How do you test for sharpness and edge retention?

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Sep 7, 2001
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I might have stumbled onto how to do a convex edge. :)

How do you fine folks test your stuff for sharpness and edge retention?

I used to cut fine ribbons of paper, the smaller and closer spaced the better. The convex edge sorta makes it difficult to do so.

:confused:
 
Well, first ya lay your left arm on the table, then ya take a swing at it with the khuk;) -- Oh, wait--that's Heber's test.heehe.

I usually try slicing thicker stuff like cardboard, wood, soft metals, bone, rawhide, leather. These target mediums should put a convex edge thru its paces, and it should hold up to all of these. 1/2 inch or more of plywood cut edge on is a good test, as you hafta blast thru 6-10 crossgrained layers of wood. Not as easy as splitting a log lengthwise (but that is also a good test).

The convex edge is certainly unsuited for slicing. Ya need a good flat grind or hollow grind to get that going.

Keith
 
"The convex edge is certainly unsuited for slicing"

:D You want to qualify that, or wait for Yvsa??:D
 
This is a convex edge:
shaveit1.jpg

Regards,
Greg
 
Originally posted by firkin
"The convex edge is certainly unsuited for slicing"

:D You want to qualify that, or wait for Yvsa??:D

Depends on how much convex is behind the edge.:) If you have a really thick convex of course it isn't going to cut as well as a flat or hollow ground knife.
But if you have a thin convex it will slice better than any other grind.
The hollow grind will beat the convex edge, but only up to the top of the hollow. From there on it has to contend with the extra pressure it takes to get the thick part of the blade through whatever you're cutting. Same with a flat ground blade.
All of the khuks that I've seen from H.I. for quite a while, with the exception of the Bilton, have all had a flat grind with maybe a tiny bit of convex along the edge.

You can read more about convex edges here and with pix to show how they work........

http://www.mhcable.com/~yocraft/sosak/convex.htm
 
Ripper--great pic. I usually consider my khuks sharp when they will slice paper like that or shave easily. I test edge holding by chopping wood, which is usually what I use my khukuris for anyway. I've got a big walnut stump that is pretty hard, and I will chop on that for a while and see how the edge holds up. I burn almond in my woodstove, and that stuff is so tough and twisted that it works pretty well for edge retention tests. It also keeps my dome nice and warm. I used to think oak was the best firewood, but almond just plain rocks.
--Josh
 
Bruise, just out of curiosity, can you describe the technique you are using to sharpen your khukuris?
--Josh
 
Originally posted by Yvsa
All of the khuks that I've seen from H.I. for quite a while, with the exception of the Bilton, have all had a flat grind with maybe a tiny bit of convex along the edge.

My question is why did the kamis switch? The oldest HI blade that I own is 2 years old, and it has the flat edge.

I'd love to see an older HI khuk in person and compare it with the current production.

S.
 
Bruise I figure if it can shave the hairs off your arms and not look like a saw afterwards it probably has good edge retention, but then that may qualify it for khuk abuse:D :p
 
:(

I use an old belt gooped with honing compound to get the rough convex profile. I hold one end with a hand and step on the other with a foot and strop. This gives the basic shape.

Then I use a ceramic rod to get a burr then strop the thing with a strop which is probably too wide for khuks.

Stropped away from the edge, tilting the spine up as the blade gets to the end of the strop.

I'm doing something wrong cuz I don't get those fine bits of paper on my floor. But I havent' played around with it too much yet. Maybe a little more stroping. I can still feel a very fine "line" of roughness left by the ceramic rods. So it may just be a matter of polishing the rest of the edge.

:confused:

When I get a digital camera I'm gonna cut some paper with scissors, put a khukuri beside it and post the pic. :D
 
Send 'em to me Bruise and I'll do it on the belt sander. Then you'll just have to strop them to keep them that way.:)

Steve
 
Bruise, if I may make a suggestion, try some wet/dry sandpaper on a mousepad or some other backing with a bit of give to it. I think it will take way too long with the belt and honing compound unless you are using a particularly abrasive honing compound. The sandpaper/mousepad combo works well, and it doesn't take much time at all. If you start with 400 or 600 grit paper, you'll have your edge shaped in no time. Then switch to 1000, followed by 2000 or 2500 if you want a really polished edge (which will help with the paper cutting) I would use the strop and/or ceramic rod as a finishing step after the sandpaper. That link that Yvsa posted earlier has some great advice. In fact that's what got me started using the sandpaper on a mouse pad. With a little practice, you should be able to get you khukuris to slice paper like that without even having to use the strop. The only downside is that it can, and most likely will, scratch the surface of you khukuris. You could probably minimize/eliminate this by taping off the sides of the blade with masking tape.
--Josh
 
The Duck is back, Bruise is thinking he figured out how to sharpen, guess we need to watch out for flying pigs and the apocolypse!
 
Originally posted by ferguson
Send 'em to me Bruise and I'll do it on the belt sander.

Thanks for the offer. Sharpening by hand is one thing I would like to learn how to do. Besides, in a post apocalyptic war zone I won't have access to a belt sander. :)

I thought about the sandpaper thing when you mentioned it in another post. In this new fangled world of optical mice, those neoprene mouse pads are hard to come by nowadays. I think I have an old Duke Nuke'em mousepad somewhere around here though. :D

Oh and thanks for the links.

Someday I'll probably find out that there's no such thing as a convex edge. :rolleyes:
 
Originally posted by BruiseLeee
Someday I'll probably find out that there's no such thing as a convex edge. :rolleyes:

Check out the new links and jpg I put in above Bruise and you will see all the different edges and proof that the convex edge does indeed exist.:p ;) :D
 
that is called "Taiwanese Imitation Katana" and have heard that called saber grind. It is like a faceted version of the convex grind, and an easy way to keep a lot of steel behind the egde.

Yes, i must admit I was thinking of an obtuse convex edge, more like on an axe. Josh has some serious convex sharpening skylz!

Keith
 
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