I remember reading some place ages ago where you could tell how sharp a blade was if you put 3 of your fingers (middle and the two on the sides) on the edge of a blade and ran/felt up and down the blade. To me, that seems insane with the edges I now see but I remember the author being some kinda big shot bladesmith. Anyone ever hear of this before?
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three finger sharp?
- Thread starter eccvets
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Yep, He's Murray Carter. 17th generation Yoshimoto bladesmith.
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Hehehe once again you're right Marc, I missed "the whole length of the blade". I do like to do the catch a ridge thing. I like to feel how aggressive a cutting edge I wind up putting on my knife. The middle of my index finger becomes a maze of microcuts when I sharpen a lot.
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This topic is frequently discussed. It is sort of difficult to comprehend what is being done with this "test".
Suffice to say it works for some. If you think about it, almost any gauge of sharpness you can come up with is going to require some insight from the person doing the gauging...and perhaps no method is truly without its shortcomings considering the different types of edges and preferences.
Suffice to say it works for some. If you think about it, almost any gauge of sharpness you can come up with is going to require some insight from the person doing the gauging...and perhaps no method is truly without its shortcomings considering the different types of edges and preferences.
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I did that with my new carbon steel Opinel last week, it cost me 3 band aids and a blood stained shirt.
Ooo that sounds.... not so good. so does anyone know what your suppose to be feeling for other then warm blood dripping from your blade?
did you happen to have some links you could share? I don't even know what this test is called so i have no idea what to look up.
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Basically it's the 'idea' of running the finger after touching the blade edge. According to him, a sharp edge will result in your nerve at the edge telling the finger not to move at all, so you won't cut yourself, because the edge has bitten the skin.
I never experience such feeling wih my polished edges.
I never experience such feeling wih my polished edges.
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I have an educated thumb.
Yup! I use that...and about 5 other demonstrations.
The silly thing is, I can use my thumb and determine (with perhaps 95% accuracy) that it is sharp enough to pass my other "tests" but I still feel the need to go through them
Cut newsprint, shave hair with minimal pressure, make a long curly shaving on a stick, fingernail test, etc. it's all silly, but that is how I enjoy my sharpening routine
To each his own, I guess!
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The only time I touch my edge with my bare fingers is to see if there are any small burs left. If i'm going for an edge with micro serrations, then I just make sure they're "biting" enough.
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Haha! My index, middle, and ring finger on my left hand all have hundreds of little micro cuts. Feels like sand paper. Although you can clean up pretty well in the shower with one of those foot scrubbing stones.
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My fingers got sweaty even reading that, though back in my stupid younger years when I was a wee lad, I did run this test quite often on my knife at the time. Needless to say, it was foolish because it looked like I had paper cuts. The slightest pressure was too much, thereby causing said cuts that looked like paper cuts.
This is what I have found when using swords (1x of which was taken to approximately 30,000 grit waterstones.)
While I am terrible at sharpening, I do understand the effects of sharpening having ran through a few dozen packs of sand paper for polishing of blades.
Anything between 80-320 grit will leave a very tooth edge and will cut just about most materials but will do poorly for push cutting until about 320 grit (when you can finally get shaving sharpness and push paper cutting if your really good at it).
There is a downside to using this level of grit, you can easily get burrs, and uneven toothy edges due to the amount of material removed with each "strop".
My theory is that as the edge is being polished by the 600-1000 grit paper, the edge's burring and toothiness is removed however something happens at a very moment as well. While no where near the level of 320 or lower grit, 1000 grit still removes quite a bit of metal so as you remove toothy edges you leave "flatter" areas as well as leaves tiny scratches in the blade following to the end of the edge resulting in little crevices that result in areas with larger surface then not allowing for your thumb to drag without being cut, but having an angle those edges that is shaving sharp.
As you move to 3000 grit and higher, the scratch marks get smaller and more dense, and as you being to polish out the edge, the crevices get smaller thus the areas with "more" surface diminish, and you bring back the drag of your finger. But it isn't the same drag as the toothy edge, this time it's just your skin being cut open, unlike the toothy edge (if you wiggle them just so slightly, you will NOT be cut).
I think that's what Murray does with his three fingers test, once the edge is pretty much flawless you should be able to just slightly wiggle, and feel the blade sink in, and eventually stop you from wiggling.
While I am terrible at sharpening, I do understand the effects of sharpening having ran through a few dozen packs of sand paper for polishing of blades.
Anything between 80-320 grit will leave a very tooth edge and will cut just about most materials but will do poorly for push cutting until about 320 grit (when you can finally get shaving sharpness and push paper cutting if your really good at it).
There is a downside to using this level of grit, you can easily get burrs, and uneven toothy edges due to the amount of material removed with each "strop".
My theory is that as the edge is being polished by the 600-1000 grit paper, the edge's burring and toothiness is removed however something happens at a very moment as well. While no where near the level of 320 or lower grit, 1000 grit still removes quite a bit of metal so as you remove toothy edges you leave "flatter" areas as well as leaves tiny scratches in the blade following to the end of the edge resulting in little crevices that result in areas with larger surface then not allowing for your thumb to drag without being cut, but having an angle those edges that is shaving sharp.
As you move to 3000 grit and higher, the scratch marks get smaller and more dense, and as you being to polish out the edge, the crevices get smaller thus the areas with "more" surface diminish, and you bring back the drag of your finger. But it isn't the same drag as the toothy edge, this time it's just your skin being cut open, unlike the toothy edge (if you wiggle them just so slightly, you will NOT be cut).
I think that's what Murray does with his three fingers test, once the edge is pretty much flawless you should be able to just slightly wiggle, and feel the blade sink in, and eventually stop you from wiggling.
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This. The three-finger test really does tell you exactly where a knife is sharp and where it isn't. If you do it properly (with just a slight wiggle and little pressure) you shouldn't cut yourself.