Are Folders Locking Mechanisms Safe?

[orthogonal1]

There is a lot of confusion over this. The "100 lbs per inch of blade length" is intended to mean that a knife that is held at the fulcrum (pivot) and has a 1" blade can support 100 pounds being applied at the tip of the blade before the lock fails. The same knife with a 4" blade would not support 400 lbs, but rather 25 lbs. at its tip. Here is some information about lock strength posted by Sal a while back:

...

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

There is a problem here.

By your calculations, we are simply dealing with torque - in lbs-inches no less.

The units of the standards are not standard torque units.

 

[harkamus]

There is a problem here.

By your calculations, we are simply dealing with torque - in lbs-inches no less.

The units of the standards are not standard torque units.

I was thinking that as well. I'm a biomechanist. I deal with torque on a day to day basis. It seems Spyderco's method of testing is in house and proprietary.

 

[orthogonal1]

Personally, I just wish some one would make a simple hydraulic press machine to make standardized tests with basic torque results for a specified deflection angle between blade and handle and results of the actual breaking torque.

 

[Padawan]

There is a problem here.

By your calculations, we are simply dealing with torque - in lbs-inches no less.

The units of the standards are not standard torque units.

They aren't my calculations, they're Spyderco's. The concept is pretty straightforward. A weight or force is applied to the tip of the blade while the knife handle is supported at the pivot. The force required to break the lock is then recorded, and subsequently "standardised" to account for the leverage generated by blade length.

 

[Josh K]

They aren't my calculations, they're Spyderco's. The concept is pretty straightforward. A weight or force is applied to the tip of the blade while the knife handle is supported at the pivot. The force required to break the lock is then recorded, and subsequently "standardised" to account for the leverage generated by blade length.

I'm pretty sure it doesn't mean the Military can only hold 25lbs at the tip.

 

[Padawan]

I'm pretty sure it doesn't mean the Military can only hold 25lbs at the tip.

25 lbs of force on the end of a 4" knife is quite a bit, and this isn't necessarily the failure point but rather what the lock is designed to hold without failing.

My understanding of the ratings is based upon what was posted by Sal and by responses to questions from other members. It's possible that the information was sufficiently ambiguous as to be interpretable in several ways, and in that case it would require some further clarification from Spyderco. It seems rather obvious that as a blade is lengthened, the same lock on a virtually identical knife doesn't simply get stronger (e.g., a Delica can support 150 lbs while an Endura can support 200 lbs.) However, Sal has stated that the company will improve broken parts on a design until they achieve the desired strength, so this possibly could explain that discrepancy.

 

[Josh K]

25 lbs of force on the end of a 4" knife is quite a bit, and this isn't necessarily the failure point but rather what the lock is designed to hold without failing.

My understanding of the ratings is based upon what was posted by Sal and by responses to questions from other members. It's possible that the information was sufficiently ambiguous as to be interpretable in several ways, and in that case it would require some further clarification from Spyderco. It seems rather obvious that as a blade is lengthened, the same lock on a virtually identical knife doesn't simply get stronger (e.g., a Delica can support 150 lbs while an Endura can support 200 lbs.) However, Sal has stated that the company will improve broken parts on a design until they achieve the desired strength, so this possibly could explain that discrepancy.

If the lock is designed to hold 100lbs in total 1" from the pivot you could lengthen the blade however much you want and simply decrease the amount of weight you put on the end. 10" blade can hold 10lbs on the tip.

I'm going to have to dig up some of Sal's posts on the subject. I recall "100lbs per inch of blade."

 

[harkamus]

They aren't my calculations, they're Spyderco's. The concept is pretty straightforward. A weight or force is applied to the tip of the blade while the knife handle is supported at the pivot. The force required to break the lock is then recorded, and subsequently "standardised" to account for the leverage generated by blade length.

So it's basically a more refined method that we see on some youtube vids where people clamp down knives and then hang weight plates on the end until the knife fails.

 

[Hitthespot]

If the lock is designed to hold 100lbs in total 1" from the pivot you could lengthen the blade however much you want and simply decrease the amount of weight you put on the end. 10" blade can hold 10lbs on the tip.

That settles it then. I'm only buying folders from reputable manufacturers: with 1/2 inch blades.



Bill

 

[Josh K]

If the lock is designed to hold 100lbs in total 1" from the pivot you could lengthen the blade however much you want and simply decrease the amount of weight you put on the end. 10" blade can hold 10lbs on the tip.

That settles it then. I'm only buying folders from reputable manufacturers: with 1/2 inch blades.



Bill

All folding knives can fail. If you're utterly determined to procure a knife that will not have the lock fail, get one of the new "lockless" knives.

AKA: Fixed blade.

 

[Hitthespot]

All folding knives can fail. If you're utterly determined to procure a knife that will not have the lock fail, get one of the new "lockless" knives.

AKA: Fixed blade.

I have some of those too!

Thanks Josh, I 've enjoyed your posts in this thread.

Bill

 

[orthogonal1]

They aren't my calculations, they're Spyderco's. The concept is pretty straightforward. A weight or force is applied to the tip of the blade while the knife handle is supported at the pivot. The force required to break the lock is then recorded, and subsequently "standardised" to account for the leverage generated by blade length.

It can be simply and takes minimal effort to be standardized by plainly indicating a torque a lock must possess.

Torque is a simple idea and stating a value allows for various blade lengths. Therefore, I don't see the value of inluding the units of "inch/lbs of lock strength per inch of blade length" being a simple torque.

Oh, yeah, the old "get a fixed blade" argument is not germane to the discussion at hand. We are discussing locking knife strength/reliability, not fixed blade strength.

 

[Josh K]

It can be simply and takes minimal effort to be standardized by plainly indicating a torque a lock must possess.

Torque is a simple idea and stating a value allows for various blade lengths. Therefore, I don't see the value of including the units of "inch/lbs of lock strength per inch of blade length" being a simple torque.

Oh, yeah, the old "get a fixed blade" argument is not germane to the discussion at hand. We are discussing locking knife strength/reliability, not fixed blade strength.

I assumed (and am still assuming) that 100lbs per inch of blade means 100lbs on the end of the blade. Using the Military as a standard, that's 4" x 100lbs = 400 inch/lbs of torque on the pivot.

 

[SilverFoxKnows]

To me the lock on a knife is sort of like a safety belt in a car. I use my knives carefully.
I could probably get by with a slip joint. I often do

Probably the best advice in this thread. Quoted because I think it bears repeating. Too many of us, myself included, have too often relied on numbers and brute force when wits and technique would have carried us farther. Just my two cents, worth what you paid.

Frank

 

[Ankerson]

All folding knives can fail. If you're utterly determined to procure a knife that will not have the lock fail, get one of the new "lockless" knives.

AKA: Fixed blade.

Yep, folders are already broken as they do fold up so they will never be as stong as a fixed blade. And yes any lock on any folder will fail if one goes past it limits.

By quality and keep junk out of the locking mechanism and it should be fine.

 

[midnight flyer]

This is a good suggestion. Lint and dirt can get into the lock mechanism on the lockbacks, causing failure. If you see a little lint in the lock, try using some tweezers to pull it out.

When I have had a lockback fail, it has been that very thing. Lint in the blue jeans gathers inside my little lock backs that ride in the bottom of pocket (as opposed to clipped to it) like the Kershaw Whiskey Gap and Al Mar Hawk. They will close and the mechanism will actually move, but not securely in the locked position.

I don't push those knives really hard so I haven't been bitten by them but a couple of times. Lesson learned. Operator failure.

Robert

 

[Hitthespot]

I agree that lint and dirt can cause a lock back to fail, but that was not the problem in this case. Even after cleaning and lubing the knife I could easily close the blade when locked. Again I wish I would have kept it for further study but threw it out.

I think there was just too much pressure applied to the back of the blade, although as I stated earlier, I didn't think it was that much.

Bill

 

[orthogonal1]

I assumed (and am still assuming) that 100lbs per inch of blade means 100lbs on the end of the blade. Using the Military as a standard, that's 4" x 100lbs = 400 inch/lbs of torque on the pivot.

Torque is in Force times distance, no division in that equation.

 

[midnight flyer]

I agree that lint and dirt can cause a lock back to fail, but that was not the problem in this case. Even after cleaning and lubing the knife I could easily close the blade when locked. Again I wish I would have kept it for further study but threw it out.

I think there was just too much pressure applied to the back of the blade, although as I stated earlier, I didn't think it was that much.

Bill

You know, not all knives are equal. And not all knives have stringent quality control when being made. Look at some of the manufacturers here that are frequently referenced as suspicious quality. Take Cold Steel for example; if you get "this knife" you are in good shape. If you get "that" knife you are an idiot.

So models and quality control also play a huge role in getting a reliable knife of any kind.

I look very carefully at the locks on any folder I buy and if it seems the slightest bit flimsy or loose before I use it, I don't buy. I have actually seen some knives at the gun/knife show I frequent that on some of the cheaper knives you can see the liner lock flex when you push the blade when trying to close it. No thanks.

Although locking blades were out there when I was a kiddo, they were very difficult to find. So when I started using lockbacks, liner locks, etc., I had already formed good habits of not pushing the knives too hard, watching my grip, and selecting the right knife for the job. To me, the lock is an insurance policy, not an iron clad promise that the knife won't close.

Robert

 

[harkamus]

Torque is in Force times distance, no division in that equation.

More specifically, Torque = perpendicular distance x force.