Mechanical manufacturing tolerances

[Halberd]

The Sebenza is famous (among other things) for the high mechanical precision with which it is manufactured. I am wondering what standard tolerances CRK have on the following two points:

1)When opening the knife, the lock bar moves sideways to lock the blade into its position. Doing so, the lock bar covers (touches) only a fraction of the blade's heel (this is intentional, since otherwise wear would end up causing play at this point). What is the fraction of the blade, that the lock bar should cover on a new knife?

2) On a closed knife, the blade should ideally be located exactly in the middle between the two handle slabs. How much offset from that ideal position is tolerated, e.g. when measuring at the blade's tip?

These questions are primarily meant for Chris Reeve. But I am also wondering what Sebenza owners think or have observed.
THANKS

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[Big Al]

Originally posted by Halberd:
2) On a closed knife, the blade should ideally be located exactly in the middle between the two handle slabs. How much offset from that ideal position is tolerated, e.g. when measuring at the blade's tip?

I'm going to give you an opinion on this second part of your question. I assume you noticed that the blade tip is much closer to the flat slab side than the lock side. That bothered me at first until I noticed the blade runs perfectly even along the flat slab side. I believe the lock slab is further away from the blade tip due to the design of the integral lock. This is what I see on mine and until someone says different I'm going to believe it is by design. IMHO

 

[JoHnYKwSt]

Regarding your first question. Anne answered that question a while back. I believe the answer was the lock bar should cover 50% - 75% of the blade tang.

-Johnny

 

[JohnW]

Originally posted by Halberd:
What is the fraction of the blade, that the lock bar should cover on a new knife?

My knife locks at about 60%. Also, keep in mind that the end of the lockbar is heat treated to around 90 Rc. If anything is going to get abraded on lockup, I would assume it to be the blade tang.

How much offset from that ideal position is tolerated, e.g. when measuring at the blade's tip?

If you have a knife with a questionable angle, call Chris. I had a knife that leaned a bit (about 4 percent), so he asked me to send it back to him for a look. A brand new Sebenza is on its way right now. Thanks Chris.

 

[Halberd]

JohnW,
Thanks for your comment. Now, when you say 4%, do you mean a lateral offset of the blade's tip equal to 4% of the blade length (on a small Seb: 73 mm x 4 / 100 = 2.9 mm or 0.11 inch)? Or did I misunderstand?


I am still wondering what the standard CRK spec could be?


JoHnYKwST,
Thanks for your hint. I did a search and found Anne Reeve's statement (11/03/98): "The spec position for the lock is to cover 75% of the blade."


On other frame lock knives I personally tend to prefer a tang coverage of just slightly over 50%. This way I feel confident that the lock will not make its way through to the opposite handle slab (because of wear)for a long time. I realize that this is about a compromise between lock strength and durability. Is there any reason to think that on a Sebenza a 75% coverage is a better compromise? Any opinions?

By the way, it is really cool to be able to have these discussions with all of you, while just sitting here in my Swiss mountains.

 

[JohnW]

Originally posted by Halberd:
Thanks for your comment. Now, when you say 4%, do you mean a lateral offset of the blade's tip equal to 4% of the blade length (on a small Seb: 73 mm x 4 / 100 = 2.9 mm or 0.11 inch)? Or did I misunderstand?

I'm sorry, I should have clarified. Looking down upon the spine of the blade: The tip was laterally deviated about 1 degree to the right. That's along the axis you get if you point the blade to right, instead of to the left. The blade edge, however, was deviated about 2-4 degrees. That's along the axis you get if you twist your wrist, as if you were scraping the air underneath the knife.

Given that Chris decided to replace the knife entirely, I think one can assume that deviations in general are not beloved by him. But he's by far the best judge; I've only looked at three Sebenzas in my whole life, compared to thousands.

I am still wondering what the standard CRK spec could be?

My other Sebenza is perfectly straight, no lateral deviations perceptible in any plane.

By the way, it is really cool to be able to have these discussions with all of you, while just sitting here in my Swiss mountains.

I agree! The modern day allows someone in the midst of a dry, hot desert, to have a chat with somebody up in the mountains, without even knowing each other. Interesting times!

 

[JoHnYKwSt]

Regarding the issue of wear, after thousands of openings I've concluded that the ceramic ball will be the first component to wear out. And this will take so long that it is not even an issue.

-Johnny

 

[FNG]

I don`t see the ceramic ball wearing out.
Machine tolerances are .010 for most; .005 for custom guns.
So, if both part machines are at replace, you could get .020 or .010.
This may help.