Are linerlocks really unsafe?

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Dec 1, 2007
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Linerlock failure seems to be a given for a lot of people, but I’m having a hard time finding information on whether this is true and how this even happens. I have read about how you can’t stab anything with a linerlock knife because it will break and you’ll cut your fingers off, but I haven’t found any actual accounts of this or, if they even happened, WHAT failure occurred with the lock.

From what I can tell, a linerlock can only really fail in two ways:

1. Pressure from the cutting action pushes the lock to the outside, effectively closing the blade. I have one knife (Benchmade Mini Ascender) with a liner lock that, when pressure is put on the spine, moves to the outside.

2. Pressure from the cutting action pushes the lock to the inside. If the lock goes too far to the inside (contacting the non-locking liner) my guess is the blade would essentially be “broke open” and thus closing it on your fingers would become impossible. This seems like a "safe failure" and thus wouldn't be a concern during use, although you'll have a messed up knife you'll still have your fingers.

In either case, pressure would need to be put on the spine of the blade for an accidental disengagement to even be possible (I am assuming you are not accidentally disengaging it with your thumb). I don’t know of any practical situation in which this would happen, unless stabbing with a knife puts downward pressure on the blade, pushing it towards the handle. But is this how it actually works?

Links, videos, and scientific explanations would all be greatly appreciated. I am not interested in any spine whack tests as this doesn’t give me any information about how the lock behaves during practical use.

Thank you in advance!
 
When done correctly not at all.

However, your lock does have a problem as it is slipping of the LF area.

A proper liner lock will disform before slipping or catastrophic failure taking place.

A recent few posts I did regarding frame locks, but many of the same principles apply to liner locks geometry.

"There are a few things I want to cover, based on my talking with custom makers and reading Bob Terzuola's book: The Tactical Folding Knife (hereafter BT), where he explains in detail the aspects of a good liner lock and the same principles are applied to framelocks.

Three points of contact:
1. Stop pin
2. Pivot pin
3. Interface between blade and spring (ie, lockface/lock engagement area hereafter referred to LF) Spring is also the liner lock, framelock.

This forms a triangle.

Now, the LF is the area lets focus on first.

BT. refers to the angle of the lock face to be between 7.5 and 8.5 degrees. Les then 5 degrees and the spring will jam. More then 10 degrees and the spring will start slipping off the LF.

Now the start of a radius lock face, the maximum therefore cannot exceed 10 degrees or else the lock will start slipping when the lock wears to that point. As mentioned as lock roll in the video when referring to the Strider.

Now.

Do not thing the angle plays the only role in the lock slipping. The finished LF can have a rough spot, not be polished enough, the spring's interface between the LF can also play a role.

Let us examine this from the Emerson website.

http://www.emersonknives.com/ekKnifeAnatomy.php

If the LF connected to the spring more in the middle or at the top of the spring where the detent is on most (point nr 3 closer to the pivot pin nr 2) then you would experience blade roll. This is when you have vertical type play but what happens is the blade actually rolls on the spring because the spring connects in the wrong place with the LF.

The picture shows the extremes of the different designs, you can have a lock that engages more then the bottom 0.90-.125" of the spring. Chris Reeve has proven this, but, you can also have a knife that engages only on that bottom 0.90" (point of contact in the picture)

Not every lock is the same. The basic ingredients are the same, but the final application is what the maker chooses. This can be seen even with Spyderco difference between the Military and the Gayle Bradly.

Now that is just the geometry of the lock.

The spring itself if it is Titanium can be heat treated or carbonized. Strider and Hinderer do the latter. This helps tremendously with wear on titanium and if done right will last you a life time. CRK and a few custom makers that I have do Heat Treating of the lock. Wear is about nun and equal to (if) steel was used.

HOWEVER. Titanium is NOT PERFECT and it can have flaws in it when received from the supplier. EVEN aerospace titanium (grade 5 titanium). These flaws only become apparent when it is used and is sometimes not even noticeable until it begins to form a problem. This is where a good warranty comes into play.

Steel used as a liner is not always the answer as well. Different steel interfaces can result in slipping. Steel on steel requires a lot of research to find what can be used and heat treated as a spring and still provide excellent wear resistance and safety.

Finally, lockup percentage is a strange thing and depends on the final user. I prefer later lockup as it usually means less chance of slipping off the LF.

I hope this helped you in some way."

At the end, if you either use Ti or Steel, the LF geometry is key.

I have Ti lock custom that I have flicked vigorously, the maker asked me to test the lock face.

Here is a video towards the end.

http://www.youtube.com/watch?v=YgNHm...1&feature=plcp

Start watching from 2.27 minutes.

BT also writes in his book there is no significance between steel and Ti if done right. A Sebenza will wear for a while and then stop. Most quality locks do this. Chris Reeve also wants a later lockup as he feels it provides a safer lock and less chance of slipping. I tend to agree. Besides. If any quality product wears out so fast, they should cover it under warrenty.

I have seen a 18 year old Sebenza. No issues. I have a Military with the steel insert. No issues. Both locks apply different end results, but the basics are the same resulting in great locks that can last you a live time.

BT also feels that the strength to weight ratio of Titanium is excellent compared to steel.

Not really. The routing that is done is to make the disengagement for the user more comfortable. STR has made Ti framelocks without any cutouts (routing) because the user wanted it only to have it returned later on because the user complained it was to difficult to disengage.

The cutouts (routing) also provide a "safe burn" for those "accidental moments" when the lock does fail due to excessive force on the blade.

A Emerson HD-7 showed this perfectly.

Emerson+HD7.jpg


http://strsbackyardknifeworks.blogspot.com/2009/07/bins-horseman-hd-and-jryan-edc-folder.html

In short

"Contrary to how many readers may feel about that picture above. That my friends is a design that deserves praise for defeating the way it was engineered to go. That HD7 above did its job and so did the designer/maker of the knife. I doubt any sutures or ER trips costing great amounts of money were needed with that defeat. We should all pray to be so lucky should we be the on the unfortunate end of a defeat ourselves one day."

The cutouts are the weakest link in a Framelock IMO.

I have been surprised by some framelocks. A kershaw vapor that I had would disengage with some force on the spine when not held in hand. When I gripped it the lock did not move as ones fingers actually force the lock in.

Titanium that is used in framelocks have to be at least grade 5 quality. It has natural spring tension if I can remember correctly.

Dwayne

Emerson knives start live out so early because it is the Mr. Emersons personal choice for his locks. I know of custom makers that also do this.

However, in my experience it is Ti liner locks such as Emerson knives (and there are many others that also do this) that are not heat treated or carbodized lock faces of the springs that tend to wear much faster. In these locks the geometry of the lock has to be as close to perfect as one can get.

Chris Reeve.....well this is interesting because he is credited as the father of the "framelock" or R.I.L.

The reason why his knives do not really have a break in period, or if it has it is very little is one thing: Tolerance.

CRK also does what I feel is good practice in that they adopt the blade to the spring, not the spring to the blade. In other words, when they fit a blade to a lock, they have multiple handles that are pre-assembled, checking in which handle the blade fits best and then if required they grind the blade LF area to mach the spring. They never fiddle with the spring or springs LF area after it has been heat treated and bead blasted to mach the blade. This is good practice IMO and great makers do this.

The only real advantage steel has over Ti is not in its wear resistance, but IMO in its impact resistance if one wants to beat the :spyder: out of the spyderco or other knife.

(I wanted to ad that my knowledge is not perfect and if any maker wants to correct me I am willing to learn, I am just sharing what I have learned from makers and books)


It does not really matter if the company is Emerson or not, the quality control needs to be good and with what ever company there have been a few melons going through. This is wear warranty comes into play.

The thing why Emerson knives wear so fast is due to the wave feature. If you wave that knife 20 times a day at full speed then the lock will wear faster.

The second question I dont fully understand, could you elaborate on it a bit before I attempt to answer it in full?

If you are referring to why CRK knives start locking up at 50%, that is his preference (mine to) and the LF is designed and executed that way.

The initial wear on a CRK is minimal due to the close tolerances on the LF and the entire knife. However, sometimes there is a rough spot on the LF that just wears smooth and the lockup will increase from 50%-60% within a few days, or weeks, but after that it would wear very very slowly. CRK wants the lockup to be between 50%-75%, but this is different on the Umnumzaan. On the Um it looks closer to 90% but it is actually 75% and I have yet to hear a complaint about the Umnumzaans LF or geometry.
 
Yes, they are terribly unsafe. Please send all of yours to me for proper disposal.

More seriously, I also don't understand why this fetish about insanely tough knives. I've never had a lock fail on me. Linerlock is a perfectly good design (I like the ones with the ball-bearing built into the lock too).
 
There are plenty of liner locks out there that I wouldn't, and don't trust. But I do not think this is because liners are somehow INHERENTLY weak as an entire group, the issue is in how a liner lock is designed and made. If well done, it can be very strong. Like the Spydie Millie. In contrast, if a liner is cheaply or poorly done, it can be a disaster waiting to happen.
 
The reputation of linerlocks for failing comes from their use on low-end knives. Liner locks can be the least expensive lock to make, so they get used a lot on cheap knives. The locks on such knives are not well made, and they fail. A well made liner lock is quite reliable.

The truer statement might be, "cheaply made linerlocks are prone to failure."
 
The reputation of linerlocks for failing comes from their use on low-end knives. Liner locks can be the least expensive lock to make, so they get used a lot on cheap knives. The locks on such knives are not well made, and they fail. A well made liner lock is quite reliable.

The truer statement might be, "cheaply made linerlocks are prone to failure."
Totally agree with what knarfeng and others said. :thumbup:
 
Totally agree on what all have said. To prevent slippage, one more factor is important: the mating surface should be dry & clean. It means extra care when lubing the pivot, no excess should flow into the mating area, especially on the blade tang.

I have axis lock failing (jumped backward) due to excessive oil on the mating surface. After cleaning & drying, no more. Tested by whacking the spine on wood panel. When tested with static pressure & light tap, it didn't fail. It seems the impact of whacking made the bar 'jumped'. The same can be thought of with liner/frame lock, especially with higher angle on the tang (see Marthinus post), the lock might be 'jarred' and at that instant, the tang angle surface would push it out. One solution some makers do is making the angle not straight, but curved inward/concave. This way, the lock will move in at lower angle, but the curve will stop it to move further. It introduces new issue: the lock might wear more at the side that faces the stopping curve and eventually lock would be convex against the concave tang curve.

The picture on Marthinus' post is also used on lock discussion by STR. Check the sticky on his subforum on Tips and Tricks.

Add note;
The LAWKS was invented as prevention against slippage.
 
Any locking device can fail. I don't use really expensive knives as my working knives in site, but I don't use crappy ones either. I have a RAT 1, a bunch of Kershaws, and some others. I use them to cut heavy stuff, dirty stuff, wet stuff, and I pry, scrape and chisel with them. NEVER had a failure, never found one to be unsafe.

I use any folding knife regardless of locking system like it is a slip joint. I try to always be careful to push or draw cut in a way that keeps pushes the blade back as to keep it locked up and I have never had a failure.

I don't spine whack, bury the point in something and work it back and forth, I pry in such a way as to overstress the lock and bend the locking bar or anything else along those lines.

I simply use them as work knives and they work just fine.

Robert
 
Liner locks are not inherently undafe, but I have had the most failures from liner locks, and they resist the least amount of closing force when compared to most other locks. There's nothing wrong with properly heat treated 420HC as a knife steel, but I would prefer S90V. There's nothing wrong with a properly executed liner lock, but I would rather have a lockback. Either way, the knife blade is made of steel, and the folder locks open - but one has better attributes than the other. Any poorly built lock is unsafe, and poorly heat treated steel is unwanted, but when done correctly, some designs are better than other designs.
 
depends on what you consider safe and how you use your knifes. if your scared, go with a fixed blade. If you want a strong lock, take a look at any of the cold steel TRI-AD lock. http://www.coldsteel.com/triadlock1.html

Show me another lock which can handle over 600lbs of free hanging/swinging weight if you think its crap!
 
I had a liner lock fail. Sort of. I was doing dumb things with it (spine whack) and it would fail repeatedly with very little pressure. The knife was not unsafe, just a little less useful.
 
Most of my work knives are liner locks and range from customs to Spydercos to cheaper models (not "cheap", just inexpensive). I haven't had any come close to failure despite being worked hard.

Andy
 
The question is a bit like asking, "is the ball bearing really an unreliable means of reducing friction?"

The answer is highly dependent on the execution and materials used.

Liner locks like ball bearings can fail. However, if they are well made from fine materials and properly cared for, they will serve a valuable duty for a very long time.
 
I'm with midnight flyer, I treat them like slippies. To me, the lock is like wearing a bike helmet. Just because I am wearing a bike helmet doesn't mean I ride with any less regard to safety.

Ric
 
I don´t like liner locks. It´s not that they are unsafe ( in fact none of my knife closed accidentally), it´s because your fingers can come between the blade and the handle when closing the knife. Not very pleasant when you just finished sharpning your knife :grumpy:.

Kind regards,

Andre
 
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