? for Ed Fowler re: bending

[fitzo]

Hello, Ed,

I was reading a thread over in the Knife Review forum, wherein you mentioned the frailty of testing by bending a knife in a vise against the steel jaws. You mentioned that small scratches could create stress points, causing premature failure. I have to agree completely.

Is it appropriate to extend this to worrying about scratches left from the polishing process? I have long worried that what I call a brush finish, with the finish running perpendicular to the edge, possibly leaving behind heavy 36 or 60 grit scratches hidden by the finer grits, creating exactly that type of stress point. This I feel could result from doing all the finish in one direction, and not varying the "angle" of the scratches produced as grits are changed.

For that matter, it would seem that filework would create terrible stresses on the spine, especially if they are cuts made from a triangular file. If so, then bending properties couldn't be expected from a fileworked blade??

Would you mind commenting on this from your point of view?

Thanks.

 

[Ed Fowler]

Wow Mike; you really asked some relavent questions. Scratches: A lot depends on the grain structure of the steel, the finner the grain the more insignificant will be scratches. 60 or 36 grit scratrches would promote quick failure. Your thoughts about changing angles is absolutely correct. I always gind to at least a 600 grit then polish at a right angle with A-16 and A-6 then Brownells 555 grey for bending tests. A deep scratch, say one left by a triangular file will promote snap to a high degree. It doesn't matter when only doing a single 90 degree flex around a sharp vice jaw as the damage will be on the inside of the bend and compress rather than stretch. If you are planning repeated 90 degree flexes, back and forth, the mark left by the vice will contaminate your evaluation of the knife, when stretched you already have a crack formed.

File work and serrates can result in stress risers that will promote premature failure. A lot depends on heat treat, grain size and nature of the steel.

Absolute uniform grain size also seems to fail before the same steel would if the grain size is a matrix. ie. uniform 12 will snap like a piece of glass while 12 and finer is very tough. I learned this while working a summer job mixing cement for viaducts for an interstate highway. We had to have so many pounds of each size of gravel and sand in each batch. I asked the inspector why, he stated the variable aggragate was much more flexible.

Grain slip promotes toughness, fine grain pormotes slip, a matrix, I believe, is very beneficial. I figured this out simply testing blades in my shop with the information supplied by Rex and his laboratory. A scratch in a blade iterrupts grain slip and promotes fracture.

As long as there are bladesmiths who ask questions and test, we will all benefit. Thanks for being one of us.

 

[SPryor Knives]

Although I know this thread was a question to Ed...I've just got to throw my two cents worth in.
I personally think WAYYYYY to much emphasis is put on these bending/flex tests. I have never, nor would ever abuse a knife bad enough to break it...even if a production knife...
You guys using these for bumper jack handles or what..??

 

[fitzo]

Thanks, Ed! Concise reply,it made me remember, again. Dang I hate this memory thing with age!

I read a metallurgy primer recently in prelude to reading Bain's book, "Alloy Elements In Steel" and they spoke of this characteristic of steel. I have to go back and re-read the segment on slip planes and such again, obviously.

The analogy to concrete gravel is excellent, thanks!

The bottom line about my question I guess is geared toward, if one is gonna want a rough-use high performance blade, have a decent finish on it with no deep scratches, realize filework can interfere with structural integrity, and if the blade gets significant deep scratching, get it repaired if one's butt is gonna depend on it.

This is what I love about knifemaking. There is never an end to learning and improvement in ones techniques and knowledge. One can immerse onesself in understanding and it becomes a lifelong endeavor, never boring unless we make it so.

Thanks, again!

 

[Ed Fowler]

Steve: WE or at least I do it because I can. I can because it is important to me. It all started when knives broke when I was using them. I found it inconvenient and hazzardous. I wanted all the tools I carried to be dependable, absolutely dependable. It is not that I would abuse a knife unintentionally, but when I need a tool and have to travel over 50 feet to get a more appropriate one I would much rather use what I have with me. Torturing knives is not for everyone, many will never need a super knife but when you do you will never forget the sound of snap.

Mike: you are welcome. Some thoughts of caution, don't let the science limit your journey. Try and test all variables that come to your vision. You have all the materials necessary in your shop to allow you to test and take knives to higher levels. When we depend upon science to explain what we did rather than where we will go we are not limited by tradition. I started reading everything I could find from the science and knew only frustration. I learned a lot of big words that taught me nothing. Now with the help of Rex the science begins to make sense, but he has his job and I mine and it works for both of us. Many times I ask what if, he says try it and let me know, then he tells me why, maybe.

 

[B . Buxton]

Interesting thread, so what is really being said here is. If a person wants a high performance blade, a person should not order one with file work up and down the spine, and if a person does and it fails when put into an extreme situation, that person should not be surprised.
I've always been against file work on a working knife for that reason, but some customers just insist on it. Whats a maker to do.
This thread will help argue the point against file work on a worker when the makers suggests against it. Thanks Ed.

I'm not saying that file work should not be placed on knives. I'm just saying on certain knives, it should not be placed. Agree or disagree??

Bill

 

[KennyC]

i seem to recall a "mad dog" knife that had filework on the spine for the sole purpose of shock absorbtion and flexibility. its somewhere on bladeforums or one of the "other" forums, i just cant remember which one..