So, how do YOU evaluate "sharpness"?

E

ewjax

Joined
Oct 31, 2005
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16
I'm curious - how do folks evaluate just how sharp their blades are?

It seems very subjective to me. For me, I typically tap the edge of the blade on my thumbnail, and gauge the sharpness by how well it "sticks". Or sometimes I slice paper, but again, that is fairly subjective - the length/ease of the cut is very dependent on how hard I swing, the angle at which I strike the edge, the stiffness/flimsiness of the paper, etc. Doing it with a relatively stout piece of paper, as opposed to something flimsy like newspaper, gives totally different results. So it is hard to gauge whether one edge is sharper than another.

I hear people talk about shaving the hair on their forearms, but to me that seems even less reliable or indicative than the thumbnail or paper tricks.

Anyone have any more reliable method than these mentioned?
 
Just feel the edge with your thumb is how i do and it works pretty well. Shaving sharp really isn't that helpful cause the edge won't be held as long usually but it will slice better. I also do the paper test on notebook paper
 
My primary test of sharpness, "Does it cut what I need it to cut, than it's sharp enough."

My favorite method is to take one of those moldable foam ear plugs and try to slice it without crushing it, it's not as easy as it sounds, try it, any flatspot on the blade will compress instead of cut it.

What's this prove?

If I need a knife to slice foam earplugs it's sharp enough.
 
I slice a Post-It, shave arm hair, feel the edge with the pad of my fingertips, and lastly I walk down a dark alley and slash ninjas across their throats.
 
I do all three at various times . . . .

For the paper trick, I always use the same type of paper, the postage reply cards you find in magazines. I look at the cut, and I also look at the edge and look for any fibers stuck the edge, that usually indicates a dull area or nick in the blade.

If I'm reprofiling an edge, I'll use a 10X magnifying lens to inspect the grind as I go. This also helps me determine when I've smoothed all the course stone filings away with the fine stone.

Lunumbra
 
T. Erdelyi said:
If I need a knife to slice foam earplugs it's sharp enough.
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Not a bad test. :) I do the same with mushroom stems, about the same level of difficulty, but they taste better than foam.
 
I like to place my blade on top of a particlar length of braided poly-blended rope and try to press cut cleanly through without slicing the rope. I then take the same rope and do a regular slice cut with as little force as possible.I also try to detect any burrs along the edge. I don't know if it is a good indicator, but I enjoy doing it.
 
I do the above but I also cut a tomato or so veggie with skin and try to get a nice even slice out.
 
If the blade 'sings' thru a page of the SMKW catalog, it's good.
If I can snap cut little narrow triangles off the above cut page, it's real good.
Well, for me, at least.
 
I cut a sheet of paper, using a straight cut, and then two angled cuts with each side of the blade. The whole edge must travel smoothly through. If it hooks or tears, that part of the edge isn't sharp. On the angled cuts, if one side cuts better than the other, I have a burr. The smoother the edge is, the softer the sound of cutting through the paper.

I also sometimes push-cut a piece of string with several points along the edge. If I've done the edge correctly, it makes this "snick" sort of sound. And the harder I have to press, the worse the blade is at cutting. It's a bit difficult to tell sometimes, the "belly" usually cuts well, and tips usually cut poorly, and blades with curves make it difficult to test all along the edge.

Most of the time, the paper test is sufficient.
 
Esav Benyamin said:
Not a bad test. :) I do the same with mushroom stems, about the same level of difficulty, but they taste better than foam.
Click to expand...
Feb 2006 issue of Blade magazine, good article on sharpening."How many passes does it take?" A.G. Russell tests sharpness by slicing foam packing peanuts. On the same line as the foam ear plugs slice test.
 
For sharpness alone, I prefer a slow heel-to-tip draw-cut through newsprint. It's very easy to sense sharpness both by felt-resistance and how silent the cut is made - very good in sensing any problem areas such as knicks or duller areas along the edge.

There is a problem with this method alone, in that a sharpened wire-edge is sensed as simply a very sharp blade edge - unless the wire-edge is folded over. This can be settled with a couple of hard-pressure slices into wood or plastic - which should fold any wire-edged area - which can then be sensed by the newsprint draw-cut.

Works for me.
 
I use a empty plastic grocery bag. I put a teaspoon in it then insert the knife blade edge up through the handle opening and see if it will cut the handle in two as I lift up.
 
Usually one of three ways, my thumb being the top way, cutting paper, then sometimes if I'm going for bragging rights I'll shave my arm and/or face.
 
Paper cutting is the most common for me, I try not to shave hair from my arms because sometimes I get carried away.

I always have several pieces of wood liying around, so I whittle a bit to test the edge, too.

For show off I take raw hide strips and cut them horizontally in paper thin slices.
 
1. Shaving arm hair. But just shaving arm hair isn't really that sharp. It's how easily that it shaves that indicates a higher level of sharpness.

2. Cutting hanging newsprint. Again, it's not just that a knife can do it, it must do it cleanly and easily.

3. Splitting hairs.

4. Cutting single-ply toilet paper without tearing it.
 
I don't like razor-sharp knives 'cos they're too thin,but for me I test like this:

1-Paper-old used notebook or catalog paper,I hold it at the corner in the air and try to slice it from the center to the edge...if the kinfe does it without hanging up it's sharp!!

2-Cardboard:lite stuff (a food box) of some sort try cutting in a "wave" rolling up-and-down...harder then you think-if the knife isn't sharp.
 
I havent tried it yet but I heard one similar to the ear plugs.Try shaving those packageing peanuts or ghost farts very snow flake thin if it slices insted of smashing you have a sharp blade.That is the A.G.Russell method according to feb.blade magizine.
 
If I can cut a letter out of a newspaper without cutting all the way through the paper, it's sharp enough. I don't get how I can do this, but the ear plug test never works for me....

My knife sees a lot of different chores. Everything from opening boxes, cutting drive belts, squeek and rattle foam, to cutting that rubbery adhesive that holds the plastic covers over the innards of car doors. Some times it comes in contact with metal and gets a ding in the edge.

Right now I'm sharpening like this:

If I have a lot of dings in the edge, I rubber band some diamond stones over my sharpmaker and use those. I do the normal sharpmaker process (40 strokes, corners flats, brown, white) at 30 degrees. Then after I'm done with all of that, I break out the ultra fine stones and do about 10-20 strokes at 40.
 
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