Liner lock vs Back lock

[kawr]

I've always wondered why it's pretty much agreed upon that back locks are stronger than liner locks. I can understand that liner locks might be a bit less safe with the chance you might accidently close it on yourself but what exactly makes the back lock stronger? I reallly want to buy a Millie soon but the only thing holding me back is the liner lock. I read alot about people who claim liner locks failing and just dont stand up to wear as well as back locks or other locking mechanisms. On a side note why does the Millie use a liner lock when its supposed to be the toughest folder in the Spyderco line up :confused:

[Blerv]

I've always wondered why it's pretty much agreed upon that back locks are stronger than liner locks. I can understand that liner locks might be a bit less safe with the chance you might accidently close it on yourself but what exactly makes the back lock stronger? I reallly want to buy a Millie soon but the only thing holding me back is the liner lock. I read alot about people who claim liner locks failing and just dont stand up to wear as well as back locks or other locking mechanisms. On a side note why does the Millie use a liner lock when its supposed to be the toughest folder in the Spyderco line up :confused:

Locks are mostly preference as all the ones made by Spyderco are done for function over form. They are all extremely robust for their classification.

I wouldn't have any problem getting a Military, Endura, or Police if needing a very large folder. The lock is less of a concern (structurally) as the preferences such as left-hand bias or some people who don't like one or the other.

For the record it's "one of the toughest" folders Spyderco makes. While you would need mechanical force to beat it (eg: breaker-bar and vice) knives like the Chinook and Manix line have it beat. The compression lock is a notch stronger than the liner lock as well. Someone can probably quote the Spyderco lock strength classifications between "heavy duty" and "MBC/extra heavy duty".

I can't speak to liner locks like the Barong/Khukuri and Gayle Bradley. The liners on those knives are quite thick.

[The Deacon]

I've always wondered why it's pretty much agreed upon that back locks are stronger than liner locks. I can understand that liner locks might be a bit less safe with the chance you might accidently close it on yourself but what exactly makes the back lock stronger? I reallly want to buy a Millie soon but the only thing holding me back is the liner lock. I read alot about people who claim liner locks failing and just dont stand up to wear as well as back locks or other locking mechanisms. On a side note why does the Millie use a liner lock when its supposed to be the toughest folder in the Spyderco line up :confused:

Don't believe the Military was ever advertised as the "toughest" folder in the line up. It's an amazing combination of light weight and a large blade. It's "tough enough" for serious use and, until recently, the toughest liner lock. But it's not as tough as some models with other locks, including the new titanium RIL version of itself. It has probably been eclipsed by the Bradley and Perrin as well.

As for the reason a well made back lock is stronger than a well made liner lock, it's a question of the way pressure on the spine of the blade is applied to the lockbar. On a back lock you'd have to break something, either the "dog" on the lockbar or the tang of the blade. With a liner lock, you are putting pressure on one end of a long arm, which can flex. I specify well made for both types as poorly made knives, regardless of lock, are accidents waiting to happen.

[unit]

I think it would be a mistake to make any assumption regarding a lock's strength based on lock type alone.

If the knife in question is a Military, I am not sure there is a great deal of concern warranted. It carries a very high lock rating for a reason.

[defenestrate]

Some good points above. I believe that Sal's standard guideline for MBC lock break strength = 100Lbs force per inch of blade length. So an MBC rated 4" blade would require 400 Lbs or more to make the lock fail. Believe the compression and BBL/CBBL are well above this. Military comes close IIRC, maybe qualifies but that might depend on a few other variables that I am probably not well-equipped to speak upon. Do some searches, you will find there is a wealth of information on lock designs and strengths with input from regular folks, highly experienced users, and even top-notch designers and engineering types. You will likely find what you seek.

[bdbender]

Round and round we go. Some people believe liner locks are stronger than back locks.

Here's a quote from a 1997 article by Bernard Levine in Knives Illustrated.

"...STRONG AND SECURE
As it worked out, Mike had not anticipated just how strong
his new lock would be. About 1984 I helped to run side-by-side
destruction tests of all the types of locking folders available
at that time. Each test involved securing the handle of the knife
without blocking the movement of its blade or spring; then
sliding a one-foot pipe over the open blade (which was oriented
edge downward), to serve as a lever-arm; and finally hanging
weights from the free end of the pipe until the lock failed.
Name-brand conventional factory lockbacks failed at between
5 and 7 foot pounds (except for one that failed with just the
weight of the pipe). A Paul button-lock knife proved to be more
than twice as strong as the best of the conventional lockbacks.
But a Walker Linerlock was nearly four times as strong as the
lockbacks. What's more, when Walker's Locker did finally fail, it
failed in the open position. Instead of closing suddenly upon
failure, as all the other knives did, it seized up and became a
"fixed" blade..."

For the rest of the article see: http://www.knife-expert.com/liners.txt

[Blerv]

I recall in many places Sal saying things about MBC locks (compression and CBL/CBBL specifically) being so strong that the knife has to "self-destruct" to have the lock fail. I recall another time he said the Chinook line broke the test equipment. =)

Here's some specific info:

Sal agrees in this thread with STR

http://www.spyderco.com/forums/showpost ... ostcount=2

My answer to this question of why it is not a public thing regarding Spyderco lock strength expectations would be something like:

Because the figures for lock strength by Spyderco are really primarily used for their own in house testing on what they expect at Spyderco from their knives and not necessarily some set in stone figures that they would expect the whole world to agree with or apply to theirs. The way Sal figured it is not something used by anyone else other than Spyderco and it is something they came up with based on their own study of the locks, although SOG and BenchMade and a few other companies also use some criteria of their own to determine the strength of their own locks in relative terms as it applies to how they see fit, how they expect them to be used etc etc. This is why they are referred to as "In House Lock Strengths" and not lock strength standard or some other such name. Again though this is just my own educated opinion. Take it for what its worth.

If you have not seen it it goes something like this as I recall. This is paraphrased from something I read a good while ago. In trying to find it to post it exactly I was not able to but this will suffice I think.

In-house Lock strength standards
Light Duty equals over 25 inch/lbs of lock strength per inch of blade length
Medium Duty equals over 50 inch/lbs per inch of blade length
Heavy Duty equals over 100 inch/lbs per inch of blade length.
Very Heavy Duty (MBC) equals over 200 inch/lbs of lock strength per inch of blade length.

The lockstrength is always given per total bladelength which amounts to about 200 lbs/per inch on the strongest of their locks.

"In other words 'heavy duty' based on Spyderco's definition is 100 lbs/per inch IIRC. So basically 100 pounds of pressure on the tip of the blade translates over the length of the handle compounded by leverage. Take the Military liner lock folder for example and for arguements sake we'll contend that it has a lockstrength of roughly 400 lbs. So based on my understanding of the formula you would only need need to put a force of 133 lbs on the handle to defeat the lock. or perhaps its to break it to beyond repair. I never fully understood if the resulting failure was a simple defeat or lock permanent damage to the strength max. Maybe Sal can answer that.


STR

[kawr]

Thanks for the input guys, great info as usual.

[THG]

I've always wondered why it's pretty much agreed upon that back locks are stronger than liner locks. I can understand that liner locks might be a bit less safe with the chance you might accidently close it on yourself but what exactly makes the back lock stronger? I reallly want to buy a Millie soon but the only thing holding me back is the liner lock. I read alot about people who claim liner locks failing and just dont stand up to wear as well as back locks or other locking mechanisms. On a side note why does the Millie use a liner lock when its supposed to be the toughest folder in the Spyderco line up :confused:

I believe that against the edge, a liner lock knife is stronger. With a liner lock, you've got one stop pin that the tang pushes against. It will take a lot to get the pin to tear through the liners.

On the lock back, you've got two potential points for failure: you've got the lock bar itself as well its pivot pin. For this reason, I believe it is more likely to fail in an "against the edge" situation.

Against the spine, I'm not really sure which is stronger. The lock back uses a "hook" that doesn't go deep into the notch of the tang. I'm not sure how much weight this can hold before breaking off. The liner lock uses a thin slab of metal that "bends" into position (and can therefore be bent out of position). I don't know how much stronger (if at all) this is than a lock back's "hook."

Of course this is all based on theory. If I had the money, then I might go out and test all of this :D

[defenestrate]

Thanks for that clarification, Blerv.. much clearer now.

[Splice]

when it comes down to it, short of keeping the trash compactor doors in the death star from closing on you, I don't think lock strength on any spyderco will ever be any issue in any kind of use that isn't purposely trying to get the lock to fail.

[The Deacon]

I believe that against the edge, a liner lock knife is stronger. With a liner lock, you've got one stop pin that the tang pushes against. It will take a lot to get the pin to tear through the liners.

On the lock back, you've got two potential points for failure: you've got the lock bar itself as well its pivot pin. For this reason, I believe it is more likely to fail in an "against the edge" situation.

Think perhaps we've danced this dance before but, the bar is a piece of hardened steel, the same thickness as the blade. The idea that it might somehow deform under a compression load is just not credible. Both knives have two potential failure points when you bear down on them while cutting. They share one, the blade pivot. The other would be the stop pin on the liner lock and the lockbar pivot pin on the lockback. I would argue that, at least on lockbacks with metal backstraps, it is highly probable the lockbar would be driven hard against the backstrap before the pivot pin would shear.

You're entitled to your opinion of which is more likely to fail, but I believe liner locks are involved in the preponderance of lock failures. Can't recall Spyderco ever having major lock failure issues with any midlock model. On the other hand the C27 Walker Lightweight, C40 Jot Singh Khalsa, and the titanium version of the C53 Peter Herbst all had very high rates of lock failure. More recently, IIRC, lock failure was also one of the issues that caused the Chicago and Cat to be discontinued.

That said, I'd have as much faith in the locks on my LH Military and Sage I as I would in my Stretch's and, from everything I've read, the Bradley and Perrin probably put both of those to shame. But the C95 Manix and the Chinook would still beat them.

[THG]

Think perhaps we've danced this dance before but, the bar is a piece of hardened steel, the same thickness as the blade. The idea that it might somehow deform under a compression load is just not credible.

We did, but we didn't finish it

I cite again: remember Vivi's thread? He had a ZDP Endura whose lock bar collapsed inward. I don't think it's that incredible.

Both knives have two potential failure points when you bear down on them while cutting. They share one, the blade pivot.

And I think you said that last time... If you want to include the pivot, then you add one on the liner lock system (1 + 1 = 2), and you also add one on the back lock system (2 + 1 = 3). I still see one more potential point of failure on the back lock.

Let me ask you this. Which of these two is more likely?

1. Jenny is a liberal.
2. Jenny is a liberal feminist.

Most people will say #2. However, the correct answer is #1. Our situation is the same in reverse.

The other would be the stop pin on the liner lock and the lockbar pivot pin on the lockback. I would argue that, at least on lockbacks with metal backstraps, it is highly probable the lockbar would be driven hard against the backstrap before the pivot pin would shear.

What exactly is this metal backstrap? I'm not sure which piece you are referring to. Are they present on the D4/E4 or Stretch knives, for example?

You're entitled to your opinion of which is more likely to fail, but I believe liner locks are involved in the preponderance of lock failures. Can't recall Spyderco ever having major lock failure issues with any midlock model. On the other hand the C27 Walker Lightweight, C40 Jot Singh Khalsa, and the titanium version of the C53 Peter Herbst all had very high rates of lock failure. More recently, IIRC, lock failure was also one of the issues that caused the Chicago and Cat to be discontinued.

Again, is this against the edge, or against the spine? I am only talking about against-the-edge force, as in the force that occurs during cutting chores. I made the specific comment that I don't know which is superior in terms of against-the-spine strength.

That said, I'd have as much faith in the locks on my LH Military and Sage I as I would in my Stretch's and, from everything I've read, the Bradley and Perrin probably put both of those to shame. But the C95 Manix and the Chinook would still beat them.

Don't get me wrong; I'm not knocking either one at all. Just to give you an idea, I have 7 Spyderco folders. 6 are back locks, and 1 is a frame lock.

[defenestrate]

THG,
Typically the purpose of a locking folder is to prevent against-the-spine force from closing the knife on the user. I think we all can agree on that. I'm not sure why you're talking about against-the-edge force-you are taking about the entire chassis of the knife in such a case because the lock does NOT operate in that direction. In principle, the stronger the lock, the closer to a fixed blade it will be in terms of dispersion of force and against-the-edge force is a> NOT what the lock rating and failure tests cited above cover and b> NOT specifically the load assumed for the lock. When open, the blade and lockbar move more as a unit under load while cutting - this is standard for the design. the load is dispersed throughout the frame of the knife. Only force against the spine is a proper determining factor of a lock's ability to, well, lock. :spyder: :)

[v8r]

You can't go wrong with a Millie.I believe it is one of the most well designed liner locking knives you will ever find.I believe this is due to the arc machined In to the blade locking surface.There is no way the lock will skip off the end of the locking surface unless you bend something. Think about this.........Sal wouldn't have called it a Military if it was a weak little Pansy of a knife.If I remember correctly it was designed with our service men and women in mind for a light weight,incredibly strong folding knife. Liner locks are not my favorite lock, but the way Spyderco designs most of their knives,you will never have a problem unless you are doing something stupid......if you need a prybar, get a prybar, if you need a knife get a knife, and so on and so forth.

[The Deacon]

We did, but we didn't finish it

I cite again: remember Vivi's thread? He had a ZDP Endura whose lock bar collapsed inward. I don't think it's that incredible.

One failure, induced by someone with a penchant for destroying knives is hardly proof of anything when stacked up against numerous reports of failure for liner locks. IIRC, he was batonning the knife, hit the handle, and fractured the lockbar.

And I think you said that last time... If you want to include the pivot, then you add one on the liner lock system (1 + 1 = 2), and you also add one on the back lock system (2 + 1 = 3). I still see one more potential point of failure on the back lock.

Just because you see it does not mean it exists.

Let me ask you this. Which of these two is more likely?

1. Jenny is a liberal.
2. Jenny is a liberal feminist.

Most people will say #2. However, the correct answer is #1. Our situation is the same in reverse.

But there's more of a chance of her being both than of her being a submissive conservative.

What exactly is this metal backstrap? I'm not sure which piece you are referring to.

The piece immediately behind the lockbar, serves as the mounting point for the lock spring.

Are they present on the D4/E4 or Stretch knives, for example?

Yes, on the stainless and G-10 versions of the D4/E4 and the CF version of the Stretch.

Again, is this against the edge, or against the spine? I am only talking about against-the-edge force, as in the force that occurs during cutting chores. I made the specific comment that I don't know which is superior in terms of against-the-spine strength.

Probably against the spine. Failures in the other direction are rare on even halfway decently made knives. So, even if you are right and that, out of 100,000 knives of each lock type two lockbacks fail from pressure on the edge while only one liner lock does, you're deeming that more significant than that out of that same group, 100 liner locks will fail from pressure on the spine while only 10 lbacklocks will.

Don't get me wrong; I'm not knocking either one at all. Just to give you an idea, I have 7 Spyderco folders. 6 are back locks, and 1 is a frame lock.

Excellent testimonial for liner locks. :D

[STR]

I've always wondered why it's pretty much agreed upon that back locks are stronger than liner locks. I can understand that liner locks might be a bit less safe with the chance you might accidently close it on yourself but what exactly makes the back lock stronger? I reallly want to buy a Millie soon but the only thing holding me back is the liner lock. I read alot about people who claim liner locks failing and just dont stand up to wear as well as back locks or other locking mechanisms. On a side note why does the Millie use a liner lock when its supposed to be the toughest folder in the Spyderco line up :confused:

Frame and Liner locks are not the strongest locks you can have of the lock types available but they certainly have many merits. Many lock backs are stronger but strength is one aspect. You have reliability to consider and then even that is a matter of perspective and even setting. I mean if you are carrying a liner lock in one pocket in the field and a lock back in the other and when you go to use the lockback it doesn't work because its got muck and some debris jammed in the lock it zeroes out all that strength and reliability right there on the spot. If you rolled around in the same muck and pull out the liner lock and it still works well, which is more reliable then? When you stop to consider that if something jams down in the lock back notch in the field its not exactly like you can reach in and pull it out with your fingers you have a lot more to consider than just strength at that point. It has to work to be strong and/or reliable. So, its both when it works. What if it doesn't?

Static load tests, strength and load bearing, whacking and overstriking the knives is all well and good and its good info. to have but its again not always applicable to what occurs at times in the human hand in actual real world use. Static loads do not account for how a lock behaves when its torqued sideways or twisted and thats something likely to occur in the hand.

Strength: How strong is strong enough? Does a knife need to hold six hundred pounds on the tail end of the knife when locked open to really be useful? No of course it doesn't. Many that will only hold 100 pounds or less do all manner of tough jobs for folks in the field everyday. Accidents happen with all locking folders. All! Its more a matter of common sense. When accidents occur its most always related to human error and not a faulty device. Cars don't wreck themselves and neither do knives.

Reliability: What is reliability? Is it just pulling the knife out opening and trusting that it will always do that? Not exactly. In some uses it could be said the liner or frame lock is reliably convenient more so than another lock type in the fact that its simply easier to operate with one hand in most users hands. It could be said that an open design is more able to allow muck and gunk to pass through the frame and that a design where you can see the lock and the moving parts and know what you are looking at and dealing with at a glance is an advantage for more reliable performance than one that is enclosed or deep inside where its dark and cannot be reached in tight spaces. This is the case just as easily as it could be argued that just because the lock back is one you flick open and closed all day long every day for 40 or 50 years and it will still work to be a hand me down for your children means its the more reliable locking mechanism.

I say if you want the Military get the Millie and don't look back. The lock does the job and if you are debating over the strength consider that as far as strength goes the Millie is probably as strong as the other good liner locks being sold that it competes against. I know its not as strong as the Para Military or other locks they offer but again strength is not what its all about. Its a solid design though. I'd get the frame lock version personally but thats just me. I doubt its any stronger than the liner lock but I just like frame locks open designs and slab design better. I also feel they offer a bit more reliability in the hand over a liner lock.

STR

[Water Bug]

when it comes down to it, short of keeping the trash compactor doors in the death star from closing on you, I don't think lock strength on any spyderco will ever be any issue in any kind of use that isn't purposely trying to get the lock to fail.

+1

Also, I look at the lock on any folding knife the same as I look at the safety on a fiream... you don't place 100% faith that it'll work each and every time.

You wouldn't chamber a live round into a semi-automatic pistol, pump-action shotgun, etc., with the firing pin cocked, with the safety set to the "SAFE" position, point the muzzle at a family member or friend, and pull the trigger... at least you **** well shouldn't be doing that. I feel the same applies for any locking system on a folding knife... the lock is there to prevent the likelihood that the blade will close onto your fingers during use and that care needs to be taken by the user to eliminate any situation or circumstance that might cause the knife to be forced to close on the fingers.

[jzmtl]

One thing to keep in mind is there are different kind of back locks. The one used by Spyderco and other companies has a square notch on blade engaged by a square on lock bar, so they actually hook together. On some other folders like buck 110, the notch is more triangular, so is the lock bar that engages it. It relies on the lock bar spring to hold two engaged. This is probably the type bdbender's quote refers to which could disengage when the spring tension is overcome.

[Blerv]

I've put a considerable degree of force on my Ladybug's blade. If that's the weakest knife they have with a lock it's pretty darn impressive.

I know a group of people who train with Endura waves and walk away bleeding every time. They haven't had the locks fail on those which should be on par with the Military give/take a few pounds.

If those guys can't get a lock to fail most people wont either. The chance it's going to fail at the worst opportune moment is even more rare. Trust in manufacturing; put the rest of your trust in statistics :p .