How Do Liner Locks Fail?

[Ironman]

Thanks everyone. From what I read, th extra thick LL on my 426 is actually good, and probably does make it safer. This is a great knife BTW, A+. I have heard that a Ti liner will somehow "stick" better than a steel LL. Anyone know if that's true?

 

[STR]

Titanium tends to gall or stick to both itself and different metals which is why many prefer it for liner locks. It typically won't wear quite as slowly as hardened 410 stainless or some other stainless but works fine with the added benefit of being able to color anodize it and a built in 'memory' that keeps the spring tension.

STR

 

[Cliff Stamp]

Flatter contacts just hold up better before the lock is stressed enough to move or spring back the other way from stress pressure but many makers just don't like flatter contacts because of a belief that it will cause the lock to work its way across the interface to the opposite side faster that way.

That is a big concern in high end knives, you would expect the expensive ones to last well a lifetime basically. How long have your flatter locks been in service and how do they wear? That being said, if locks fold with just 65 lbs of force on the end they should have warning labels on them and the work lock is a bit of a misnomer.

-Cliff

 

[Confederate]

On many knives I've personally tested that have had sharply angled contact areas, they cannot hold more than 65 pounds of weight at the lanyard end of the knife before the lock slides right off the blade....

Yep. The LAWKS system is very good about preventing that, but I wonder which is better, a liner lock with LAWKS or a good framelock. Most of the framelocks I've seen seem to be fairly bulletproof.

 

[the-swexan]

i believe Orangejoe nailed it.i have never had a linerlock slip .but i have had my fingers disengage the lock
my 2cents

 

[STR]

Yep. The LAWKS system is very good about preventing that, but I wonder which is better, a liner lock with LAWKS or a good framelock. Most of the framelocks I've seen seem to be fairly bulletproof.

A couple of the LAWKs system knives I've had from CRKT like the Serengeti folder set up were actually made of some pretty flimsy thin steel that didn't instill the utmost in confidence to me as a very solid lock for the lock so to speak. It worked but I never fully trusted it since it could in fact be pushed very easily inward.

Personally I trust any frame lock more just because of the fact that you can get your hand in behind the lock to do what the LAWKs system does in a liner lock and the harder you grip the more trustworthy the lock should become for you on a knife where your index finger can actually come into physical contact with it to secure it. To me it seems easier to just take any liner lock folder with a scale on it now and do a cut out around the lock removing a portion of the handle scale that is blocking access to the lock making room for more than one finger to get in behind the lock and come into physical contact with it like a frame lock does.. If you do it so its exposing the lock like it is in a typical frame lock so you can physically prevent the lock from moving back off the interface if need be during hard use its a good idea and as you can see here its possible to do and still make the folder very attractive to look at.


If you look at this link to a Bob Terzuola folder here that is technically a liner lock with some frame lock features in my view you can see that even something this simple done to the overscale of G10 or whatever handle is on the knife now can do wonders for lock reliability. I can't say if Bob is the inventer of this or not but in my opinion its as good if you take it just a bit further and take out more than just enough for the index finger to make the lock more stable under load which is why we like frame locks. Your fingers are worth it.

http://www.bladeforums.com/forums/attachment.php?attachmentid=59733&d=1157575519

The lock in his link is a lefty liner lock made by Bob but you can see that the lock is exposed enough on both sides (non lock and lock side) of the folder and just enough to allow the index finger to secure the lock during use. This is thought by some to be a great idea. I think its a better idea if you take out enough scale to allow both the index and the middle if not more fingers to get behind it. Another way to do this is like Chris Reeve does with his Mnandi folder where the lock is exposed a bit. I think I like the Terzuola design a little better but both ideas are better than blocking the lock completely away from the index finger with a handle scale if you ask me. The fact that this is not done more often is just another of the many proofs I can see that we are dealing with an industry in denial about the true reliability of the liner locking folder. If this were the auto industry those safety issues would be recalled and corrected or at least owners would be given that option.

In answer to another question. I have not really seen any problems making my lock interface flatter on my own frame locks. I have not had any problems making my lock relief cuts less extreme in thinness to spring the locks either. I speak of this in my forum in a thread about a Camillus Cuda Maxx repair you can read if you want to come over and find it. I have some old liner locks in 410 stainless Paul Bos heat treated to RC 45 for me that are in excess of 8 years old still out there in the hands of users. One of the oldest is still a favorite knife according to the owner and he says he has used it hard and daily. Being in Israel though, it isn't like I can examine it easily. Some of my older ones have sharper angles than I would probably do today but they apparently have worked well enough. Thats just it with liner locks though. As Joe Talmedge and other testers of locks have also noted on more than one occasion in more than one thread, liner locks are unpredictable. You can have one for years, have spine whacked or tapped the spine every now and then and tested it for reliablity by the method I describe in another post with pressure on the spine never once seeing it defeat only to suddenly have it fail for no apparent reason. Then it can be reliable again and seem fine. In my own testing I have seen this also.

Many people on other forums call me a liner lock hater among other things. Say what you want though. If anything I say leaves you with more information to judge for yourself I think you will see the truth as I did. When Joe first posted his feelings about liner locks I was one of those getting into him heavy about it defending it blindly. I might add that I did this to the point that it is probably true that from then on him and I never got on with each other as well as perhaps we could and I have to live with that. I thought liner locks were it. I thought wrong. Look at them for what they are taking your ego, your emotion and your loyalty to a maker or a knife out of the picture for a moment and you will see that a frame lock is simply better and a liner lock with a frame lock feature like I state above is too. For that matter Walker and Lake have a great idea also, although I fail to see the need to make it automatic. Something about that auto lock on all the latest Columbia River Knife and Tool knives reminds me of the automatic seat belts forced on us by auto makers a while back. I don't mind the idea. I just don't want it forced like that.

One thing about that question of how long the liner lock lasts is that no one can really predict or come up with an accurate answer that could be proven. How long any lock lasts before it starts to show wear is dependent on many factors like type of uses, longevity of the uses for % of hard vs less difficult tasks over time and the person involved with it. As I've said many times, once the human hand gets involved there is little to be said for what stats or testing can really predict. Some folks are just hard on stuff no matter how well made something is. Others can have something and make even one not made that strong last and last hardly showing signs of wear. Other factors include how the lock up was mated. Just look at how many different theories there are in the market right now for the 'proper' way to make a liner lock better.

I mean its very much varied as to how its done when it comes to making liner locks and you can see anything from a slight secondary bend in the lock to make the mating surface of the lock hit flatter on the interface as seen in the Kershaw Ricochet, some early Cold Steel locks and even later ones which I will gladly post pics of if you can't see it with your own eyes by simply checking it out. Or you can see flatter contacts, concave contact areas on the blades, angled sharply with convave grinds on the blade, and angled sharply flat grinds on the interface, and locks made with distinct differences from one side of the blade to the other that are obviously done on purpose like I've noted on Dozier's customs and all manner of how much of the bottom of the lock touches the blade among other things. I have also noted that some makers feel the lock interface contact should be the same for a liner lock as a frame lock while others equally as credentialed argue otherwise. We also see a lot of difference in opinion as to how much lock should come out to contact the blade. I don't know who is right or wrong, if there is a right or wrong or how to prove it. I only see what I see in my shop to tell you about.

For that matter getting back to when a liner or frame lock travels all the way or most of the way across the interface. I have seen knives in my shop years ago for something small, like a pivot screw needing replaced, or a scale fixed that cracked, or for bead blasting scratches off the blade and as is normal for me I log all knives coming to me in my book when it arrives and from who, for what and how much it will cost noting in my log when I checked it in details about it before I even touched it. These will include anything from small cracks in the handles noted, lock play before I touch it, and anything else I make note of. I do this for the customer as well as myself so I know before I dig into it what I'm dealing with. I still miss stuff on occasion though of course, I'm only human. When I do this, many times I discover things unknown to the owner. Other times I simply make note of it like that the lock was all the way across the tang but that it showed no blade play.

Some of these come back to me for something else in the future. When that happens I get to see the knife again obviously and for something else usually and sometimes years later, which has happened with several knives now that I worked on years back that are coming back to me for low rider clips since I started offering those to customers. What I note after having worked on them for something else before when I saw them again is that I find myself noting that no change has occurred in the lock since the last time I worked on it so it remains to be proven really if a lock needs service or readjustment, replacement or any attention at all just because it has travelled all the way or most of the way across the tang, especially on frame locks. I am sure to many makers that this is nothing more than normal wear. If the lock functions doing its job with no vertical movement still allowing the user to use it and close it easy enough it may actually be fine for a long long time after this and perhaps would stand up to more weight, more spine whacks and other tests once it is that far out behind the blade. It only makes sense in my mind that it would be harder to defeat being that far in to secure the blade.

STR

 

[STR]

I will add that the only time I've seen it a real problem when a lock travels all the way across the contact (other than when it allows play if that happens) or interface of the blade is when the owner of the knife allows some lateral blade play by letting the pivot pin get loose. In this case on some thinner liner locks the blade play from the loose pivot makes it possible for the lock to slip in between the liner and the blade into the space the washer fills allowing the lock to defeat, sometimes bending the lock or kinking it right there at the jam depending on the amount of force being applied when this occurs. An oversized washer on the non lock side can prevent this in a lot of designs though.

In the same scenario with a frame lock that is obviously thicker than the space between the blade and liner that the washer fills up there is little chance of it wedging in there even if the pivot is sloppy loose. So if there is no vertical blade play and the user is happy with it there is really no way to know how long it can stay that way and function fine.

STR

 

[tirod3]

Therefore - use liners thick enough they can't possibly slip in the blade/grip gap to jam half closed, or a pivot washer to fill the same gap.

Thin liners that can slip past the interface aren't necessarily weak, but the design is.

I appreciate your log book comments on liners that have been no problem, even after years of use, just because they are "all the way over" on the interface. I have read so many complaints here about a variety of knives with that situation, but the posters continue to see that as a quality issue and defective in and of itself, when their experience and pictures obviously show that nothing is going to happen, especially with thicker liners.

Frankly, they don't know what they are looking at - but you didn't say that!

 

[STR]

Frankly, they don't know what they are looking at - but you didn't say that!

No and I wouldn't say that but that does bring up another point. One of the things that I have also noted from end line users in presenting whether their lock is a 'good one' or not is the 'credentials' of the maker and how that can play into trust of a lock or trust in a maker or company and while its all well and good and certainly worth weighing in your decision before you buy the knife I think that people forget that the knife should speak for itself in the end based on the condition its in each time its cleaned and maintained and that all knives are as unique as we are as individuals. Just like people they age, they wear, their skin cracks, they get blemishes, and from this natural aging as well as use and abuse it more often than not has nothing to do with how well it was made or by whom when you develop a problem with one. With that said, circumstances are sometimes responsible for lock failures and accidents and not the knives or the makers of said knives. Neglect on the end line users part is many times the real fault. I mean lest face it if you have a car and don't take care of it very well, don't expect it to function flawlessly all the time. It won't.

Also, we are all only human. It doesn't really matter how many books the maker of a knife has written, how famous the maker is or how much metallurgical skill, knowledge, or experience they have, or if they have mechanical engineering degrees or anything else when it comes to the individual knives and circumstances behind why and when a lock fails. I see them all from all levels of the craft and in price ranges from very very high end expensive knives to the lowest priced China made knives on the market and yes even some of my own and for some normal as well as bizarre reasons.

Locks can defeat. They need to be looked over and even tested over time to make sure you are still getting that same level of function and that they still deserve that trust you have handed over to them regarding your fingers. In the event that one defeats its most always when you least expect it when your guard is down which is why I always stress that for hard use knives folders do one thing fixed blades don't do and thats fold. Doesn't matter if its a top line axis lock or the gents liner lock. You should always be wary of them regardless of any hype you might read. This goes for all locking type folders. I'm sure people can relate to this that have carried a knife for years.

All manner of things can happen to change the lock up of a folder. If its a trusted daily knife it deserves some daily or at least some routine weekly care and going over and your fingers are worth that believe me. Pocket lint can take the most trustworthy well built lockback and turn it all around for you in the time it takes to flick it open and use it to cut down a cardboard box to fit in the trash can. The next thing you know you are in the ER with your wife holding your hand asking if you are going to pass out while you are being stitched up by the on call doctor. Yes it happened. My wife reminded me of it just tonight. According to her it looked like a murder was committed in our kitchen. Only 4 stitches, and many years ago. (we were still newlyweds) Live and learn. Know your folders and inspect them regularly, you can thank me later when you remove that debris before it causes you a big doctor bill too.


STR

 

[hlee]

For the record, my benchmade apparition fails the spine wack test. Just as STR describes, the tang ramp is angles such that with a stiff wack on the spine of the blade, the lock bar moves back toward the open position. I never noticed this before, but I will be mindful of it in the future.

 

[DRider]

My only liner lock that failed testing was due to a bad angle on the blade ramp. Just as hlee notices, pressure moved it toward open. About one minute with a flat needle file fixed the angle and it worked well for years after that (until I killed it batonning some wood).

Actually, I'll mention that lock failure too. I knew it was probably fatal to the knife (it wasn't an expensive one) but I did it anyway. I was batonning away, till I noticed that the pressure had pushed the liner all the way over and past the tang ramp, wedging it permanently open, or nearly open. I remember an interview with Michael Walker, long ago, where he mentions something like this: a properly done liner lock, if it fails, will fail by jamming the knife open - the safest failure you can have.

 

[Sword and Shield]

While I'm not a historian, I think you are correct. As I understand it Michael Walker was one of the early guys making liner locks. Chris Reeve liked the concept and decided to beef it up by using the full thickness of the scale as a lock.

I simply love the simplicity of the CRK Sebenza.

Technically, the earliest version of a liner lock would be the old Cattaraugus leaf lock from ca 1900. Far before framelocks, or even before Chris Reeve was even born.

 

[Confederate]

I don't think the reliability of a liner lock has much to do with the brand or the price you pay (—though the odds of finding a lemon probably increse as price drops).

Materials do play a significant role in the reliability of a liner lock. When force is applied to the top of an extended blade, the liner material's strength should be adequate enough to hold. But then one has to worry about the blade pushing the liner to the left, catching between the blade and the liner lock. If the liner lock material is thick enough, the blade will gall against the blade and prevent it from closing on one's fingers.

As for me, I don't trust any liner lock, with the exception of CRKTs, equipped with the Lake and Walker Knife Safety. I greatly prefer lock backs and frame locks, which I believe are stronger. Recently I was astounded to see that dealers were still selling Smith & Wesson Magnesium HRT liner locks for upwards of $45-$50. (Perhaps if one chews on the magnesium handles, one can get one's daily magnesium requirements, but otherwise, what a horrible rip-off for a Chinese knife. Even the ones made in Taiwan, which are infinately better, are not worth the money in that price range!)

With the dangers liner locks pose to those who do active cutting work of heavy materials, I'm surprised that no one has actually done a test on liner locks to show how and when they're apt to fail.

 

[STR]

With the dangers liner locks pose to those who do active cutting work of heavy materials, I'm surprised that no one has actually done a test on liner locks to show how and when they're apt to fail.

This has been done repeatedly by Joe Talmedge and others showing the weakness in lateral twisting torque maneuvers as well as other issues with indenting but as to the original liner lock history, here is what I know, or at least can verify.

The liner lock has been around since the 19th century in Electricians knives. I still have several old Boker, and Camillus knives as well as some Klein folders with this work hardened brass lock on them and even though play developed on many of them they hardly ever failed due to the flat contacts and the fact that folks using them knew they were just a safety mechanism to help keep the screwdriver from closing when pushing on it to turn a screw in an outlet or wall plug cover plate and nothing more. If you pushed too hard you felt the blade move and you simply knew at that point to get a better screwdriver that can take a bit more abuse or back off a little.

In the 70s before the Walker innovations to the locking mechanism Gerber was selling a PK folder in their Sportsman line that I happen to have three of and one is their version of the electricians knife which is a two blade with the locking screwdriver. These locks, although brass function exactly like modern liner locks only the knives are technically slip joints since they did in fact have back springs.

When Walker was given what many consider bad advice about patenting his design it was due to these type locks already being out that he was advised as he was. However he made some changes that probably could have secured him more than a registered trademark for the name "Linerlock". Noteworthy of these changes are the obvious lack of a back spring and a hardened blade stop pin to replace it and the true one hand operation, as well as the detent ball and the sloped interface for contact and stepping the lock up to stainless steel and later titanium for the lock material.

There are some obscure reports of old Japanese knives that were dicovered basically considered the first folding knives that we today call friction folders. Some of these have reportedly been seen with liner locks made from carbon steel, and bronze but I have not personally seen them. I have read about them in catalogs like the Japan Woodworker and others that deal primarily in Japanese traditional cutlery though. If true it takes the liner lock, and more accuratley the ones similar to today with no back springs but a stop pin instead back to around 150 years ago or more. The Japanese have reported that these were probably copies of older Chinese razor knife designs but again none of that has been verified or proven as I understand it. Both of these countries have long histories involving cutlery and metallurgy skills handed down over generations though so there may be some truth to it but until something more concrete is found it will always be considered nothing more than speculation at best.

There are also a number of articles about early Roman folding knives from the 1st century, as well as reports of findings of Viking friction folders and more from European explorers as well as Egyptian knives. We'll probably never know but its suspected that the first locking folders were put to use around the same time that trousers were first equipped with pockets and that the first folders were probably for concealing in a sleeve or other tight space for use as defense weapons.

STR

 

[Confederate]

To me, it seems that it would be fairly easy to build in some sort of safety into the design of liner locks. That is, 1) if force is exerted that would cause the liner lock to fail; 2) the very mechanics of failure would kick in to keep the blade from closing on one's fingers. Perhaps it could be that the liner itself could graduate in size further down, becoming more substantial. This could effectively jam the mechanism before it could close to a harmful degree. Perhaps notches could be incorporated into the design in some fashion. Many knives also have flipper guards, but I have no idea how effective they are.

I've searched the Internet for photos of liner lock failures in vain. They just don't seem to be out there. No finger injury photos, either. I've also searched for LAWKS failures as well, and though I've heard anecdotal reports, there's nothing I can hang my hat on. As far as I can tell, the LAWKS does its job of either stopping or jamming the mechanism before fingers can be sliced.

 

[STR]

It is a great idea that LAWK's system. No doubt its necessary also. I really think we are living in a world where the industry of knives is in denial about the liner lock and what it can really do. Hard use is not one of them and this is obvious. I think its pretty sad when the industry as a whole sees one of the guys responsible for the design recognizing its pitfalls and coming up with a great fix only to see so few use it.

I don't know about pictures but you can find numerous reports of liner lock failures right here on these forums my friend. Several came up within the last two months on the Emerson forum alone.

STR

 

[Confederate]

It is a great idea that LAWK's system. No doubt it's necessary also. I really think we are living in a world where the industry of knives is in denial about the liner lock and what it can really do. Hard use is not one of them and this is obvious.

Amen. And here I thought it was just me. Your earlier comment about the LAWKS shim being flimsy is true; however, the shim only needs to be strong enough to block the lateral force of the blade, which is significantly less than the downward forces directly against the liner lock. If that lateral force is enough to demolish the shim, the blade could follow its natural course downward, with disasterous results. So far I've never seen that happen.

I don't know about pictures but you can find numerous reports of liner lock failures right here on these forums my friend. Several came up within the last two months on the Emerson forum alone.

I'll take a look, but I'd love to see some pics. Thanks for the replies!