Indications of knife sharpness

[Dustin]

How can one determine how sharp the edges of a knife are?

 

[Dustin]

How do you deyermine how sharp a knife is after it has been used over a period of time,without actually using it?

 

[TheBadGuy]

Personally I just shave some hair off my arm or leg. If it doesn't do a smooth clean shave, I take it to the Sharpmaker

 

[TheBadGuy]

Oh Yeah, WELCOME TO THE BLADE FORUMS!!!!!

 

[Steven Roos]

When the hair jumps off my arm before the blade even gets there, then it is sharp!

The arm shave test and the paper shave test are a couple good ways to tell.

 

[wolfmann601]

When you drop it on your toe and do not realize you have sliced your big toe down to the bone until you feel the warmth of the pool of blood on your heel.

 

[Rev. Pete]

How can one determine how sharp the edges of a knife are?

I have three tests: thumbnail, shaving, paper slicing. Most knives have to pass at least the first two tests. Workday EDC knives have to pass the third test because they are used for packages and envelopes. First, the thumbnail test. I rest the edge of the blade across the width of my off-hand thumbnail. If it grabs, it passes, if it slides off it fails. The second test is the shaving test. This is dangerous. You could cut your arm very badly so I don't recommend it. To do the shaving test I just gently scrape the hair on the top of my offhand forearm. The blade angle depends on the knife, but perhaps 10-20 degrees from parallel to the arm. If the hair shaves off clean with no pulling it passes, anything less (such as a few hairs cut but others remain) it fails. The final test is brutal, especially for utility knives with thick blades. I hold one short edge of a piece of paper with my off hand. I push the point through the middle of the paper and steadily pull the blade toward the other short edge. If the paper is cut cleanly with no tearing it passes, otherwise it fails. Lately I've been experimenting with looking at the edge through a jewelers loupe but I'm still getting up to speed with that technique.

 

[Rev. Pete]

Thumbnail test:

 

[Rev. Pete]

Shaving test (start) (remember, this is very dangerous, so don't do it):

 

[Rev. Pete]

Shaving (after):

 

[Rev. Pete]

Paper (start):

 

[Rev. Pete]

Paper (finish):

 

[catmath 1911]

Rev. Pete,

What kind of knife is that? It's pretty sweet!

catmath 1911

 

[VampyreWolf]

I have 3 test, since I've had knives of all 3 levels...

1> food prep(if it doesn't slice a ripe tomatoe, it ain't sharp enough)
2> paper slicing(Grab a peice of paper, and slice at an angle, starting about 2-3" ABOVE sheet, slicing towards a corner
3> shaving cleanly

I'm running out of arm hair on my left arm, started on my right, and have about 5-6 patches on my legs. I finish my sharpening on the Spyderco 303MF DoubleStuff whites(where I have freehand control), and strop on the case.

 

[DEA]

i only tried the arm hair shave test ONCE
it worked with my kobun, but i got so unnerved i swore off it
the paper test is much more convenient
find some paper (actually newspaper is much harder to slice cleanly, and is a very good way to tell if your knife is really sharp) lying around the house and there you have it

 

[Rev. Pete]

What kind of knife is that? It's pretty sweet!

Thanks! That is a little Dozier Neck knife I picked up at Blade show this year. There is a link to a scan of it in the second message in this thread. Very sharp knife and an amazing price.

 

[TheBadGuy]

Here is some more info and tests for you


http://www.bladeforums.com/forums/showthread.php?s=&threadid=221404&highlight=edge+tester

 

[logan5]

I like the thumb (or any finger) nail test. It really does work and you can tell if any part of the blade is dull. I do the test on the tip, middle and back of the blade.

And the best part is there are no funny looks and the inevitable questions from people that notice bald spots on my forearm. But I will admit, that when I feel like shaving hair (hey it happens sometimes), I go for the leg. It’s a lot more out of the way and even if I’m in shorts not that many people are checking out my legs. Or at least no one has ever asked why I have a bald spot on my leg like they have about my arm.

 

[the possum]

The test I use most is the simple shaving test. I can tell by the way the blade feels on my skin if it's sharp enough for my purposes, even if it doesn't take a single hair off. Another tip: I got a bit tired of having bald patches running up and down my arms. People kept asking what happened to me. So now, I don't actually shave them off. I can tell if the blade just "grabs" the hair how sharp it is.


My second test is more precise and only used for knives that must be "scary sharp". Pluck a single hair from your head and hold it by one end only. No cheating. Don't pull the hair taut between two hands or something. It must be completely unsupported. Now try to whittle it with your knife.
If the blade can cleanly cut the hair off along the whole length of the edge, the blade is *sharp*.
If you cut halfway thru the hair, and it curls and bends over, it is almost sharp.
If all you can do is cut curls off it down the full length of the hair, it still needs some work.

 

[J. MacDonald]

There's way too much hair on th earm in that pic for him to be a real knife knut. My left fore arm hasn't had that much hair in years. Even where it's not bald, the hairs are in some sort of regrowth pattern.

This post is of course tounge firmly in cheek.

jmx