Dcdavis
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I’m taking your advice. Idk why I’ve kept following it this long
Sebenza 31 Lock Rock?!
- Thread starter HikingIsLife
- Start date
MrStabby7
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The blade on my 31 was off center too. I purchased mine at blade show from the CRK booth and noticed it right away. I asked them while I was there about it and they said it wouldn't affect the performance but I could send it in if I wanted the washers refit. A little lame for a $500+ knife but the sebenza is still one of my favs.Well heck, I was in on page 1 of this thread so I might as well chime in now that I’ve been carrying a small 31 almost daily for 2-1/2 months….
Sample size = 1, so take it FWIW.
My knife has some lock flex.. It doesn’t feel like the lock going to slip or fail, at all, but it’s more noticeable than my other CRK’s when I’m bending it over a table.
So I don’t bend it over a table and I don’t worry about it. I suppose following this thread since inception has tempered my opinion, but there it is.
My biggest gripe is a blade that’s a bit off center, not my expectation for a CRK, but it’s centered enough for Benchmade or Spyderco standards, so I decided to roll with it.
It does sound like there have been some lemons gone out over the course of this thread. I won’t deny that.
So CRK had a knife at their booth with an off centered blade, you noticed it and bought it anyway? Did they resolve the problem?
MrStabby7
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Yes, and no. I decided it would be ok and they couldn't refit it there.
So first of all let me apologize for beating the dead horse here.
But I wanted to comment because I have spent a good amount of time thinking about what the lock rock is caused by and what it means and I wanted to summarize my findings and thoughts because the information is spread out all over the place.
From reading descriptions (including Tim Reeve's) of the up/down play, aka lock rock or flex, it is fairly clear to me that it happens when cutout part of the lock is flexing. The cutout flexes such that when pushed to the point of breaking, it forms a little elbow stick out to the right (on a right handed knife gripped cutting edge down). This is what Tim describes happening when he intentionally broke the lock with a hammer.
The 21 did not break in this manner, rather the lock just disengaged/failed with a lesser force. The 21 also flex less than the small 31. So the question is why the small 31 flexes more than others. In trying to answer this question I have identified only two relevant variables in the physical system of the lockbar:
(1) The amount of tension, or how hard the lockbar wants to push toward the non-locking scale. Great tension toward the opposite scale might cause the lockbar to want to flex more, because its resting position is more bent over. However, a stiffer bar could also cause less flex, and indeed increased lockbar stiffness/tension seems likely to be a way to mitigate lockbar flex, rather than its cause. Which leads me to the most likely true cause of the increased lockbar flex in the 31 vs 21:
(2) the angle of contact between the lock interface and the tang. If the force from the tang on the 31's ball is pushing more toward the non-locking scale than was the force from the tang on the titanium lockbar on the 21, this could also cause more flex to happen.
If I am indeed correct, and there is both greater lockbar tension and a more opposite-scale-directed force from the ceramic ball, the silver lining of this increased flex is that the lock is less likely to fail by slipping out than the 21.
Submitted in partial fulfillment of my degree in armchair sciences,
Yours truly,
Toivo
But I wanted to comment because I have spent a good amount of time thinking about what the lock rock is caused by and what it means and I wanted to summarize my findings and thoughts because the information is spread out all over the place.
From reading descriptions (including Tim Reeve's) of the up/down play, aka lock rock or flex, it is fairly clear to me that it happens when cutout part of the lock is flexing. The cutout flexes such that when pushed to the point of breaking, it forms a little elbow stick out to the right (on a right handed knife gripped cutting edge down). This is what Tim describes happening when he intentionally broke the lock with a hammer.
The 21 did not break in this manner, rather the lock just disengaged/failed with a lesser force. The 21 also flex less than the small 31. So the question is why the small 31 flexes more than others. In trying to answer this question I have identified only two relevant variables in the physical system of the lockbar:
(1) The amount of tension, or how hard the lockbar wants to push toward the non-locking scale. Great tension toward the opposite scale might cause the lockbar to want to flex more, because its resting position is more bent over. However, a stiffer bar could also cause less flex, and indeed increased lockbar stiffness/tension seems likely to be a way to mitigate lockbar flex, rather than its cause. Which leads me to the most likely true cause of the increased lockbar flex in the 31 vs 21:
(2) the angle of contact between the lock interface and the tang. If the force from the tang on the 31's ball is pushing more toward the non-locking scale than was the force from the tang on the titanium lockbar on the 21, this could also cause more flex to happen.
If I am indeed correct, and there is both greater lockbar tension and a more opposite-scale-directed force from the ceramic ball, the silver lining of this increased flex is that the lock is less likely to fail by slipping out than the 21.
Submitted in partial fulfillment of my degree in armchair sciences,
Yours truly,
Toivo
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This has been covered quite extensively. The ceramic ball interface introduces a pivot point
Modernflame
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Imagine the blade being supported by three contact points that form a triangle: the pivot, the stop pin and the ceramic ball on the lock face. The large Sebenza forms a wider triangle than the small, thus providing more support for the blade. That, along with actually having a beefier lock bar, is why the large is less susceptible to lock flex. Again, most any frame lock will flex under enough load. The small 31 just flexes more. The subject of contention is whether or to what extent that actually matters.
Ah the distance between the pivot and ceramic ball contact point is another variable I did not consider. If I understand you correctly, it is analogous to how there is more torque in the center of a spinning wheel, then on the outer edge so the small 31 has to deal with with more torque than the larger one.
Edit: Now that I have the knife in hand, I notice that it actually flexes diagonally, both toward the spine of the blade and the opposite scale. As someone else said the ball functions as a pivot point: the lockbar can move because there is only one round contact point: the difference between standing on a chair vs. an exercise ball. I can't say for certain which lock design is stronger because, like all of us, I haven't done extensive testing but the flex toward the opposite scale seems like a good sign that it won't slip out.
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Owned two large sebenza 31s traded one for a strider. Ive never had a issue with either both solid lockup. The only way I see lock rock being an issue is if someone is pressing hard enough down on the spine of the blade forcing all the pressure on the large ceramic ball and titanium Lockbar creating a flex.. in my head im trying to picture this scenario. Walk into a room and you see a someone prying their knife in a awkward way trying to make it flex. When you ask wtf they are doing they reply "I read on the internet that sebenza 31s have lock rock" then I laugh and explain to them that their using their knife wrong. Does anyone else think this is a little ridiculous?
I just think it is fun to try to understand the properties of different locks. Obviously there is a minimum acceptable lock strength for a given person or application and for me the small 31 exceeds that minimum threshold, but there is still the question of by how much it exceeds it. It seems like the issue of this thread has mostly been about the aesthetics of up and down blade play, so I wanted to shift the conversation back towards performance of the lock which is more important to me.
Officer's Match
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I still think that CRK should have kept the ball groove on the blade tang lockup surface. My Large Inkosi (with ball groove) exhibits no flex.
My large Inkosi flexes just as much as my large 31 and 4 Zaans I owned.
if I can put down my armchair scientist hat and pick up my armchair engineer hat, it seems to me that having two ceramic balls and two contact points between the lockbar/tang would reduce flex, but the shape of the tang might have to be modified significantly.
Officer's Match
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Yes, but was it the initial batch LI with the ball groove? (see pic) It stops the "creep" of the ball sliding on the blade tang.
They were all 2020 or 2021.
My 2016 small Inkosi does not have the ball groove as well as my 2022 Large Inkosi. Both show less “lock rock” than my small sebendza 31, an amount of movement I would consider insignificant. I don’t think the ball groove does much and that’s probably why it’s been eliminated.
Officer's Match
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What it does is prevent the lockbar from vertical motion in lockup. Without the ball groove, squeezing the grip will induce lockbar flex wherein the ceramic ball is moving on the blade tang. While it isn't much of an issue, I personally prefer the more solid feel of the version with the ball groove - it doesn't move when gripped firmly.
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Lol, I've owed quite a few CRK over the years, and recently purchased a small 31, I never noticed and lock rock until I started reading these threads and really gripped the blade and put some pressure on it, and yes I can feel a little movement, no doubt it's from the ceramic ball because non of my 21's have it, but my Small Inkosi does also. At the end of the day it doesn't bother me one bit because I'm not going to be applying pressure on the spine of the blade when I'm cutting something, and the fit and finish in every other way is still up to the standards I've always appreciated from CRK. The design, blade shape, steel quality, heat treat, ergo's, etc, is what I love about my Sebenzas and Inkosi's. IMHO the only way you're going to have perfect non moving in any direction blade is with a fixed blade knife.
So glad I found this thread. Was just about to pull the trigger on a small 31. Will it effect anything in the long run? No. But let's face it, that rat 2 knife will do 99% of the things the small sebenza will do. And it'll do it without lock rock and you'll save 450 dollars 
.
A $450 knife should be...perfect plain and simple and to try and say it's a design feature is hilarious lol. Now if hinderer would just make more small xm18 non flippers
.A $450 knife should be...perfect plain and simple and to try and say it's a design feature is hilarious lol. Now if hinderer would just make more small xm18 non flippers
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I've struggled with blade play on knives before and am about as OCD as they come when spending big money in things. I check for blade play ridiculously...alot of pressure. I've had two different ZT 562 CF that both had slight vertical play. Ive bought and sold peobbaly 20 PM2s that all IMO have slight side to side play. I'm carrying a sage 1 that has 100% no blade play in any direction. Same can be said for a large xm18, and syderco Southard I have.