How do you test sharpness?

P

pinkfloyd101

Joined
Sep 24, 2008
Messages
187
I have read many threads and it seems like everyone has their own way to test their knives? How do you test yours? Shave arm hair? Push cut computer paper? Slice newspaper? Whittle hair? Cut rope? Etc?

I usually do three quick tests. I start by seeing how easy the blade starts to cut my skin on my thumb with very very little pressure. Then I see how easy it shaves arm hair against the grain, and then put cut newpaper to make sure the blade it good the whole length. You?
 
i usually just rub my thumb on it if it cuts a bit its good enough for me, however if you dont want tiny cuts on your thumb paper is a better idea
 
just keep a fresh supply of kittens handy, wait, I mean...

I usually do the arm hair test, and a bit of the thumb test to see how easy it starts to cut. Then I'll run it through printer paper a couple times.
 
How the process usually goes for me:

1.) After I sharpen my knife, I strop it. If I see little tiny bits of leather being picked up on the edge of my blade, that's a good sign of things to come...

2.) There's a special sort of 'hissing' sound that I (hopefully) will hear when I draw the blade along the leather as I'm stropping. That's another good thing...

3.) After stropping, usually I'll very carefully put the edge to a few fresh hairs on my forearm, and see (again, hopefully) how easily it takes the hairs off. If all is right in the world, hairs will almost 'jump' off at the lightest touch. If all is not quite perfect, and I have to 'dig' a bit with the edge (usually leaves a li'l red scratch on my arm), then I'll take it to the strop again, very lightly...

4.) Once I'm happy with how it shaves, I'll slice one of my many grocery store receipts laying around (I save 'em just for this purpose). Usually don't have any issues doing this, it'll cut 'em, but it's all about how easy it happens at this point. The sharper my edge is, the smoother and quieter the cut will be. Almost whisper quiet, if (again) all is right with the world. This is also the best time to check the full length of the cutting edge; if it doesn't bind up or catch as I draw the edge it's full length through the paper, I know the edge is in good shape. That makes me HAPPY! :D
 
I use a similar method but I don't cut any paper because it can cause damage to avery fine edge. Though the cutting yourself sounds kinda morbid it is a really good test. If it will cut without moving the blade and feels "sticky" you know you have a very sharp edge. I still do the arm shave test but I think that more from habit after doing it for so many years. I have acquired a "feel" for all the different levels of sharpness so the only test that works fo me now is whittling hair. Their are many other methods to the madness but feel and hair whittling are my main ways of testing sharpness.
 
surely someone can devise a rig to test cutting ability!
knife on an arm that measures downward force required to cut through a piece of rope or something like that.....
 
They make them, their called CATRA machines.
 
Last edited:
I finish an edge by stropping in the palm of my hand. This way I can confirm that the final burr has gone.
If the edge will then slice cleanly through kitchen roll, it's sharp enough for me.
 
I pull my finger tips lightly across the edge.
Started doing that as a meatcutter almost 30 years ago.
 
What I've discovered is that sharpening is a progressive sickness just like knife collecting.

With knives, you start off with a Wal-Mart Gerber, and pretty soon you've worked your way up CRK, Strider, and customs. It's exactly the same with sharpening.

As I get better at sharpening, what was good enough before now isn't even close, and I'm far from being a sharpening expert. The first time I got a knife to cleanly shave arm hair I was thrilled and shaved half my arm. Now, shaving sharp is kind of the minimum, and I'm looking for edges that "pop" hairs off. I haven't gotten into the hair splitting sharp, but it's probably on its way. :rolleyes:

And I haven't even begun to approach the level of obsession of some people around here.
 
I usually do TPT or arm hair, it's easy enough to feel the difference in the way the hair cuts. When going further than just edc duty, I'll make sure it whittles hair, slice toilet paper, push cut rolling paper, or shave some of my face. These are checks for polish, sufficient sharpness to shave arm hair comes at double digit grit, and I finish at 6 digit (mesh)
 
Like others I test sharpness by push cutting paper and shaving arm hair, but thanks to others here on BF I've learned two new methods that I really like.

The first is the fingernail test. Set the blade on a nail at a very slight angle and if it is sharp the blade will bite into the nail and not slide off.

nail1.jpg


nail2.jpg


The second method doesn't involve any cutting at all and may be the best method once you get use to it. Just hold the knife up to a bright light and let the light reflect off the edge. You may have to experiment to find the right light and position to see. But once you figure it out you can see if the edge is evenly sharpened or if there are any places that are rolled or chipped very clearly.

light.jpg


Hope this helps.

Chris
 
cgmblade said:
The second method doesn't involve any cutting at all and may be the best method once you get use to it. Just hold the knife up to a bright light and let the light reflect off the edge. You may have to experiment to find the right light and position to see. But once you figure it out you can see if the edge is evenly sharpened or if there are any places that are rolled or chipped very clearly.
Click to expand...

+1 :thumbup:

Yes, this is becoming a more useful check for me also. I usually do it after I've done my shaving/paper slicing checks. I've come to recognize that if the blade isn't quite plunging into the paper as effortlessly as I'd prefer, it's usually because the edge (or a small section of it) is rolled to one side or the other. That's when I'll hold it to the light as described above, and look for the shiny areas on the edge. It's nice when it's perfectly straightened out, and the edge effectively 'disappears' as it's rotated into the light.

This is almost universally helpful in inspecting folding knives' edges that might've come into contact with the inside of the backspacer. Some folders don't allow adequate clearance between the blade edge (usually somewhere near the tip) and the backspacer, and the edge smacks into it when the blade closes. Always leaves a 'flat spot' at the point of contact, and a telltale nick in the backspacer. More than a few times, I've noticed the flat spot on the edge when holding it up to the light this way, and now it's one of the first things I look for when inspecting a new knife.
 
Thumbnail test and shaving armhair.

It also depends on the use for the knife.
 
cgmblade said:
Like others I test sharpness by push cutting paper and shaving arm hair, but thanks to others here on BF I've learned two new methods that I really like.

The first is the fingernail test. Set the blade on a nail at a very slight angle and if it is sharp the blade will bite into the nail and not slide off.

The second method doesn't involve any cutting at all and may be the best method once you get use to it. Just hold the knife up to a bright light and let the light reflect off the edge. You may have to experiment to find the right light and position to see. But once you figure it out you can see if the edge is evenly sharpened or if there are any places that are rolled or chipped very clearly.

Hope this helps.

Chris
Click to expand...

+1 This is my method also, except I use the bright light first, then once the entire edge looks good, the fingernail test. I then shave some hair off my arm, habbit I guess.
 
You must log in or register to reply here.
Back
Top