Degradation of Sharpness - Carbon Leeching?

[titus010782]

Took a common finishing nail (3/4") and placed it on a book as a padded support.
I first pressed into the nail lightly using the belly of the blade (supposed to be 58-60 RC). The nail indented with a nick slightly. No visible damage to the edge of the blade.

Next, I placed the belly of the blade on the nail and battoned it hard with the palm of my hand. The nail bent significantly, but there was no visible nick or other damage. The khukri fared worse... I now have a ding in the blade. It didn't chip - it just rolled.

Not clear how hard the nail or the blade are - but when I see Wolf describing butchering an oak tree and then shaving afterward - I think my blade is significantly softer.

I dont like the sound of the khukri losing against the soft steel nail...dont like that at all.

 

[Wolf_1989]

Yeah it sounds like yours might be a little on the soft side. I reckon that happens considering the Kamis harden the edges the old fashioned way. There's always going to be some variance with any items made by hand.

 

[MrMike]

In your opinion, is this a reject? Realistically weighing hardness vs. toughness and the ability to resist chipping or cracks.

(I have a very small hairline stress crack at the very tip of the blade... was planning on just filing it out but now I just don't know.)

I'll let others weigh in... thanks.

 

[Andrew Colglazier]

Can you post pics? It would be good to know exactly where on the blade you tested against the nail.

Andy

 

[MrMike]

Can you post pics? It would be good to know exactly where on the blade you tested against the nail.

Andy

Sorry Andrew - no pics - already reprofiled the edge last night using 600 grit paper.
The deformation was a little more than half the width of the nail diameter itself - the nail is 1/16" stock.

I'll send some pics after my chop testing this weekend. It's all about durability, but not the need to endlessly resharpen every time you use it.

 

[MrMike]

Can you post pics? It would be good to know exactly where on the blade you tested against the nail.

Andy

One last thing - I skimmed your response - apologies for not directly answering your question - the dent occurred in the sweet spot, about 1" back from the apex of the belly curve (toward the handle, not the point). This had been the hardest part to sharpen, so it must be somewhat harder considering.

 

[Andrew Colglazier]

It's all about durability, but not the need to endlessly resharpen every time you use it.

Yes and no. I use most of my khuks pretty hard, and I have been known to pay less than adequate attention and smack a nail once in a while.

Nails will generally make a mark... just about every time. Not a big mark, but.... a mark. These blades have a lot of mass behind the edge, not unlike an ax blade. And having hit nails with axes and hatchets, they will usually show the result as well.

But the edges, even after hitting a nail, are completely usable for long after. A little rolled spot won't stop the blade from doing its job.

I count on having to do some touching up on my blades after use, since they often end up in the dirt while being used. With my working blades, I rarely take the time to gently set them on the ground when using them, they are often tossed unceremoniously to the dirt.

But they always clean up pretty good! :thumbup:

Andy

 

[titus010782]

In your opinion, is this a reject? Realistically weighing hardness vs. toughness and the ability to resist chipping or cracks.

(I have a very small hairline stress crack at the very tip of the blade... was planning on just filing it out but now I just don't know.)

I'll let others weigh in... thanks.

I dont know how to shake this one. It should not have stress cracks near the tip. The Kami make the sweet spot and belly end hard while leabing the tip softer for "prying". If it is cracking in the area used for a pry bar, thats bad.
Speak to Aunty Yangdu about this.
When my M43 arrives, its getting the works and will be tested Uncle Bill style.
That means a full body weight bend test, prying and hardness etc.
HI make the best in the world. I dont think we want HI getting a bad name because of a few overlooked blems.
Quality control is paramount

 

[MrMike]

Titus, this may be what is needed. I'll learn a lot more this coming weekend after continued edge testing on a properly sharp blade.

I really would find it hard to part with this CAK though, after spending so much time getting it sharp. I've never used the tip to pry anything. I noticed it after connecting with a knot in a tree branch. I did full lateral prying and the body of the blade held up just fine.

I wonder if all of this is secondary worrying if there IS actually harder steel under the skin? Of course, that's the gamble. I found the link where users discussed filing the edge back 1/8" to expose the harder steel. If that's the case, I don't want to trade it in - as nice as Yangdu's return policy is.

 

[Cpl Punishment]

I've mentioned before that I filed the bevel back on a few of my users to remove the soft material until the file "skates", and then sharpen from there. No edge problems since on those. If you don't want to part with the CAK, you can try that. Otherwise, ask Yangdu what she'd recommend.

 

[titus010782]

Mike, you could try Cpl's method. Use a 2nd cut (smooth) file and just work the edge a little first.
I dont know how the outside could be soft and the inside hard, but this is what the guys are saying and they know because they have lots of khuks and its a trial and errored fact.
You should just make Yangdu aware first.
Either that or contact Steve Ferguson and ask him if he will sharpen it for you. He would no doubt test the edge too and give his opinion

 

[Yvsa]

I'd be happy to put a nice convex edge on one for any of you gentlemen. No charge, just return postage. I've never had any of mine lose sharpness in the scabbard.
Steve Ferguson sferguson2@triad.rr.com

I shelved the technique of sandpapering length of the blade. I spent a fair amount of hours this weekend hand sandpapering from the bevel to the edge in short controlled strokes with 600 grit. There is a flat spot near the curve of the cho that still needs to be profiled but for now, a huge improvement. It's double the effort.

I can now cleanly slice copy paper and that's never happened before. I thought the aesthetics would be ruined, but the satin finish of the bevel actually looks quite nice when done carefully. Now - for the edge retention test. We had a snowstorm this weekend in Wisconsin so I couldn't do some chop tests. I oiled it and stored it. Will check again this coming weekend and test on some hard dry maple.

It is noticeably sharper. The tooth of the sandpaper is why. I did not go down to 1500 grit this time. Those mini-serrations are the key.

Mike unless this is something you absolutely must settle for yourself in your own mind then keep after it.
One thing I've learned from living as long as I have is when I'm having a problem with a skill I have that I've been particularly proud of for some time is that it's sometimes best to seek a 2nd opinion.:thumbup:

If indeed the hardness is defective Steve can figure it out on his belt sander while you're thinking about it and you'll have a definitive decision whether to send it back or accept it as a soft blade.
Sometimes a softer blade can come in handy. They need to be sharpened at a more obtuse angle in order to hold an edge for any length of time but being easier to sharpen because it's softer means you could simply sharpen it with a file at home, or in the field.
I've got a scar on the inside of my left forearm that testifies to how sharp you can get an edge with a plain ol' flat bastard file.

I'm going to be surprised if after taking as much as 3/32" off the edge that there isn't a hard area underneath like it's supposed to be, but as good as the HI kami's are they can sometimes drop the ball and......... especially around the time of Dashien, hope I spelled that right.

On the other hand take this as a rant from an old fart who wonders if he still knows from where he speaks at times anymore.




.

 

[titus010782]

Yvsa has a good point. At the end of the day, a Khukuri is a tool. A slightly softer one can still be used. I am still worried about those stress cracks though. Any news on that?
You can do a magnetic particle test on the blade surface of you like to check for cracks.

In fact, here is an open invitation to anyone on the forum who wants their blade tested for stress cracks.
I am a certified NDT inspector and will do a magnetic particle and ultrasound (if applicable) test on the blade. The test can find cracks even a few microns wide and subsurface too. The ultrasound test will find internal laminations in the steel. These are non-intrusive tests, this means they do not damage your blade steel. I do this everyday at work, so it would not be an trouble.
Same as Uncle Steve, just send the return postage to me by paypal or whatever.
PM me if anybody wants this done.

 

[Wolf_1989]

Take a real close look to be sure if it is indeed a crack and not just a mark from grinding. I have a khukuri with what I thought was a crack in the blade between the Cho and the bolster; by taking a closer examination with a magnifying glass it turned out to be merely a grinding mark.

 

[MrMike]

Thanks for the new posts on the subject, guys. Unfortunately, I could not test the blade outside this weekend. We had subzero windchills with a high of only seven degrees both days. I spent some time sanding out the flat spot near the cho.

Your thoughts on the stress crack. It is a crack. Very minute, but it is still there. The length is a tad over 1/16" and is about an eight of an inch back from the very tip. It angles back toward the bevel at a slight diagonal. All told, I can probably grind this out over time and it won't present a problem.

Of course, whacking the crap out of it to see just what it will do is probably the best medicine right now. Ferg, and Titus - I appreciate the offers for analysis. Outstanding cameraderie on this forum. I'll hold tight until I test further before going that route.

I did test it this weekend by whacking it hard on an oak plank about 3/4" thick secured to my work table. I hit the sweet spot three times and the blade passed without incident. No rolls or dulling. I'm impressed by how tough the metal is. At the end of the day, I'd take this over risking chipping the blade on a rogue nail.

Stay tuned....

 

[MrMike]

Well after two weeks of very foul weather I was finally able to get out and do some hard testing today on a very sharp edge. I cut up a bundle of fallen dry maple branches knocked down after a winter wind storm - each one being about as big a round as my thumb. Effortless, especially when using the straight edge behind the belly (near the cho).

I then proceeded to heavy splitting of some hard maple and apple wood. Each was about a foot in diameter. I struck them hard and then used my hand to batton the round full force, bringing the round down on the chopping block. This CAK is a very effective splitter. Six were quartered without issues. On one the blade got stuck so I laterally pried it hard while holding the wood with my foot. The wood split clean through.

Finally, I did some cross cut tests (full force) on apple branches two inches in diameter. When I first got the khuk, I was disappointed by the cross-cut performance - the blade was not sharp at the time. Today, chips were flying and each was severed with two hits. Amazing difference.

Bottom line - The edge held even though it may not be near 60RC, it's still very sharp - sharp enough to cut photo copy paper. No dings, no wavy edge. I really don't care if it dinged after the nail test. I need it to hold an edge when chopping hardwood and after a 45 minute workout it did just that. This blade will be an awesome camping companion.

Sher makes an amazing blade. Thanks much Yangdu for a superior product! This is one I'm definitely handing down to my son.
Note the cold blue job on the khuk and karda. Came out nice. Nice even battleship grey without being too black. She doesn't rust anymore. Horn handle with swirl pattern is gorgeous.

Sharpened with 600/1500 grit sandpaper, final strop on leather stick with green chrome oxide.

 

[MrMike]

alright - what's the trick to posting inline photos, guys?

 

[Karda]

alright - what's the trick to posting inline photos, guys?

You forgot to include the http:// part of the code is all mike, pull up a quote of this post and study the difference.

Your pics are nice.....But Humongously Huge!

 

[Wolf_1989]

Ah yes a CAK made by kami Sher.

That horn handle is stunning! It has an almost tiger-stripe pattern to it which is is fitting considering what kami Sher's name means.

:thumbup:

 

[Carolina River Rat]

That is one of the more beautiful horn handles I've seen. That one along with another I saw in the picture thread that was almost transluscent green.