Destructive testing

M

mikeS

Joined
Apr 7, 1999
Messages
1,015
How much of this do you do, and is it important???

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Sola Fide
 
You are talking about torturing the knife until it is usless?. I think testing in this way is very important for the maker to feel confident in his/her finished blade.In the ABS we are required to bend a finnished forged blade to 90 degrees to see what happens. I have broken many before I learned the proper way to heat treat. I am into bending damascus now for my masters performance test in a couple years.
 
How many knives do you test per knives sold?

Is there a way of proving the knife without the desrtuctive test?
I have a lot of questions about this.

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Sola Fide
 
Mike, I test blades when I change materials and/or heat-treat methods. I never bend stainless because Paul Bos does the HT. and I know it will hold an edge but wont pass the 90 degree flex test at his reccommended hardness. The carbon steels are hard on the edge, spring temper in the middle and soft on the back. Thats one reason they bend so nice. With testing and noting the results I can evential get the good combination of toughness and edge holding.
 
Thanks, that makes sense to set the parameters of a new material or process.
I guess what I'm looking for is a way to prove the performance without the destruction of the blade.

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Sola Fide
 
Mike, for what it's worth, I take my semi-finished and sharpened blade that I've drawn the back on and chop on a good solid oak or hickory knot till my arm gets tired. I know the back will flex because I drew it back. If my edge rolls it's too soft. If it chips it's too hard. If it wrinkles a little it's a slight bit thin on the edge. I want it to look like it did when I started. I do this on each blade. It tells me a lot, short of destroying my blade. May not be the best but it works for me. Hope this can be of some help. mike w
 
M L, thanks, I use the brass rod test, the oak knot sounds like a good thing to add.

I have passed the ABS journeymen test the minimum requirement as I see it, I'm looking for more checks.

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Sola Fide
 
Mike I have passed my JS also. The brass rod test should be used for each blade. I demonstrate this for prospective buyers. Its always impressive to the Ones who are worried about flexing it themselves.
 
Mike,
For me, about every dozen knives or so I will pick one at random and destroy it. This does a couple of things for me. First it re-proves that I'm staying on the straight and narrow with quality. Secondly it gives me a chance to check out grain structure on the interior of a blade. Every blade must pass the brass rod, or it doesn't leave the shop. For as simple as that test is, I feel it's possibly the best test to determine the correct working hardness for a blade.

Max,
For an explaination of the brass rod test, take a look at http://www.caffreyknives.com/testingart.htm


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Ed Caffrey "The Montana Bladesmith"
ABS Mastersmith
www.caffreyknives.com
 
hey ed, next time you get to the one youre gonna od...just send it to me and I will do it ok.....LOL......and why does Bruce only waste the Finnish blades??
smile.gif


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http://www.mayoknives.com


 
m l williams :


If it wrinkles a little it's a slight bit thin on the edge.
Click to expand...

What is the thinnest you can grind an edge and still have it durable enough for the knot chopping? Steel? RC?

-Cliff
 
Cliff, there are more variables in that answer than there is time to write. Mike is measuring that on his blades with his edge. Any numbers he might give you would not apply to anyone else's blade or edge, regardless of the steel.

Fact is a knife can be fashioned to pass almost any destructive or nondestructive test you want to challenge it with. That may or may not tell you much about how that knife will perform in its intended use.

How many you test and how is determined by the variances in your process. Forged blades, differentially tempered, have more variances than a homogenous steel blade with a set tempering schedule. It makes sense that the additional heating and hammering cycles induce changes that are not present in what we stock removal guys do. What they end up with may well be a better steel, but it a more complex process getting there. The quality control demands are more complex, so what Ed is doing is controlling his process by checking his reproducibility every dozen blades.

I grind my blades in 20-30 blade batches. That's what goes to Paul Bos. From each lot there is always one that isn't cosmetically as nice as I would like, so I beat it up. Sometimes I take its edge down to nothing to see how it breaks. Sometimes I do things like cut nails just for orneryness. Mostly this is teaching me how much farther I might push the envelope in some blade designs and features. It tells me nothing about how the other blades in that lot are going to fare in the real world. That is determined by all those other variables I mentioned above.

When I have a dozen customers tell me, "gee, that's a hell of a knife", that's the real world test. I'm not trying to see what I can get by with. I want to know by how much one of my blades can exceed expectations. I do that by shifting a dozen variables on every knife I make depending on the customers' stated goals and uses for that knife, or my intended goals for a spec-built knife. It is unrelated to what any other customer may want or think.

At the PKA show this last weekend, I had a 5-1/2" fighter with a fancy handle on the table. The show was in Denver and the audience was more field use oriented than tactical. Two customers picked up that knife and asked how it would do as a hunting knife. I told them very clearly it had the wrong blade shape and edge design for dresing and skinning deer or elk. In the clearest posssible terms I told them it was the wrong knife for what they wanted. One of them bought it anyway.

That knife will shave brasss rods all day, but it will drag badly while skinning, and he will end up using up (dulling) the forward 1/2" of blade without touching the rest of the edge. There's too much point and not enough belly. The handle is angled for leverage, lowering the point far too much for skinning use, but it will split briskets all day. The edge is heavy for incidental edge to edge contact, and will wear him out trying to resharpen it. The blade is brushed, not mirror polished, so it will likely accumulate fat and drag even more.

And at the end of the day I suspect it's lousy for cutting cardboard. These are not simple equations, and there are absolutely no universal tests that can gauge all blades, individually or differentially.

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Jerry Hossom
www.hossom.com
The Tom & Jerry Show
 
Jerry :

there are more variables in that answer than there is time to write.
Click to expand...


There are no variables, the answer is simply the thinnest that he has ground which has withstood the test. The question becomes harder if you are asked it about a steel which you have not worked with and have to try to figure out how the change in strength, ductility, and impact toughness will require the profile to be changed. But it is far from impossible to be answered. Which is good as makers do it all the time (the better ones anyway) when they redo a knife design in a different material and have to adapt the geometry so as to be optomized for the new material.

I have asked this basic question many times (how thin a profile would be functional) and recieved many detailed answers. Some makers have actually exchanged sketches as we discussed the kinds of stresses the blade would recieve (for light vegetations like this, for harder woods more like this, how are you swinging? ok then you would want to thicken/lighten it). Many makers are willing to openly discuss knife design in detail being very specific- some are not.

-Cliff
 
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