Locks, Lock Strength and "Cutting With The Spine"

Vivi

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There's been a lot of words in many threads being exchanged on the topic of locks and just how someone should use a locking folder. I'd like to get discussion going on this particular topic, hopefully getting input from people knowledgable in this area.

A lot of people recently have stated things to the effect of, "I never cut with the spine of my blade so I don't care what your knife did when you spinewhacked it." To you people, I ask, why do you carry a lock knife if you don't need the lock then? Furthermore, if I showed you a knife of mine that failed a wrist snap spinewhack to a hard surface, would you be interested in buying it from me or carrying it as your EDC? Why or why not?

I don't know how you use your knife. But personally, there are times where I do want a lock, which is why I've moved away from exclusively carrying a Swiss Army Knife like I used to do. I don't "cut with the spine of my knife" either, but I do sometimes load it. If I'm cutting through thick, heavy material, sometimes I place my left palm on the spine of the blade to apply additional force. If I'm cutting foods, such as slicing up a carrot or peeling an apple, I'll tap the spine of the blade on a cutting board or rim of a trash can to knock off the food scraps, which is the same action of a spinewhack (So yes, it does have real life application). Many piercing cuts require attention and care to not load the spine at all, such as poking into a large melon or thick cardboard boxes. When it the outdoors, my folders will get used to do light chopping through grasses and other vegetation and more rarely on wood. Sometimes when swinging a knife around I've accidently hit the spine on something, though this is rare. On occasion I've used a baton to cut through wood, metal and other tough materials, and this too can load the spine.

This is only my personal knife usage, I'm sure others can come up with other ways they "cut with the spine."

Why am I pointing this out? To show you, that yes, there are times where the lock is stressed when using a folding knife. Most of the things I've listed I've done with my Swiss Army Knives, such as tapping the spine of the blade on the cutting board to knock off apple peeling and the like. Why should my slip joint SAK be able to do this, but many claim doing the same thing to a lock knife is abuse? This seems contradictory to me.

If I can purchase, for 20$ from Company X, a liner locking knife that can take full arm swings to the spine (I consider this abusive and don't normally spinewhack my knives this way), why should a 50$ or 100$ liner lock knife from Company Y fail a wrist-snap spinewhack? Am I merely paying for fancy materials, rather than a higher level of craftsmanship? This seems contradictory as well.

These are all expectations I have being a fairly educated knife buyer (At least compared to the average Joe). Many of my friends will have absolutely no hesitation taking a 5$ Maxam knife and batoning it through wood using improper technique (That is, hammering right near the tip of the blade and keeping the knife locked). This technique stresses the lock very much, but these 5$ knives have, so far, held up to the abuse. This is just one example of what the "uneducated public" expects a locking knife to be able to do. I bring this up because what many here would argue as abuse pales in comparison to things other people do every day with their folders. Not saying I condone these actions, just using them for a point of comparison.

I would like to hear what others have to say, I've typed enough.
 
And valid points, Vivi! On several occasions, here and on other knife forums, I have had to justify why I choose to always check the locks on my folding knives. My personal feeling is, if you are going to use a locking folder for any more than a show piece, you should really make sure your lock holds!

I am not talking about whacking the spine of your folder with a pickup truck, I'm talking about performing an occasional "spine tap" with sufficient force, visually checking the locking mechanism, checking lock reliability while "white knuckle" gripping the handle, and applying mild pressure against the locking mechanism. In fact, I whole-heartedly suggest using the lock test parameters kindly laid out by highly intelligent folks like Joe Talmadge, A.T. Barr, Sal Glesser, and STR!

The fact of the matter is, no matter how carefully one cuts something, in real life there is always the possiblity of the spine of the blade contacting something by accident! I have done it and I have seen it done! If one intends to use their knife in a situation where time is of the essence (think emergency/rescue applications for example), then they should realize that the situation might not be coducive to careful cutting (cramped area/objects moving/victim moving). Heck, even using a folding knife for field dressing an animal could likely result in the spine of the blade inadvertantly contacting something.

My personal feeling is, if your locking folder might see any use beyond taking up space in a safe or hanging on a wall, you owe it to your fingers to check the reliability of your lock!

Regards,
3G
 
And valid points, Vivi! On several occasions, here and on other knife forums, I have had to justify why I choose to always check the locks on my folding knives. My personal feeling is, if you are going to use a locking folder for any more than a show piece, you should really make sure your lock holds!

I am not talking about whacking the spine of your folder with a pickup truck, I'm talking about performing an occasional "spine tap" with sufficient force, visually checking the locking mechanism, checking lock reliability while "white knuckle" gripping the handle, and applying mild pressure against the locking mechanism. In fact, I whole-heartedly suggest using the lock test parameters kindly laid out by highly intelligent folks like Joe Talmadge, A.T. Barr, Sal Glesser, and STR!

Nice post. I always check the locks on my knives when I get them. I'll usually open them a lot when they're new to break them in some, visually check the locks, give them spine pressure with my palm and some light taps on the wooden arm of a chair, in addition to other routine checks like seeing if there is any play, making sure all the handle screws are tight, testing sharpness and examing overall F&F. If a knife is just for collection purposes I wouldn't care, but knives that I use every day need to be secure and in proper working order.

I think there might also be some confusion about spinewhacking. When someone says spinewhack, I might mean a light wrist snap on a piece of wood and they might mean a full arm swing into the same. I remember seeing the Subcom lock failure video where the person did exactly that, and I think that's taking it a bit far. If you're doing destructive testing to the point of failure go for it, but if you just want to test your lock I think that would do more damage than anything else. Steel is tough, but hit it hard enough and it'll bend, dent or deform in some way.
 
Great posts guys. I buy locking knives to prevent the chance of the knife becoming a guillotine to my fingers. And though I don't do things that would directly go against the lock in an abusive manner, I like to know that the lock will be secure, especially for the "just in case" moments.

If it's in my price range and I like the knife design, then I'd rather have a stronger, more secure lock than not for the same reason that I would like a higher performance steel than not.
 
A lot of people recently have stated things to the effect of, "I never cut with the spine of my blade so I don't care what your knife did when you spinewhacked it." To you people, I ask, why do you carry a lock knife if you don't need the lock then? Furthermore, if I showed you a knife of mine that failed a wrist snap spinewhack to a hard surface, would you be interested in buying it from me or carrying it as your EDC? Why or why not?
I won't own a knife that fails a spine whack test. My spine whack test consists of a light strike on a soft surface, and a light strike on a solid surface. If you buy a folder with a lock, you are paying for this feature. I don't buy cheap knives, so I fully expect my knife to be free of defects. I expect a folder to stay locked until I make a deliberate effort to disengage it. All locks can fail, but I expect a certain degree of strength and reliability.
 
A lot of people recently have stated things to the effect of, "I never cut with the spine of my blade so I don't care what your knife did when you spinewhacked it." To you people, I ask, why do you carry a lock knife if you don't need the lock then? Furthermore, if I showed you a knife of mine that failed a wrist snap spinewhack to a hard surface, would you be interested in buying it from me or carrying it as your EDC? Why or why not?

First of all, I DO carry knives that don't lock. I actually prefer them over locking knives in many cases. If I feel a lock is essential for the task at hand, that task calls for a fixed blade knife, not a folder.

If you show me a knife of yours that has been subjected to a wrist-snap spine whack, I will not be interested in buying it whether it passed or failed. I prefer not to buy knives which have been subjected to deliberate abuse.

Just for fun, look up "leverage" sometime. Measure the distance from the pivot pin to the tip of the blade and the distance from the pivot to the center of the lockface on your favorite locking folder. Now calculate the effect of leverage when you apply force to the blade against the lock. You might be surprised at just how much force you are actually applying to the lock. It gets even worse when you start figuring in shock loading, kinetic energy transfer, and the rest of the physics involved.
 
I often carry slippies. I am careful never to depend on the lock of a blade when I cut. I don't pry with a blade. I don't cut with the spine. But I do check locking blades with a mild spine whack on the sole of an old sneaker. I don't check them all the time, but I do check them once.

I won't carry a slippie that has a broken spring. Nothing to hold the blade open. A small seemingly innocuous movement could cause it to close on my hand. For the same reason I want to know that the lock on a locking blade works. Because the lock is the only thing holding it open. A small seemingly innocuous movement could cause it to close on my hand.
 
Yablanowitz you make a good point there. Physics is never wrong. i dont ever do the spine whack test i will put hand pressure just to make sure the lock is solid, but i would not want to purposely abuse the knife. If it is a whack to a wood chair or somthing of that nature i dont think that is abuse in less your swinging the knife. but a light tap to make sure it stays is fine. The other day i cut this nest of spyder eggs off one of my plants and some of the eggs stuck to my blade i wacked the spine on a soft branch to remove the crap from my blade. Otherwise i dont use it to do pull ups with or hang from.
3GuardsMen i do agree STR really knows his stuff he completly made my CQC-15 into a left handed Ti Frame Lock its amazing. I carry it everywhere.
 
I prefer not to buy knives which have been subjected to deliberate abuse.
Well, that would be your own personal definition of abuse, yet you are presenting it here, as if your opinion is an accepted standart. Sal for example disagrees with you, obviously many others on the forums disagree with you. Assuming that we are talking about reasonable and responsible spine "whacking" (I never liked the word), all Spydercos are "spine whacked" in QC. I guess I hope you don't own any Spydies.

Just for fun, look up "leverage" sometime. Measure the distance from the pivot pin to the tip of the blade and the distance from the pivot to the center of the lockface on your favorite locking folder. Now calculate the effect of leverage when you apply force to the blade against the lock. You might be surprised at just how much force you are actually applying to the lock.
I think it would be unfair to Vivi to assume that he doesn't know what leverage is and how it applies to pivots. He has been around for a while and he has participated in threads were leverage and torque as they pertain to locks and pivots have been discussed. I think quite a few of us that have been around for a while are well aware of what kind of force you can apply to a lock, thank you for your concern. And precisely BECAUSE we know, we are also aware that there are lock types and mechanisms that when executed well, will stand up to some sever leverage. I suggest, you re-read a few of STR's posts who has written about this in great detail and in great depth and who has a great deal of personal experience.

To carry a fix blade is simply not an option for many of us or not on all occasions and a well designed folder will go a long way towards what a fixed blade can do. And no it will not do ALL a fix blade can do. It is a compromise, but one that is well worth looking at. Quite obviously most people agree with me as the locking folder is the largest market segment these days BY FAR. I think the fixed blade - slip joint crowd has kind of missed the train (assuming that is about the lock and not simple preference) - locking knives have come a long way in the past 20-30 years.
 
There's going to be some time, some place that you want or need to stick the point of the blade through something. If the lock fails, you lose a finger. You have to have confidence in your lock. So, you test it.

Once I ran over one of those 5 gallon industrial plastic containers on the freeway, it fell off the truck right in front of me. It jammed solid between my tire and the frame of the car. I got the car to the side of the road but it was undrivable that way. I had a good knife and went under the car. It was stab into the plastic, and cut... stab, then cut... until I had it in pieces and could remove it and could drive away. Try that without a locking blade? Forget about it!
 
How someone should or should not use a locking folder is really a personal thing much the same way the kind of edge a person wants is or what a person considers sharp. Some prefer a very course edge like a 220 Grit DMT diamond puts on an edge while others will go for the 8000 grit water stone. Some feel that if a folder locks it means its supposed to be invincible and some have a little more common sense and are more practical and cautious about how they use them even if they do happen to lock opened. Still others seem to think they can just fall asleep at the wheel now that they own a knife that locks and use it more recklessly than one that does not lock open. This is a recipe for a nasty lesson in life though as many have learned in a not so easy way.

Knowing your carry knife is a good idea. Being in tune with it and how it feels, functions, sounds etc are all something you should focus on also and pay attention to. This way if something changes you are right there on top of it. Don't be out of tune like my wife with her car. She can drive that thing daily and hear it running normally as it should every day for 5 years and not notice that it now sounds like a typewriter going down the street and requires some attention. This is not paying attention to your tool in my book and something you have to teach yourself if it does not come to you naturally. If you are one like my wife, take your everyday knife out and give it a closer exam. Pay attention to those things, look it over inside and out, note how things come together, spaces and gaps from side to side, and get to teaching yourself what it should be when normal.

Periodic checks of the system of your folding knife is necessary and recommened. Check the nooks and cranny areas, the recesses, stop pin or lock bar, spring condition and anything else that stands out to you as well as forcing yourself to look at some that don't. How you do any testing is again a personal thing but many get a bit carried away I think and like many things in life knowing when enough is enough is a bit of an art. Think of it this way. If it was your car you don't drive up to 50 mph everyday or even every month and slam on the brakes hard locking them up to make sure they work. This is wear and tear that is needless and hard on more than just the brakes. Spine whacking your folder by the computer more than rarely is akin to this same treatment of your car. Its needless abuse and will just weaken it that much more for when you really do need it to work. Test it yes. But just like taking a pill for a headache more is not necessarily always better. Only test your lock long enough to know it is functioning properly and then put it to work.

STR
 
Personally, I think a lot of people get their panties in a wad over which type of lock is the best or the strongest, and whether or not they can beat on bricks and bottles with the spine of their blade and not cause the lock to fail. Grow up! Locks on folding knives are a comparatively recent innovation. Men used to know how to use their knives without cutting themselves, even back in the Dark Ages (figuratively speaking) when all they had were friction folders without so much as a spring to help keep the blade open. Using a folding knife correctly is not rocket science, folks. Didn't your daddy teach you anything?
 
Well, that would be your own personal definition of abuse, yet you are presenting it here, as if your opinion is an accepted standart. Sal for example disagrees with you, obviously many others on the forums disagree with you. Assuming that we are talking about reasonable and responsible spine "whacking" (I never liked the word), all Spydercos are "spine whacked" in QC. I guess I hope you don't own any Spydies.

As I recall, Sal stated that it was a mild tap, rather than a wrist-snap whack. They may really whack them during design and engineering testing, but not each and every one of a production run

I think it would be unfair to Vivi to assume that he doesn't know what leverage is and how it applies to pivots. He has been around for a while and he has participated in threads were leverage and torque as they pertain to locks and pivots have been discussed. I think quite a few of us that have been around for a while are well aware of what kind of force you can apply to a lock, thank you for your concern. And precisely BECAUSE we know, we are also aware that there are lock types and mechanisms that when executed well, will stand up to some sever leverage. I suggest, you re-read a few of STR's posts who has written about this in great detail and in great depth and who has a great deal of personal experience.

To carry a fix blade is simply not an option for many of us or not on all occasions and a well designed folder will go a long way towards what a fixed blade can do. And no it will not do ALL a fix blade can do. It is a compromise, but one that is well worth looking at. Quite obviously most people agree with me as the locking folder is the largest market segment these days BY FAR. I think the fixed blade - slip joint crowd has kind of missed the train (assuming that is about the lock and not simple preference) - locking knives have come a long way in the past 20-30 years.

I agree that folding knives are far more convenient than fixed blades. I am not allowed to carry a fixed blade knife at work, so I do virtually all my work with folding knives. Most tasks can be safely performed with a slip joint folder if you use proper technique and care.

In my opinion, the lock on a knife is more akin to the seatbelts and airbags on a car than the brake system. Yes, they are a lot better than they were 20-30 years ago. Yes, they may save your life when things go wrong. Yes, I visually inspect them frequently to check for signs of wear or damage. But I don't impact test my locks any more often than I impact test my car to ensure the airbag deploys properly. If the engineers and manufacturers have done their jobs, it will. I'd rather trust to my own alertness and driving skill to avoid accidents than rely on the airbag to prevent injuries, just as I prefer to rely on my own skill to keep my folding knives from closing on my fingers than relying on a mechanical device to prevent injuries. You may feel differently. They are your fingers. It won't hurt me a bit if you learn the hard way that no mechanical device is 100% reliable.

As far as me picking on Vivi, I'm sorry, but if he really does know these things, why are we still beating this dead horse?
 
Interesting discussion.

IMO a safe and reliable lock on a folder extends its scope of use and versatility. I really wouldn't care to try to bore a hole in a piece of wood with a slipjoint, or use one for self defense, for example.
 
Locks on folding knives are a comparatively recent innovation. Men used to know how to use their knives without cutting themselves, even back in the Dark Ages

Not true. Folding knives with a large variety of locking mechanisms were in common use during the Age of Migrations (formerly called the Dark Ages).
 
Just for fun, look up "leverage" sometime. Measure the distance from the pivot pin to the tip of the blade and the distance from the pivot to the center of the lockface on your favorite locking folder. Now calculate the effect of leverage when you apply force to the blade against the lock. You might be surprised at just how much force you are actually applying to the lock. It gets even worse when you start figuring in shock loading, kinetic energy transfer, and the rest of the physics involved.

The definition of leverage is all well and good but how does it relate to lock strength during practical use?

In certain circumstances 100 is an insumountably large number, in others a miniscule measure dismissed easily. The mind boggling numbers one can generate by taking simple measurements and multiplying them are meaningless to the keen observer.

Take for example your calculation from another thread about damage to a mid-lock folder:
Measuring your pictures on my screen shows me a ratio of about 17:1 between the blade length and the lock length. That means any closing force applied to the tip will be multiplied by 17 when it is transmitted to the lock face. That lock face has a surface area of about 3 square millimeters, or about .005 square inches. Tapping the tip of the blade on a hard surface with a force of 5 pounds is exerting a force of 17,000 pounds per square inch on the lockface. Doing that repeatedly is going to cause peening, no matter what kind of steels are involved. A heavy spine whack of 20 pounds exerts a force of 68,000 pounds per square inch to the lock face.

If we continue the equation 68,000 lbs/Sq/In turns into about 340 pounds on the .005" lock face. The 5lb spinewhack would thus produce 85 pounds of force on the lock face. Now, what does all this mean? Nothing, there isn't any way to quantify these numbers or apply them against other measurements to give an adequate indication of strength. The knife may have been defective and 340 lbs/Sq/In may have been 1/10th of it's actual strength, there isn't any way to know.
 
The definition of leverage is all well and good but how does it relate to lock strength during practical use?

Breaking it down to real world applications if you apply 100 pounds of pressure on the tail end of a long knife like say a BenchMade 804 it would translate as more weight at the pivot and lock contact on the blade than the same 100 pounds of weight on the tail end of a Buck Strider Mini 881 folder. Its all about leverage. That same 100 pounds could easily be 400 pounds at the lock contact on a longer knife but fully half that on a smaller one if not less.

STR
 
Breaking it down to real world applications if you apply 100 pounds of pressure on the tail end of a long knife like say a BenchMade 804 it would translate as more weight at the pivot and lock contact on the blade than the same 100 pounds of weight on the tail end of a Buck Strider Mini 881 folder. Its all about leverage. That same 100 pounds could easily be 400 pounds at the lock contact on a longer knife but fully half that on a smaller one if not less.

STR

I understand as much, but aside from general concepts (knives with shorter blades and the same lock are stronger; i.e. Manix/MiniManix) does this even apply scientfically to lock discussion? I think it is a red herring, does not apply other than conceptually.
 
I don't follow that. The Manix and Mini Manix are different. The handle is shorter and the blade is shorter on the Mini for example.

I would not consider it conceptually based if it can be applied to practical use in a repeated experiment.

STR
 
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