sharpness test

S

superc

Joined
Sep 30, 2003
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What is the best test for knife sharpness?

It is recognized that a knife that won't leave a bald spot on your arm is dull. However, trust me when I say, that simply passing that minor test does not qualify the blade for usage as a face razor. Several additional levels of sharpness exist above the simple can 'shave my arm' level. How do you test for them?
 
push cut newsprint, slice toilet paper, cut light thread on a scale, chop through a freestanding cigarette paper roll

I don't think anyone uses their knife as a face razor, geometry is much too different.
 
superc said:
What is the best test for knife sharpness?

It is recognized that a knife that won't leave a bald spot on your arm is dull. However, trust me when I say, that simply passing that minor test does not qualify the blade for usage as a face razor. Several additional levels of sharpness exist above the simple can 'shave my arm' level. How do you test for them?
Click to expand...

To me the simplest final sharpness test is whittling hair:

http://www.youtube.com/watch?v=sI_iqAyb3xA

http://www.youtube.com/watch?v=FZZa1Ng5bzY

However I usually do thread cutting test to measure sharpness precisely.

Thanks, Vassili.
 
Some more - the Murray Carter 3-finger test, cut an empty plastic bottle or empty tin can in half (can/bottle standing up), cut a rolled up piece of phone book paper (similar to the cigarette paper test), can it tree top arm hair, or look at the edge with a loupe or microscope. Splitting hairs is tough with 1" long fine blond hair!

Picture009_0001.jpg
 
OK, I understand your tests and the various goodies you're cutting, but I have a question. After you've spent some time honing, and stropping and you think you've got the best edge you can get for the steel, why would you test it on a tin can, cardboard, paper, etc. You only determine that the blade WAS sharp....in most cases you have to re-sharpen or at least retouch the edge after such test, and then you're not sure if you got it back to where it was unless you perform the test again.....thusly you create an endless circle of tests and the first deer has yet to be dressed! When do you stop? Are we testing the edge or the technique for getting the edge? My hair is about 15 inches long, snow white, and splitting it has yet to be accomplished. Sooo, I guess I need to work on my technique. I have to say, I don't use dull knives for anything....especially ones which have cut cardboard or tin cans. I've dressed a good many animals with a few swipes of my blade on a diamond rod or a ceramic. Never had a failure.
 
oldscrimmer said:
After you've spent some time honing, and stropping and you think you've got the best edge you can get for the steel, why would you test it on a tin can, cardboard, paper, etc. You only determine that the blade WAS sharp....in most cases you have to re-sharpen or at least retouch the edge after such test, and then you're not sure if you got it back to where it was unless you perform the test again.....thusly you create an endless circle of tests and the first deer has yet to be dressed!
Click to expand...

Not if you're using D-2, M-2, S30V, 3V or other quality steel. :thumbup:
 
Ben Dover said:
Not if you're using D-2, M-2, S30V, 3V or other quality steel. :thumbup:
Click to expand...

Now we're thinking!!! There wasn't any mention of the type steels when the question was asked in the first post. Ben's got it right, if you're going to extreme test a knife, make sure the steel is right for the test you chose. We surely don't want folks to be testing our theories of sharpness on crappy steel and tell us then we don't know what we're talking about.
 
For my use I believe that the test is in the using.

I know my blades are sharp after a session with the stones.

They meet my new standards and far exceed what I had before reading this forum and far exceed my methods prior to getting the GATCO. My EDC blades get sharpened, shave some hair from my forearm and go right into the pocket. The kitchen blades get sharpened, cleaned, placed in the block to await the trial.
 
oldscrimmer said:
OK, I understand your tests and the various goodies you're cutting, but I have a question. After you've spent some time honing, and stropping and you think you've got the best edge you can get for the steel, why would you test it on a tin can, cardboard, paper, etc. You only determine that the blade WAS sharp....in most cases you have to re-sharpen or at least retouch the edge after such test, and then you're not sure if you got it back to where it was unless you perform the test again.....thusly you create an endless circle of tests and the first deer has yet to be dressed! When do you stop? Are we testing the edge or the technique for getting the edge? My hair is about 15 inches long, snow white, and splitting it has yet to be accomplished. Sooo, I guess I need to work on my technique. I have to say, I don't use dull knives for anything....especially ones which have cut cardboard or tin cans. I've dressed a good many animals with a few swipes of my blade on a diamond rod or a ceramic. Never had a failure.
Click to expand...

What is wrong with hair whittling? Believe me - no need to resharpen your blade after this test ;)

If you just able to cut hair by gentely touching it (touching it as it shown on video) - it is about 40 g sharpness.
Next level - you split hair - kind of longf diagonal cut - it is about 30g sarpness.
Finally - whittling hair with long shave - 20g. The best sharpness I see so far.

I have relatively thin Slavic (Russian) hairs maximum 2" long. You should cut hair opposite to hair shell structure - from top to the root. Once you have about 50g sharp hair start bouncing on the blade because of this shell structure (look like palm tree of pine).

Why it is important to have initial sharpness good - see my edge retention test - http://www.bladeforums.com/forums/showthread.php?t=509097

In short - better sharpness you have at start - longer it take it to get dull (for good steel blade like Lauri Progressive Tempered which cost under $20 blade or modern Friction Forged D2).

Thanks, Vassili.
 
Viassily,

Interesting. The 20gm edge at what bevel angle (included)? I can get it with my rzor but not ordinary knifes. At 30 dgres included I can't get under 45gm with any steel. At 25 degres I can get my M2 home made knife down to the 30s but not under.

Cheers
Frank
 
Frank Hillary said:
Viassily,

Interesting. The 20gm edge at what bevel angle (included)? I can get it with my rzor but not ordinary knifes. At 30 dgres included I can't get under 45gm with any steel. At 25 degres I can get my M2 home made knife down to the 30s but not under.

Cheers
Frank
Click to expand...

Mine all are around 30 degree. I use 15degree stand and it sets the angle. But my 20g may be different from your 20g - can you whittle hair with long shave at 20g?

Thanks, Vassili.
 
hardheart

Lansky then SM

I was wonderin if how sharp a blade can be got is tied to bevel angle. I mean yiu'll never get a 90 degre edge that sharp. So is it obtainable withj say 40 degre?

Cheers
Frank
 
hardheart said:
I don't think anyone uses their knife as a face razor, geometry is much too different.
Click to expand...

It's all about the water temperature. I wouldn't want to try it with a cold mountain stream, but I did (once) use water heated over an open camp fire and an old Dove and a bar of Octagon... The water heat is crucial to the job.
 
Frank Hillary said:
hardheart

Lansky then SM

I was wonderin if how sharp a blade can be got is tied to bevel angle. I mean yiu'll never get a 90 degre edge that sharp. So is it obtainable withj say 40 degre?

Cheers
Frank
Click to expand...

do you have the ultrafine rods or strop after? I think Vassili is stopping at 0.1 micron diamond, I have some 0.3 micron lapping film. The fine sharpmaker rod is about 3 micron.
 
hardheart


hardheart said:
do you have the ultrafine rods or strop after? I think Vassili is stopping at 0.1 micron diamond, I have some 0.3 micron lapping film. The fine sharpmaker rod is about 3 micron.
Click to expand...

I have the UF rods and I strop on Braso, then 6&1 micron diamond and then finesh of on Dialux Bleu.

Cheers
Frank
 
I pressed a Krein reground and Wilson re-heat treated small Sebenza into face shaving duty when I was at Disneyland and the Bic "Comfort 3" disposable razors I bought hacked up the left side of my face. Using extreme care I got a close shave with no cuts and some small razor bumps on my neck (I usually get less/smaller razor bumps with my Fusion in MUCH less time) on the right side of my face. The knife has a .007"-.008" thick edge, with a 10 per side edge with a tiny 15 per side microbevel, and was finished to a .05 micron finish on 3M lapping film, and was whittling hair. The knife wasn't quite as sharp as the Manix in my other pocket (the Manix takes a better edge) which I had shaved my face with before, but the thinner edge and blade really seemed to help with shaving and hitting the tight spots. I don't recommend this unless you absolutely have to shave and don't have a suitable razor, and be sure you use a pure push cutting motion if you do, as getting a slicing motion would open up a nasty cut, I would imagine.

Mike
 
Frank Hillary said:
Vassili



Yes. Can even do it with a stainles Opinel at 30 degre

Cheers
Frank
Click to expand...

20g - means 20 gramm forse needed to cut cotton thread on scale, not degree of edge angle. It is explained in detail in steel edge retention testing thread. Sorry, for confusion.

Thanks, Vassili.
 
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