Whittling Hair vs. Cutting Hair

AFAustin

AFAustin

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Which ranks higher on the sharpness scale: a blade that whittles hair or a blade that cuts a hair in two?

Let me specify. As to the former, I mean drawing an unsupported hair across a blade which whittles it, producing a "curly Q". As to the latter, I mean performing the same motion but the blade instead cuts the hair in two (or almost in two such that it falls to the side but is still barely attached).

If I am reading this explanation of the Hanging Hair Test right, it looks like the sharpest edge cuts rather than whittles: http://www.coticule.be/hanging-hair-test.html (BTW, as to HHT-1 "violin", does he mean when the hair sort of bounces along the knife edge but doesn't catch yet?)

I searched a bit on this forum for the answer, and the best I could come up with was an old thread where two members disagreed!

Any enlightenment would be appreciated, including a basic explanation of the physics involved.

Thanks,

Andrew
 
I can sharpen a knife just about as sharp possible, like your afraid to use it sharp. And to me the hair whittling and physics etc, is reading way to far into it.
 
Oh,I think he gets them sharp but with some of the techniques and different honing materials some of the folks on this forum use sharpness is taken to a higher level than those of us using say a fine India followed by stropping on leather.I and others like me benefit from those who seek the ultimate edge in the same way our everyday automobiles benefit from the racing teams efforts.
 
Most of the time, an edge that will cut an unsupported hair is capable of whittling also, but just isn't at the correct angle when the attempt is made, so it cuts all the way through. It's just like when you whittle a piece of wood. If you angle the blade too steeply into the wood it will grab and dig in too deep to whittle. The same thing happens with the hair except that it just severs rather than stopping the blade from going further in.

As far as the violin hht-1, yes, this means that the hair catches on the edge but then skips, catches again then skips, etc. The hair and the edge are normally positioned at nearly 90° to each other for this test, otherwise even an HHT-1 edge can sometimes cut the hair.

These HHT tests are most useful for judging whether a shaving edge is sufficiently refined on a straight razor. The test can be used for a knife also but isn't really all that practical or useful there as it is for an actual shaving blade. For me, if my knife is for slicing tasks I don't even worry about testing it after I am sure that the bevel was properly set. For lighter duty ultra-narrow angle and push-cut knives if the knife will tree-top arm hair I call it done.
 
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I think that HHT's are useful as a test of sharpening skill.

If you can get that sharp, then you can get an edge good enough for whatever edc purpose you'll need.

Its just a matter of forming the apex well and knocking off the burr.

If you can't do it, you're probably not as good as you think you are.
 
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I have tried a bunch of times to get pics of split fingerprint whorls at 40x, but the subject is way too squirmy...
 
Theres different types of whittling as well , just splitting a hair and then stopping before passing all the way through is not all that difficult. Doing something like this where you can re whittle the same section of hair several times before running out of hair thickness to whittle is much more difficult



When its that sharp then the angle that you attack the hair from makes the difference , cutting it 90* to the strand (like cutting rope) causes it to fall off , just like a good HHT , getting it perpendicular and you can make little curls all day...
 
Sadden said:
Theres different types of whittling as well , just splitting a hair and then stopping before passing all the way through is not all that difficult. Doing something like this where you can re whittle the same section of hair several times before running out of hair thickness to whittle is much more difficult

When its that sharp then the angle that you attack the hair from makes the difference , cutting it 90* to the strand (like cutting rope) causes it to fall off , just like a good HHT , getting it perpendicular and you can make little curls all day...
Click to expand...

Agreed.
 
Thanks for the comments, gentlemen.

Sadden, this part has me confused:

Sadden said:
cutting it 90* to the strand (like cutting rope) causes it to fall off , just like a good HHT , getting it perpendicular and you can make little curls all day...
Click to expand...

Geometry is not my strong suit but I think a 90 degree angle is the same thing as perpendicular...?

Andrew
 
AFAustin said:
Thanks for the comments, gentlemen.

Sadden, this part has me confused:



Geometry is not my strong suit but I think a 90 degree angle is the same thing as perpendicular...?

Andrew
Click to expand...

And English is not my strong suit :) Poor wording on my part , you are correct. 90 = Perpendicular in this context (The hair and the edge of the edge making a "T" Shape). The correct word for what I was trying to say is 'laterally".

Corrected:

When its that sharp then the angle that you attack the hair from makes the difference , cutting it 90* to the strand (like cutting rope) causes it to fall off , just like a good HHT. Whittle it laterally and you can make little curls all day...
 
Sadden, thanks for the clarification. Nice curly Qs, BTW.

So far the consensus seems to be that whittling a hair demonstrates approximately the same degree of sharpness as cutting a hair, with the different results simply caused by different cutting angles.

My experience, though, makes me wonder in that I use about the same angle of approach and yet sometimes I whittle, more often I cut (and a lot of the time I don't do either :o).

Andrew
 
Andrew, it might have to do with apex final inclusive angle. A 40* is rather hopeless in whittling if the blade-hair is angled at say 30*. Same blade-hair attack angle with 20* inclusive apex will whittle easier, if you follow Sadden's lateral explanation.
 
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