Degradation of Sharpness - Carbon Leeching?

M

MrMike

Joined
Jan 22, 2006
Messages
147
Alright - I love my new CAK... but have to admit I'm a tad more than frustrated by the amount of time I've put in keeping an edge. Got it back in November and it was made by Sher. A real beauty. It's one of those that just seem to be made for the user.

In a previous post I noted that it was dull on receipt. So dull it wouldn't cut much more than cheese. I'm serious.

I've sharpened it using sandpaper to what I consider field-sharp, and have consistently noticed that the edge dulls over time from being in storage for just a week. I get a great edge and after a week of non use can tell that the edge has lost its bite - how can I tell? I run it carefully down my fingernail and it doesn't shave any longer. The other telltale sign is light reflects off the edge in a "toothy" or serrated pattern in some spots that almost resembles chipping on a micro level. I'll sandpaper the edge so it "zeros" this tooth with 600/1500 paper, strop and store. A week later, same issue.:eek:

WHY is this happening? Bad temper? Uneven composition at a microlevel? Steely mentioned a while back that sometimes in the forging process carbon is leeched from the surface resulting in a softer shell than the good tempered steel just underneath this layer. Could you expand on this detail? I'm sure it would be helpful for others.

I'm not jumping to the conclusion that I have a defect without further testing but my wife thinks I'm a tad nuts for spending the amount of time babying this work of art. For the record - I'm not going to use a belt sander. I believe in the least amount of metal removed to maintain an edge. I gotta say, from experience going down to 1500 grit is a waste of time.

At this point, what do I do?
 
I'll wait for the experts to weigh but sometimes you simply have to remove a few mm of steel to get to the "good stuff". Since you haven't gone to that extreme yet ( I assume), you might have a bit to go before you hit the harder steel.

It might be a less than ideal. However, I would wait for one of the "real deal" experts to put in their 2 cents before i jumped to that conclusion. If it doesn't get any better, let Yangdu know. She'll get it straightened out;)
 
Hmmm.. I am in no way an expert, but will add my 2 cents anyway.
What you could do is go down to a tooling shop and get them to do an Equotip hardness test on it.
the test only leaves a tiny indentation on the metal but will accurately give you a hardness rating, usually in Brinell. HI claims an average hardness of 60 Rockwell (C) for their working edges. The equivalent in Brinell should be around 620 to 670.
Or you could do a simple wire nail test first.
Hardwire nails are around 450-500 Brinell.
If you slowly press the edge of the blade into the nail until you make an indentation, either in the blade (BAD) or the nail (GOOD) or both (BAD).

When my M43 arrives, I plane to do a full metallurgical review on the blade, right down to material analysis (we got one of those fancy gadgets too!)
Will post results on the forum.
Generally 5160/90 steel does not get as hard as 60Rc, but I think the Kami use a silica/carbon rich additive.

Personally, I would prefer a harder edge and just be careful about chipping.
Uncle Bill reccomended a few simple tests for you Khukuri, like a bend/strength test, cutting tests etc.

If the blade fails these tests, then it is covered by the lifetime warranty.
Unless you left it in the fire and its softened up!

I dont think HI would drop its standards. They are the best and will remain so.
 
MrMike says: "I'm a tad nuts for spending the amount of time babying this work of art."

MrMike, you hit the nail on the head. These khukuris are works of art FIRST, and anything else, second. It's good to keep that in mind. My Chitlangi is beautiful, and it has a place of honor in my knife collection. I'm glad I bought it, but I would never even think of using it for much of anything. Too heavy, too dull, too hard to sharpen, awkward to carry around, etc. But as art..... well this one tops them all.

Love these khukuris for what they are, and don't try to make them what they are not, and you will be much more satisfied with them.
 
My Chitlangi is beautiful, and it has a place of honor in my knife collection. I'm glad I bought it, but I would never even think of using it for much of anything. Too heavy, too dull, too hard to sharpen, awkward to carry around, etc. But as art..... well this one tops them all.
Click to expand...
:confused:
So what you're saying is that it's just an attractively sculpted representation of a real kukri?
 
The_Shadow said:
These khukuris are works of art FIRST, and anything else, second. It's good to keep that in mind. My Chitlangi is beautiful, and it has a place of honor in my knife collection. I'm glad I bought it, but I would never even think of using it for much of anything. Too heavy, too dull, too hard to sharpen, awkward to carry around, etc. But as art..... well this one tops them all.

Love these khukuris for what they are, and don't try to make them what they are not, and you will be much more satisfied with them.
Click to expand...

Ummm, I beg to differ that they are simply works of art with no user qualities. ALL my khuks are users first and their true beauty (for me at least) is in the using. Now your Chitlangi may not be a user (understandable), but all mine are, from my 18" M-43 down to my 9" Baby AK. Are they beautifully made and do I enjoy looking at and fondling them? Hell yes, but I also enjoy using them in the yard, around the house and in the kitchen. Just last night, I used my 16.5" WWII to carve up a whole rotisserie chicken for dinner and then used it this morning to chop a package of frozen chopped sirloin in half. I also think that one of the best parts of ownership for me is getting that hair-popping edge on them after use. This is just my opinion, but suggesting to someone who bought one of these to not use it and just appreciate it as art is doing a disservice to HI and these awesome knives.
 
Billy516, your experience is much different than mine and I sure do wish it wasn't! Glad to hear you can get your khukuri to do real work, that must be fun. I have tried, but just can't get mine to take an edge. I even bought a belt sander and got some sharpening belts, but no joy. I have had it for years now, and like I said it's a beauty but not something I would trust when the chips were down. Now that's my experience, and I am glad yours is different!
 
Shadow, you might consider shooting Yangdu a note about your khuk or seeing if one of the sharpening Gurus wouldn't mind touching it up for you.

I can assure you that of the over 50 HI pieces I have, I would trust any one of them to perform flawlessly under the most serious and dire of circumstances. The only ones that I have not sharpened up and test fully are the ones that really are art first and tool second, and even those probably would do the job...I'd just cry afterward:p

Seriously, if you are having that sort of problem getting it to take an edge, shoot Yangdu an email. HI products are NOT just for show:)
 
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
 
If there is any moisture or vegetable matter or any other corrosive (ESPECIALLY from fingers being run across the edge to feel how sharp it is) you will see sharpness fall off because the edge will oxidize. Any non-stainless steel will suffer from this, from a Kabar to a $2000 Ed Fowler hunter. Before you put your khuk back in its sheath, always make sure it's clean so that deposits of corrosives don't end up down in the sheath, and if it's going to be put away for awhile, have the last thing it touches be an oily cloth. Non-stainless steel is superior to stainless in almost every way for big working blades like these (and yes, they are indeed working blades) but this added requirement of edge maintenance is one of the costs of the higher performance in other areas.

And I'd like to match ferguson's offer on the same terms (just so he doesn't get swamped :) )---I'll convex any HI khukuri for the cost of return shipping. These work horses deserve the opportunity to work, and with the right geometry they excel.
 
t1mpani said:
If there is any moisture or vegetable matter or any other corrosive (ESPECIALLY from fingers being run across the edge to feel how sharp it is) you will see sharpness fall off because the edge will oxidize. Any non-stainless steel will suffer from this, from a Kabar to a $2000 Ed Fowler hunter. Before you put your khuk back in its sheath, always make sure it's clean so that deposits of corrosives don't end up down in the sheath, and if it's going to be put away for awhile, have the last thing it touches be an oily cloth. Non-stainless steel is superior to stainless in almost every way for big working blades like these (and yes, they are indeed working blades) but this added requirement of edge maintenance is one of the costs of the higher performance in other areas.

And I'd like to match ferguson's offer on the same terms (just so he doesn't get swamped :) )---I'll convex any HI khukuri for the cost of return shipping. These work horses deserve the opportunity to work, and with the right geometry they excel.
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you are ALSO a legend!

For all my reading up on metallurgy and limited personal experience with sharpening, I would not have thought of the edge oxidisation thing unless it hit me on the head.
Very good point. Thanks
 
Steely_Gunz has over 50 HI khukri.

Were do you keep 'em all?!?!?

Sigh, I have a long way to go.
Waiting fo rmy first Khukri, an M43.
 
I would do the outfit that made it a favor and write them describing what you have observed and give them a chance to correct it. Customer feedback is a significant contributer to future quality - if the maker cares.

Unless you are one of the few with very few with acid skin, the natural oils from your fingers should actually preserve the edge.

It is nice to hear about someone who uses sandpaper to sharpen a knife rather than the fancy sharpeners and training wheels! Try using some 320 grit.
 
Ya check with Yangdu, see what she says.

If you want something really sharp you have to remove metal to thin out the angles and refine the edge. I feel bad when I see people shell out $150 for S30v then use horribly blunt angles because "that's what the factory edge was."

Belt sanders only remove "too much" metal if you use too coarse of a belt and press too hard. After you regrind a factory edge to make the angles lower/sharper, all you're using on resharpenings is the 1200 grit belt and/or a leather one with green compound. This combo removes minimal metal, but gives you a polished sharp edge.

The beauty of a belt sander is if you chip out an edge or get a horribly profiled machete/knife/sword, you can easily grind down the bevels until you're just at the edge, then switch to finer belts to finish off the working edge bevels. Just keep a pail of icewater nearby to dunk the blade in so it doesn't overheat as you're working.

I used Lansky stones/clamps for 15 years and they're still great for some of our smaller knives, but a 1"x30" belt sander with Lee Valley belts has replaced 99% of my sharpening. Our knives have never been sharper, and sharpening has never been easier or faster.

The knives still last just as long as before because you never touch the edge with low grit belts. You lower the angles -to- the edge the first time you sharpen with low grit belts, but when you reach the edge you switch to and stay with high grit belts/leather belt w/compound for years and years.

Only go back to low grit belts again to re-lower the primary angle again years later, or reshape a bad chip/blade failure.

Also because sharpening is so fast and easy, if you have a knife you think is good enough to warrant a lower angle/sharper edge, you grind it. If you have a chopper that is losing the edge too quickly, you re-shape a steeper one. No sweat.

The biggest problem my friends and family always had is they'd try to endlessly re-sharpen the crappy factory profile rather than grinding in a better one. The first time my wife tried my knives after we got married she was trimming fat off beef and she thought she was using a razor because the blade sailed through without any resistance. It's all about the angles.

Just remember to let the belt do the work, you concentrate on holding the knife at the correct angle and pulling it across the belt smoothly. If you're grinding a new angle and it's taking too long, use a coarser belt, don't press harder. Keep the icewater near and dunk the blade after each pass, wipe on a towel, do the next pass.

I was sharpening a friends thick "survival" knife and it didn't even have an edge, it looked like someone had tried to cut a boulder with it. I had to use a 80 grit belt to reshape a primary grind angle, then I smoothed it with 120/320/600/1000/1200 grits then the leather belt with green compound. The satin finish looked almost like the factory finish so I had to warn him it was now very sharp.

You can't make an omelette without busting eggs, and you can't have a sharp knife without removing some metal. If knives were all razor sharp and all lasted a million years no one would buy more. Sharpen 'em and use 'em, they sure aren't going to visit your grave when you're gone.

sharpen.jpg
 
titus010782 said:
Steely_Gunz has over 50 HI khukri.

Were do you keep 'em all?!?!?

Sigh, I have a long way to go.
Waiting fo rmy first Khukri, an M43.
Click to expand...

You'll love that M-43. Mine is a often trusted companion when there is wood to chop:thumbup:

Actually, I think my collection is probably down to 30ish these days. I have gifted several of them away to friends and family members that needed a good reliable blade. I don't believe in selling them as many of them were gifted to me as well. My "profit" from these blades is getting to know them by hand, finding so many great friends through these bladesm and the honor of being a tiny blip of stitch in the rich tapestry of HI.

As for where I store them....all over the place:D I have a couple in my truck, a couple in my office, a few by the bed, a few in a drawer, and huge trunk full of them in my garage. Also, I tend to gravitate toward HI's smaller blades. It's a lot easier to rack those up in a hurry.

How did I get to 50+...well I dunno. I started off with a village model in college, then picked up a 15" AK that a customer couldn't sharpen and returned to Uncle Bill. Then I got out of school and had some disposable income being a bachelor and working lots of overtime. After that...it gets fuzzy:D I'm thinking a couple of them were in heat and stored to close together in the trunk;)
Please keep in mind that we have forumites that have well over TRIPLE digit collections:eek:

Edit to add: Steve and T1mpani, you guys are very generous with your offer:D
 
I haven't experienced this phenomena at all. Where do you live? Anyplace with a very high humidity level?

My khuks are sharpened with user edges. I don't attempt to put a hair splitting edge on them, as, for what I use them for (heavy chopping) such an edge is no advantage.

I sharpen using a belt grinder, which slicks them up rapidly.

Andy
 
I've experienced this with nearly all carbon steel blades.

Now for me they are still very sharp, but say I have them shaving hair. Over time they will get to the point where they won't shave hair but will be very sharp still.

I have no idea why I always just figured since it was a carbon steel blade and I like my edges very fine that there was some slight oxidation that was affecting it.

I have noticed less of this effect if stored really well oiled.

Once again I'm not talking a HUGE difference in sharpness, but perceptible to me.
 
PS.

I myself would rather have a slightly soft khuk blade. They can be sharpened or pounded back if they bend or waver.

If the edge is very thin and hard you run the risk of chipping which is worse IMO.
 
Even after all these years, I am astonished at the goodness of spirit of some of the H.I. folks.


Thank gawd we got that cranky old ndn to balance things out. :)





Kis
enjoy every sandwich
 
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