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Thumb nail test question

The TNT is my physical check after a visual check for the bevel. As in the video I have the blade perpendicular to my nail and don't go anywhere near the "half moon" (it's scary enough higher up on the nail). And I never used the TNT during the progression. Only when checking for a set bevel.

With only the blade weight the edge will "grab" or "drag" and feel as it it were cutting through the nail and you are about to lose your thumb. Of course it isn't and you don't, but it sure feels like it at the time.

I've never felt it "vibrate" and it doesn't feel "smooth". There is "resistance", "drag", and the feeling of "cutting" as if the edge were parting the nail, though it isn't actually cutting. Honestly, it's hard to describe, but unmistakable when you feel it. I would guess that a "vibrating" or "smooth" TNT result would mean the bevel was not set consistently, or that you are performing the test differently than I do.
 
Interesting thread. I never imagined that the TNT was such an esoteric matter. It seemed pretty straight forward to me. I don't find the TNT scary at all, but then again, I don't make a full pass of the razor's edge across the thumbnail. Rather, I do it in short sections along the edge, starting from the heel and ending towards the toe. This let's me know, by the immediate grab or not, whether the edge has arrived or areas that need more work.
 
The full pass let's meet feel if the "grab" is consistent along the full length of the edge. The bevel must be set consistently along the full length to get a good shaving edge at the end of the progression which follows.
 
The TNT is my physical check after a visual check for the bevel. As in the video I have the blade perpendicular to my nail and don't go anywhere near the "half moon" (it's scary enough higher up on the nail). And I never used the TNT during the progression. Only when checking for a set bevel.

With only the blade weight the edge will "grab" or "drag" and feel as it it were cutting through the nail and you are about to lose your thumb. Of course it isn't and you don't, but it sure feels like it at the time.

I've never felt it "vibrate" and it doesn't feel "smooth". There is "resistance", "drag", and the feeling of "cutting" as if the edge were parting the nail, though it isn't actually cutting. Honestly, it's hard to describe, but unmistakable when you feel it. I would guess that a "vibrating" or "smooth" TNT result would mean the bevel was not set consistently, or that you are performing the test differently than I do.
Checking for a bevel would be more like place the razor at a 45 degree angle on your thumb nail and see if it grabs.
But checking for a damaged edge or a good edge on your thumb nail (shaveable edge) would be to place it straight down on your thumb (90 degrees) and drag it lightly over the side (so that the entire edge hits the nail), if you feel a bump in the edge then it means it's damaged, but a good refined edge feels smooth and slightly vibrates.
If an edge just slides towards the end of the nail at 45 degrees at the bevel stage, then it means indeed that the bevel has not been set.
 
My thumbnails actually feel a bit textured (not glassy smooth), so I worry I
might damage the edge if I tried this
 
Hair and fingernails are made of much of the same material, keratin. When you pull a dull razor overy your beard it does not cut, grab, shear, cleave, catch. Over your nail with a little practice you can recognize these same sensations. With a shavable razor drawn upon my fingernail, the sensation I get is "if I don't stop, it will cut right thru and draw blood". How easily do you get scared and back-of? Try it yourself, test your squeamish factor. Then you can judge for yourself. Shaving is the ultimate proof, but thumb nail test or the awkward pinky finger test, HHT test or tree trimming all will give you feedback as indicators for your mental library of what sharp really is, or how sharp is sharp enough.

Alex
Question, I tried the finger nail test on a new buck #110 knife. The knife slides right over the nail not grabbing anything. Just like a dull razor sliding across. The problem, this knife is razor sharp. According to the test, its dull as crap. Any comments please.
 
All tests are subjective, as is the term “razor sharp” when referring to a knife edge.

Look at the bevel, with magnification from the side and straight down on the edge.

What do you see?
 

rbscebu

Girls call me Makaluod
Question, I tried the finger nail test on a new buck #110 knife. The knife slides right over the nail not grabbing anything. Just like a dull razor sliding across. The problem, this knife is razor sharp. According to the test, its dull as crap. Any comments please.
Bevel angle at the edge may also have a lot to do with it. If you think that it is razor sharp, shave with it ATG on your face and see how you find it.
 
Question, I tried the finger nail test on a new buck #110 knife. The knife slides right over the nail not grabbing anything. Just like a dull razor sliding across. The problem, this knife is razor sharp. According to the test, its dull as crap. Any comments please.


Your q. here is actually a very good demonstration of how the thumbnail test works...

A sharp but extremely refined edge (like a razor after finishing) will glide on your nail more than a sharp but toothy edge (like a razor after bevel set). So in this way the refined edge can actually feel more like a totally blunt one. Whereas a perfectly set but non-refined bevel will never feel similar to being blunt using the nail test, cos the teeth will make it dig in and grip. That make sense...?

As @H Brad Boonshaft said - it's a highly subjective test, you need to do it a lot in order to dial in how things feel for you, on your your nail. But once you do it's also extremely accurate. I use it every time I sharpen anything... and I have the thumbnail to prove it!


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