An informal comparison- bowie & khukri

[the possum]

My friend "Bob" (not his real name) helped me eliminate a couple pesky racoons, and we used the opportunity for an informal learning experience.

We shot them out of the tree, and used the two carcasses to compare my bowie knife and modified khukri. Learned a lesson on edges. No, I don't have any pictures and probably wouldn't want to post something this gory on a public forum anyway. Just thought somebody here might be interested.

As we replayed the situation I mentioned having to hit the coon with my khukri several times to finish it, and never did manage to sever the neck completely. I figured this was a good opportunity for an informal test. I drew my khuk again and took a strong whack at one of the carcasses, which only left a gash about 2 ½” or 3” long. What the??? I tried again, striking a little further back on the edge, right at the curve of the belly. Got about the same result- the cut beneath the skin was actually wider than in the skin itself. A third strike hit his back leg, and it about severed the leg bone and flesh, yet the skin was only shallowly cut. This indicates to me a problem with the edge. I was hitting with plenty of power, and the edge was about the same as I usually put on my bowie knife, which is a very coarse finish. But it couldn’t get through the tough skin. At first I thought the edge must have just been plain dull, but really it wasn’t too bad.

I told Bob to give it a try with my bowie knife, and he made a very light wrist cut on the same coon carcass. He only let the tip of the blade strike, and let his grip relax so the knife only had the momentum from his wrist action. It cut a gash about twice as deep as I had managed with full blows from my khukri. So then I told him to try on the other carcass, and he made a pretty good swing straight down into it, which went about 3/4 of the way through. I told him to try again, but this time, draw the blade in towards himself just as it was about to make contact. He took a decent swing, but not full power, and I heard the blade thud. There was only a small crease visible in the coon’s fur, until I pulled it back to inspect the cut. The half I tugged on came clean away from the back half of the carcass- the thud was the sound of the bowie imbedding itself a couple inches into the dirt.

This coarsely finished edge is about ideal for the type of draw cutting I normally do with the bowie. But this comparison showed me just how bad it is for the khuk. Now I had known polished edges would work better for push cuts all along, but really without seeing it side by side, I wouldn’t have thought the difference would be that dramatic. I can’t really do any sort of draw cut with that blade, as the curve pretty much automatically creates a straight shearing cut. Hell. That means I gotta polish the edge down good and keep it very sharp in order to be effective, which sucks since I also use this blade for clearing brush around the farm and it’s sure to be damaged every time I use it. Thus sharpening will take a lot longer than I’m used to with my bowie. I’ve already taken it to the fine diamond stones and big ceramic rod now, so next time I’ll have to see how it compares.

This experience reinforces my belief that the skin (and partly the fur) are pretty tough to get through. The edge sharpness needs to be optimized for skin (and type of cut/swing involved), and the geometry for bone. The flesh itself is not an issue if the above two requirements are met.

 

[thombrogan]

Great review and revelation, Possum!

For your khukuri, get some power tools. A Harbor Freight 1"x30" sander is only $50 delivered/$40 picked up and you can get a felt belt from HandAmerican or leather belt from Lee Valley for $4.50 felt/$20 leather and some buffing compound almost anywhere for a few bucks. If you have already applied the khuk's edge with your diamonds and ceramics, the soft belts and buffing compound make great for fast/easy maintenance (just don't leave the leather belt on the sander or you'll be out $20.

 

[the possum]

Holy crap dude! Thanks for that link. I already have a 4"x36" belt sander, but could never find belts finer than 100 grit locally. But Hand American offers 10 different grits from 60 to 800 (and the felt) for $3 each. That sounds like just the ticket for helping with some up coming projects, besides sharpening.

"Bob" asked me to help him make a short sword, and I'm also gonna make a falchion for my dad, so those belts would really help speed up the finishing process. Thanks again!

 

[thombrogan]

No problemo. Now be honest. There is no 'Bob,' is there? You think light wrist-flick cuts, however effective they may be, are so unmanly that you created an alter-ego for such work.

Anywho, another place for belts is www.customsandingbelts.com They don't go as fine as 800 grit, but they have faster-cutting belts made of ceramic, zirconium, and AO for any sander. Ever try dropping an edge with an 80 grit SiC belt? It leaves a finer finish than any 80 grit belt should ever leave and it cuts slower, too. Ironically, those same features are what will make your HandAmerican 800 grit belt ideal for sharpening.

 

[Cliff Stamp]

Now I had known polished edges would work better for push cuts all along, but really without seeing it side by side, I wouldn’t have thought the difference would be that dramatic.

Numbers rarely make the impact of first hand physical handling.

That means I gotta polish the edge down good and keep it very sharp in order to be effective, which sucks since I also use this blade for clearing brush around the farm and it’s sure to be damaged every time I use it. Thus sharpening will take a lot longer than I’m used to with my bowie.

What extent (depth and frequency) of damage are you talking about?

On an related note, I noticed the same thing when I worked with a custom parang I have made a few years back. I had it lightly recurved to trap vegetation, horrible idea.

-Cliff

 

[the possum]

Now be honest. There is no 'Bob,' is there? You think light wrist-flick cuts, however effective they may be, are so unmanly that you created an alter-ego for such work.

Tell ya what. If you'd like, I'll send you the whole story from our misadventure. I got pretty wordy this time, but if my first post didn't offend you, ya might enjoy the rest.
Thanks for that other link too. I'm checkin' it out now.

What extent (depth and frequency) of damage are you talking about?

The entire end half of the blade/edge will be visibly blunt & reflecting light- you can see it at full arm's length. And then there will be nicks and rolled sections within that. I had to get out a ruler here to estimate (from memory) the depth of the nicks... Most are probably less than a milimeter deep, but occasionally I've have one or two nicks over 2mm deep. Definitely more than I'd want to do entirely with a fine stone or ceramic. This is from hitting wire, concrete, glass, scrap steel, rocks, and dirt while clearing weeds and small trees around the farm. This will happen inevitably every time I use it for this purpose, which is lately about once a week or so.

On an related note, I noticed the same thing when I worked with a custom parang I have made a few years back. I had it lightly recurved to trap vegetation, horrible idea.

I'd be interested in hearing more about that. Do you already have a writeup somewhere on your impressions?

 

[Cliff Stamp]

Definitely more than I'd want to do entirely with a fine stone or ceramic.

Yes, in general for such knives I file them sharp and finish with a 600/1200 DMT stone if I want a coarse finish. Adding a highly polished micro-bevel is only a short amount of time, somewhere around five passes per side with the stone for each grit per stone length of edge. For the harder knives I use a coarse stone rather than a file, but polishing the very edge is the same.

Do you already have a writeup somewhere on your impressions?

Not in detail, I will be adding a section shortly. What I find interesting about much of this these discussions are a "discovery" of what was common knowledge when hand tool use was more common. I will spend a great deal of time exploring aspects of cutting ability and performance and then read about the same general principles in a book about chisels. There is a reason why a parang and sickle have inverted edge curvatures and while the physics of the cutting action may not have been understood by the operators they did know in detail how the blades acted in use. The same general trends are seen in all tools, slicks for example, large chisels commonly used on large timber, often had the edge crowned which is a light curvature to allow them to produce a better finished cut. The curvature allows the wood fibres to travel down the arc of the edge adding a slicing motion. A perfectly square edge will produce a more ragged cut at the same level of sharpness as it is a straight push. This is also why axes have lightly curved bits and why a katana has an upswept blade. They are all using the ability of a draw or slice to spread force out over a longer area of the blade and thus produce a much deeper cut with a set load. It is just one more example of "leverage" where you use a longer application of a lower force to equal the work of a heavier force for a shorter period of time. High school physics would probably have a lot higher attendance if there was a lot more swordplay involved.

-Cliff

 

[the possum]

Yes, in general for such knives I file them sharp and finish with a 600/1200 DMT stone if I want a coarse finish. Adding a highly polished micro-bevel is only a short amount of time,

1200 grit is a coarse finish to you, eh? When I use that term I'm talking about the edge left by a 120 grit alumina oxide stone. Certainly I can see that it's no problem to polish the edge with a few passes of a ceramic rod or something if you're already beginning with 1200 grit. But I don't think I could go straight from 120 grit to the ceramic. I guess it's really not that big a deal either way- if that's what I gotta do to go from a completely unacceptable level of performance to exceptional, then that's what I gotta do.

Numbers rarely make the impact of first hand physical handling.
What I find interesting about much of this these discussions are a "discovery" of what was common knowledge when hand tool use was more common.

Yeah, the difference was very dramatic. Imagine trying to whack a pillow covered with chainmail. That's about how effective the khukri's edge was.

I guess this was a revalation to me since I'm not as accustomed to a downcurved blade that totally prevents drawing the cut. I didn't notice the difference when chopping small trees and stuff, since the edge geometry plays a bigger role there than the edge finish. But I haven't gotten to use it on the coons as much. The two mediums react very differently to the edge. And I had never seen a problem with this finish level before on my bowie or the fodder knives I grew up with, since they allow the kind of cut/swing that can take advantage of this edge.

This is also why axes have lightly curved bits and why a katana has an upswept blade. They are all using the ability of a draw or slice to spread force out over a longer area of the blade and thus produce a much deeper cut with a set load. It is just one more example of "leverage" where you use a longer application of a lower force to equal the work of a heavier force for a shorter period of time.

I guess that's another reason why I didn't expect such a difference. Even at the tip, the edge is still curved more than an axe. I thought the shape would create some amount of slicing motion to compensate, but it wasn't nearly enough to make up for lack of draw on the swing. On a related note, I'm betting that if I struck further back on the edge where it's angled to the target more, it would help. But, I can't do that because then the tip of the blade hits the ground, stopping it before it can even make contact with the coon.

I read gun and knife magazines every day in high school physics.

 

[hardheart]

The entire end half of the blade/edge will be visibly blunt & reflecting light- you can see it at full arm's length. And then there will be nicks and rolled sections within that. I had to get out a ruler here to estimate (from memory) the depth of the nicks... Most are probably less than a milimeter deep, but occasionally I've have one or two nicks over 2mm deep. Definitely more than I'd want to do entirely with a fine stone or ceramic. This is from hitting wire, concrete, glass, scrap steel, rocks, and dirt while clearing weeds and small trees around the farm. This will happen inevitably every time I use it for this purpose, which is lately about once a week or so.

a bit OT, but this is the way my edges look on any of my knives when I use them. I used to have a hard time following what other people said about edge performance when they cut 8 billion yards of cardboard or hemp and then restored the edge to spooky sharp with 2 passes on a strop. Then I realized that my working blades suffer real abuse by the estimation of many people on BF-especially sine they're folders.

I do find this comparo interesting, because my big blades are all soft, and I generally like them that way because I have shredded blades before, and I think I'd rather that than high energy fractures and flying shrapnel. So I stick with rough edge finishes because I have to reapply them all the time, and polished edges are pretty lousy for longevity. Don't work with wood much, but used a cane knife to help delimb an oak tree once

I'm not really surprised by the results. With the elasticity of the skin, cushioning of the fur, and the compressing of the flesh, even a big khuk is gonna have trouble hitting with the pressure necessary to cut.

 

[the possum]

a bit OT, but this is the way my edges look on any of my knives when I use them. I used to have a hard time following what other people said about edge performance when they cut 8 billion yards of cardboard or hemp and then restored the edge to spooky sharp with 2 passes on a strop. Then I realized that my working blades suffer real abuse by the estimation of many people on BF-especially sine they're folders.

I know what ya mean, man. I've read guys who say they can touch up the blade with a few swipes on their pants leg or a piece of cardboard, and that's all they ever need. They just told me more about how they use their knives, than about their sharpening methods. Wonder how many pairs of pants they'd wear out before getting my khukri sharp again...

 

[Daniel Koster]

LOL!!!

The edge sharpness needs to be optimized for skin (and type of cut/swing involved), and the geometry for bone. The flesh itself is not an issue if the above two requirements are met.

Well said.




Don't tell this guy he should be using a bowie instead of a kukri:

As Cliff has said before (and will say again, I'm sure) it's all about edge geometry.


FWIW, I have experienced the same sinking feeling of chopping at something with a really good-looking/good-feeling whack and getting no results. I either have to adjust my technique or examine my sharpening (or both sometimes!)

 

[hardheart]

Makes me think of something else, the caracsses were on the ground, right? I think you need some follow through to properly present the kuk edge, but I could be wrong

 

[the possum]

Don't tell this guy he should be using a bowie instead of a kukri:

Oh, sorry there; didn't mean to give this impression. I'm not trying to put down the khukri at all here. Only pointing out that I was using the wrong kind of edge on it. Hopefully the new edge will rectify the situation.

Here's one of my bowie in action. Usually it can do the task in one swing, but this one was already partly frozen. Went almost all the way through at first...

Deer

 

[Cliff Stamp]

1200 grit is a coarse finish to you ...

Typo.

But I don't think I could go straight from 120 grit to the ceramic.

No, that's too big a jump. I generally go x-coarse DMT, fine dmt, then x-fine. Or 200 silicon carbide, 800, then 4000 waterstone. Finish on 0.5 micron chromium oxide if I am at home. Shape the bevel with the coarse abrasive and then just finish the last bit with the polish. The polishing doesn't take very long as it is only on a small part of the bevel.

-Cliff

 

[guncotton]

Please excuse if I missed this but who made the kukri and the Bowie. can you post pictures of them?

 

[Cliff Stamp]

I do find this comparo interesting, because my big blades are all soft, and I generally like them that way because I have shredded blades before, and I think I'd rather that than high energy fractures and flying shrapnel.

This is an unfortunate side effect of so many steels used in the larger knives being horrible choices as they are very brittle when hard so they are left soft to compensate and then they are then easy to indent.

I know what ya mean, man. I've read guys who say they can touch up the blade with a few swipes on their pants leg or a piece of cardboard, and that's all they ever need. They just told me more about how they use their knives, than about their sharpening methods.

Indeed. My Mora 2000 for example has 2 mm of edge worn off from sharpening and I don't really do anything hard with it. It just gets used a lot. I also remove minimal amounts of material when I sharpen. I have had to regrind most of my knives due to the edge thickening from sharpening and use. Some of them had the entire primary regound, my EDC SAK for example. I have lost count of how many times I have reground the Tramontina bolo. I am also usually fairly careful, but even then, with a lot of cutting you will slip once in awhile. My personal favorite is when you tune up an axe just perfectly and on the first chop into a tree it hits a spike, or you were careless and didn't check the trunk and it is infested with ants and the axe sails right through and goes deeply into the dirt and of course goes right into a rock. That is of course always the day you didn't take the file.

-Cliff

 

[sodak]

Great post as usual, Possum! Thanks for all the info!

 

[the possum]

I do find this comparo interesting, because my big blades are all soft, and I generally like them that way because I have shredded blades before, and I think I'd rather that than high energy fractures and flying shrapnel.

This is an unfortunate side effect of so many steels used in the larger knives being horrible choices as they are very brittle when hard so they are left soft to compensate and then they are then easy to indent.

Right now I'm in the process of getting some L6 stock to work with. That's a steel that can be both hard and tough at the same time. (At least according to everything I've read. Will see how it goes.) I'm gonna have it marquenched to 58 Rc with the short swords.

My personal favorite is when you tune up an axe just perfectly and on the first chop into a tree it hits a spike, or you were careless and didn't check the trunk and it is infested with ants and the axe sails right through and goes deeply into the dirt and of course goes right into a rock. That is of course always the day you didn't take the file.

Yep. Know how that one goes. 'Course with me it's more often a big blade rather than an axe.

Please excuse if I missed this but who made the kukri and the Bowie. can you post pictures of them?

Why not. Khukri:

This is a Dui Chirra model from Himalayan imports, which I modified heavily myself. I went into details about the modifications here if you're interested.

Here's a picture of the bowie:

I made this one myself- it's just a "beater" for work. It's 5160, which I had Joe Walters heat treat to form Bainite. Went into some more details here, but have written lots more about it if you do some searching.

 

[Cliff Stamp]

Yeah, I have had the same thing happen to a large blade as well on many occasions. Usually right when I want to do an edge retention comparison so I have a couple tuned well and on the first few swings plow right into a rock covered by brush. I'd be interested with how the L6 58/Bainite turns out.

-Cliff

 

[the possum]

Cliff- perhaps I used the term incorrectly, but the short swords will be through hardened to a martensitic structure and tempered. I was of the understanding that marquenched only referred the process where the blade is quenched to just above MS temp, and then slowly allowed to drop below to form martensite after the piece has equalized in temp. I thought they used Ausquenched to refer to the process that produces bainite. Guess I better get the terms straightened out, 'cause I was wanting to mark the blade as such.