Shaving sharp, not that good as criterium is seems.

B

Bart student

Joined
Nov 17, 1999
Messages
676
Hello Folks,


Yesterday me and my friend had a discussion about shaving sharp as a mesure for sharpness. I said that shaving sharp is about as good as my BM 806 D2, which I just resharpened on my grinder with a special belt. It shaved on both our arm easy, simply taking off hair right at the base without pressure. Then my friend argued I made the edge too thin. He took out his Spyderco military, which was sharpened on a spyderco 204. He had to push noticeably harder to get it to shave, but it would take off hair too. Then I tried and I couldn't get it to shave, no matter what I did, I tried so hard I had to use bandages twice on my arm.

We were kinda amazed.. it shaved on his arms, but not on mine. When I got to think about it, I have had several knives which should come with shaving sharp edges, from all the reviews, but several needed resharpening to shave. Like the CR sebenza, the SERE 2000, the Becker magnum camp. In any case, I don't really care, since I like to resharpen knives.

But it did raise question about the criterium used to measure sharpness, shaving or not. I like thin blades and thin edges, because I usually use my knives carefully and light, and I resharpen way before they go dull. I really can't stand fat edges, my best examples of these are the becker campanion and a greco 5 inch MST. Both of the needed some serious edge regrinding, so I traded them off.

So what do you think? Is shaving a good criteria? I can make mild steel shave too. 420J2 can shave.. 440 is often used in razors
I suppose a fysical criterium like geometry of the blade and edge in degrees would be a better criterium. No-one ever tought about this?

thanks for the answers in advance,

Greetz and take care, Bart.
 
Bart,

It seems to me that no one has ever bothered establishing a hard-and-fast criteria for determining sharpness, because that topic is almost as subjective as a knife's visual appeal.

Each person needs to determine what they consider "sharp" and then figure out what they have to do to get there. For me, personally, I don't have a single standard, although hair-popping sharpness is certainly amongst my comparators. Others include: the ability to skive leather, the ability to push-cut leather, the ability to skin a tomato, or the ability to shave paper.

Many of the knives that I make do not go to customers with a "shaving-sharp" edge, simply because it's overkill, in many cases. And while some makers might take it as a sign of sloppiness or not "going the extra mile," I would counter by asking which was more useful to the customer--an edge that worked, and went longer without needing touchup, or a shaving edge (that they never use) which requires constant attention? Oh, sure, if I made a straight razor for someone, you bet your life it would take off hair at a touch! But for a camp knife, that might be used to split kindling or dig a latrine-hole, something more utilitarian is more often appreciated.

Finally, we come to the issue of technique. As you pointed out, while your friend could shave with his Spyderco, you could not, no matter how you tried, even to the point of injury (I still, by the way, have what I'm sure is a very similar scar on my arm from the first time I shaved with my Spydie...*Important note* Serrated edges are NOT good examples with which to demonstrate sharpness to one's friends. :rolleyes: ) This is the same reason that one person, given the same knife as another person, might not be able to cut a free-hanging rope (or might not be able to cut it as cleanly, might not be able to cut as many, might not be able to...you get the picture). HOW you use the knife will certainly affect not only the type of edge you require, but your results.

See? So, aside from taking a protractor and measuring the edge's angle, and other, purely mechanical means, I have yet to see a universally-accepted method of determining "sharp." I hope this helps out...and how's the winter been, so far, in Belgium? Shaping up to be a nifty nasty one, over here.
:)
 
While I am prone to walk through life with patches of hair missing from my arms (and sometimes legs ;)) from testing blades as I sharpen, I don't rely on it either.

We all know that a wire edge can shave but as soon as you try to cut something for real it will fold.

I have also heard people using a finger nail test. Basically you put the sharp edge of the blade ona finger nail and roll the blade sideways slowly to see how far it will go before it loses grip and slide off of the front of the nail. I have played with this method and feel that it is more dependant on the angle of the edge than sharpness, of course a really dull blade will not cut the nail enough to grip at all, so it does work to tell if a blade is really dull, but that's easy.

So basically I just use the knife until it is getting close to no longer meeting my needs, then resharpen it. Works like a charm :)
 
cpirtle,thanks for the great tip.I just tried the finger nail roll with a few knives.I think its one of the best ways of discovering whch angle to use when sharpening
I have also heard people using a finger nail test. Basically you put the sharp edge of the blade ona finger nail and roll the blade sideways slowly to see how far it will go before it loses grip and slide off of the front of the nail. I have played with this method and feel that it is more dependant on the angle of the edge than sharpness, of course a really dull blade will not cut the nail enough to grip at all, so it does work to tell if a blade is really dull, but that's easy.
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I think the best test is to cut material you intend to cut with your knife! Lately though I've been cutting on a piece of dowel I have left over from a project. The ease of cut and smoothness of the wood from the cut tell a lot about the sharpness of the edge.
 
I don't think that your shaving technique was wrong with the Spyderco. It is simply not as sharp as your Benchmade. The shaving problem is that your hair is harder to shave than your friend's and/or your skin is easier to cut than his. This is a big variable in shaving sharpness measurements.

I have found that as I age (I'm now 53) my arm hair is thinner and harder to shave. It is easy to shave arm hair on my 19 year old son. The hair is kind of wirey. He is a brown haired guy nicknamed davolfman. His hair folicles hold the hair straight up stiffly for shaving. My other son is blond. His hair likes to lie flat and tips over easier when trying to shave with a knife.
 
I sharpen my knives on a fine diamond stone, until the edge can no longer be seen by the light reflecting off it. I sharpen until this edge will readily bite into my thumbnail when lightly pulled across. Sometimes, I will strop the edge on the back of an old leather belt, but find that is not usually necessary.
 
Thin or thick has nothing to do with sharpness (same goes for edge polish), and yes, I think shaving is a good indicator of sharpness. At least it tells you the angles are meeting properly-which is all sharpness is. It's not a good indicator of cutting ability, though. That's where the level of polish, thickness of the edge, and the material behind the edge come into play.
You can probably get any knife, made of any steel, to shave. How well they actually perform in use is another story.
Lots of fun to experiment with (well, it's fun for me):)
 
Well said Owen.:)
I prefer the newspaper test...if you can cut curves in newspaper without tearing it, it's sharp.

Paul
 
After shaving arm hair, I always do a slicing test next. I got a length of ~1" thick rope, the hardest poly I could find (and therefore the hardest to slice) from the hardware store. I always use the same rope, so eventually I developed a sense of what a knife should be able to do in one slice.

Joe
 
It seems to me that no one has ever bothered establishing a hard-and-fast criteria for determining sharpness, because that topic is almost as subjective as a knife's visual appeal.
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I think there are three issues here.
1) Initial sharpness
2) Edge holding
3) Blade geometry effectiveness

There are objective means of measuring all three.

The problem of subjectiveness arises because different tasks require different geometries, which in turn effects edge holding and intial sharpness.

For example, a very thin bladed knife (such as an opinel) will usually out perform a thick knife in cutting soft items such as tomatoes. Thin bladed knives cut with less force than a thicker one simply because there is less drag from the blade.

The same thin bladed knife will fail quickly when trying to cut something hard - such as soft copper wire. In fact, it might not even complete the task. This is because there is not enough steel behind the edge to prevent it from folding, and because it requires the loss of less steel to make it dull.

A thin, super razor scary sharp edge may work great if you intend to slice up ripe strawberries, but it is probably not what you need to break down 1000 boxes.

It all depends on the task at hand. Many knives are a sort of compromise - trying to be thick enough for the hard use tasks while still thin enough to use in the kitchen.

I think that arm hair shaving, cutting free hanging toilet paper, slicing circles in paper, etc, are good tests of inital sharpness. If you can accomplish this with a thick edged knife without creating a wire edge - you have a sharp knife indeed.

I usually don't try for scary sharpness in my blades. I usually aim for at least a basic level of shaving. I try to maximize edge holding for the tasks I usually encounter.

Sometimes, a more dull "toothy" edge will vastly outperform a polished razor edge.

Once again, it all depends on the task at hand.

-- Rob
 
I use the shaving the arm test (I almost always have at least on bald spot.) And the paper cutting test. I use the business reply cards you get in magazines. The slightly thicker paper gives a little more resistance and the rougher fibers help in two ways. After cutting the card look closely at the edge of the paper where you cut, I use a 10x magnifying glass. If the edge is "fuzzy" because the fibers have been pulled rather then cut, then you know that you could keep going on your fine stone. Then use your magnifying glass on the edge itself. If there are fibers stuck to the edge of the blade, then you keep going!

I use a variation of the fingernail test to feel for flat spots or small chips in the blade. I run the blade at a right angle to the fingernail, right on the edge. It's pretty easy to feel any defect in the edge this way.
 
Edges that are too polished do not cut poly rope or other hard type materials they slide right off.
I am always amazed at the number of knives that are carried for so called defense that are hair flinging sharp, but a slash against even a nylon jacket might just slide off with no bite at all or a very shallow cut. We will not even address a leather jacket.

So you need a hair shaving edge, but with enough bite to dig into the material being cut. What I have been doing to achieve mine is sharpening with the sypderco diamond stones, then using the corners of the white stones until it just shaves. Then there is still plenty of bite in the edge to dig into slippery materials, like leather and poly rope etc. Take a new Chris Reeve one piece and your great super tough survival wilderness knife will not cut hard poly rope. It slides right off, until you put a lot of pressure behind it. Hence first thing I do with these highly polished edges is run them gently along the sypderco 204 grey stone edges a couple times to rough it up a wee bit and put some bite into it. Now for a chopper blade, I just polish the heck out of it. The force of the chop does the cutting and it stays sharper longer in highly polished trim as there are no micro serrations to break off. I agree the best tests are the actual materials you may end up cutting.
 
Bart student :

So what do you think? Is shaving a good criteria?
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It tests edge alignment mainly. It tells when you have hone both sides of the edges to meet and they are free of any burr and all damage / wear has been removed. Even very coarse edges can shave, for example 100 grit AO, which leaves micro-teeth so large you can feel them with your thumbnail, can still shave with little force on the skin, no irritation.

It is a good indicator of how the blade will cut very slight materials well. A blade that fails to shave will also tend to fail to cut flimsy materials like light paper and plastic, threads and the like. It will also see greater resistance when push cutting various materials, such as soft foods or vegetation in general. You can really see a large difference on light grasses for example.

However, it isn't in general a good test of overall cutting ability because it doesn't "see" any part of the blade beyond the very edge and this part of the blade has a significant influence on cutting ability when you are making deeper cuts. To look at this you will want to cut a material which exerts forces on more of the blade such as the rope that Joe described.

So yes it is a good test, but it isn't all inclusive, you need to do other things as well.

-Cliff
 
A good test will be to take your blade to a waxing salon for women and see if you can do some landing strips without them knowing it wasn't waxed! LOL!
 
Apparently the Razor edge system has a sharpness tester - can anybody comment on its effectiveness? Is it similar to the fingernail test?
 
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