??? For sharpening gurus? They don't feel that sharp.

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okbow68

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Mar 17, 2011
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When I sharpen one of my knives and I do the "three finger" test I just don't get that oh ?!$& that thing is gonna cut me good feeling. However they will shave arm or leg hair easily. I use DMT Duosharp stones down to EF and then strop with green compound. I use one or two coins as an angle guide depending on the knife during the whole process. I look at the edge with a 30X loupe and I don't see anything wrong no burr and it appears to me at least that the edge comes together and apexes fine. What am I missing here?
 
Stropping on green compound is going to smooth out your grind texture and eliminate many of the "microserrations". Do your best to eliminate the burr straight off the stone and strop with some plain leather or two layers of newspaper wrapped around a stone - see if that makes a difference.
 
I'm not sure I see the problem. If it cuts fine, looks good under the microscope, what do you need to fix?

Toothier edges and more acute edge angles make it feel scarier to the fingertips. Do you know what the edge angle is on this? If its up at 50 degrees it won't feel that sharp but still might shave.
 
I don't get the "3 finger test" either. I assume (in this test) that you are feeling for something other than a fear of getting cut, but I don't have a sense of what it is. It took me a while to get up the nerve to run my fingers down the blade because I was genuinely afraid that I would indeed get cut. I guess I have enough sense not to push hard enough. I somewhat recently learned how to sharpen well enough to shave hair and push cut paper, and now find that level of sharpness relatively easy to obtain. Maybe this test would be better if I were getting my knives even sharper still. Maybe the "tester" has to develope an intuition of how easily the blade MIGHT cut them if they pushed just a little harder. I don't know.

I'd love to hear more from others who use this test and find it helpful for them.
 
Belker said:
I don't get the "3 finger test" either. I assume (in this test) that you are feeling for something other than a fear of getting cut, but I don't have a sense of what it is. It took me a while to get up the nerve to run my fingers down the blade because I was genuinely afraid that I would indeed get cut. I guess I have enough sense not to push hard enough. I somewhat recently learned how to sharpen well enough to shave hair and push cut paper, and now find that level of sharpness relatively easy to obtain. Maybe this test would be better if I were getting my knives even sharper still. Maybe the "tester" has to develope an intuition of how easily the blade MIGHT cut them if they pushed just a little harder. I don't know.

I'd love to hear more from others who use this test and find it helpful for them.
Click to expand...

Very gently, holding the knife by the handle with your non dominant hand edge up, lightly rest the pads of three fingers on the edge, your thumb on the spine to precisely control pressure. Very gently rock your fingers back and forth along the edge using a very small movement. The amount of pressure needed to get the edge to catch enough on your pads that they stay put while your fingers rock is a measure of how sharp it is. You're not trying to slide the fingers along, you want the pads to "stick" to the edge. Done properly, the sharpest of knives can be safely tested this way. Murray Carter explains a bit further that if it feels sticky and can shave arm hair, an edge is considered "sharp". Not as sharp as it can get, but serviceable.

An edge can shave arm hair and even facial hair in some cases but not feel "sticky", usually the result of too much stropping, rounding the apex a bit.
 
The 3 finger test is tricky because you're basically cutting yourself, but only into the very first dermal layer. You can feel when it cuts this layer and almost feels like a tingly type of sensation. In my opinion, the test is basically if you can do this with such little pressure that you don't cut the skin underneath. You can see the same thing by putting the blade on the side of your index finger at an angle, and slicing into the skin a bit. You will actually be able to see where you're filleting underneath the dermal ridge and fingerprints and whatnot.

It doesn't sound very safe to do this, but you know, I've actually accidentally nicked myself trying to shave arm and leg hair than doing either of those finger tests. I think really it's just not that dangerous because the amounts of pressure you're using, the edge is never going to really sink in.

Basically, if you can put your finger on the edge with barely any pressure and get the edge to start cutting then it's sharp. I don't really find it that useful myself because I think it's a matter of experience how much you can actually gleam from doing such a thing, and often times an edge that isn't really all that sharp will feel just the same as one right off the hone to me. So I don't really find it that telling myself.
 
Well, I think you can tell a lot by touching the edge with your fingertips, but the real test is how does it cut. The comment about over-stropping is dead on, and goes along with my earlier statement that more obtuse angles won't feel that sharp. A kitchen knife at 15 degrees inclusive will feel way 'stickier' than a tactical folder at 50 degrees, even if both are sharpened perfectly. Overstropping will basically produce a very obtuse microbevel.

Okbow68, if this bothers you, try going back to your EF duosharp. Do as good a job as you can on that stone, then test the edge before stropping. Does it feel stickier? If so, then probably you are overstropping. Try using light pressure on the strop, dial back the angle just a bit, and only do a few strokes per side.
 
Different steels have different feels. Those with large carbides (relatively speaking), such as D2, S30V and VG-10 seem to have more 'bite'. These seem to cut better without stropping, as that tends to remove some of the micro-serrations. Steels with smaller carbides (S35vn, CPM-154, 420HC, SAK steel, and just about all high carbon steels) have a silkier or smoother feel and stropping seems to improve these edges.
 
For those of curious about the three finger test, here's an excerpt from his Blade Sharpening Fundamentals video in which he explains the technique:

[youtube]2k1o70tMHYM[/youtube]

edit: the one critique I would say about this video clip is that it doesn't demonstrate how little pressure you apply to a sharp blade. When he said, 'let me get a dull blade', the knife he started out with was dull; just not as bad as the second knife he demonstrated with. To me this gives the impression that the three finger test involves more movement along the primary edge, even on a knife that isn't 'a dull blade'. This is just my speculation.
 
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The three finger test is done the same way you use a thumb to feel a edge, its not special and has no advantage over any other way and actually if you read below you will find the ring finger is shared by two nerves so you could be getting mixed signals.




All of the nerves that travel to the hand and fingers begin together at the shoulder: the radial nerve, the median nerve, and the ulnar nerve. These nerves carry signals from the brain to the muscles that move the arm, hand, fingers, and thumb. The nerves also carry signals back to the brain about sensations such as touch, pain, and temperature.

The radial nerve runs along the thumb-side edge of the forearm. It wraps around the end of the radius bone toward the back of the hand. It gives sensation to the back of the hand from the thumb to the third finger. It also supplies the back of the thumb and just beyond the main knuckle of the back surface of the ring and middle fingers.

The median nerve travels through a tunnel within the wrist called the carpal tunnel . This nerve gives sensation to the thumb, index finger, long finger, and half of the ring finger. It also sends a nerve branch to control the thenar muscles of the thumb. The thenar muscles help move the thumb and let you touch the pad of the thumb to the tips each of each finger on the same hand, a motion called opposition.

The ulnar nerve travels through a separate tunnel, called Guyon's canal. This tunnel is formed by two carpal bones, the pisiform and hamate, and the ligament that connects them. After passing through the canal, the ulnar nerve branches out to supply feeling to the little finger and half the ring finger. Branches of this nerve also supply the small muscles in the palm and the muscle that pulls the thumb toward the palm.

The nerves that travel to the hand are subject to problems. Constant bending and straightening of the wrist and fingers can lead to irritation or pressure on the nerves within their tunnels and cause problems such as pain, numbness, and weakness in the hand, fingers, and thumb.
 
somber said:
For those of curious about the three finger test, here's an excerpt from his Blade Sharpening Fundamentals video in which he explains the technique:

[youtube]2k1o70tMHYM[/youtube]

edit: the one critique I would say about this video clip is that it doesn't demonstrate how little pressure you apply to a sharp blade. When he said, 'let me get a dull blade', the knife he started out with was dull; just not as bad as the second knife he demonstrated with. To me this gives the impression that the three finger test involves more movement along the primary edge, even on a knife that isn't 'a dull blade'. This is just my speculation.
Click to expand...

Thanks for the link - I need to rewatch my video...Some of my confusion comes from two reasons. First, when he's testing edges he just finished, seldom does one see any real movement along the edge - looks more like a very light wiggle 9edge is too sharp to allow any real movement). Second (and going under this assumption ) is if I can slide my fingers along an edge with anything but the absolute slightest of pressure, its a fail - if it catches on the pads immediately with slight contact, its a pass.

Even with my poor technique this has become my default quick test prior to any cutting and I do feel its quite informative. Rubbing my thumb pad across the edge tells me nothing anymore. I'll rub from spine to edge to feel for burrs, and a three finger test followed by some quick paper cutting to listen for pitch and felt resistance.
 
another thing to consider with the 3 finger test. our finger pads are not universally the same. i'm a pro cook, my finger regularly touches hot things, i have develloped calluses from this (plus scars etc) taht are so thick i can grab food on my plancha/pan without any pain. do you think this test will work the same on me and the average office guy ?

i don't, in fact i don't believe in this thing at all. the only thing it does for me is feeling nothing until i get cut to blood every single time i try
 
Test edge using news print: able to slice cut - it's sharp. Clean push cut - very sharp. If the edge is toothies (sub 2k then strop), you get an edge that bite/grab (thumb-test). For a super refined edge (0.5micron or narrower), you get tingling sensation (n/a for pwet and others with tough working hands). When avail, use sunlight -> edge -> 20x loupe -> eye reflection test, if virtually no reflection (mostly a grey/black line) -> awesome edge.
 
pwet said:
i'm a pro cook, my finger regularly touches hot things, i have develloped calluses from this (plus scars etc) taht are so thick i can grab food on my plancha/pan without any pain. do you think this test will work the same on me and the average office guy ?
Click to expand...

Considering Murray has hand forged over 17,000 knives and sharpened over 50,000 with his hands over the course of 24 years, yes, I would say that if it works for an ABS Mastersmith that it will work for a cook or an office guy, too. Otherwise wouldn't Murray get cut all the time? If this is how he measures all of the knives that he sharpens, why would he continually use a failed system for 24 years? A system that, from what you say, wouldn't allow you to detect a sharp edge, and if that edge is sharp, because of callouses, you will simply cut yourself.

It's a test that takes some skill and practice.
 
what i'm telling you is that i don't have much sensations on my fingertips, and there are other like me. so a test depending only on sensations on the fingertips is probably not the best for everyone. to be more precise when i cut myself doing this i barey feel it.

can you accept that something that works for you may not work for everyone ?
 
@robs I did go back to the duo EF and it definitely felt stickier. I think maybe I am rounding the edge a bit stropping not paying attention to the angle and lifting off the stop the correct way. However it may be that I till don't get that oh crap feeling with my edges. I should have explained I do know what that's feels like just not with my edges :grumpy::grumpy::grumpy:
 
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