When "Good" Knives Break

Minuteman · Jul 21, 2003

I, and many others of this forum, have suffered the ill fate of buying a relatively expensive knife, putting it to work, and having it break under moderate to minimal stress and practically zero fatigue. When I say break, I don't mean small chips and dents. I mean large chips, missing chunks, and snapped blades.

Cliff and I have both experienced this in a big way with Ontario products -- I won't buy any more. But it has shown up in Camillus and many others as well.

For this reason I have suggested that it is better to stay away from high RC blades that are pushing the limits of material and geometry on blades that your life may depend on. In other words, a Martindale Golok that needs to be sharpened frequently is better than an Ontario RTAK that is ready to snap if you hit it too hard once or twice. High performance and warranties aside, what I want in this case is confidence.

Well, Wayne Goddard raised an interesting point in the August issue of Blade magazine, and that is that these blades may have been broken when we bought them. Micro cracks can occur during heat treatment are are often brought on by too coarse of a grind on a blade being heat treated. The cracks are so small they go unnoticed until you apply a little stress, then a catastrophic failure occurs.

The good news in this is it is possible to predict these failures by simply checking for cracks. Wayne suggested the low cost solution of buying a $10 Radio Shack 63-1133 microscope and going up and down the edge.

However, the fact that Swamp Rat is doing penetrant testing on every blade is getting me very interested in their products. I assume this means that this is done on Busses as well, but I have not heard them claim this. I would like to see penetrant testing become more common on serious working blades. To me BK&Ts are cheap enough that I would gladly pay a little extra to know that the blade is free from quenching cracks.

Cliff Stamp · Jul 22, 2003

Most custom knives, or other high end small shop knives you can make an arguement that they should be individually checked. However for mass production knives, this isn't going to happen. In fact it is rare that even random samples are tested as whole batches can be flawed and still see the public. That I think it pretty sad, but testing simply isn't that common.

Regarding cracks, the khukuris that you buy from Himalayan Imports are all inspected by multiple people before sold and are graded based on the fold lines, or rarely cracks, in the blade. Thus you know what you are getting before you buy. This can't be done in many blades due to the extensive coatings which hide the surface grinds. Cracks would also be difficult to spot due to usually very coarse abrasives being used to form the edge.

I would agree though it would be very nice to see the Swamp Rat practice of crack checking to be univerally accepted, along with the other random checks on quality control they do such as bending, heavy impacts and the like.

-Cliff

Minuteman · Jul 22, 2003

I believe it was Bill Moran I once heard say that an experienced bladesmith could whack the spine of a forged blade across the nose of the anvil and "hear" if there were any cracks. The idea being that a blade with no cracks would "ring" musically, but one with a crack would have a duller sound.

Don't know how reliable this method is, but it only takes a few seconds and is certainly cost effective. It would only work on a bare blade. After it was assembled the handle, guard, etc. would provide too much damping.

As far as Swamp Rat doing penetrant testing is concerned, they must have the cost down very low. Their prices seem QUITE reasonable to me. That includes the fact that they're differentially hardening, too, which no one else seems to be capable of in a production setting.

Cliff Stamp · Jul 22, 2003

People with a lot of experience can do some pretty amazing things, however there are not a lot of Bill Morans sitting around in the various shops.

What should be done however is random testing from every batch. This would make a large reduction in variance, and completely eliminate the possibility of bad batches.

The Swamp Rat line is very cheap indeed considering the R&D, QC, performance and warranty. The new D2 line broadens the scope of work significantly.

-Cliff

Minuteman · Jul 22, 2003

So if you could buy one of their blades in either SR101 or D2, which would you choose? The saying that keeps ringing in my mind regarding D2 was from one of the custom knife makers who said, "D2 takes a terrible edge and holds it forever", or something like that.

I can definitely see applications for a steel like that, and I know D2 is supposed to exhibit superior toughness, but I like my knives SHARP.

dsvirsky · Jul 22, 2003

Originally posted by Minuteman
So if you could buy one of their blades in either SR101 or D2, which would you choose? The saying that keeps ringing in my mind regarding D2 was from one of the custom knife makers who said, "D2 takes a terrible edge and holds it forever", or something like that.

I can definitely see applications for a steel like that, and I know D2 is supposed to exhibit superior toughness, but I like my knives SHARP.

If you have any doubts that D2 can take and hold a great edge, do a search of the forums for comments about Bob Dozier and his knives.

Cliff Stamp · Jul 22, 2003

For general toughness, choose the differentially tempered 52100 blades. The slimmer D2 blades are more optomized for cutting and will do it better than the 52100 knives, but do not have as broad a scope of work. There is no problem with sharpening D2 with proper hones. I have used several example, customs and production blades.

-Cliff

thombrogan · Jul 22, 2003

D2 can take a great edge, the same as any other steel. It's not one of my favorites, but it's very good.

bensano · Jul 22, 2003

Originally posted by Cliff Stamp
Most custom knives, or other high end small shop knives you can make an arguement that they should be individually checked. However for mass production knives, this isn't going to happen. In fact it is rare that even random samples are tested as whole batches can be flawed and still see the public. That I think it pretty sad, but testing simply isn't that common.

-Cliff

This might be cost effective for a large manuf.
http://www.cambridge-en.com/Ultrasonics/Resonance spectroscopy.html

--Ben

Minuteman · Jul 22, 2003

Bensano, thanks for the URL. This looks like a great, low cost inspection process -- probably cheaper than penetrant testing and without the waiting time and clean up.

You do realize, of course, that this IS the Bill Moran inspection process that I described above, except the ringing is being "heard" by a microphone and "judged" by a computer.

Good ideas always need to be explored...

Jeff Clark · Jul 22, 2003

The ultrasonic test method would have extra complications when applied to a knife. The typical tolerances are looser on the knife and the structure is less symetrical than the components that they use in their add. It would take some experimentation to find multiple "good" signatures and then call most everything else "bad". You would probably benefit from the relatively large size of the knife.

BTW, the tapping process is what you do when you are buying antique china. You flick it with you fingernail in several places. You get a duller sound if there is a crack. With a knife I would probably tap it with the shaft of a screwdriver will suspending it by a thread.

Minuteman · Jul 22, 2003

Jeff, I agree, a hand ground blade will have some consistency issues, but hopefully and crack would have a unique enough signature as to make it easily distinguishable from geometry variations.

mete · Jul 22, 2003

Sound, whether sonic or ultrasonic has long been used to test for many things.I'm sure something could be worked up for knives.Magnetic particle testing would be better for production knives than dye penetrant. In any case ,if the knife proves defective a good company will stand behind their product.

Minuteman · Jul 23, 2003

Originally posted by mete
In any case ,if the knife proves defective a good company will stand behind their product.

Mete, continuing a point I made earlier, if I am using a knife in my back yard, or 30 steps from my pickup truck, then warrantees are fine. To be honest, I have never had a manufacturer do anything other than quickly ship me a new knife when I sent them one back that had a problem. This includes Ontario -- they were very helpful. Same goes for Cold Steel.

The issue here, however, is that if I am going to carry a knife into a situation where my life is depending on it, we are talking about a different story. If I'm eight miles from my pickup truck and slip down a steep bank into the creek when it's 33 degrees out with a 20 MPH wind, I'm essentially dead if I can't use my knife to get a good fire going. In this instance warrantees mean nothing. Penetrant testing or some equivalent verification method, on the other hand, might mean everything.

I think most companies are pretty cavalier about throwing "survival" related terms around relative to their products. I have purchased some of these knives, that in the creek situation I describe above, would have definitely failed when I needed them most. Many people buy these same blades and head out into the boonies.

Cliff Stamp · Jul 24, 2003

Well quite frankly, a lot of the blame lies on part of the consumers. If people are willing to put up with that behavior, you can't really expect knife companies to change it. The users must start to be far more demanding on tightening QC measures.

-Cliff

storyville · Jul 24, 2003

Originally posted by Minuteman
If I'm eight miles from my pickup truck and slip down a steep bank into the creek when it's 33 degrees out with a 20 MPH wind, I'm essentially dead if I can't use my knife to get a good fire going. In this instance warrantees mean nothing. Penetrant testing or some equivalent verification method, on the other hand, might mean everything.

[...] some of these knives, [...] would have definitely failed when I needed them most. Many people buy these same blades and head out into the boonies.

Good thread, Minuteman, with a lot of good points. One should not blindly trust warranties, as most are designed to protect the co. over and above the consumer. "We will replace or refund, at our discretion, BUT... EXCEPT... VOIDED IF... ," etc., etc. "Abuse," of course, is almost always defined by the manufacturer, and usually after review of a failure and not before the consumer's purchase.

Another obvious point, worth repeating, is to work and test the knife extensively in the backyard, or only 30' from the truck, so you have a good understanding of the knife's abilities in the unfortunate event that you slide into that freezing creek. The "emergency scenario" shouldn't be the first time one tests out the capabilities of a knife, or any gear...

Glen

Jeff Clark · Jul 24, 2003

My compliments too, Minuteman, you helped me decide what I'll pick as my next survival type knife. A knife that is optimised for toughness and has been tested seems like a natural choice.

I am not as sensitive to the breakage issue as some people. I've almost never broken a knife blade off right at the handle or shattered one. Those are the only failures that would tremendously reduce the usefulness of a blade in an emergency. I'm generally not worried with most knives.

Minuteman · Jul 24, 2003

Originally posted by storyville
Another obvious point, worth repeating, is to work and test the knife extensively in the backyard, or only 30' from the truck, so you have a good understanding of the knife's abilities in the unfortunate event that you slide into that freezing creek. The "emergency scenario" shouldn't be the first time one tests out the capabilities of a knife, or any gear...
Glen

Storyville, this is an excellent point and one that hasn't really been mentioned here yet, but a knife that has been thoroughly used, without any problems, is probably A-OK and most likely doesn't contain hidden cracks.

In general, it would be far more trustworthy than a shiny one out right of the box. Most of the problems I have had were with new ones. I would think the fatigue life of a good blade (free from cracks) would be VERY long for even the lowliest alloys.

Cliff, you have broken a few blades along the way, were the majority of them new knives -- or just subjected to higher than previously encountered stresses?

Minuteman · Jul 24, 2003

Originally posted by Jeff Clark
I am not as sensitive to the breakage issue as some people. I've almost never broken a knife blade off right at the handle or shattered one. Those are the only failures that would tremendously reduce the usefulness of a blade in an emergency. I'm generally not worried with most knives.

Jeff, you're right, if you still had enough of a stub left to work with, you could get by. Even if you had one snap off at the tang, you could still probably pick it up and beat the spine with a baton. Maybe even while grabbing it with your multi-tool for a makeshift handle. In a bad situation, you would do what you needed to do.

On the other hand, I would prefer to have things go better, whilst they were going so poorly...

Cliff Stamp · Jul 25, 2003

Very few of the knives I have seen broken were from stress buildup over the long term as generally this takes a *lot* of work in a tough knife. This can be solved (or at least minimized) by having the blade periodically stress relieved (a temper at a reduced temperature to allow the steel to relax).

Most breaks are fast and immediate and I could induce easily within minutes of getting the knife. It often takes weeks for this to happen however as from experience I chose the work done in the reviews to get the most information out of the knife as possible, which means do the hardest stuff last.

There is always the chance that in doing work to evaluate a knife you are putting stress on the knife which could cause it to fail in use prematurely. However from my perspective, using an untested product is taking a much higher risk.

One of the most important things you can do if you are seriously interested in performance is to ask the maker or
manufacturer about the abilities of the knife, being specific about other knives you have used, and making it clear that you intend to verify any and all claims made and asking clearly if what is being stated is covered under the warrenty.

-Cliff