does lockbar thickness really matter?

Artfully Martial

Artfully Martial

Joined
Jun 8, 2005
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It's a common understanding in the knife side of the world that the thicker the lockbar (be it liner or framelock) the better. But I don't this is quite so obvious.

In particular, lockbar thickness as a criteria is ambiguous. Where does the thickness matter? The interface with the tang? The cut out? Average thickness?

If we assume it's the interface, then is the thickness simply wasted in knives with early lockup (that's the vast majority of folders)?

If we look to the bar itself for thickness, ignoring the percentage lockup with the tang, perhaps it makes more sense. But what about the cut out? It seems like the cut out would be the obvious point of failure, and it is, by definition, the thinner part of the lockbar. And if this is so, why don't we much variation in cut out thickness?

If the weak spot is the cut out, why not reinforce that area? Put its back against the g10 scale for instance, instead, as is common, letting the cutout face the scale. Or can we fill in the gap with g10 on a 3d machine scale to reinforce it?

At any rate, assuming that lockbar thickness is a crucial factor in lock integrity, what does that actually mean? That's the central question here.
 
I am with you. I feel that the thickness of the lockbar doesnt matter if the cutout is only 1/4 of that. It's like a chain and it is only as stron as the weakest link.
 
How far down on the frame the cutout is matters, too, since the bar functions like a lever under compression. :)
 
Well, my understanding is that what really matters (especially in framelocks) is the cutout thickness. I've noticed that in STR's blog where he had posted some images of failed framelocks that all of them had failed on the cutouts. That's why I've alwayes wondered why people are so fascinated how thick a given frame slab is when it really doesn't matter. It's quite natural for something to fail at it's weakest point and in a piece of titanuim/stainles steel the weakest point is the cutout.

Now wether the cutout should be smaller or not in my view should be determined by the knife's purpose. If you want a knife for abuse, you can make it with little to no cutout, but for a knife that's designed for purposeful use I simply don't see why change anything on the designs that are in use now.
 
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You're right, it's not obvious and it's not right. There are some very detailed posts by STR on this topic in various places here.
 
Good post, i don't think it matters as much as most people think it does. :)

That's why I bought a DGG SnG (very thin in the pocket,) and love a well made liner lock :thumbup:
 
As I understand it, a liner under compression, assuming the lock angles are correct, will buckle when it fails. Thus, the thicker the liner, the more resistant to buckling it will be. I'm not sure if it applies to steel liners, but I know that when tillering wooden bows, reducing the bow width by half reduces the strength by half, but reducing the bow thickness by one-eight also reduces the strength by half.

As for the cutouts on framelocks, it seems that even though they are thin, the thin section is localized to a very short area, making buckling proportionally more difficult, as I think it depends on the ratio of thickness to length.

This is just my view on it, I"m not an engineer, so it could be totally wrong. STR can probably set you straight on it, as can a few of the other engineers I know we have lurking around on this forum.
 
I have a titanium framed liner lock with a lock bar of .095 thickness. It has no cutout and it is no problem to unlock. I would prefer less material taken out of the cutout at the expense of it taking a little more thumb pressure to unlock the liner.
 
nightman said:
I have a titanium framed liner lock with a lock bar of .095 thickness. It has no cutout and it is no problem to unlock. I would prefer less material taken out of the cutout at the expense of it taking a little more thumb pressure to unlock the liner.
Click to expand...

For the win!:thumbup:
 
STR, has posted extensively on this topic and done a very good job of it. I have one of his HEMAN Titanium frame locks which has no relief cut out all. Gasp, thats right no relief cut at all. I love it, I also have a couple of Missions that have relief cuts of 0.08 thick which is thick compared to many "hard use" titanium frame locks. I bought a digital caliper and will not keep a titanium frame lock is the relief cut is thinner than 0.075, that is why I don't have many knives.

Nightman and Charlie Mike are both like most other knife nutz and would like to see less metal removed from the relief cut or thicker relief cuts. I also would like to point out on all of the titanium frame locks I have, the lock bar face is thicker than the blade tang. Meaning even when it slides all the way from years of use, there will still be some metal exposed beyond the blade tang. I"m of the mind set that hard use tools or things marketed as such should be over engineered, over built or super adequate in every aspect.

Look up the STR post on this subject and there are many and get your answers. I'm going to change my user name to "OVERKILL"
 
That's why I now carry a Demko custom.
 
Good points. I would say the thickness of the face/lockbar matters to a point. If the lockbar is cheap knife thin and the gaps on either side of the blade are considerable then the lockbar could slip into those gaps more easily under extreme use. With a wider face, even if the lockbar is pushed against the other handle slab it will not fail and slip into the gap.

However on most quality frame or even liner locks we deal with under appropriate use it probably doesnt matter. Such as a Sebenza's lock bar being a couple thousands of an inch thicker then an Alias or DGG Strider like SoLo said.

Also with a wider face/lockbar you can argue that it will only get stronger with use and break in as more % is in contact with the blade tang.

In most opinions it probably just looks and feels better. A thicker lockbar inspires more confidence, whether a placebo or not.

I only mentioned this because the other points were covered.
 
This is why a well done liner lock is just as strong as a frame lock. They just get a bad name because it's so easy to put out an unsafe and unreliable liner lock, as many CCC's have.
 
+1 Demko custom, thats a serious cutting tool right there. Let me add one last thing, titanium frame locks can and do FAIL. STR has done a bunch of test regarding this and also had a number of failed knives sent to him as he was a repair man for one of the big knife companies for a while on top of doing his own thing. Let me say this if a lot of people knew just how little pressure it took to cause lock failures on a number of these "hard use" titanium frame locks, they would not be happy.

My theory as to why you don't see a lot more lock failures is the fact that a significant portion of these hard use titanium folders are safe queens or pocket queens not really seeing any kinda of use. Another big portion of these blades while used are used gingerly by people paying close attention to what their doing (which is good by the way). So essentially a lot of these knives are not actually being "used hard" or as some would say here "abused". All of this dramatically reduces the potential for lock failure as essentially the knives aren't really seeing a lot of actual use.

One could argue that this negates the need for actually having a more stout or robust lock, well then don't market these as "hard use" cutting tools, even though most of the owners that have em don't use em as such, their still supposed to made for it. Kinda like a Porsche not many of the owners drive me like they were designed for but the car will still perform like it is supposed to.
 
MikeC said:
+1 Demko custom, thats a serious cutting tool right there. Let me add one last thing, titanium frame locks can and do FAIL. STR has done a bunch of test regarding this and also had a number of failed knives sent to him as he was a repair man for one of the big knife companies for a while on top of doing his own thing. Let me say this if a lot of people knew just how little pressure it took to cause lock failures on a number of these "hard use" titanium frame locks, they would not be happy.

My theory as to why you don't see a lot more lock failures is the fact that a significant portion of these hard use titanium folders are safe queens or pocket queens not really seeing any kinda of use. Another big portion of these blades while used are used gingerly by people paying close attention to what their doing (which is good by the way). So essentially a lot of these knives are not actually being "used hard" or as some would say here "abused". All of this dramatically reduces the potential for lock failure as essentially the knives aren't really seeing a lot of actual use.

One could argue that this negates the need for actually having a more stout or robust lock, well then don't market these as "hard use" cutting tools, even though most of the owners that have em don't use em as such, their still supposed to made for it. Kinda like a Porsche not many of the owners drive me like they were designed for but the car will still perform like it is supposed to.
Click to expand...

:thumbup:

Let me say this if a lot of people knew just how little pressure it took to cause lock failures on a number of these "hard use" titanium frame locks, they would not be happy.
Click to expand...

I seen it first hand. I was shocked then sick to my stomach at what had just happened.
 
It does matter to me how thick the lock is, but that's mostly on liner locks. A good example would be my Emersons which uses a thin titanium liner lock. The lockbar quickly moves to the right in the course of a couple of months. Bladeplay is also quite significant and develops quickly as a result.

Early lockup doesn't seem all that important looking at my Sebenza, which has over 75% lockup and doesn't budge an inch. The lockbar also doesn't seem to move any further.
 
JMHO - Ultimately/physically yes (thicker in this case means stronger), in EDC use, doesn't matter. For many if not most EDC purposes and reasonable technique/skill a slip joint will function just fine. This is of course assuming the rest of the knife especially the lock bar/blade features are well built, line up properly, etc.

The cut out is to please 95%+ of people. With a solid bar the tension would be so great you most likely couldn't easily "flick" open/close your knife. Check out one of STR's responses to a similar thread...

http://www.bladeforums.com/forums/showthread.php?t=808644&highlight=frame+locks
 
mlanghornes said:
As I understand it, a liner under compression, assuming the lock angles are correct, will buckle when it fails. Thus, the thicker the liner, the more resistant to buckling it will be...
Click to expand...

That sounds about right to me.

The lock-bar on a Liner Lock (and Integral Lock) is always being compressed at an angle. If the liner were anchored directly beneath the blade then it would be compressed straight on and would, in theory (with a perfectly shaped perfectly centered lock-bar) flatten out instead of flexing. With the liner beside the blade it is impossible to align it with the direction of the pressure being applied to it. If you apply enough pressure, the lock-bar will bow out.
If you make the lock-bar thick enough, it will resist flexing well enough to fail by other means before it starts to bow.

On a proper Liner Lock, the lock-bar is actually supposed to be curved. There are probably several reasons for this, but thinking about it now, one of those reasons is probably to control the direction the liner bows when compressed. If the lock-bar is straight, it will have the opportunity to bow toward the unlocked position, if you have the bar permanently bent bowing it toward the locked position, it should be less likely to fail.
I would still rather have the lock-bar thick enough that it doesn't easily flex though.
 
Thicker is not necessarily better.

Assuming anything by looking at something without understanding the design and execution is dangerous.

I look at it this way. If more than a handful of people on this (or any other) forum THINK a thicker lock bar makes a tougher knife....you can bet you hind-end that a manufacturer realizes an opportunity. It would be as easy to specify a thicker lock bar as it would be to spec a different color lanyard...and neither change is necessarily made to enhance strength...but it might boost sales!

Does a thicker blade make the knife stronger? Let me ask that another way...if the force needed to bend or break a 1/4 inch thick (well made) blade is some number of times greater than the force necessary to tear your arm off you body, do we need an even thicker blade? Some portion of the market answered "yes"....and some manufactures made it happen.
 
Artfully Martial said:
It's a common understanding in the knife side of the world that the thicker the lockbar (be it liner or framelock) the better. But I don't this is quite so obvious.

In particular, lockbar thickness as a criteria is ambiguous. Where does the thickness matter? The interface with the tang? The cut out? Average thickness?

If we assume it's the interface, then is the thickness simply wasted in knives with early lockup (that's the vast majority of folders)?

If we look to the bar itself for thickness, ignoring the percentage lockup with the tang, perhaps it makes more sense. But what about the cut out? It seems like the cut out would be the obvious point of failure, and it is, by definition, the thinner part of the lockbar. And if this is so, why don't we much variation in cut out thickness?

If the weak spot is the cut out, why not reinforce that area? Put its back against the g10 scale for instance, instead, as is common, letting the cutout face the scale. Or can we fill in the gap with g10 on a 3d machine scale to reinforce it?

At any rate, assuming that lockbar thickness is a crucial factor in lock integrity, what does that actually mean? That's the central question here.
Click to expand...

Its not so obvious you are correct. Generally speaking it seems the only people/makers/manufacturers that say the thickness or the flexing doesn't matter are the ones that have made them that or still do. Honestly I don't know anyone that can really say they feel assured by the fact that simple spine pressure makes the liner lock they carry visibly flex under the light load.
Most feel that if it flexes that easy its unreliable. In testing thats not always the case. You can test some that jump right off the blade freeing it up and watch the blade snap shut hard and test others that the lock moves toward a tighter lock up. The nature of the lock type dictates that it begins self destruction from the first opening so its pretty easy in testing to develop vertical play. I've been surprised at the number of users that are not bothered by a little play and simply figure its just going to happen, and they've learned to live with it.

In an ideal world where the pressures exerted are always correctly directed at the stop pin the lock is of little concern so long as its staying put. As we know its not an ideal world and in use, particularly harder uses its quite easy to apply spine pressure to the tip of the blade quite easily. This is where a good lock pays for itself in my book. For liner locks I like at least a .050 thickness personally. These are harder to flex and quite noticeably more difficult to flex than a .040 lock liner. I don't feel now and never have agreed with anyone making a .040 or even a .045 liner lock and calling it hard use. Whatever though some do and thats fine. Apparently they work fine for a lot of folks. I wouldn't own it though.

Regarding the thickness at the interface or contact where the blade and lock meet: Most people just assume the entire lock contacts the blade. It does not. In fact the inside corner on the bottom third area of the lock should be all that contacts the blade. Actual surface area of the contact on a frame or liner lock can be pretty close to the same size on many knives. Only on certain models such as the already mentioned Sebenza where a concerted effort is made in the build quality do we see a more evened out larger foot print of contact over the same bottom third area of the lock contact. This I believe is perhaps the key difference between the Sebenza and other production folders. Chris has the best engineered lock contact of all production folders and while others will tell you they make their contacts the same way as Chris the truth is anyone can see at a glance comparing them side by side that only in theory are they the same. In practice Chris goes above and beyond to insure a more refined larger foot print area. How many Reeve locks do you have that stick and bind terribly? Not many I know. There is a reason for that believe me.

As for the cut out. Oh boy. Here I've already covered it so much in other posts I really don't know if I want to type it again. Most users would complain terribly if makers or manufacturers began making frame locks with thicker lock cuts. Only a person really wanting that extra strength and not really minding the extra baggage that comes with it (harder to close, harder to flick, more wear on the detent ball etc etc) will want that. Oh you can refine it down and find a happy medium with experimentation and by limiting the thickness of the slab you use as I did by using my .095 solid bar frame locks but overall a .125 or thicker lock simply has to have a lock cut of some kind to be functional or it will just be a failure to even try to use it. The only real draw back to a thin thin thin lock cut on a frame lock is when the folks buy one and decide to carry their frame lock clip less. Most clips act somewhat as a block for excess lock travel out the wrong way when closing the blade. This excess travel or hyper extension of the lock can cause it to lose spring tension. Its not reported often enough to worry with a whole lot but it has happened enough to make it a real world possibility.

STR
 
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