Bk-9 failure

Ethan Becker said:
Hey Bushman and all...

If by cedar you mean Eastern Cedar Or Juniper I have encountered some of the damndest convoluted conglomerations of mixed up knotty crud you can imagine....I love the smell of the stuff and it is reputed to keep mosquitos at bay so I have split a bunch of it over the years and the knots of both the Eastern Juniper (Junipera Virginianus) and it's cousin the western juniper have incredibly hard knots. Amazingly, the outer white parts can be so soft they can be dented by your thumbnail......The lower, inner twigs and small limbs are some of the best fire starting material ever and, the dried bark when frotted is excellent tinder......Burn the knotted twisty crap whole if possible.....Saves a BUNCH of frustration......

All Best....

ethan

All Best....

ethan
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i'm convinced the big man upstairs made such trees to test our metal

so to speak

consider it a challenge :)


Bladite
 
Bladie,

AARRRGGGUUUUGGGHHH, I was writing my long reply and just lost it due to inactivity.
How do I stop Blade forums from doing that?



Toooj
 
Toooj said:
Bladie,

AARRRGGGUUUUGGGHHH, I was writing my long reply and just lost it due to inactivity.
How do I stop Blade forums from doing that?



Toooj
Click to expand...

Regrettably, I don't believe you can. What I do in those cases where I know I'll be writing a long post, is to write it in a lightweight word processor, then copy and paste the message into Blade Forums.

Hope that helps.
 
Bladite, Mete, Chenko,
First of all: A great discussion. I (Ethan too) appreciate the marketplace of ideas where we can have different opinions and experiences expressed without the contention found on other forums and the internet. We can all ”agree to disagree without being disagreeable”. I also think this is what separates Ethan from a lot of others in the knife business.
I have been in the knife industry for over 23 years with four different companies. It has been my willing task to examine thousands of broken blades from customer returns. (For me, the most important reason for getting the returned blade from the customer is not to verify a return claim but to examine the blade.) I make the above statement, not to brag but to verify a lot of blades have been eyeballed. Ethan and I have worn out a lot of bodies in our knifetime.
I have also examined hundreds of blades in controlled lab and real world testing in order to understand blade fractures. My lab setup was this: I fixed the blade (edge up) by the tang in a fixture. This fixture was able to be rotated so that the edge could be tilted either side to any angle.
The force was supplied by a swinging moment arm that would drop accurately onto the edge of the blade. The impact head could be adjusted for weight and shape. It was fixed at the tail end of the knife and duplicated a swinging motion of the knife (in reverse) The blades were situated either completely vertical or angled and the impactor head was varied to supply a different weight (force) or impact shape on the edge.
In a nutshell, if the blade was held vertical, weight was added until a half moon chip broke out. The center of the impact was the center of the semi circular chip. It had mostly squared, perpendicular edges. If we put too much force the blade would chip and almost instantaneously shear completely in half. The impactor shape also had a bearing on the break. Smaller, sharper edges would chip out or break the edge quickly while larger rounder impacts didn’t. I think the force was spread over a wider area. Mete, this validates your thinking on the difficulty chopping small Hemlock knots as opposed to larger knots.
When we angled the blade by varying degrees, we could also get the edge to chip out. The chip shape would not always be a half round chip but had different shapes. The edges were not square but had a tapered, flaked edge like a knapped piece of flint. Just for all to know, the testing was all over the map but some trends did start to emerge. I also wish I had a high speed slo-mo camera to see what was going on.
Bladite: your link was spot on. While I originally thought about the differences between the glass and steel micro structures, the more I reread your link, the more the saw the similarities between that article and what I observed. When I observe Flint Knappers flaking off chips, their chip edges mirror the edges that I was able to produce on angled strikes. I also note that it doesn’t take a lot of force to chip off a flake nor does the graver have to be harder than the flint. Just enough force to start a fracture. (The fine point of the graver certainly will magnify the PSI force so that it exceeds the strength of the flint) I think the same applies to the steel edge. So Chenko and Mete, I agree with you on this lateral/torsional impact aspect. But I still stand firm on my belief that a square straight on hit can propagate a fracture if the strength of the steel is exceeded or the steel structure has inclusions or Retained Austenite. I also agree with Bladite that the vibrational shock is responsible for the chips. The notion that the grabbing of the blade creates fractures does not ring true with my testing. The crack or complete fracture happens with a high degree of impact and suddenness. The torsional grab in tenacious material would enable the tempered steel to: withstand the force, flex and return, not suddenly fracture. I use the example of martial artists breaking bricks. The impact is forceful and extremely fast not a slow grab and twist. That is, unless I am not understanding you, Chenko. If I am misrepresenting your thoughts, I apologize.
The obvious solution would to thicken the blade and edge. However, I want all to look at the reverse side of thicker. A thinner blade /edge requires a lot less force to penetrate any material. Less force to apply to the edge, less force to chip out the edge. Edge quality gives Ethan’s blades superb cutting and slicing ability. Thicker means more weight, more difficulty in balancing of the knife. A knife that is more bludgeon than cutter.
Much of the lab testing was to optimize grinding and heat treat processes. Improper heat treat leaves Retained Austenite which causes hardness/strength differentials in the Martensite structure. This causes stress risers and cracks. This Retained Austenite will eventually turn into Martensite….Untempered Martensite. Again this causes the same but opposite stress risers resulting in cracks. When I started in the knife industry, the old timers were adamant about reducing/eliminating Retained Austenite and the longer I am in the business, the more I concur. Grinding burns and heat stresses the steel in a very similar fashion.
Okay, I’ve had my say. Whichever way you believe, I thank you for patience and interaction. As Bruce Lee (a Good Daoist) used to say: Absorb what is useful, discard what is not”. You may do the same with this.
In the end we are all here because we like Becker Knives, Ethan and each other’s company.
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Best Regards,


Paul Tsujimoto
Sr Eng
Prod Dev and Qyal
KA-BAR Knives
 
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Thank you, Toooj, for a cogent explanation of whatever the heck you're talking about.:D

Just kidding. This is an exceptional post that explains — once and for all — the types of things that cause these fractures, in a way that even the non metallurgists among us (like me) can understand.

Agreeing with other things you've said; we do have a great group of people here drawn by common interest: Becker knives. But it's much more than just the knives alone (wonderful as they are); it's that everyone who comes here contributes to the whole, and they all get along well together. More than that, though, is that Bladite does a very good job of moderating — and compiling the FAQ's, too.

As if those things weren't enough, you and Ethan pop in and let us know what's happening. That's a big thing, really, and not seen on many forums.

And the other thing you said: "In the end we are all here because we like Becker Knives, Ethan and each other’s company." And I have to say that we enjoy your company, too, Toooj.

Now tell us more about the tweeners.:D
 
crystalline materials... well, even diamonds cleave :)

even sandworms... '''Paul Atreides: May your knife chip and shatter'''

tooooj: Casio sells a series of VERY excellent ultra slow motion capable video cameras. while we're not talking 1,000,00:1, we are talking reasonably realistic numbers for pro-sumers.

i'm will to bet a donut, and if you could map the patterns, you'd find what i'll just call "first order shockwaves" for certain strikes resulting in "half-moons"...

other kinds of breaks are just that imho, imperfections in materials.

until we can have a material that is god-awful strong and *not* crystalline, we'll keep seeing half-moons (that's NO moon...)

so, continue the righteous and scientific myth busters style testing...


Bladite
 
Hey Toooj, I sent back my knife, but did a bone head thing and forgot to put a note inside. My address and name are written on the package due to the fact that I had a thrid party send it out. I'd give you my home address and phone number ,but I would rather not on a public forum.

You can indentfy my bk-9 by the chip (obviously) and the fact the center grip bolt is missing. (I lost one awhile ago, bought a replacement but kept it. I didn't figure Ka bar needed my replacement bolt.)
 
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So the knife(a BIG chopper) broke because it hit wood??? Wood. Just wood right? It didn't hit diamonds, just wood. :confused: I'd be super pissed! That's what the damn thing is made to do!

I use .mil issued knives all the time in terrible conditions and they never break! Bend, dull, and get loose, you bet. But they don't BREAK!

Something is seriously wrong :thumbdn:




Free knives, as many as he wants!!!
 
This is so interesting, THANK YOU mr. Tsujimoto and mr. Becker. I will be reading all that you wrote again to fully understand it (my English is ok but I'm still not mother language) and also try to relate your words with a couple of other documented blade failures on other camp knives. Thank you again, that was great! :)
 
beerswimmer said:
So the knife(a BIG chopper) broke because it hit wood??? Wood. Just wood right? It didn't hit diamonds, just wood. :confused: I'd be super pissed! That's what the damn thing is made to do!
I use .mil issued knives all the time in terrible conditions and they never break! Bend, dull, and get loose, you bet. But they don't BREAK!
Something is seriously wrong :thumbdn:
Free knives, as many as he wants!!!
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guess you never chopped a lot of hemlock. read the whole thread? hemlock IS like chopping rocks. silicates/quartz to be more accurate. diamonds? i'd expect diamonds to break :>


Bladite
 
Diamonds - how do they cut up a large diamond ?? With hammer and chisel they cleave it [batoning if you like !] along specific crystallographic planes !! They spend a long time making sure they find the right plane !
 
Beerswimmer, I have seen $5000 commercial thickness planers get severely damaged from hemlock wood. The feed inlet, the table, and the 6 blades and revolving blade holder (blades were 1/2" thick). all shattered when a hemlock knot went thru.

The OP sent his BK9 back and is being taken care of by Kabar.

the company that made the thickness planer did NOT take care of the wood shop owner that bought the planer.........

nuff said.
 
hell, we've always burned hedge at the hunting lodge (the Chateau) every winter during deer season, and i ve seen knots in it do the same thing batoning with hand made knives fashioned out of old files that were as big and stout as it gets. good steel isnt indestrustable, thats just a fact
 
Hemlock is wood. Wood! Wood beat the heat treated steel. Wood beat steel and everyone is ok with that??? Wood took a chunk off of a knife that was made to whack through wood and it's OK because....??? Itks wood! Maybe I don't get why it's OK for this? I cut through frozen(-40F)wood, nails, bones and metal cans with .mil issued knives and they do just fine. What am I not undestanding about this BIG knife?? Not trying to cause drama, but come on...wood?
 
It does sound a bit counter intuitive to think that wood could chip steel. Many woods are stronger than steel, by weight. The silicates that are deposited in many knots are basically the same as stone. It can happen. It's the balance between hardness, toughness, and blade geometry. The BK9 is very durable yet slices as well as many of my chef's knives. When you put that geometry to the blade, there is a tradeoff in toughness. I personally use a hatchet for my main chopping duties and use my knives to cut stuff. I love the BK9 and wouldn't change it. It will take most all that people throw at it, while slicing better than most of the "hard use sharpened prybar type knives" Mil spec knives often have a much lower RC value to make them very tough. The tradeoff is edge holding. They do ok, but not well compared to many other steels at a higher RC value. :D
 
cody1 said:
It does sound a bit counter intuitive to think that wood could chip steel. Many woods are stronger than steel, by weight. The silicates that are deposited in many knots are basically the same as stone. It can happen. It's the balance between hardness, toughness, and blade geometry. The BK9 is very durable yet slices as well as many of my chef's knives. When you put that geometry to the blade, there is a tradeoff in toughness. I personally use a hatchet for my main chopping duties and use my knives to cut stuff. I love the BK9 and wouldn't change it. It will take most all that people throw at it, while slicing better than most of the "hard use sharpened prybar type knives" Mil spec knives often have a much lower RC value to make them very tough. The tradeoff is edge holding. They do ok, but not well compared to many other steels at a higher RC value. :D
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parts of hemlock are very soft. the knots and such might as well be rock.

rock hemlock :)

rock maple

ROCK LOBSTAH


Bladite
 
The thinner grind and sharper edge of the Bk-9 is what attracted me to it. I realized there was a chance of it not being as strong as my other big knife, an Ontario sp-10 ,but liked that the bk-9 was a slicer and a chopper.

The ontario has a much more obtuse edge. So far it seems rather indestructable, but sllicing with it, or poping hair off my arm (like my bk-9 would) is something it just won't do unless I reprofile the edge. I guess my point is, I saw the bk-9 as an all around knife, not just an indestructable chopper like my sp-10. It's all about trade off. More obtuse edge on the bk-9 and we lose that precious, sharp, slicing edge and I think we would lose some of the major charm to the bk-9. It would just become another chopper that isn't much good at anything else.

(Not that I don't love my sp-10. Been with me for 8 years now. Another great knife for the price, and also made in the USA. I loved both my bk-9 and sp-10)
 
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