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

mikepapa1 said:
You are correct Bill but this does not appear to be one of the earlier 25's with the press fit stop pin.. the only reason I say that is it looks like it is a screw head.. and the press fit stop pins did not have a screw head on the lock bar side. But I of course could be wrong.
All the best, Dave
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You are right Dave, my 25 has the newer screwed-in stop pin, not the press fit. I do not remove it because I can't!!!!...and lord knows I've tried!!! CRK put so much lock-tight on that screw, and torqued the living daylights out of it on the lock-bar side that the only way I could remove it would be to use pliers and scratch everything up. Having said this, I feel this is perfect, and is perhaps what CRK intends. There was no lock-tight on the front slab screw for the stop pin, so I just leave the stop-pin attached to the back slab and never have to worry about aligning it after cleaning or maintenance (for the noobs out there, the 25 stop-pin has a flat side that must face the blade or they interfere. The original 25 had a press-fit pin, and the new ones are just screwed in).
 
GatorFlash1 said:
I don't understand #1 point (big geometry dummy here). If the pivot is held between the slabs at 90degree, perpendicular, I don't understand how the blade could deflect unless there is some weakness in the handle design that allows shift or movement between the slabs that changes the perpendicular position relationship between the pivot and the slabs.

Of course sloppy machining with loose tolerances would cause deflection but with today's tooling these seems somewhat unlikely.
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If you think about it, it all has to do with radius. In a perfect world, where they pivot and blade hole are machined perfectly, and never wear, you are right it makes absolutely no difference and everything should remain straight and true. However, we know that the pivot and the blade hole will have some looseness of fit, and we also know that some wear will increase the gap between the two. If you have an equal amount of looseness (play) in the pivot, the larger diameter will result in less apparent side-to-side play in the blade. If you can imagine the blade swinging left and right with whatever play there is, the smaller pivot, with the same amount of play, will result in a greater amount of left and right travel by the time you draw the angle out to the end of the blade. This is because the fulcrum is further from the tip of the blade, so a small amount of movement in the pivot, results in a larger movement of the tip of the knife. With the larger pivot the fulcrum is further from the centre, and thus the blade may deflect to the same overall angle left or right, but the overall movement is less. Hope this makes sense......

Also important is the same change in fulcrum location, will give the blade less leverage against the pivot, resulting in less wear, and less stress on the pivot to deform, or shift.
 
kwazyjuice said:
Yes indeed kid... But aren't both held the same way in between the slabs??

Which would only say give more steel around the blade, but not making the screws any stronger. The diameter of the screw gives it more strength. Not the bushing. Which like I said adds more steel around the hole in the blade not giving more strength than the larger diameter screw.

Right...? :D
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I see it as different. The pivot screw on the 25 passes right though the slabs. On the 21, the bushing is captive between the slabs. The bushing does not rotate, the blade rotates around the bushing, which is held firmly between the slabs by both the pivot screw and stop pin screw pressing the slabs together. Again....I really don't know which is the stronger or better design, and I think all CRK designs are strong ones. I was just pointing out that the 21 has rock-solid tough pivot design, even though the appearance of the screw heads might not make you think so. The 21 bushing is as large as the 25 and Umnumzaan Pivot, and has the benefit if being backed-up by the slabs holding it firm when it comes to side-ways forces against it. Just my thoughts........I promise everyone that if I win the lotto, I hire a laboratory to do a destruction test on all CRK models......gotta go buy a ticket.
 
rexromic said:
Interesting and educational post,great pics as well, thanks Kidcongo.
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Thanks everyone for giving this all a read and for your encouragement. It's a great group on this forum and a there are a lot of experts on staff. I am glad I can add something to the mix in my way from time to time.
 
Lol! Wahooo! That would be great to win the lotto :D

Anyways, I hear your points bro... Great thread my freind
 
kidcongo said:
If you think about it, it all has to do with radius. In a perfect world, where they pivot and blade hole are machined perfectly, and never wear, you are right it makes absolutely no difference and everything should remain straight and true. However, we know that the pivot and the blade hole will have some looseness of fit, and we also know that some wear will increase the gap between the two. If you have an equal amount of looseness (play) in the pivot, the larger diameter will result in less apparent side-to-side play in the blade. If you can imagine the blade swinging left and right with whatever play there is, the smaller pivot, with the same amount of play, will result in a greater amount of left and right travel by the time you draw the angle out to the end of the blade. This is because the fulcrum is further from the tip of the blade, so a small amount of movement in the pivot, results in a larger movement of the tip of the knife. With the larger pivot the fulcrum is further from the centre, and thus the blade may deflect to the same overall angle left or right, but the overall movement is less. Hope this makes sense......

Also important is the same change in fulcrum location, will give the blade less leverage against the pivot, resulting in less wear, and less stress on the pivot to deform, or shift.
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Now I get it. You are speaking of the play after lots of abrasive wear between the blade and the pivot. With the exceptional steels, and exceptional tolerances used in manufacturing these high-end knives, I was scratching my head about a 5 degree slop in side-to-side blade movement comment.

I imagine if you work in a cement factory with lots of gritty stuff in the air (and knife) you could experience that kind of wear. It would be interesting to see some pics of the pivot and blade joined together knives that have a fairly large side-to-side movement. I wonder if a gap is visible.

It is the fact that the knife with the larger pivot will have less wear and hence less side-to-side play than would a knife with a smaller pivot that would have greater wear given the same amount of usage, and if they both have the same amount of wear the location of the fulcrum is the key.

Thanks, great thread and pics.
 
Awesome thread, Cody. I'm saving this one for future reference. Sorry for being stupid, but why did the bushing pivot disappear after the 21?
 
powernoodle said:
Awesome thread, Cody. I'm saving this one for future reference. Sorry for being stupid, but why did the bushing pivot disappear after the 21?
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Thanks.....not a stupid question. Many have pondered it at great length! I would say that it's a combination of things. Certainly the labour involved in the hand-fitting part of the 21 bushing is eliminated (see blade HQ vid), as is some of the issues with the hand-fitting not being perfect all the time, which might speed up production. At the same time I think Chris Reeve wanted to do something different with the 25 pivot. I don't necessarily thing the 21 bushing is the 'be-all-that-ends-all", and there is something to be said for having some adjustment there as in the 25. My first 21 arrived tight and took about a year of use before I could tighten the screws all the way down. The 25 can be as perfect as you want to make it right away. Still you cant beat the easy maintenance of a 21 when it's fit is right.
 
This is a fantastic thread! I have had an Umnumzaan for a few years and just picked up a Large Insingo the other day. Having the Insingo has made me truly appreciate the smoothness of the 21 pivot, it is MUCH smoother than my Umnumzaan. Seeing your pictures got me wondering, did you play around with any of the phosphorus bronze washers on other knives? I ask because I am not wondering if I could make my Umnumzaan as smooth as my Insingo.
Thanks again for the comprehensive thread.
 
kidcongo said:
Thanks.....not a stupid question. Many have pondered it at great length! I would say that it's a combination of things. Certainly the labour involved in the hand-fitting part of the 21 bushing is eliminated (see blade HQ vid), as is some of the issues with the hand-fitting not being perfect all the time, which might speed up production. At the same time I think Chris Reeve wanted to do something different with the 25 pivot. I don't necessarily thing the 21 bushing is the 'be-all-that-ends-all", and there is something to be said for having some adjustment there as in the 25. My first 21 arrived tight and took about a year of use before I could tighten the screws all the way down. The 25 can be as perfect as you want to make it right away. Still you cant beat the easy maintenance of a 21 when it's fit is right.
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I don't necessarily think this is the reason why the bushing disappeared or went away. It was more about efficiency than anything else..Including hand lapping the bushing. You essentially go from two parts to one..Cutting your parts in half.
Also to note..The tolerances on the bushing, to the pivot itself were ridiculous. The pivot is even more ridiculous than the bushing as it has the ID thread and the OD is tight toleranced. (+.0002 -.0000 or something along that order) A human hair is around .003-.004 for reference. All numbers are in inch if you wondered.
It's a very small part to machine..It takes a special micrometer to check it. Kindof a mashup of a torque wrench and a micrometer. This is a problem because as the insert on the lathe tool starts wearing, it creates more tool pressure and holding that tolerance with it becomes impossible.
Being such a small diameter, it's A) Hard to check correctly/consistantly and B) Thin walled to be machining these tolerances on.(going from memory- been a very long time since I have seen this system)
The bushing itself wasn't that big of a deal..but still not the easiest thing to check. Using pins to check the ID and an micrometer to check the OD. The pins are tricky as they are in graduations of .0001. It takes the right feel to check as well as some common sense.

Ok, so now that I have explained the previous, I can now explain the reason for change. You are taking two parts that are difficult to machine and check to one part. The OD of this part is bigger, the wall thickness has increased. It saves 50% of the parts involved and reduces human error. (opportunities to screw up the parts- the more you touch them or machine on them, the more likely you are to introduce error).
All-in-all..It's a win on both sides.
 
Thanx Cody for the Great informative thread. It must have taken quite a while to do.....time well spent and Very informative. I'm sure all of

us learned something we didn't know about the knives we use and enjoy so much. :thumbup::thumbup:
 
Dear Kid,
Great stuff. Thanks for going to the effort. As a noob, I didn't notice till I took the 25 apart, the flat on the stop pin. Could you add some detail about how that should be oriented. The knife went back together fine, but inquiring minds need to know. It looks to me like the flat should be facing forward and slightly down??

I guess I will introduce myself while I am here. I am mostly coming from the kitchen knife world owning a bunch of shigs and doi, suisin, etc. and am fairly new to folders but not to sharp edges. I own a handful of crk's and benchmade and the odd spyderco.

Thanks,
Seth
 
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Actually, ignore that question. Now that I see where the clearance needs to be it is obvious - just didn't quite see it with the knife assembled. But since I asked; is it preferable to leave the handle together and pull the blade out like a 21 even though one washer has a tab? I think I went a bit OT...
 
Sweiss said:
Actually, ignore that question. Now that I see where the clearance needs to be it is obvious - just didn't quite see it with the knife assembled. But since I asked; is it preferable to leave the handle together and pull the blade out like a 21 even though one washer has a tab? I think I went a bit OT...
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Sweiss,

I leave the stop pin on my 25 (mine is the new screw type) attached to the lock slab. I don't remove it, and as mentioned it's on there for good anyways from the factory with extra Loctite or torque. I don't find it affects cleaning, and then I don't have to worry about orientation. One thing you could do if you want to remove it, is scribe a line around it in the Ti with a pin or scratch-awl to give you reference if you need to re-align.
 
This just complicated my life:) I have a large S 21. I want one larger knife for use in backpacking and fire starting chores mostly, maybe other harder use tasks which I haven't defined right now. I almost had myself convinced to sell it and pick up a S 25. One of my main reasons was the 'stronger' pivot on the 25. Now I don't know if it is worth it. The 25 is more involved to take apart and put back together. Not sure it would be worth the difference in what I could sell my 21 for and what the 25 would cost. I know the 25 has a a stouter blade, but I would imagine the blade on the 21 is no slouch. I would be interested in opinions. I'm having trouble making up my mind. And I can't afford both the 21 and 25.
 
ecallahan said:
This just complicated my life:) I have a large S 21. I want one larger knife for use in backpacking and fire starting chores mostly, maybe other harder use tasks which I haven't defined right now. I almost had myself convinced to sell it and pick up a S 25. One of my main reasons was the 'stronger' pivot on the 25. Now I don't know if it is worth it. The 25 is more involved to take apart and put back together. Not sure it would be worth the difference in what I could sell my 21 for and what the 25 would cost. I know the 25 has a a stouter blade, but I would imagine the blade on the 21 is no slouch. I would be interested in opinions. I'm having trouble making up my mind. And I can't afford both the 21 and 25.
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I guess the question is whether there are any posts regarding a broken, bent, or cracked 21 blade or pivot. I have never heard of such a thing. Maybe its worth asking in a post? I've done quite a bit of camp chores and bushcraft with my 21 without issue and used it as my work knife for over a year. For fire making I tend to use my Bravo 1, so I've not beaten on the 21 with a log or anything. It might all be perception, which was one of the purposes of my post.
 
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