Rehashing "flex"

What tests do you use Kevin? I know you use a charpy tester, a rockwell tester, and microscopes to develop and test your heat treating methods but what tests do you do on each blade to ensure that it is up to spec?
 
Kevin R. Cashen said:
The edge flex thing is like the file test, adequate if you are not all that particular. It will get you in a wide range but will not tell you anything specific. I would say that the file test can be more accurate since it at least measures a form of hardness (abrasion or scratch hardness but not penetration), while the brass rod flex test tells you a whole lot about how thin you ground the blade and not as much about heat treatment as people would like to think. People who hold it up as the definitive test are simply blowing hot gas. The only way the test can tell you about heat treatment is if you push it to the point of yielding and then you have a kink in your edge- kind of like the nice fellows in the middle ages who would tie rocks to your daughter, toss her in pond and then tell you the great news that she was not a witch after all! Hey that’s great, but it is rather moot point now isn’t it? And of course if you have a good hardness on your edge it will flex like crazy if it is thin. Are we looking for a certain amount of deflection every time? Are we looking for a certain amount of force required every time? If it is a set amount of deflection forget about however you heat treated it and just grind it thinner to meet your mark. If you want to really lay on it and not deform it at all simply grind it thicker. I personally think there has been a lot of slight of hand and misdirection involved in many of these popular tests that make the presenters knives look great, either in their own mind or in the public. Flexing over a rod will get you inside a huge ball park if that is all you need, but it is not a real definitive or even accurate test overall.
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Mother bleeper! I was just coming back to this thread to ask just such a question, and maybe ask if there was anything better.


I think I have a knife that was overheated in the process of thinning it out post-factory. It's ZDP, takes a WONDERFUL edge, but loses it just as quickly. Any suggestions?

I may try the file bit, but I was hoping for something a bit more... specific. I probably have access to a Rockwell tester at Uni, but that only tests flats, and I doubt it got THAT heated.
 
Chris Meyer said:
I posted these video clips from Tim Zowada's "Bending and Bustin' Demo" a while back (with Tim's permission).
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Chris, I looked everywhere for those links yesterday and finally gave up! You ought to post a link in your signature to these files or something... or if you need them hosted elsewhere because of bandwidth or whatever, give me a yell!
 
#1. On Stiffness:
"The only way to change "stiffness" is to make it thinner or thicker." Kevin

“Indeed in matters of stiffness geometry is the bottom line. Increasing the amount of material to resist tensile forces on one side and compressive forces on the other is how you make things stiff.” Kevin

““Stiffness”, or the amount of force it takes to pull a blade over in a vice, is based upon the cross section and has nothing to do with heat treatment!” Kevin

#2. On three pieces of steel with the exact same geometry and composition:
“If all three were fastened at one end on a bench and then had 20 lbs suspended off the other end they would all deflect exactly the same under 20 lbs. As you increased the weight the annealed one would be the first to bend and not return to true if the weight is removed. The other two would take much much more force to reach that point, but the tempered one would still have a little life left after it began to yield while the fully hardened one would just snap with very little if any deformation.” Kevin

“So the "harder" bars would take more weight to break or permanently bend but take the exact same force up to the elastic limit of the weaker one.” Jason
 
Intuitively...

If you take three pieces of steel with the exact same composition and geometry, one hardened, one hardened and tempered, and one annealed,... in the final analysis,... The hardened one will be the hardest to bend. The hardened and tempered one will be the most springy, and the annealed one will bend the easiest.
 
I have read every post on this thread. Many of them were far to technical for my level of education. Much of the terminology , I am not familiar with.
Like many people on this site, I am a visual learner, text can only do so much, to educate me. On the other hand; If I can see it demonstrated it becomes clear. {A picture is worth a thousand words]
I appreciate Mr. Cashen's great wealth of knowledge. I read and reread his post and try my best to absorb some of what he is saying.
This goes for others on this site with a lot of technical information to share.

What was being discussed, here, only became clear to me when I watched Tim Zowada's videos, posted by Chris Meyer. Thanks Chris!
Try to keep us visual learners in mind when you post.

Remember, to us, a picture is worth a thousand words and sometimes more, like in this thread.

Fred
 
The metallurgy, or science on this thread, though interesting and true,... falls under the catgory of "inapplicable gibberish", as far as I'm concerned. It does more to confuse than clearify.

It really just depends on which "perspective" you want to look at this from, intuitive or scientific. I think intuition transcends science,... but either way you look at it all boils down to the exact same things.

... back to square one. :)
 
I apply 'inapplicable gibberish' all the time ,it works for me !! It worked for guys like Martens, Bain ,Gunier, Preston and many others too ! The vorpal blade went snicker snack !!
 
There's that phrase again, "It works for me". Can you expalin that in scientific terms?

I have to admit that I did get caught up in the silliness of it. Curious things were being said and it was fun.

But the bottom line is that,... there is nothing new about any of it, and there isn't anything here that we don't already know and apply to bladesmithng on an intuitive level... Hey! "It works for me"!

I don't see any point in arguing about it or discussing it any further... except for fun! :)
 
We can do practical, we can do aesthetic .We can be intuitive ,we can be scientific. HOWEVER , there is no reason why we can't combine and make something aesthetic/practical and use intuitive/scientific. My definitions -- mechanic ,makes things practical, -artist,makes things aesthetically ,- and the rare craftsman who combines the aesthetic and practical !!
 
I find it useful in my quest to try to make my beautiful vorpal blade into something practical that won't go snicker-*SNAP*

of course I was the guy that pissed off the fine art photo establishment at RIT by insisting that fine art photos be well crafted in addition to being beautiful (dust spots, fixer stains, scratched negatives etc. didn't say art to me, just sloppy and lazy)

-Page
 
In don’t necessarily agree with mete when he say that it “works for him”, because it does just work for mete, it works for everybody whether they care to believe it or not. Every moment we don’t fly off into space, every time we start or stop our car rolling, every hammer blow, every ounce of steel ground, filed or chiseled, they are all complete validation of Newton’s boring gibberish. It works before we accept it whether we like it or not, and it works with us and for us after we understand it. And that is a point not to forget, if we choose to deny reality it can be endless insurmountable obstacles for us to trip over with our self imposed blind folds, or we can study it in order to understand it and allow it work for us. The laws of physics CANNOT be defeated, when faced with something that cannot be beat do you want it working against you or do you want to be able to make it work for you?

Intuition is all right, but let’s not get carried away, how many peoples intuition told them that heat treat determined stiffness before encountering the information we have discussed in this thread? The intuition of virtually every person I have met that had not previously studied this (including myself), believed the opposite.

Jason Magruder said:
What tests do you use Kevin? I know you use a charpy tester, a rockwell tester, and microscopes to develop and test your heat treating methods but what tests do you do on each blade to ensure that it is up to spec?
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Jason that is where things gets touchy as far as what I do as opposed to everybody else. I have methods and equipment that are kind of nerdy all the way around. Much of it is not practical for most folks who just want to enjoy making some knives. For most, simpler tests get them by and I have no business telling them what to do. It is only when folks start believing that tests are telling them things that they are not that I feel the need to open my yap. Occasionally I still run a file across an edge just to ease my mind, but I am well aware of what that tells me and more importantly what it can’t tell me. I can’t say I bother pushing my edges against a brass rod, but I often impact my edges with a brass rod to test for impact strength. The guy who’s tools and materials are laden with inconsistencies and unforeseen variables, as the tradition tools of the smith are, needs to test every blade at almost every steep to insure quality control, this is the replacement for consistency and tight control. Inversely predictability, consistency and tight controls can free one from the burdens of having to double check every operation, and its product.
I am currently developing an impact test specifically for knife edges, it will of course be slightly destructive but it will be one more tool in the direct determination of knife qualities.

Fred.Rowe said:
I have read every post on this thread. Many of them were far to technical for my level of education. Much of the terminology , I am not familiar with.
Like many people on this site, I am a visual learner, text can only do so much, to educate me. On the other hand; If I can see it demonstrated it becomes clear. {A picture is worth a thousand words]
I appreciate Mr. Cashen's great wealth of knowledge. I read and reread his post and try my best to absorb some of what he is saying.
This goes for others on this site with a lot of technical information to share.

What was being discussed, here, only became clear to me when I watched Tim Zowada's videos, posted by Chris Meyer. Thanks Chris!
Try to keep us visual learners in mind when you post.

Remember, to us, a picture is worth a thousand words and sometimes more, like in this thread.

Fred
Click to expand...

I hear you Fred, being mathematically challenged I am a very visual learner myself and often need to draw things out to fully grasp them. But I can only post what I have at the time. What I do post already consumes quite a bit of time, taking time to develop useable images for every topic could quickly become a full time job. The only reason I can post the graphics that I do is because I already have them from my webpage or a presentation that I have done for a lecture or a class. If folks would like to send me a check for time spent illustrating in order to compensate for shop time lost, I would be happy to provide any drawings or charts folks would like. In the mean time a little thing called Google will get you just about any image your heart may desire.
 
Hey, these are probably stupid questions, but I have a couple.

1) Mete mentioned epee blades. I have also noticed a wide disparity in the force required to flex epee blades. I seen epees that I can bend very easily, and others that take quite a bit of force to bend.

I don't see any drastic differences in blade geometry that would result in such a disparity in flexing force (as far as I can tell, they don't take a permanent set after this)

So, what is going on here, am I actually bending the blades past the elastic limit without realizing it, or am I missing something geometrically, or am I just crazy?

2) Japanese swords were differentially hardened (I know this is done on some modern European swords as well) . I can't imagine that this was done for no practical reason. What is the reason then?

Thanks :)
 
1. If the blades have the exact same cross sections then they are the same within the elastic range, if you are seeing any permanent set at all then you are beyond the yield point and the elastic modulus no longer applies, but the one that took that set easier was softer.

2. before the advent of intentional alloying in modern steels the best way to control toughness was connected directly to hardness, if you wanted for it not to break you made it softer. Japanese swords, and early European ones for that matter, were made from VERY simple steel. You could have it hard and brittle or you could have it soft and tough. If you wanted it hard and tough one way to accomplish this would be to make it soft down one side and hard down the other. But this is all in consideration of impact strength which is slightly different in some ways from continuous flexing. I never liked how prone to bending katanas were if you didn't cut straight on, and have noticed modern European swords can suffer from the same issue if made the same way, except Japanese swords are much easier to straighten than a differentially hardened double edged blade should it get kinked. Modern alloying will however allow us to have both hard and tough in one heat treament by something like the addition of a little nickel or silicon. Thats what we call progress;).
 
James Muehlner said:
Hey, these are probably stupid questions, but I have a couple.

1) Mete mentioned epee blades. I have also noticed a wide disparity in the force required to flex epee blades. I seen epees that I can bend very easily, and others that take quite a bit of force to bend.

I don't see any drastic differences in blade geometry that would result in such a disparity in flexing force (as far as I can tell, they don't take a permanent set after this)

So, what is going on here, am I actually bending the blades past the elastic limit without realizing it, or am I missing something geometrically, or am I just crazy?

2) Japanese swords were differentially hardened (I know this is done on some modern European swords as well) . I can't imagine that this was done for no practical reason. What is the reason then?

Thanks :)
Click to expand...

When I first get an epee blade from out of the box it is, if it is well manufactured it is pretty much poker straight. If the epee blade is mounted in a hilt and taken straight into the list due to the variations in how thrusts are delivered it will eventually develop bends in several directions, and ultimately as it builds up stress where those different bends start to overlap if will fail, unless it is a maraging blade it will probably break at least somewhat sharp and possibly perforate my friend on the receiving end. I typically will take a blade and work a set into it bending it in one continuous curve slightly beyond it's elastic limits so that as it bends it bends in the same direction with the force spread out over a good portion of the blade.
Many of the epee blades that are being sold lately have somewhat inconsistant grinds, and some even have soft spots that will yeild considerably before a section next to them. With the multiplicative effect thickness has on the stiffness, a milimeter if difference in a 2 millimeter thick section will have a very real effect on the stiffness while not being that easy to spot on a casual inspection. If your epee has a slight curve in it (hopefully in the direction the V points to) someone has trained it. yes, taken it slightly beyond the elastic limits, better that than failure.

-Page
 
hear you Fred, being mathematically challenged I am a very visual learner myself and often need to draw things out to fully grasp them. But I can only post what I have at the time. What I do post already consumes quite a bit of time, taking time to develop useable images for every topic could quickly become a full time job. The only reason I can post the graphics that I do is because I already have them from my webpage or a presentation that I have done for a lecture or a class. If folks would like to send me a check for time spent illustrating in order to compensate for shop time lost, I would be happy to provide any drawings or charts folks would like. In the mean time a little thing called Google will get you just about any image your heart may desire.


I hear what you are saying, Kevin. Google and other search engines are a real boon to the information age.
As far as the check being in the mail; the pittance I could afford to send would not buy many high priced cigars.
I do appreciate the large amount of personal time you put into your post.
They are always well written, and highly technical in nature.
I personally think that using less technical language, at times, would allow more people to both understand and participate in the discussion. Again; a picture is worth a thousand words, especially to those not versed in the subject being discussed.
If I am speaking in front of a crowd, on a subject that I know well, I tend to use language that I am comfortable with. That language does not always inform those that I am speaking to.
If my purpose is to educate, I have found that using language they can understand, along with visual aids, is more beneficial to them learning.
After all that is why I am there. As a teacher, I am not there to impress them, I am there to teach them.
Thanks again for what you have taught me. I appreciate it very much, Fred
 
By definition intuition is always correct. If it isn't correct, then it isn't intuition. Hey! It worked for Einstein.

What bladesmith works within the elastic limit of an annealed blade? :D

... It's what happens after that point and how heat treating effects it that is of more concern to us.

It's not just geometry or heat treating,... it's geometry and heat treating together. :)
 
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