how sharp is sharp enough?

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rctk1

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I have this habit of getting all my knives hair popping sharp, if they are not HPS "hair popping sharp" then i am not satisfied. I tried sharpening my kuks "ang khola" the other day including my Pen knife using the strop method, belt sander method, lansky, Apex, and i also tried using a grinder using Steve's paper abrasive but i still cant get the knife HPS. My intent for this knife is to use it as a trail knife cutting 3"-4" trees and occasionaly some that may be larger. how sharp should this knife be? if i am able to get the knife to my standards would it be detrimental to the edge when hitting hardwoods? so far most of the knives are able to cut paper with a little drag to it but even then there are area's of the blade that will only smash the paper as it goes through. any suggestions? thanks
 
They're sharp enough to use right now, so take 'em out and put 'em to work. They will eventually become dull enough to need resharpening. Resharpen them and put 'em right back to work. By repeating this cycle you will accomplish two things; A. The edge will, in time evolve to what you want it to be, and B. From the experience gained, you'll have a better understanding of how sharp the edge actually needs to be. I suspect you'll discover that the majority of field tasks performed with a khukuri do not require an edge that shaves cleanly, i.e. hair popping sharp.

If you do require a khukuri that is that sharp, try snagging a villager, their edges don't tend to get rounded off by the various buffing wheels that produce the beautiful mirror polish on the regular khuks. The several villagers I've owned all honed up to shaving sharp with just an Arkansas stone and a strop. Naturally, the regular khuks can be brought up to the same level of sharpness, they just generally seem to require a bit more time and effort.

Sarge
 
With sandpaper and steeling, I can most of mine between paper slicing and hair shaving sharp. A passage in my late uncle's Boy Scout handbook addressed the question for axes: "Your axe should not just be sharp enough to chew, but sharp enough to bite", or words to that effect. My khukuris are sharp enough to easily bite. ;)

Bob
 
some people find the mirror polished khuks have a thin layer of burned edge - eg, softer steel. You might find the steel improves after a sharpening or three.

As for the edge needed, I think paper slicing is good enough for most work, but what do I know? I'm one of the new guys.
 
I've owned lots of knives from custom manufactures to regular off the shelf knives, the only other steel that has given me a hard time was my spyderco using sv30 steel. how do you use the sandpaper and steeling method on your kuks? one of my kuks no longer has a convex grind but a regular bevel, I'll try the knife out later and if i dont like the way it chops i'll go back to the belt sander and reprofile my knife back to a convex edge. thanks
 
I gave up on the razor sharp paper slicing sharpness. I found that if you want to slice paper cleanly, it has to be past razor sharp.

Neither do I slice paper very often with my khukuri, nor do I shave. I have a razor for that purpose.

I just keep 'em somewhat sharp. You will get cut if you drag your finger along the edge, that's enough for me.

regards,

Keno
 
What Sarge and others have said works for me. I shave daily with a straight razor - and don't keep my khuk near as sharp.

Keeping it like a well honed kitchen knife does everything I need, and doesn't require a touch-up after every use. It's seemed to me that attention to cutting technique is at least as important when slicing cleanly through 3" branches as that last 5-10% of blade sharpness.

t.
 
rctk1 said:
if i am able to get the knife to my standards would it be detrimental to the edge when hitting hardwoods?
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No, the sharper you get it the more durable it will be, push cuts on hardwoods are best done with a very high polish.

-Cliff
 
No, the sharper you get it the more durable it will be, push cuts on hardwoods are best done with a very high polish.

-Cliff
Click to expand...

Of course, which is why power tools used to split wood are usually sharpend by Gilette to achieve a razor sharp edge ;)

I'd say while an edge with a polished, 5° included angle is plenty sharp, I'd rather not use it for chopping hardwoods.
The problem with such an edge is that it will likely get damaged if you're angle is a slight bit of or if you hit something unexpected, such as a nail. Your mileage my vary of corse.

Keno
 
You need a sharpie marker.

Run the marker down the edge - both sides. Now, repeat your sharpening technique. Make sure you "wipe" the marker off entirely. If you aren't, then there's the problem.

Every once in a while a sharpening job will be kicking my butt and I'll be getting impatient/frustrated/etc....and then I'll get out my sharpie marker...run it down the edge and repeat. Never fails. I always find out where the problem area was and I'm able to get 'er sharp.



The other possibility is that your edge is "too thick". While you don't want an edge (or grind) that's too thin...you still need to make sure that it's not too thick. This is botched many a sharpening job for me. Failure to properly reduce the edge thickness. When I go back and redo it, always improves sharpness.
 
I believe Uncle Bill used to question why guys were so keen on getting their khuks razor sharp. He used to say something to the effect that he used khuks to chop wood and a razor to shave with.
I like mine to have a good polished edge, but it does not have to make the hair jump off my arm. My straighter blades that I slice with I keep sharp enough to cleanly shave hair from my arm. The AK bowie, Munk Chunk, Seax, and Sarge/KPH all fall into this catagory. I like to keep my 12-15" khuks pretty sharp, but not as sharp as the straighter blades. A jack-of-all-trades level of polish and sharpness is fine.
I like to keep my rest of my khuks at a roughly full polish, but the sharpness is not really a big factor. Using a chakma and butcher's steel I can bring my chopping khuks to a good enough edge that they will bite deeply into the wood but won't deform. The won't shave the skin from your thumb, but they will split it open...or take it off;)

Jake
 
It all depends on what you want your blades to do. I need a much higher level of "sharp" and a smaller included angle on carving gouges, and I finish with a strop. I use a coarse strop with 1200 grit Clover Compound and then a finer one. I don't like waterstones for knives or carving tools.

With kukhuris, I really don't expect to do much chopping, and so I don't bother with a chopping sort of bevel. I sharpen them like a kitchen knife, and finish up with a hard Arkansas.
I don't bother to strop.
I use an India large gouge slip for the curve.
 
richardallen said:
I'd say while an edge with a polished, 5° included angle is plenty sharp, I'd rather not use it for chopping hardwoods.
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I would want about 30 included at the very edge (last 1/16") for chopping hardwoods, depends on the steel and the exact type of wood (knotty vs clear mainly) but somewhere in that area. But I was speaking of sharpness, or condition of the edge and not its gross geometry. Wood tools for push cutting, are kept very sharp and at those high sharpness levels stay cut better for longer, see Elliotts work on planer blades for example. The angle they need to be sharpened is adjusted to give the necessary strength, but this is a different matter than sharpness, Elliott quantifies both in detail.

Splitting tools such as mauls are usually not kept extremely sharp, not because it is a detriment, but just because the majority of the cutting ability comes from the raw impact power and the wood isn't actually cut as much as the grain is torn/burst apart so there isn't the same level of advantage to having a really sharp edge. You can see a benefit to initial entry on a GB maul vs a hardware store maul, as you can shave with the GB maul as you can with all thier axes, but the first time you miss the wood, or cut through it and hit the ground, both edges will have the same level of sharpness, essentially none.

http://i7.photobucket.com/albums/y269/CliffStamp/fiskars/hatchet/fiskars_gb_wood.jpg

There is a shot of a small pile of wood cut, two hatchets. Before the cutting the edges are raised to the ability to push cut newsprint on a 90, this is above shaving. They can maintain this edge through a cycle of 250-500 chops and still have the ability to do fine work, including cutting the paper, the Bruks lasts longer, the Fiskars is significant softer. I do the same with the Ang Khola's I have, I just have not used them in awhile. Essentially when you make an edge sharper you are cleaning it of debris, weakened steel and aligning it in a crisp centered path, obviously this makes it stronger and more durable as well as making it cut better.

http://i7.photobucket.com/albums/y269/CliffStamp/fiskars/hatchet/fiskars_log.jpg

It also reduces tendancy to glance, and even increases corrosion resistance. Of course there is the tradeoff of time of sharpening. If it takes you a half an hour to make a small improvement then this probably isn't work the time as you could cut a lot of wood in that period. But with proper use of abrasive grits and micro-bevels, sharpening should be minutes anyway.

-Cliff
 
Oh my god, I got CS'ed.

Cliff, just for the argument's sake, wouldn't you agree that an edge with a 5° included angle is sharper than an edge with an 30° included angle? I do believe that this is "speaking about sharpness", since a blade's "gross geometry" has got a lot do to with sharpness. I am sure you'd have a hard time getting a 90° angle sharp.

If we can agree that a 5° edge can get sharper than a 30° edge, then you will see that your statement was a bit over the top - "the sharper you can get it" can be too sharp for certain purposes ;)

sincerely,

Keno
 
Daniel Koster said:
You need a sharpie marker.

The other possibility is that your edge is "too thick". While you don't want an edge (or grind) that's too thin...you still need to make sure that it's not too thick. This is botched many a sharpening job for me. Failure to properly reduce the edge thickness. When I go back and redo it, always improves sharpness.
Click to expand...

This is what I suspected after reading the initial post. A too thick profile will thwart all attempts at obtaining a fine cutting edge, because it sets a lower limit on the cutting edge bevel. In this situation you generally have to remove quite a bit of steel to slim down the profile in order to make a fine edge possible. You can use a half round file if you lack power tools, or a belt sander with a coarser grit than you ordinarily use for sharpening.
 
richardallen said:
... wouldn't you agree that an edge with a 5° included angle is sharper than an edge with an 30° included angle?
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No, sharpness is the condition of the edge, irrespective of its angle or thickness. Now at a given level of sharpness, in general the cutting ability is higher for a lower angle and thinner profile, but there are lots of things which influence cutting ability such as for example the orientation of the handle, but would you say you have "sharpened" the blade by adjusting the handle?

The defination of sharpness equating it to cutting ability is a common one, but it leads to many myths about performance such as the above link of a high level of sharpness (shaving) to weakness, usually attributing it to straight razors or similar which were brittle because of the very low included angles and not the actual condition of the edge itself, which as noted gets more durable as it is made sharper, not less.

I actually have blades by the way with edges that are 5 degrees included, when fully honed I can measure the sharpness and they are near idential to blades honed at 20 degrees per side. There is a slight advantage because any physical measurement of sharpness is actually one of cutting ability, but you can focus it on the sharpness element alone by cutting very fine media, I use baisting thread and very light cotton cord, newsprint works well also, this will pretty much ignore the gross geometry and focus just on the last micron of the edge.

Elliott does similar in his work on planer blades, he uses a more optimal thread (more consistent and lower cutting point), and shows similar results and also shows micrographs of the wear.

-Cliff
 
arty said:
It all depends on what you want your blades to do.
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A key point. Someone carrying a khukuri as a weapon would have a legitimate reason for maintaining a different edge than someone using their khukuri to dig potatoes.

Cliff Stamp said:
Splitting tools such as mauls are usually not kept extremely sharp, not because it is a detriment, but just because the majority of the cutting ability comes from the raw impact power and the wood isn't actually cut as much as the grain is torn/burst apart so there isn't the same level of advantage to having a really sharp edge. You can see a benefit to initial entry on a GB maul vs a hardware stone maul, as you can shave with the GB maul as you can with all thier axes, but the first time you miss the wood, or cut through it and hit the ground, both edges will have the same level of sharpness, essentially none.
Click to expand...

Exactly. For some tasks there is a sharpness it is not cost effective in terms of time and energy to maintain.

richardallen said:
Oh my god, I got CS'ed.
Click to expand...

Actually, you're a lucky guy. ;) Cliff, though sometimes argumentative, is actually quite knowledgeable. He wrote a good part of the sharpening section of the HI FAQ. http://www.himalayan-imports.com/faq/Sharp.htm Just a warning, if you start debating the meaning of "sharp." Cliff has a lot of stamina. I think he would give Bill Clinton a good run for his money in a debate on the meaning of the word "is." :D

There is also the possibility for a khukuri user to sharpen different parts of the blade differently. For instance, for many of my utility khukuris, I like the sweet spot significantly convexed for durability when chopping, but the interior "draw knife" portion with a flatter grind and sharper.

If you are going to be chopping it is good to be aware that at a certain dullness probability of glancing increases. At that point, even if it is not efficient in terms of time to touch up the blade, it is advisable in terms of safety.
 
Uh Keno, to get a 30 degree included angle, you'd be sharpening the blade at an angle of 15 degrees on each side. That gives a pretty sharp edge. If you're talking about grinding your edge at 5 degrees on each side, your included angle equals 10 degrees, a bit thin for all but the lightest of cutting. And if you no kidding mean an included angle of 5 degrees (2 1/2 degree bevels) you've just about surpassed surgical scalpels.

I think we're over-technifying the matter. I put a thin, toothy edge, on knives I'll slice 'maters with, and a thicker, more polished edge on choppers. Sort of a tool for the task kind of thing. ;)

Sarge
 
I test my blades on 1/4" ply. My 12" Pen chopped much better after a trip to the stones.

It is always important to get rid of the burr. It weakens the edge, and interferes with cutting ability.

I don't take the time to get a convex edge, since I am not likely to cut down any trees. The convex edge is great for a strictly chopping tool, since it helps to strengthen and maintain the edge. However, I always want a finished edge - read that as a sharp edge.

The bevel angle - the coarse geometry - is changed depending on what I want the blade to do. For example, if I wanted to cut hardwoods with a tool, I would want a more obtuse angle than for softwoods. Chopping wood requires a different contour than slicing turkey!

Cliff Stamp is right on in all of this.

For a plane iron used to work on hard maple, I would want the sharpest edge I could get - and that would mean going up to at least an 8000 grit waterstone....perhaps stroping as well.

I wouldn't bother with that for a kukhuri, and a hard Arkansas would be more than enough. Fishing fillet knives need a sharper edge than a general purpose kitchen knife - I stop at a Norton Soft Arkansas for most kitchen knives.

I have no trouble sharpening any khukuri to a shaving edge, but I just don't usually take the time to get them to the leve of "sharp" that I would want for a plane iron or a carving gouge.
 
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