Calling all those familiar with folding knife designs

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stillshot2

Joined
Jun 6, 2014
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I have a ZT 0200 and when taken apart, I noticed the lock bar has a strange piece that is drilled out of it, which would seem to only weaken it. It is seen near the end that makes contact with the blade in the photo below. Also, I don't understand why the lock bar is thinned out so much near the other side where it flexes. Is this only to make it easier to flex it and disengage it? Is there any way physically speaking that these two processes can add strength to the lockup? If so, I would like an explanation from anyone who is familiar with knife designs. It seems Ken Onion knows what he is doing but at the same time it seems doing these 2 things is a waste of time and can only make the knife weaker. Let me know what you think. Also, I give credit of the photo to member jake_lucas, whose photo I found in another thread.

1a8c7a94c1fe4a0e04267cbf506cbc7d_zps4cc351dc.jpg
 
My understanding is that it is thinned out so that it is able to flex (try bending the thicker part of the lock bar), and in regards to the hole near the jimping it wouldn't be any weaker than the thinned out section of the lock bar. Perfectly fine and I have no problems with any of my ZT's using the same or similar designs.
 
I figured the lockbar was thinned so it could be bent, but any idea why they bothered making the hole near the jimping? What purpose would this serve?
 
I'm not 100% sure to be honest, could be anything from slight weight reduction to a locating hole from manufacturing? I would guess that it has to do with the manufacturing process but I could be completely wrong.
 
stillshot2 said:
I figured the lockbar was thinned so it could be bent, but any idea why they bothered making the hole near the jimping? What purpose would this serve?
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You've almost got the principle;

The thinning at the rear of the lockbar is what makes it a spring. (which it essentially is, and a necessity for a frame-lock design)

I can't speak to the semi-circle across from the thumb notches, but I certainly don't see any inherent weakness induced by it's presence.
 
The hole in question could be part of the surface machining process, only KAI knows for sure.
 
RevDevil said:
The hole in question could be part of the surface machining process, only KAI knows for sure.
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True. When I saw it, I assumed it was a hole punched in by the vertical mill so that the slot below the lock bar could be cut. Gotta start somewhere!

But, I have no special knowledge of what KAI does or what sorts of machines they use to do it.
 
The more I speculate, I think you may be right that it is a place to start cutting in the other direction. It actually is starting to seem like it was well thought out since putting it there gives more surface area for the edge of the lockbar to contact the blade, as opposed to putting the hole in the corner like on the 0566 as seen below. What do you think?

IMG_0118_zps67e4a72c.jpg


(Once again not my photo, credit given to solidorange)
 
It certainly looks like a machining hole. Most comapanies do like that 0566, or put it at the other end of the slot. Some more innovative companies actually encorporate it into the design, like the widened portion of the lockbar cut in a shirogorov 95, or some customs, but most production companies do it like that. It's not a bad method if that's what it is, since it hides the hole, and like was said previously, doesn't reduce surface contact at the interface.

Just my .02
 
The round cutout is there to prevent a crack from starting at that area of the metal. It defocuses stress risers.
 
thinning the lockbar where the lock hinges makes it more durable. Not in the sense that you can abuse the knife it without it breaking, but in the sense that the thin material in the cut out area will bend without breaking, if the lock bar didn't have this "compliant mechanism" (if you want to do some more research) the lock bar would crack where the material is repeatedly bent. Think of a fillet knife, the thin blade is flexible and can be flexed within reason and it will spring back indefinitely, a thicker bladed knife won't flex and if you try and force it to flex it will bend and stay bent or it will break.

Regarding the cutout in the lock bar, it's probably where the laser pierced the material, normally this is done at a distance at least the thickness of the material away from the cut, on the side of the cut that will be discarded. You can see in the hole just below the stop pin and the hole below the lanyard hole in the photo that the pierce was on the outside of the hole (at about 9 o'clock,) this is sometimes done to reduce the possibility of leaving a burr inside a hole. These two holes were probably used for fixturing and needed to be burr free. In the case of the lockbar there is no reason to pierce on the inside of the profile but since the pierce needs to be approximately the thickness of the material from the edge of the cut, there isn't enough room to pierce in the lockbar area without adding some extra clearance. I can't explain why they didn't decide to pierce somewhere else though, piercing on the outside of the profile and cutting into the jimping would camouflage the lead-in and lead-out adequately.
 
That makes sense that the 2 holes near the lanyard hole and below the blade stop pin are most likely for fixturing. I was starting to wonder about those holes next so you just answered that question before I even asked. I don't know much about laser cutting so this helps clear up a lot about why knives are made the way they are. The fillet knife example also is a great analogy.
 
The only purpose of those round cut-outs is to prevent the metal from developing a stress crack. They've been a standard design element since way before laser tables or water jet cutting.
 
There isn't much your are going to be able to do to to zt0200 short of intentionally trying to break it that will hurt it. I best the crap out of mine and it had no issues.

Don't worry about these silly things and go out and enjoy the knife. Both concerns were correctly addressed above.
 
@scurvy092: I know it is tough and I do enjoy using this knife on a daily basis. Since I look at it every day I was just interested in to find out the reasons for some of the holes and designs. Thanks guys for the responses
 
Like everyone else has already said, it's thinner so it can be bent. As far as the hole, it's probably just a way the weight freaks can say "My knife is 0.00001oz lighter than yours" but I don't know why you're concerned about weight with an 0200
 
stillshot2 said:
@scurvy092: I know it is tough and I do enjoy using this knife on a daily basis. Since I look at it every day I was just interested in to find out the reasons for some of the holes and designs. Thanks guys for the responses
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Then I suggest you re-read your original post because it comes across as a guy trying to criticize a knife more so than a guy just looking for info.
 
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