locking scheme.


anyhow, back to CRK knives..

lots of you own sebenzas i'm sure, which incorporates a full lock-face mating. how many of you worry about the framelock wearing to the other side? i surely do.

i think the ceramic ball idea is ingenious. the titanium wears because it's softer than the blade steel, simple. so why not insert another medium between the titanium and blade steel to increase durability??? brilliant!


but here's what i don't get. why minimize lock face surface area? crk inserted a wear resistant bearing but then made the surface area tiny so.. isn't all that force increased and localized on that tiny surface? that's bad, no? that will increase wear, yes?

here's an idea? how about a larger ceramic ball? increase surface area and increase material hardness. or, how about two ceramic balls? double the ceramic detent life, double the surface area, halve the force/friction!




and speaking of that, why not put in two ceramic ball detents on their normal framelocking sebenzas. because the detent does get flat and wear out, and that sucks because then the knife doesn't pivot as smoothly. this does happen, and it happened to my sebenza as well as some of my more carried sngs.
 
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I'll make it short. Got & use Umnumzaan and it's EXTREMELY smooth, silent and lock is rock solid. That design requires HIGH precision in manufacturing but... CRK is #1 in manufacturing quality FOR YEARS. It's a great knife. BTW, I still have couple of Sebenzas :)
 
Midget said:
here's an idea? how about a larger ceramic ball? increase surface area and increase material hardness. or, how about two ceramic balls? double the ceramic detent life, double the surface area, halve the pressure/friction.
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wellll....technicaly (mathmaticly) speaking, when a sphere touches a flat surface, there is no surface area, just a point.

In reality, there is a small surface area when it comes to the two materials. You have to take into consideration the fact that each material has "give" to it, the steel way more than the ceramic in this case. So yes, a larger ball will give more surface area, but VERY VERY minimal, and so minimal that it would be VERY VERY unlikely to have an effect, let alone be able to measure or discern the differences.

When it comes to the detent, obviously a larger ball along with a detent of equal "diameter" will have more surface area.

Now the math that must be done to find ball/detent surface area is TRICKY! trust me, im in school for this crap


now someone post an audio or video file of a sebenza opening and a Umnum opening. I want to hear the Umnum "SNICK" when it opens.
 
right right ok i'll bite on the contact point of the sphere being a "point" not surface area. it'll be a "point" for what, like, 5 minutes? the ceramic ball wears over time and it'll flatten out, and we have contact over a small surface area.

and the ceramic ball does wear out. it happens on the ball detent on my sebenza. it happens to the ball detent on my strider(s). it happened to every linerlock/framelock i own. that's ok, because the ball detent is kind of a non-vital part of the folder-- it just makes it smooth to open/close. but you're telling me crk put that SAME ball detent behind the lock, which IS a vital part of the folder, and is saying it'll decrease wear?



i cannot wait for a few months down the road to see photos of the lockface on the umnumzaans. that, and the blade tang. i just can't figure out why the bearing thing is an improvement over the full titanium lockface. that is... unless there were two bearings! or how about like a small, ceramic plate that's pressed into the titanium instead of a ball?
 
I still do not understand the preoccupation with lock bar wear.

All moving, mating parts wear. That is the way things are in the physical world. You either have to have an acceptable replacement modality and interval for the part, or a means of adjusting it, or the part's life has to exceed the life of its need.

Under anything I can think of as being close to normal operating circumstances, the Sebenza's lock mechanism is going to have a very long service life - certainly at least on the order of a decade, probably longer. If the end of the lock bar does begin to show wear, there is a very simple adjustment modality built into the design: A thicker stop bushing can be installed. We're talking about adding a few thousandths or maybe a hundredth of an inch to the bushing in order to move the lock bar interface back into spec. This could be done several times without any perceptible change in the blade's orientation.

Surely that has got to allow for a service life that exceeds the life of the owner.
 
I believe premature wear is caused by unnecessary manipulation, over and over again. I always retard the locking bar except when the knife is actually working.
 
Lycosa said:
I believe premature wear is caused by unnecessary manipulation, over and over again. I always retard the locking bar except when the knife is actually working.
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I guess that might be an issue. You'd have to be cycling the thing a LOT, though.

My oldest Sebenza has been in service for about 8 years. Very conservatively, I can say for sure it's been cycled 6,000 times, and there has been no movement of the engagement point that I can discern. Definitely no significant movement.

So surely we could triple that number to arrive at a usable service interval for the stop bushing. That's 18,000 cycles, for Pete's sake. You could easily triple that by replacing the bushing twice, now we're at 54K cycles.

Still not seeing a problem.
 
I'm not an engineer but IMHO a convex surface mated to a concave surface is stronger than 2 flat surface on same angle or a different angle. I think this is one reason for the ceramic Lock ball. I haven't seen back of tang on the umnumzaan to see if it is concave ground but I suspect it is. I may be wrong would like to hear from CRK on the subject of lock change.
 
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