Important technical thread on Shop Talk...

Jim March

Jim March

Knifemaker / Craftsman / Service Provider
Joined
Oct 7, 1998
Messages
3,018
I've started a tech thread that relates to Khukuri steel and other Nepalese bladework.
http://www.bladeforums.com/ubb/Forum12/HTML/001347.html

If possible, I'd like to reserve that thread for "tech info" only on the subject at hand, rather than veering into a general Khukuri/Nepal discussion such as we see here. Bladesmiths like Darrel Ralph won't want to scroll through the kind of 40-post monsters we routinely enjoy
smile.gif
(and I really *do* mean "enjoy" in a non-sarcastic fashion!).

Thanx!

Jim
 
Jim, thanks for posting the tech thread. I checked it out and found it most informative.
 
The tech thread on Sword Forums was interesting but also gave me a deep chuckle. All those highly-qualified modern 'experts' trying to sidle around the fact that 'primitive' kamis can apparently do something that the 'experts' deem impossible (or at least very difficult.) Sort of like the early aeronautical engineers who proved conclusively that bees couldn't fly.
I remember a thread not long ago where a member offered to get a good micrographic and chem analysis of HI steel, if supplied a 1" square of it. Did anything ever come of that? (Maybe it would be better not to find out that bees can't fly...)
 
It's an interesting thread, Jim, and I will visit from time to time -- when I have time!

I have not seen it with my own eyes but Pala and Gelbu both tell me that only springs are used for the khukuris at BirGorkha. I don't know what the other shops are doing today but when I lived in Nepal khukuris made from springs were an exception rather than the rule.

I may send a khukuri over to the test house and get some papers and see what they say.

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Uncle Bill
Himalayan Imports Website
Khukuri FAQ

 
Water is the oldest known quench medium. It's been used since biblical times. So it's got a pretty proven track record. But there are many factors that may enfluence a successful quench.

Jim March's suggestion that it may be due to khukuris unusual thickness is very interesting. I think most modern smiths never work with anything thicker than 5/16" stock. So that may change the equation?

Also the suggestion that the forging process may reduce carbon content so that it's no longer straight forward 5160 is a possibility.

I have a few questions. Is the water poured from the kettles at room-temperature or boiling hot? Is it just water, or maybe a brine, like salt water or some sort?


 
At BirGorkha the water comes straight from the tap, kept at room temp., poured very slowly on each side of the blade. If the blade is just a smidgen too hot it'll crack the edge. Has to be just right or you are in for trouble.

In villages without running water, the water comes from spring or stream. Nothing added. Just water.

Kumar hardened up his 3/16 special with good results so I am not sure how much the thickness of the stock has to do with the success rate. And, they harden karda and chakma which sometimes are less than 1/8 inch thick.

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Uncle Bill
Himalayan Imports Website
Khukuri FAQ

 
Dang, I forgot about the Karda and Chakma! However, those aren't going to take any "flex stress" worth talking about, so if the hard/soft border is a bit abrupt or they're uniformly over-hard they might indeed chip and crack. It doesn't matter because one is a slicer and the other a polisher.

I already posted on that thread about how Shop2 (now BirGhorka) should have better control over the steel supply so we can assume that in all cases they're starting with 5160. The edgeholding we've all seen suggests that they're not dropping the carbon content significantly at the forge.

They must have had access to leaf springs for at least, what, 50 years? More?

Jim
 
Thanks for keeping this thread afloat, Jim -- it's an interesting issue!

I asked a Q in Shoptalk about 3 months ago re: leaf springs, when I first started looking into this "khukuri thing" (!). There were two points of interest for this discussion (if I remember correctly):

1- not all leaf springs are made of 5160. Some may be made of steel with as little carbon as 5140, I believe. (FYI, the 3rd and later digits, "60" or "40" or whatever, refer to the carbon content: the 100 in "52100" refers to approx 1% carbon, 60 in "5160" roughly equals 0.6%, etc. 5160 is technically a "medium-carbon" steel, but knifemakers love it because it essentially performs like a super-tough hi-carbon...)

2- as the leaf springs used by the kamis is essentially recycled, it is essentially heat-treated twice by the time it is fashioned into a khukuri. So even if it "begins life" as 5160, it ends up an auto leaf spring w/slightly less, and even less as a khukuri.

But what I don't understand is how the khukuris are able to keep a KEEN edge for a long, LONG time...!

Glen
 
At a guess, they're pounding carbon back into it during the "heat'n'beat" process. This is quite common; wood-based fires always have carbon floating around. Some old-time smiths used to put in "extra carbon" with the addition of animal-based carbon sources, especially bone, feathers, all kinds. This is part of where myths about blades being "alive" may have come from, the metal was thought to have "eaten" the animal by-products and gained "power" that way...what was really going on was a carbon increase, especially at the surfaces. You get a bit of "case hardening" effect.

Jim
 
Since it opened its doors BirGorkha has used only springs and Kumar used a couple of worn out files for a Kobra or two.

I think I will send a little 12 inch Ak over to the metal test house and see what they think the steel is. As mentioned, it has gone thru a couple of different processes and has been shaken around pretty good for maybe 50 years. I don't know anything about metalurgy but I'd guess the molecules have taken a beating of sorts. What this would do to a chemical analysis or however they test steel I'm not sure. It would be interesting to find out, though.

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Uncle Bill
Himalayan Imports Website
Khukuri FAQ

 
Uncle Bill,

You might just want the shop to send you some one square inch samples of their springs. I don't know how they collect springs but, is it possible the kamis have a favorite truck they like to strip? It'll be really cool if you can tell them "okay, those Mercedes have the 9260, the Volkswagens have the 6150, and the Chevys have the 5160."

I hadn't thought of the springs as being previously heat treated. So basically they come of the trucks at 48-50 HRc. Then heat treated a second time. Hmmm. . . this complicates things.
 
I have absolutely no scientific basis for it, but I believe that being on a truck as a leaf spring for some years 'does something' to the steel. Some years ago I acquired an old Chevy truck helper leaf, and thought to make myself a primitive bowie of it. I asked a local blacksmith to anneal, profile and flatten it for me. Then I intended (silly me) to use a bench grinder, files and a belt sander to put in the bevels. That steel hadn't been annealed; my friend handed it to me 'as quenched', and a file or belt sander wouldn't move it. I tried to anneal it with a torch, without success. Thinking it must be very brittle, I subjected it to tremendous abuse with a sledge, as the end of a prybar, and leaving it in the weather. It wouldn't rust, either. I think it's still under the porch at my old dwelling, to this day. That metal had 'work hardened', I theorized, to the point where it was some kind of magic steel. I may go back and look for it someday! If you had a Ford, YMMV
smile.gif
 
Thanks for interesting post, gunhou.

I used to take the manufacture of a khukuri with the proverbial grain of salt until I tried it myself. After I tried and failed I developed the proper respect for the skills of a master kami.

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Uncle Bill
Himalayan Imports Website
Khukuri FAQ

 
Very interesting thread with regard to the 5160 issue and water quenching. I'd love to see how the master bladesmiths figure this one out, as it seems none has yet come up with a solution to this interesting mystery.

Harry
 
Harry, a master kami will succeed in getting the hardness he wants 99 times out of 100. Experience tells him just the right color he wants and just how fast to pour the water. If the blade is too hot it will crack or warp. If it is too cool it will not harden up to the desired Rc. If he pours the water too fast, cracks and warping. Too slow, and the blade will be too soft.

After considerable practice I could get close to what I wanted about 8 times out of 10. My first attempts -- may of them -- resulted in warped and cracked blades and a lot of swearing.

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Uncle Bill
Himalayan Imports Website
Khukuri FAQ

 
Us "Westerners" want to reduce it to a science. I'm starting to think that's the wrong approach...just go ahead and let 'em treat it as an art and they'll do their best, especially if we're talking about an old master like Bura.

Jim
 
Hi All,
Metal smithing is more art than science, always has been and probably always will be. No one ever knows everything about it. The more you learn, the more questions you have. Forging does not remove carbon.....Heat does... That's how you burn steel. 5160 is a simple steel that is very forgiving in heattreat. In this day of wonder steels too many people forget about just how good some of the old standbys are (just not stain resistant), like 5160, 1095, 1075 and 52100 for example.
Dan
 
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