standard test for sharpness?

J

Juramentado

Joined
Aug 23, 2003
Messages
185
Is there a commonly accepted way of determining the sharpness of a blade? I use the same old shaving-hair-from-my-arm test but is there a more objective way of checking whether a blade is sharp or needs sharpening? I find myself obsessively sharpening my knives on my Spyderco Tri-Angle and maybe I'm looking for a way to put the brakes on this obsession. :)
 
Nope, I don' t think so.
Everybody pretty much tests the sharpness of his/her blades with their own way. I guess you will just have to set up a standard for yourself (like you did, shaving arm air) and sharpen up to that point.

My personal standard is slicing newsprint btw.:)
 
I run the blade lightly trying to shave the hair off the back of my head, without touching skin or anything. Cutting letters off newspaper or magazines is a good one too. Smoothly cutting paper works as well. For the really OCD among us, ever more difficult tests lead to more and more sharpening. Be careful what you ask for.
 
Hair whittling is a good test, a knife will shave hair at many different levels but to whittle the hair is much harder.

Hair shaving= good
Splitting hair 1-3 times= very sharp
Splitting hair 3-5 times= Stupid sharp
Splitting hair beyond 6 times= now your just having fun :D
 
Juram,There is a standard for testing knives cutting ability,sharpness, edge retention,ect..Its the C.A.T.R.A. machine.However, there are only a handful of them in the U.S. and access is restricted w/ those companies.So, we cut paper,manilla rope,shave hair and make up some other tests to determine sharpness.DM
 
knifenut1013 said:
Hair whittling is a good test, a knife will shave hair at many different levels but to whittle the hair is much harder.

Hair shaving= good
Splitting hair 1-3 times= very sharp
Splitting hair 3-5 times= Stupid sharp
Splitting hair beyond 6 times= now your just having fun :D
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Splitting hair? Human hair? Is that even possible with an ordinary folding knife?

That's going to set me onto a new frenzy of sharpening LOL!
 
There is a standard for testing knives cutting ability,sharpness, edge retention,ect..Its the C.A.T.R.A. machine.However, there are only a handful of them in the U.S. and access is restricted w/ those companies.So, we cut paper,manilla rope,shave hair and make up some other tests to determine sharpness.DM
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DM is correct some of the major co.'s use a CATRA. It tests sharpness & Edge holding. Many of the custom makers use manila rope. If you're just testing for sharpness you could use shaving arm hairs, paper, etc.
 
Juramentado said:
Splitting hair? Human hair? Is that even possible with an ordinary folding knife?

That's going to set me onto a new frenzy of sharpening LOL!
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I prefer to use newspaper, I cut them into large rectangles and I put a stack of all of them in a box for testing sharpness, if it zips right through with no effort at all when you try to push cut, then it's sharp enough for me.
 
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Juramentado said:
Is there a commonly accepted way of determining the sharpness of a blade? I use the same old shaving-hair-from-my-arm test but is there a more objective way of checking whether a blade is sharp or needs sharpening? I find myself obsessively sharpening my knives on my Spyderco Tri-Angle and maybe I'm looking for a way to put the brakes on this obsession. :)
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I have statistic thread test - 21 cuts like this.

http://www.youtube.com/watch?v=1Ftbus7LbtU

But to have fast check - whittle hair:

http://www.youtube.com/watch?v=aQPwHu4lxsQ

Thanks, Vassili.

Other test:

http://www.youtube.com/watch?v=AwojRPH7ztM

http://www.youtube.com/watch?v=3B2fqdVS8J8

http://www.youtube.com/watch?v=tgJSPLVF2Wc
 
I agree with CATRA comments - or better yet SEM pics like Verhoeven's that allow the edge to be measured. For me there is a distinction between cutting ability and sharpness - sharpness is edge diameter, and cutting ability is the force and slice required for the cut. Sharpness could be measured by observation, and cutting ability can only be measured by cutting something. Sharpness is independent of edge angle, and cutting ability can be largely dependent on edge/blade geometry. Coarse edges complicate the definition of sharpness.

For a polished edge, one of the "gold standards" I use is cutting up rolled up pieces of phone book paper. If the knife is sharp enough, the only technique required is the ability to hit the paper. And if you think it is dangerous (it has been mentioned), obviously you have never cleared any brush with a knife :D. You can also do it with printer paper to make the cut easier. And if you store your old phone books in the garage (or any moist untreated space) it can be nearly impossible. Clearing brush with a large knife this sharp is amazing if you're used to a dull old machete.

Picture009_0001.jpg


 
Broos said:
I agree with CATRA comments - or better yet SEM pics like Verhoeven's that allow the edge to be measured. For me there is a distinction between cutting ability and sharpness - sharpness is edge diameter, and cutting ability is the force and slice required for the cut. Sharpness could be measured by observation, and cutting ability can only be measured by cutting something. Sharpness is independent of edge angle, and cutting ability can be largely dependent on edge/blade geometry. Coarse edges complicate the definition of sharpness.

For a polished edge, one of the "gold standards" I use is cutting up rolled up pieces of phone book paper. If the knife is sharp enough, the only technique required is the ability to hit the paper. And if you think it is dangerous (it has been mentioned), obviously you have never cleared any brush with a knife :D. You can also do it with printer paper to make the cut easier. And if you store your old phone books in the garage (or any moist untreated space) it can be nearly impossible. Clearing brush with a large knife this sharp is amazing if you're used to a dull old machete.

Picture009_0001.jpg


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I tend to stay away from paper roll chopping tests and bottle cutting tests since this...... :o






Photo-0076.jpg


3stitches with 2 more stitches underneath(deep stab :o)
 
James_Terrio said:
You're doing it wrong. :D Keep your free arm out of the way. :thumbup:

Just teasin'... I have a similar scar on one of my thighs... long story.
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I actually stabbed my arm like 5 seconds after I chopped a bottle, if it was while chopping the bottle, it would be much worse, I guess swinging sharp stuff around brings a bit of carelessness if you get away with it.
 
Chopping bottle and paper is fun, but it is proven that it has nothing to do with sharpness. I did same with knife with ruined edge. But it is fun to do, if you are careful.

Thanks, Vassili/
 
To really test sharpness and cutting ability the test shouldn't take any skill to do the test.
 
I use paper to test the sharpeness of a edge. By observing how it cuts the

paper, I get alot of answers from it. :thumbup:
 
For kitchen knives I just touch the edge to the back of a thumbnail as if you were going to shave off a thin layer. If it slips over the nail surface then it's dull. If it grabs it's sharp enough for routine kitchen duty. A knife that passes this test won't necessarily shave arm hair. And a knife that shaves arm hair won't necessarily whittle hair.

A variation on the "shaving arm hair test" is to do so without touching the skin surface, i.e. tree-topping. A tree-topper will likely also be a hair whittler.

Then there is the paper push cut test. Hold a sheet of printer paper with one hand so that the top edge is horizontal. Then with the other hand holding the knife, cut down, perpendicular to the paper edge. It is easy to do near the hold point and more difficult further away. For me, knives that push cut printer paper beyond 4 to 5 inches from the hold point will also whittle hair. The push cut test can also be done with newsprint or phone book paper, etc. although the results won't be directly comparable.
 
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