A tale of three pivots. Dispelling some myths about CRK folders (maybe)

When talk starts up again about the 25 having a larger pivot, I have an uncontrollable urge to bump this thread. Sorry about that
 
A bit confusing, but technically, it is larger. The 21's pivot relies on the bushing for size, but still uses a smaller thread for capturing the scales.
 
bhyde said:
A bit confusing, but technically, it is larger. The 21's pivot relies on the bushing for size, but still uses a smaller thread for capturing the scales.
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Technically, I would define the pivot as the surface the blade rotates around (IE, the stationary plane), and the pivot size, as the diameter of that surface. In this case, they are identical in size. I think that method of defining a "pivot" stands up to the most scrutiny, but there are certainly other ways to look at it, and I welcome dissenting views.

With the pivot sandwiched between the scales, I bet money the 21 would be the strongest if tested against lateral force, but I can't afford to find out.
 
I could probably model up the pivots in FEA to find out (finite element analysis), but my gut feel is,..I cannot thread the larger pivots of either the Umnumzaan or the 25 into that of the 21-
That would be the inherent weakness I am talking about.
One of them is I think 1/4-20 and the other is a 5-40 IIRC

1/4=major diameter with 20 threads per inch
5= machine screw size, which in this case is around 1/8in diameter and 40 threads per inch.

Don't get me wrong,..Lateral forces would have to be tremendous to break either..BUT, to say one is bigger than the other is misleading.
 
bhyde said:
I could probably model up the pivots in FEA to find out (finite element analysis), but my gut feel is,..I cannot thread the larger pivots of either the Umnumzaan or the 25 into that of the 21-
That would be the inherent weakness I am talking about.
One of them is I think 1/4-20 and the other is a 5-40 IIRC

1/4=major diameter with 20 threads per inch
5= machine screw size, which in this case is around 1/8in diameter and 40 threads per inch.

Don't get me wrong,..Lateral forces would have to be tremendous to break either..BUT, to say one is bigger than the other is misleading.
Click to expand...

Now you have me confused. In the photos at the start of this thread, I have put all of the pivots through the pivot holes in each of the blades, and proven the pivot holes and pivot surfaces, are identical. What is the part that would not fit? My argument is they are the same size, which I think I proved, but maybe not?
 
kidcongo said:
Now you have me confused. In the photos at the start of this thread, I have put all of the pivots through the pivot holes in each of the blades, and proven the pivot holes and pivot surfaces, are identical. What is the part that would not fit? My argument is they are the same size, which I think I proved, but maybe not?
Click to expand...

The mating pivot parts for the 21 are 5-40-Something like that as far as the thread size.
The mating pivot parts for the 25/Umnumzaan are 1/4....

That is the THREAD size Cody- You are right that the outside diameter of all pivot parts,...an important distinction...all parts..the same diameter. But, for the 21, the fastener size is smaller without the pivot bushing. The head of the pivot for the 21 where it transitions from pivot to capture (head on both sides of scales) is still smaller.

It's an easy point to illustrate size in diameters from one great knife to another..it often, it's more difficult to quantify the difference in perceived strength from the 21 to the 25 style (which includes the Umnumzaan).

In the end, I think the changes from the 21 to the 25 style were less about strength and more about streamlining manufacturing. More bang for the buck...It takes less to create the 25 style than the 21, but harder to change an iconic knife that started it all..Your pictures and description are PERFECT examples of this. Everything is the same except the pivot bushing combination..


To summarize- You proved that the pivot assemblies work across the folding line- But the fasteners are very different. The diameter of the pivot changes through the scale..not the blade.
Push the umnumzaan/25 pivot through a 21 ;)
 
All I can say I my lord, what are you people doing to your knives.
 
Very informative, and entertaining discussion. Thanks. What I would buy as my perfect Sebenza? Blade shape/thickness/jimping, and finger cutouts of the 25, sandwiched into the simpler adjusting screws and bushing of the 21. No additional handle holes. I also favor the larger lock bar "thumbing surface" of the 21. Twenty- five is often difficult to get proper purchase on that opposite surface. I will call it the Sebenza 23...;-)
 
Bumped for bubbagump, regarding the "beefed up pivot" of the umnumzaan. Not beefed up, just different.
 
Thanks for bumping up this thread Cody. Always a pleasure to read these interesting facts about the Sebenza (21 & 25).

Some really head scratching discussion between you and bhyde as well.. :D
 
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