Torque question

I haven't done enough personal testing to satisfactorily answer your questions, but here is the jig Ed uses for his testing.
Quite easily made if anyone has the desire.
Tim Zowada also does some amazing demos regarding lateral strength in reference to hardened as compared to unhardened steels.
IMGP0655-1.jpg


IMGP0653-1.jpg
 
No, this is not a torque wrench. The torque wrench is the tool that attaches to it - like a ratchet - which measure foot/pounds of pressure. It attaches to this "jig".
I think the absence of posts to this topic has more to do with the placement of the post! It would probably get a LOT more response in the "Maker's Forums" .
Fully hardened blades bend - they just break sooner than those knives differentially tempered or selectively hardened.
For instance,"selectively hardened" will mean only the edge was hardened.
"Differentially tempered" will mean that the temper was drawn "differently" at a much higher temperature on the spine than was the cutting edge to remove more hardness/brittleness to prevent cracking when bent! Get it?
The differentially tempered blade will have been fully hardened where the selectively hardened blade only had a hard edge to begin with.
Some makers will tell you that they would prefer to have tempered martinsite then unhardened austenite!
The tempered martensite has the "potential" of having a higher torque rating at the same degree of bending as does the un-hardened austenite. If you harden some 5160 or 1084 and then draw the temper back at about 500 degrees, you make a really nice spring. If these were your choices for a knife blade, and IF! you did your homework and heat treating correctly, you might get some considerable bend in your blade and still have it return to full straight. The unhardened "selectively hardened" blade may take a "set" at the same degree of bend.
Maybe.
Then there are grind variables such as flat, hollow, and convex, to name just a few.
On and on.
As a maker, I could spend an entire week testing all the variables on my knives, and not get any knife making done!
I am not at that point where I can afford the luxury of testing everything I do in all of its available ramifications.
My knives perform well, and my customers keep buying them repeatedly!
I must be doing something right.
I do some simple testing on each knife to ensure that my "recipe" hasn't changed from one knife to the next.
I'm fairly confident that my knives will perform any duty they are subjected to in the normal realm of cutlery.
I do not have one of these jigs - but may someday!


www.andersenforge.com
http://www.kbaknives.com/knifeconstruction.html
 
I sure hope you don't think having austenite in a blade is a good thing....you're going to have some VERY disappointed customers if that's the case. Also, a full hardened blade with snap before a differentially hardened blade, but the differentially hardened blade will take a set long before the fully hardened blade snaps.
 
kbaknife said:
It IS if you want an un-hardened spine! What do you think happens when you edge quench a blade or clay-back a blade?
You don't get martensite in the spine.
Click to expand...

You get pearlite, NOT austenite....
 
kbaknife said:
You're right. Point is, there's a purpose for having other formations besides martensite.
Having formations besides martensite is NOT a bad thing.
Depends on where it is.
Thanks for the correction.
Click to expand...

You're welcome. :)
And, you're right, mixed formations is not always a bad thing, it just depends on what you're after. Personally, the only time I want pearlite in my blades is when I'm after a hamon. Otherwise, I prefer the strength of martensite. Others mileage may vary. ;)
 
KBA,
Thank you, that's the best explanation I've heard so far. With the terminology, not being a maker I do tend to get lost in it. But, I am interested to learn about it. To understand, the differentially tempered blade will have a greater lateral strength than a selectively tempered blade, which has a soft spine and just a hard cutting edge? Having the fully hardened blade drawn back in the tempering process to a lower hardness to make the spine tougher, and give it an added spring. (to return to true, when flexed) Right?

Is there an ideal range of Rockwell hardness at the spine? in the 30s or 40s, 50s? .. for a standard differentially hardened 4" hunter. What and why?

This may not be the correct place to post the question, just figured custom knives encompasses a lot of folks, and I would like to hear what people that buy knives prefer also. Whether people care...
David
 
I would have to say that, for the most part, even for someone not trained as a knife maker, you understood almost exactly what I said!
Now, is what I said correct?
Did you ever hear that one saying: "I know you think you understood what you thought you heard me say, but what you don't understand is that what I said is not what I meant!"
Just kidding.
There are so many variables it's in calculable.
Steels, heat treating "recipes", makers, sizes, grinds, ad infinitum.
Then, we'll throw Tim Zowada in the mix!
Last year at Ashokan, he gave a demonstration of using a fully hardened blade and a completly un-hardened blade. They took the EXACT amount of poundage to bend the same amount!!
Go figure.
These tests probably are only valuable to the individual maker who makes all of his similar blades by the same process. Know what I mean?
Comparing my blades handled one way to Phillip Patton's blades treated a different way tell you only one thing - they're different! That mine bend more or less than his do at a certain distance, says what? I dunno.
The blades aren't the same to begin with.
I stick my test blades in a vise and it takes a LOT more energy to bend them than they should ever encounter in their natural life as a cutting instrument.
They are not pry bars.
To be quite honest, my searching always leads me in the direction of the proper heat treatment that ends up with a knife that CUTS well.
There's an old saying in the Blacksmith Industry that leaves a LOT of leverage in an argument between the forging community that heat treats their own steel and the stock removal stainless maker who sends his blades out to be heat treated by the professional, and this leverage is in the hands of the stainless guy!!
That saying is : "The most a blacksmith can hope for is to end up with a piece of steel that is as good as the one he started with!"
We, as knifemakers, have FAR MORE opportunities to ruin a perfectly good piece of steel than we do opportunites to make it better. And that's the truth.
(I'll probably get tarred and feather for that statement!)
I have no idea of the ideal Rockwell hardness at the spine.
I do, however, personally know and often communicate with two Master Smiths who would more than likely give you two exactly opposite answers to that question.
I'm not even going to attempt to answer it!
Actually, this is a great place to ask these questions, and I hope this does NOT turn into any type of controversial thread.
I'm a pretty easy going Knife Maker, and I am proud to have this opportunity in this life to make some of Man's oldest tool.
I always make the most aesthetic knife I can manage to put together. I test them all for cutting abilities and I do chop as much as I need to to be certain the edge is not so brittle as to chip, and I want to cut a lot with it and have it still shave hair, whether it be an EDC, a hunter, fighter or a Bowie.
Thanks for letting me talk.
 
Jared: Some 52100 bearings, in order to stand up under high shock applications are heat treated in such manner as to leave a layer of 20% austenite in the bearing (inside, away from the bearing surface), this makes them tougher.
 
I'll bet that the lack of response is because the use of the torque "method" of testing a knife tells little between knife maker "A" and knife maker "B".
There are just so many variables involved that can result in different readings.
They can BOTH be excellent knives!
But, if ONE knife maker uses the torque readings as but one more tool in an already rather large "heat treating tool box" to test his blades, since he is the one doing them all, then it is probably going to benefit him in another way of monitoring and controlling his consistancy.
And I think it is beneficial to the knifemaker to use everything at his disposal to ensure consistancy.
It just doesn't seem to be a standard method of comparing one maker's knife to another maker's knife because of the variables involved.
 
kbaknife said:
Then, we'll throw Tim Zowada in the mix!
Last year at Ashokan, he gave a demonstration of using a fully hardened blade and a completly un-hardened blade. They took the EXACT amount of poundage to bend the same amount!!
Go figure.
Click to expand...

I'm pretty sure you meant to say "flex" instead of "bend". If you're still within the range where both bars just flex and return to true, then they should take the same force. But once you get permanent plastic deformation on the soft bar (i.e., it bends and stays bent), the hardened bar will keep flexing and returning to true. By the time the hard bar actually gets far enough to stay bent, it should take like 4 times more force to get there. (If I remember his demostration correctly.)

There are several ways to end up with a knife that's stout enough to serve a given purpose. Stiffness and strength are highly dependent on cross section/thickness. If you want to leave the spine soft, you only have to make it a little thicker to compensate, and/or use convex grinds. Etc.
 
Good job! Flex.
You're right - that's how it went. (It's been a year now!)
Wasn't that a cool demo??!! I thought so.
I'll be there again this September to soak up as much as I can.
I have also found the convex grind to give me the stiffest blade to "flex" the farthest and return true.
Thanks for the clarification.
 
You must log in or register to reply here.
Back
Top