Edge failure... help

[ferguson]

The edge was self-evidently too hard OR too thin -- for the material struck --with that force -- at that angle.

Tom, That's what I wanted to say, but couldn't figure out how to.

Steve

 

[munk]

If the chips are deep, you have to reprofile because left alone the edge is vulnerable to more breakage. If they're shallow I leave them alone. If I thought the task the khuk was undertaking was worth continuing, I'd switch to a khuk with a more appropriate edge profile. If I didn't have a more appropriate khuk, I'd modify the injured one to task.

Sometimes it's good to have a khuk with a slender profiled edge. I wouldn't change it because one afternoon I wanted to chop bone, if 364 other days it was chopping wood just fine.



munk

 

[Yvsa]

I think there's an optimum convexed edge that will serve most purposes from being a good wood chopper to a good bone cutter. Once in a great while you will get a khukuri with such an edge, or you can put one on yourself with some diligent work.
I'm really glad to see the newer khukuris coming with thicker and more convexed edges than they have in a long while.
It's a great improvement on the kamis work and I believe it will lead to less damaged edges.:thumbup:

 

[munk]

Credit where credit is due; I think you're right about the blades (as usual) and everything has improved under Yangdu's stewardship.



munk

 

[Howard Wallace]

I'm with the "reprofile" crowd.

How many of you have "used up" a HI khukuri?

By the time you've sharpened it down to a Sirupati (about the year 3072 by my calculations) you will have a lot of memories to go with your thin fighter.

By 3586 you should have a nice fillet knife.

 

[Aardvark]

"In the year twenty five, twenty five..."

 

[Thomas Linton]

How much of the width of the blade is hardened? Tain't 100%.

 

[Cliff Stamp]

A thicker, convex edge would be better. RC 48 would be better.

At that soft you are going to have compaction problems, most steels have maximal impact toughness at or near their maximum hardness, A2 is around 60 HRC for example, if you drop it lower the edge will indent easier and fracture easier at the same time. You don't really need massive edges to deal with bone chopping, 15 degrees per side and 0.025" thick, v-ground, will handle a lot.

Heavy bone is like concrete block - only tougher.

Concrete blocks have rocks in them which is fairly hard on a knife edge, it isn't a serious problem for any of the normal cutlery tool steels, you just grind the edge down with the impacts and smash it in due to direct impaction. It is however worse than bone, a rock axe will readily cut up bone, a bone axe will readily get mangled on a concrete block.

I would not grind all the steel out, that is a fair waste, I would just take a small rod sharpener and work in the bits to sharpen them and they will gradually fade away with repeated sharpenings.

-Cliff

 

[Thomas Linton]

At that soft you are going to have compaction problems, most steels have maximal impact toughness at or near their maximum hardness, A2 is around 60 HRC for example, if you drop it lower the edge will indent easier and fracture easier at the same time.

So, to a high limit, harder is tougher? That would certainly be good. So a chisel in A2 should be at 60 RC?

You don't really need massive edges to deal with bone chopping, 15 degrees per side and 0.025" thick, v-ground, will handle a lot.

I have a lot of respect for your knowledge. I have a lot of respect for Dick, as they have been making professional butcher's tools for generations - still do.

[A] rock axe will readily cut up bone . . . .

Way OT, but have you tried to chop cow thigh bone with stone tools? I know that the use of stone tools to butcher game has been studied on a fairly large scale. I thought I read, watched, and heard that the animals were disassembled by cutting the tendons and ligaments and the bones smashed open (for marrow or to fit the pot) with fairly blunt tools. Perhaps Yvsa can comment while I find my books and notes. I know the celts I own have nothing like a cutting edge, and I have tried obsidian knives (very sharp but chip pretty easily).

When I worked one summer for a butcher's shop (Del's Meats -- owned by a good, knife-loving guy now long departed from this mortal coil.), we used saws to "cut" bone. The cleavers were to be aimed at joints of pig and cow, or so Del thought.

I doubt that HI will be making stone khukuri to solve the problem being discussed, but who knows?

 

[munk]

I think we should do a psych study and find differences between the 'sharpen out' crowd and the 'reprofile' crowd. For instance, does the reprofile crowd have cleaner cars, toilets, desks etc? Do more of the reprofile crowd polish their chos than the sharpen crowd?


Obviously, I'm just kidding.

munk

 

[bigjim]

I think we should do a psych study and find differences between the 'sharpen out' crowd and the 'reprofile' crowd. For instance, does the reprofile crowd have cleaner cars, toilets, desks etc? Do more of the reprofile crowd polish their chos than the sharpen crowd?


Obviously, I'm just kidding.

munk

reprofile crowd = sexually active
Sharpening crowd = Massively repressed or at least constipated.

This is just a guess.

 

[BrentH]

Originally Posted bybigjim - This is just a guess

Well, I'd reprofile.. But between cold showeres & meditation -
Have not had time for the other, for two years!!

And - Oh yeah.. work. Due to the Matrimonial Property Act.

 

[raghorn]

For instance, does the reprofile crowd have cleaner cars, toilets, desks etc? Do more of the reprofile crowd polish their chos than the sharpen crowd?

There's a reason why I deliberately do not post pictures of my "shop." It's schizophrenic, bordering on psychotic. Not a clean car or toilet within 100 feet.

reprofile crowd = sexually active

I think you might be onto something there.

The real reason I think it's wise to remove flaws from the edge is because they could propagate into cracks if you ignore them and continue to use the blade.

NOTE: I am not a metallurgist, nor do I play one on TV. I'm not going to debate this point, so don't bother challenging me on it. Let's just call it FAITH and leave it at that.

 

[munk]

The real reason I think it's wise to remove flaws from the edge is because they could propagate into cracks if you ignore them and continue to use the blade>>>>>>>>>> Raghorn

Only if they're large. Otherwise, I remain loyal to sharpen and forget. The little ones shown on this thread I would sharpen and not reprofile.
The main threat in a large chip is the exposed and weakened area around it. You could chip out more edge. That is more likely what would happen. I think cracks are very rare. Now, I'm not a knife expert, just a user, but enough knowledgable people take this view so it would seem substanciated.

The poster who said it would take a lifetime to wear beyond the hardened zone, even with reprofiling, sounded corret to me.
Do what makes you happy.

munk

 

[Thomas Linton]

. . .
Do what makes you happy.

A worthy goal.


And thanks to those who are happy helping others. (Double the Mod's salaries I say! )

 

[munk]

Originally Posted by munk
. . .
Do what makes you happy.



A worthy goal.


And thanks to those who are happy helping others Thomas Linton


You know, Thomas Linton, I have no problem with circling back to the same three or four simple universal truths, repeating them over and over, in new context, as long as the forum kicks around.

For a tired, troubled almost intellectual but for sure worried brain, I love the reminders. How many staggering discussions have we on this forum that have turned 'inexorably' towards the plain truth and simple peace? Lots.

Thank goodness. Or as Ibear told me recently, 'so be good for goodness sake'!


munk

 

[jamesraykenney]

"In the year twenty five, twenty five..."

ARGHHHHH... Beat me to it!!!

 

[Cliff Stamp]

So, to a high limit, harder is tougher? That would certainly be good. So a chisel in A2 should be at 60 RC?

A2 peaks at most properties at near max hardness, from 1800F with a cold treatment you get 62/63 HRC at 350F, this hits one of the torsional peaks, is very close to the maxium torque failure (high strength) and has a decent level of maximal deformation (ductility).

You can also temper at 700F from the same quench, which hits the other torsional impact toughness peak, loses about 10% of maximal torque, and gains about 50% in maximal deformation and drops to 58/59 HRC. So for light utility cutting you would use the first and for heavy duty you may want the extra ductility of the second.

Way OT, but have you tried to chop cow thigh bone with stone tools?

Yes, but more in terms of smashing than cutting, there are not a lot of decent flakeable stones locally so the stone axes I make are more hammers and throwing clubs than actual axes. I have made some and used them to fell wood and it is more effective than without them but way slower than a normal axe, like comparing walking to riding a bike to driving a car. I have also made a fair amount of bone tools, needles mainly but some barbed hooks, spear head and such. I want to make a large bone knife using just stones to grind it, I usually cheat and carve them with steel knives.

One of my friends has promised some flint so I have some time planned for some shaping soon, this is a very different media than most local stones which are much harder and need to be ground to shape (I usually cheat again and use modern power tools). Flints can be made very sharp and very thin but are very brittle, so shaping an axe from them needs a nice convex very thick bit. There was an interesting bit on discovery awhile back showing how axe heads changed in curvature as materials were tougher/stronger.

I thought I read, watched, and heard that the animals were disassembled by cutting the tendons and ligaments and the bones smashed open (for marrow or to fit the pot) with fairly blunt tools.

There is no need to actually cut bones to take animals apart, and in general no need to cut bones at all, my uncle learned it from the inuit who will readily take a part a full carbou with a small knife, he has done it with a leatherman on a bet. Bone chopping just like any other form of cutting has a lot to do with technique, the more skill you have the less knife you need.

-Cliff

 

[munk]

And a real guru does it with his bare hands...or was that Liver Eatin Johnson?



munk

 

[Howard Wallace]

There is no need to actually cut bones to take animals apart, and in general no need to cut bones at all, my uncle learned it from the inuit who will readily take a part a full carbou with a small knife, he has done it with a leatherman on a bet. Bone chopping just like any other form of cutting has a lot to do with technique, the more skill you have the less knife you need.
-Cliff

From Zhuang Zi, the great Daoist philosopher, (translation from http://hkusuc.hku.hk/philodep/ch/zhuang.htm )

Cook Ting was slicing up an oxen for Lord Wenhui. At every push of his hand, every angle of his shoulder, every step with his feet, every bend of his kneezip! zoop! he slithered the knife along with a zing, and all was in perfect rhythm, as though he were dancing to Mulberry Grove or keeping time as in Qingshou music.
"Ah, this is marvelous!" said Lord Wenhui. "Imagine skill reaching such heights!"
Cook Ting laid down his knife and replied, "What I care about is a tao which advances my skill. When first I began cutting up oxen, I could see nothing that was not ox. After three years, I never saw a whole ox. And nownow I go at it by spirit and do not look with my eyes. Controlling knowledge has stopped and my spirit wills the performance. I depend on the natural makeup, cut through the creases, guide through fissures. I depend on things as they are. So I never touch the smallest ligament or tendon, much less bone."
"A good cook changes his knife once a year because he cuts. A mediocre cook changes his knife once a month because he hacks. I have had this knife of mine for nineteen years and I've cut up thousands of oxen with it. Yet the blade is as good as if it had just come from the grindstone. . . . "
"Despite that, I regularly come to the end of what I am used to. I see its being hard to carry on. I become alert; my gaze comes to rest. I slow down my performance and move the blade with delicacy. Then zhrup! it cuts through and falls to the ground. I stand with the knife erect, look all around, deem it wonderfully fulfilling, strop the knife and put it away."