Lockfailure and injury

[Woodcutter]

Hello to all you forumites. This is Owen Wood, alias, Woodcutter and the newest member of Sal's R and D team! To give you a bit of background, I am South African born and bred – a custom Knifemaker by profession (since 1978) – a founder member and past chairman of the Knifemakers Guild of Southern Africa. I have been doing business in the USA since 1982 (Kansas City Guild Show). Many who follow the hand made scene know my work.

My family and I have recently moved to Colorado to join SPYDERCO. The first few months have been inspiring; so far I have been involved with the Ulu and with the, dare I use the words, Native Chief (Two days leave, Sal?) I used the standard Native extensively, opening a container full of boxes and parcels of tools and equipment, which had arrived from South Africa. It performed so well that it has become one of my favorite tools, but I would like the blade a tad longer for more general use.

I have been hanging about in the wings of the forum for a few weeks, getting a handle on the current threads. The comment that has been flying around about lock strengths is extremely interesting and in order to put this into perspective for me I would really like to find out just how many knife users out there have been injured by a failed or defeated lock.

May we make a distinction between a lock that defeats – i.e. it disengages without actual failure of the parts and a lock that fails with either permanent distortion or breakage of one or more of the parts forming the lock

Speaking to the guys in customer service it would appear that most backlocks defeat due to muck building up in the locking notch of the blade – preventing the lock from engaging properly. Liner locks defeat due to poor design or manufacturing. Ideally the locking tongue should bend across the cavity of the knife, as it fails,permanently preventing the blade from closing!

I would very much appreciate your comment.

Woodcutter

 

[copfish]

Welcome to God's Country! I love Colorado! Charlie @ Ironstone/Spyderco talks highly of you and raves about your knives. I had an EDI Genesis 1 lock fail when I tried the "spine whack" (more of a spine tap) test. I was holding the knife in my left hand and lightly rapped the desk, causing the blade to flick shut on the tip of my left ring finger. Just carved the 1/8" of the tip off. Bled a lot, no real long term damage, as all I did was lose a few layers of fingertip. I am glad EDI sharpens their knives almost as sharp as Spyderco. Holler if you get up to Woodland Park, great place for the "Symphony above the clouds" July 5th.

[This message has been edited by copfish (edited 04 July 1999).]

 

[Corduroy]

I've never been injured by a lock failure. I just wanted to say "welcome!" and make a quick comment about the spine-whack test.

Instead of trying to hold the knife in a "safe" way when performing this test, I grasp the knife in a firm "hammer" grip, edge-up, and then throw a heavy, folded towel over my hand and wrist. This protects me should the knife close, which several have (though no Spydies to date). I strike the spine against my desk or a similar object hard enough to leave a mark, and try to strike at least 2/3 of the way out on the blade for leverage. I'd call this abuse if I had not seen that many well-made folders will take this treatment repeatedly without failure, damage, or noticeable change in action. It isn't something I recommend doing for fun, though, just once or twice when you get the knife and maybe every six months to check for wear.

OK, back to folks hurting themselves

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-Corduroy
(Why else would a bear want a pocket?)

 

[Joe Talmadge]

Owen,

It never occurred to me that the locks would fail on a locking folder, until I started using my knives harder. One day I noticed a funny problem on a liner lock (custom) I had. When I gripped the knife firmly, the lock would disengage slightly. I was nervous about this but continued to use the knife cautiously. When the lock did auto-release on me I was kind of ready for it, and took pressure off the blade in time before it swung shut on me. That's my failure story, no injury.

After that I became interested in lock reliability. RELIABILITY, not strength. Most locks from good quality production companies and custom makers are plenty strong enough for me. It bothers me that people have been reacting to lock-failure stories by emphasizing strength instead of reliability.

Anyway, after that, I started working on lock tests that would stress the locks a bit, for both normal-use and for hard-use. AT Barr helped out with a bunch of tests of his own. As I started testing, I became totally shocked with the number of locks that failed -- and how high $$$ knives did NO BETTER WHATSOEVER than low $$$ knives, at least for liner locks.

From my testing and the stories I've heard, I think your CS department is basically right. Liner locks can fail to engage due to dirt in the mechanism (I've had this happen when pocket carrying), but autodisengagement problems happen from manufacturing problems, and show up in white knuckling, torquing, and spine-pressure tests. Lockbacks also can fail to engage due to dirt in the mechanism, and are also susceptible to white knuckle failures depending on where they're placed. A few lockbacks fail the spine whack test, but this is more the exception than the rule.

I'm sure you know the solutions to these problems WAY better than I do, but here's my feelings, love to hear any comments you might have:

Fixing liner lock problems... I'd rather we fix these problems by moving to other lock types, frankly. But if we insist on fixing the liner lock, here are what I think are some common problems. If the washers are too small, torquing can move the blade tang too much and cause auto-disengagement. If the tang angle is too high, the liner can more easily slip off. If the liner is too easy to reach for disengagement, it's generally too easy to white-knuckle fail by accident. Enough pins to keep the frame extra rigid also seems to help.

Lockbacks, it's a matter of placing the unlock button somewhere that your hand won't accidently hit it. Scooping it out like David Boye does might help, as does making sure the spring is nice and firm.

Joe Talmadge
jat@cup.hp.com



[This message has been edited by Joe Talmadge (edited 04 July 1999).]

 

[Corduroy]

I want to add that to adversely affect a linerlock, the washers have to be thick as well as small in diameter. Benchmade uses very thick washers to avoid milling a space for the lock to overtravel when the ball is riding on the blade. A consequence of this is that there is always slight lateral play from the compressible washers. Using filmy-thin washers like the Military and Cricket, I doubt the diameter would make much difference in allowing the blade to have lateral play.

-Corduroy

 

[Jeff Clark]

I've had a lot of experience with cheap lockback knives. Like other lockbacks they can fail from crud in the lock, but they are also subject to lock wear. The notches wear such that the back strap wants to slide up during pressure. Wear also rounds the outer corner of the lock notch which shortens the distance that the lock needs to ride-up before the lock pops loose. Deeper notches, tighter tolerances, and better steel seem to be the solution.

 

[David Williams]

Woodcutter,

The only injuries I have are from improper cutting techniques, but that is another thread

I thank you for taking up this crusade as I have been wondering what all the hubbub is about. I have never broken a knife, never had a lock failure/defeat. The only close call was with a locking SAK snapped open the last few degrees of blade travel and flipped the knife in my loose grip resting the edge against my finger. Yes I should have had a better grip and should have been paying better attention but that really surprised me.

I emailed Sal with my idea for a variation of the linerlock. I don't expect anyone to use it but I won't hold it against them. I would just like to know how feasible it is after you mention muck in the lock.

 

[HiltonP]

Owen,

Great to see you on the Forums . . . just love the handle . . . little bit more manageable than your South African one !!

I think linerlocks got their "bad name" in this department because of the grade of titanium used in many of the earlier designs. Once the "springy-er" titanium (6AL4V) made its appearance the lockup became more secure and positive.

I've mentioned this point in another thread but . . . the very action of cutting (i.e. the direction of pressure) is such that it is forcing the blade open, regardless of whether you are cutting down, away, towards yourself, or sideways. The only way a lock can fail & injure is for the knife to twist in your hand. Lockup is therefore only one aspect of a safe knife design. Grip dynamics are another.

Regards, HILTON

 

[bald1]

Owen,

It is certainly great to see you joining in here on the forums

! I again want to express my gratitude for the warm reception and time you and all the others extended me during my visit the week before the Blade show.

My only bad experiences were when much younger and that with a locking folder of conventional design. My cutting technique and a lot of dirt contributed to the lock failing with the back of my hand being cut. I've learned a lot with age

. I've become very cautious of folders when used to do very hard work preferring instead small to medium sized fixed blades (like the Spydie Moran). I too have done my share of inspecting and conducting of the "AT Barr" tests. The best have handles that flat will not flex and very tight tolerances in the lockwork. Any compromise in either contributes to an accident waiting to happen. I've also found that the cost of a knife has no correlation to non-flexing handles and "fitted" lockwork... inexpensive mass-produced and custom both have failed when tested or pushed hard.

-=[Bob]=-

PS I wanted to e-mail you privately but your e-mail address isn't listed here. You had planned to grind two samples of a "new material" for testing after the Blade Show... have you? and how did things turn out?

[This message has been edited by bald1 (edited 06 July 1999).]

 

[Woodcutter]

Many thanks to all of you who have responded to this thread. The hubbub that has surrounded the question of lockstrength had raised expectations of a flood of responses!!
Is this as big an issue as we think? I have an idea to post the question on other forums.What do you all think?

I think that the spinewack test is very important. Certainly, the way in which a liner lock responds to dynamic loading is somewaht different to it's reponse under static loading. We can only learn so much from static loading, and I look forward to the day when we perform a controlled dynamic test on a lock where the velocity of the blade at the point of test is known. My gut tells me that we may well be surprised!

As for high dollar knives not outperforming the less expensive knives, perhaps the custom maker a) having put many hours of love and care into making a blade is loath to test it to destruction and b) does not have the resources to do the sort of testing that SPYDERCO does. I am not surprised by this observation.

The question of the blade torqueing in the handle is also important and I tend to agree that the thinner the shims the better.

At any rate, to sum up, to date we have one injury from a failed lock and one whilst performing a spinewack test!


Woodcutter

 

[lbwheat]

Welcome Owen;

I've never had a lock failure, But I think that is because of two things,No cheap knives and keeping my knive free of dirt and lubricated. I'm looking forward to being able to see some of your handy work both with Spyderco and your custom pieces through the Spyderco Direct Store. I work in retail sales so I haven't many chances to attend the knife shows.I've purchased a couple of Chris Reeves pieces and one Elishewitz Specter,But mostly factory pieces and most of those Spyderco. I'm up to about forty now and still going. I can't wait to see what exciting new projects you will bring to the Spyderco family.

lbwheat

 

[Schlager]

My last lock failure was two years ago with my Spyderco Endura. I held it in either a sabre grip or hammer grip and whacked a piece of 1/2" plywood. The blade closed on my index finger.

Inspection of the locking bar showed only about 1/32" engagement when open and locked, this was way too small amount.

I've not used this Endura since, and is regulated to duties no more dangerous than bathroom duties to cut toilet paper wrappers.

Also, I've not purchased another Spyderco since, even though the new ones I've seen have much better lock engagement. I've purchased a Large Voyager, and when I want a toothy edge, that is the blade I reach for.

Someday when I get frisky, I'll remove the blade and mount it in a handle for a more usable sheath knife. -Brian

 

[Cronnacht]

The only misfortune I've had with lock failure was my first Benchmade, and AFCK mini. The liner compressed and the serrations bit a chunk out of my knuckle. No real damage other than to my pride as a "knife guy". The gang at Benchmade were very concerned and requested that I send them the knife right away so they could determine why the lock failed. Apparently hard use can wear away the surface of the liner at the lock-up point, causing the lcok to slip. They repaired the knife and returned it to me. I've since lost that AFCK mini, and have replaced it. No damage to my consumer confidence!
-Jim

 

[Kysa]

My experience with lock disengagement came from my own misuse of the knife. While trying to use my mini-AFCK blade to pick up a small box heavier than expected (by stabbing into it), it disengaged and sliced a hunk out of the top of a knuckle, leaving a bloody scene!

No fault of the knife, just the idiot user!

 

[TheBeak]

this one falls into the relm of operator error, or wrong choice of tools, maby.

i had a police model close itself on the back of my thumb/hand once. i was cutting a series of lines under tension, the lines were at ankle level, headed over the side of the boat i was working on at the time. i was cutting up from below the lines. seems that the lock release in the middle of the frame got depressed my my fingers and by the third cut or so the snap up as the blade cut through the line made me jerk up closing the blade arround my hand. teeny cut, more supprise than anything.
not a falure so to speak, but a liner lock may not have done this.

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'Till next time,
Rich the kite guy

 

[Nakano 2]

Welcome Owen. Approximately 8 years ago while talking knives at a local gun shop, a friend and employee of mine showed me his well used Police model after I questioned its lock strength. After he snapped it open, he said "Watch" and proceeded to hold handle in one hand and blade in other and applied downward force to the blade spine and handle simultaneously and the lock failed! Very similar to snapping a pencil in half. My eyebrows went up and he said to try it on mine. Donning a pair of old work gloves I proceeded to try to "snap my pencil" and voila! The lock failed as well! I do not know of the condition of his but mine was well used but never abused or to the extreme. I did notice though there was enough blade play to be of concern. It has since been retired.

BM Leopards. Easy to defeat the linerlocks. Sent mine back 2X for warrantee. Still closes with a modest whack on the spine from a padded armrest of my sofa. A reply from the BM forums was that it was not made for this type of testing. Uh huh... It too has since been retired.

L8r,
Nakano

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"To earn a million is easy, a real friend is not."

 

[sing]

Never been hurt by a lock failure, probably because I am aware of the possibility. I had a CRK&T Apache which I purposely bought for "marital blade craft" use. Did alot of drills with it on hanging objects. No prob. Read JoeT's warning about linerlocks and tested the Apache. The most modest of taps defeated the lock -- not once, twice but consistently! If were not careful in orienting the blade doing drills the lock could have failed with serious consequence. In a real situation where things happen fast and furious, it's very possible that one may not orient the blade right or it gets hit on the spine by something. This Apache would have surely fail in a situation which one can least afford it. Given that linerlocks can work well initially and fail later because of wear and tear, the reliability issue is too much of a concern for my peace of mind. Thus, no more linerlocks for me, especially in a martial blade crafted oriented knife. The only exception for me right now is my KFF in which the linerlock is well designed and heftier than any I've seen. Even this one, I test every so often.

With my lockbacks, I am extremely meticulous about keeping the lock notch clean. I check them often and clean them often.

I guess my take on locks is like that with car brakes. I don't need an accident to prove that using a car with faulty brakes is a no no. Don't use the car unless the brake is fixed or replaced. Same for some of the locks and knives.

sing

 

[Cliff Stamp]

Sing has made an important point, its not the actual happening that is important but the possibility. A knife may fail at the upper limit of use which you may never even use. However that limit should be well defined and you should be secure it in existance.

Knives are an odd lot in one respect as people tend to be fairly forgiving in respect to accidents. A lot of other products have much harsher reactions to people injuring themselves with them due to the products fault. It seems to be expected with knives which is plain wrong.

-Cliff

 

[Sal Glesser]

Sing & Cliff - very wise words. I had cut my finger when a lock defeated. It was a drilling/turning/twisting activity. Owen and I discussed this and he said that this particular motion contains most of the evils that can put the most test to a lock. A little thought supports this comment.

It would seem wiser to try to find a solution rather than just accept the fact and "tell the customers that they shouldn't do that" (make a law?).

So....What does twisting do? what are the forces? what are the effects of these forces? and what can we do (as manufacturers) to reduce or eliminate this potentional problem that everyone (for some reason) uses a knife for? This should probably be another thread???
sal