Rockwell Hardness Tests on Two Khukuris

C

Craig Gottlieb

Joined
Mar 8, 1999
Messages
1,760
I just got a fax from Ron Hood, who runs www.survival.com (many may have heard of him). As part of another upcoming article on the GH khukuris, he sent two off to be Rockwell tested. Here were the results, measured on the blades' sweet spots.

BHOJPURE: Spine 22, Midsection 45, Edge 54
PANAWAL: Spine 25, Midsection 46, Edge 55

Of course, these are only two khukuris picked at random, so measurements differ blade to blade. However, I'm interested to see what you all think of the "point spread."

Any comments?

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Craig Gottlieb
Gurkha House
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Craig, looks like the hardness is very consistent from blade to blade. I doubt if factory made blades could come close to that high a consistency, since a lot of their hardness seems to have to do with their placement within the oven/kiln. And I wonder how many years it would take a kami to develop such a consistency from blade to blade. I'm impressed.
 
There was an article no too long ago in Fine Woodworking that talked about Rockwell hardness scale. They used a micrometer stylus to measure the amount of damage that had been done durning testing. I would like to see the same kind of testing done on kukhris. Yes it is quite amazing that the kamis can determine the hardness of a blade by instinct. Having done some forging and knife/sword making as a hobby, it is quite amazing indeed.

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Nothing says love quite like a sharp knife... Now if my wife only believed that.
 
Generally speaking, I would guess that the more "normal" sized khukuris exhibit better, more consistent hardening. Just a hunch, but I bet it's "harder" (no pun intended) to temper a huge blade. Thoughts?

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Craig Gottlieb
Gurkha House
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Craig,

Looks like pretty good edge and mid section hardness numbers. Looks like the edge will require just a little bit more steeling or sharpening about as much as a Ka Bar. I am surprised the spine is so soft. It does not seem to be hardened at all. Would making it a bit harder say 45 Rc make the blade more resistent to bending?

Will
 
I`m also very suprised at the hardness #s for the spine. Is it possible that it`s a mistake? I make some knives out of leaf springs myself (generally 5160) and they are partially air hardening. If you don`t bury them in hot sand (or something similar) to stretch their cooling rate out a few hours they get too hard to drill or file easily. I`d estimate that state to be quite a bit harder than 25. The rest of the #s look pretty good. I would have thought the edge to be bit harder too because of their good edge holding but sometime the #s don`t tell the whole story. Marcus
 
Marcus, in your opinion, would the softness of the spine indicate that perhaps the khuks that were tested were not actually made from leaf springs?
 
I wouldn`t presume to even guess about that. I`m no expert but the numbers quoted for the spine *sound* softer than any steel capable of being hardened at all would be after the type of zone hardening the kamis perform. Quenching the edge still draws heat out of the rest of the blade at a much faster rate than if it were just sitting and cooling. I`ve done some 5160 blades where I only heated the half of the blade facing the edge(using an oxy/acetelene torch),then edge quenched them and the spine is still hard enough to hammer on and difficult to file. Most machettes are in the 45 +/- zone and they file or dent just a bit harder (if any) than the spines of these blades. I`d rough guess the spine of my Bhojpure to be more like 33-45rc. I think if the spine were that soft the blades would bend much easier than they do also. It`s really not important though what the numbers are,as long as the knife works right and GH khukuris certainly do that!
smile.gif
Marcus
 
Are there any details about where and when this article will be published? Thanks.
 
Leef: No idea yet on the date, but I'll keep everybody posted. As for the softness of the spine, I was a little surprised, but not too surprised. One of the features that I like about our khukuris is that the edge is rather soft. This gives, in my opinion, a blade that will never "snap" under duress. Personally, I'd rather have a bent knife than a broken one in an emergency situation.

Cliff Stamp would be the best person to comment on this issue. He's actually bent a Bhojpure with EXTREME weight applied.

As for the Spring issue, I'm certain that they were made with Springs. I won't buy "Rail Common" khukuris because although they can be tempered, nothing beats the steel as it came from the auto/truck manufacturer. Just my thoughts here.

Of course, when I get back from Nepal in late March, early April, I'll have a load of info to pass on to everybody.

I'll even be undertaking a very special project (one among many) while there. I think everybody is going to like this one. Marya and I are actually taking a class on this so we can do it. What is it? A khukuri video documentary, of course.

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Craig Gottlieb
Gurkha House
Blade Forums Sponsor
 
Craig, what a great idea -- a video documentary on khukuris! Without a doubt you'll be able to sell a bunch of copies of the video (I'm assuming that you'll be marketing it). In fact, I'd like to go ahead and place my order now.
 
I think that I could find space on my shelf for a documentary on kukhris.

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"Clear a path for the Kukhri or it will clear one for itself"
 
Steven: What a vote of confidence! And you haven't even seen my photography skills yet (not to mention my acting skills)
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Yeah, we're going to take a really high quality video camera - one that will allow digital editing on the computer - and shoot some good footage of "kami interviews" along with shop action sequences, general Nepal stuff, etc.



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Craig Gottlieb
Gurkha House
Blade Forums Sponsor
 
Concerning the RC's quoted for the spine, yes they are very soft. They indent visibly when struck with a hard object. For reference the RC rating for the A, C and D scales is calculated as 100 - 500 * t. Where t is the penetration of the indenter (the different scales are just different loads). This means you can calculate a depth ratio = (100-RC_1)/(100-RC_2). Try this for a couple of numbers and you will note that to see the significant level of indendation on the khukuri spines the RC needs to be quite low.

Will :

[spine]

Would making it a bit harder say 45 Rc make the blade more resistent to bending?
Click to expand...

Yes. As long as you don't go that high that you lower the ductility and bending causes fractures. That is why in general you don't want 60 RC prybars.

Craig :

[referring to me]

He's actually bent a Bhojpure with EXTREME weight applied.
Click to expand...

I had my brother do some prying and he could not bend it and he is about 190. It could take my whole body weight which is about 275 give or take. It took a two handed side pull leaning on the blade to bend it. I could have straightened it and thus not significantly effected its functionality (aside from the loss in prying strength).

Note I saw a significant difference in quality between the SN1 and the Bhojpure, it seemed that Craig's blades made a large jump in ability in such a short time frame. It would not surprise me if the AK's and such he is getting now are better than the Bhojpure I had.

-Cliff
 
Cliff: The one AK "sample" that I sold to Steven F seemed to be leaps and bounds "better" than the Bhojpure. So only time will tell, when the "standard length" AKs get here, whether your statement is correct. I sure hope it is.

CLIFF: What would be the ideal rockwell hardness for a khukuri spine?

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Craig Gottlieb
Gurkha House
Blade Forums Sponsor
 
Craig, since you are not having constant problems with khukuris being returned bent there is little reason to have them hardened to increase strength. In general you want the spine hard enough to resist bending but not that hard that the ductility and toughness are in the fracture level (which is why you soften it in the first place).

As for specific numbers, it is not like you can say X is the level as it depends on the steel and the heat treat. The only way to figure it out is to make blades different ways and test them.

-Cliff

[This message has been edited by Cliff Stamp (edited 02-09-2000).]
 
Hi Craig, basically the Rockwell "C" method of hardness
testing involves placing the test piece in what amounts to
a fancy press that has a diamond-tipped cone shaped penetrator
on the end of it, and that in turn is manually pressed against
the material to a specified amount of force (10 kg I believe)
The dial on the machine is zeroed then a lever is tripped and
the machine applies a standard load to the penetrator (150 kg
usually) As Cliff stated earlier, what the machine actually
measures is the depth the diamond penetrator is able to indent
the material given the standard load.

Whew! that was rather longwinded, hope it made sense
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not bad for my first post *grin*

 
Sumo: Welcome! We're honored to have your first post be with us. And it does show far greater knowledge of things-knife than my large head contains! Who was Rockwell anyway?

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Craig Gottlieb
Gurkha House
Blade Forums Sponsor
 
Wasn't he the guy who did those drawings of children for the Campbell's soup cans?
 
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