Should I be concerned over a small sweetspot?

M

M4cr0s

Joined
May 1, 2012
Messages
92
Ho khuriacs!

Tonight I did the first etch on the WWII I acquired a couple of weeks ago. It was my first attempt with Ferric Chloride (FeCI3) too. The etching went fine. The hardened area that appeared cause me some concern though. Frist thing, the tip is hardened. Will have to be a bit carefull with it I guess. The belly is hardened too, although the hardening stops a little bit before (towards the point) than where I'd expect. The hardened portion is also very thin/narrow, something that makes me concerned if I'll wear through it over years. Am I just being silly?

Here's a shot.
18_WWII_FeCI3_etch.jpg


Mac
 
Have you run a file along the edge (as if sharpening) to confirm that the dark spots correlate with hardness? If the file glides across like on ice that part is hard...if it bites a bit more then it is a softer zone.
 
@ bric
I dug out the best quality files I got, some Husquarna saw chain files, round and square. They definitely bite a bit more in the areas indicated to be unhardened. Same with my other khuk. I have sharpened this khuk already and took of a bit of the soft, polished metal but I haven't used this one much yet.

@ czombie
I don't have much other choice I guess. I fear though that after a couple solid jobs with some dings in the edge and a bit of filing and sanding I'll go through the hardened steel even if the piece show no issues in practical use so far.

Mac
 
I highly doubt it will ever be an issue. Use it in good health:)
 
Hmm? Maybe you could temper the tip down some? The heat treat does seem odd. Hopefully the differences are not extreme. Perhaps you might try a new sweet spot heat treat?
 
I would leave it alone and not worry so much about it.
The pattern you are seeing there is probably only the absolutely hardest parts of the steel.
5160 is notoriously hard to get a hamon to show well and properly.
The khukuri is most likely fine. If it isnt, it is covered under warranty.
 
Thank you guys, I feel reasured now. It's a beautiful and well-made khukuri that takes a fearsome edge. I recall that it was a little hard to get it shaped and sharpened by manual means (sandpaper) in the last (closest to the handle) part of the recurve where the etch indicate the thickest hamon. I'm really looking forward to using this for what it is intended. I'm not at all worried about having it resolved if something in fact is wrong. I just want a good light "18 khukuri like this and use the heck out of it ;)

Mac
 
This what I saw after I put a patina on my WWII with vinegar:

WWIIPatina007.jpg

WWIIPatina006.jpg


My tip also showed to be hardened. I haven't had any trouble at all, but I haven't hit the tip on anything either. Good luck.
 
If you got a kukhri made from mild steel it wouldn't be hardened anywhere.
I can't see what the problem is. Are you worried because you think the "hardened" part might be brittle (i.e. not properly tempered)?
Or do you really think that a chopping implement should not be hardened at all?
If the Hardened parts were say 55 rockwell and the soft parts say 45, would you still be concerned?
Don't forget a Kuk is used for more tasks than just chopping, and an axe is not much good at skinning a bear.
A brass rod test would probably set your mind at ease.
http://www.caffreyknives.net/testingart.htm
 
parbajtor said:
If you got a kukhri made from mild steel it wouldn't be hardened anywhere.
I can't see what the problem is. Are you worried because you think the "hardened" part might be brittle (i.e. not properly tempered)?
Or do you really think that a chopping implement should not be hardened at all?
If the Hardened parts were say 55 rockwell and the soft parts say 45, would you still be concerned?
Don't forget a Kuk is used for more tasks than just chopping, and an axe is not much good at skinning a bear.
A brass rod test would probably set your mind at ease.
http://www.caffreyknives.net/testingart.htm
Click to expand...

I'll try to explain yet again, I think you got me wrong. I'm worried because this is a large ("18) khukuri whose main purpose is being pushed it into wood with great speed and force. It is ill suited as a butter knife or scalpel (although it certainly gets sharp enough for the latter purpose). A crucial component of the khukuri design and principle is a hardened portion of the edge whose job is to blast through stuff with minimal damage to the edge. The rest of the blade is essentially a very stiff shock-absorbing spring, nothing else. The combination of excellent craftsmanship, great build quality and service is the reason we buy these khukuris and put them to actual use. Yes, even unhardened steel will of course chop wood, it is steel after all, but it will likely take more damage than hardened steel. If it is thin, like the edge of chopping tool, it might roll, thus being a lot less suitable for my intended purpose. So, that's why I asked if there was any reason worry.

My humble apologies if appear cross or something, that is certainly not my intention.

Mac
 
M4cr0s said:
I'll try to explain yet again, I think you got me wrong. I'm worried because this is a large ("18) khukuri whose main purpose is being pushed it into wood with great speed and force. It is ill suited as a butter knife or scalpel (although it certainly gets sharp enough for the latter purpose). A crucial component of the khukuri design and principle is a hardened portion of the edge whose job is to blast through stuff with minimal damage to the edge. The rest of the blade is essentially a very stiff shock-absorbing spring, nothing else. The combination of excellent craftsmanship, great build quality and service is the reason we buy these khukuris and put them to actual use. Yes, even unhardened steel will of course chop wood, it is steel after all, but it will likely take more damage than hardened steel. If it is thin, like the edge of chopping tool, it might roll, thus being a lot less suitable for my intended purpose. So, that's why I asked if there was any reason worry.

My humble apologies if appear cross or something, that is certainly not my intention.

Mac
Click to expand...

I understand that, I apologise if I came across as sarcastic, not my intention.
It's just that Hardness is relative. The fact that you can see a kind of Hamon shows differential hardening/tempering and by itself is not necessarily a concern.
As you say, the edge needs to be suitably hardened, the rest of the blade behind the edge is a shock absorber.
The question is, is the edge suitably hardened for the tasks it's likely to perform?
Rockwell files, the brass rod test, a Rockwell Tester or just plain use/abuse it are the only ways of knowing for sure.
 
@parbajtor

I think that Mac's question was in regard to how the etch revealed a hardened zone and shape other than what he expected (as in the images below) and he was wondering if this was a cause for concern.

These images are not mine, but found on the internet:
scan0001-1.jpg

fruitwoodblade2.jpg

images
 
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