What makes a blade sing?

S

Sparljo

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Oct 20, 2006
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What is it that makes some blades ring when they are used or sharpened?

I have only experienced this with two knives in the past, and I am curious as to what exactly causes it. Is it a matter of thickness of stock combined with length? Are there other factors at play?
 
In my limited experience, it seems the thinner blades have more of a ring to them. Probably easier for a thinner gauge of steel to vibrate during use/sharpening and produce sound. My ulu is the most "musical" piece in my collection, with a nice "schwing!" sound during sharpening or steeling with a chakma.
 
I have never heard a blade sing, myself, but I would have to guess that whatever you are using the knife for is exciting the natural frequency of the blade. Thinner blades would probably be "Whippy-er", and thus have a lower natural frequency that is more likely to be within the human hearing range.

~$.02
 
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My hollow ground Loveless has the ring, so the taper might have some influence on the harmonics of the blade.
 
I've had a couple of knives in the past that displayed that fascinating characteristic. It had me wondering too for a long time. I'd put it away until now.
Thanks. Now I'll be awake all night again pondering this.:p

If anyone has an answer to this, please save me from insomnia.:o
 
Remember that sound is just a bunch of vibrations in the air at the correct frequency to be interpreted by our ears. To make a ringing noise you want the blade to vibrate as long as possible. Different shapes will presumably give you different tones, longer and thinner is usually better.
I can get my swords to make some pretty sweet sounds, but never had much luck with knives.
 
My SG2 bladed Kershaw JYD sounds like a tuning fork when you run your thumb lightly across it. I love the sound. Probably how thin the edge of the edge is--harmonically vibrates or something.
 
Actually any knife without a lot of damping acting on the blade (e.g., from soft scales, loose pivot, or a muggy hand gripping too tight) should be able to sing at some frequency---wherever its natural frequencies happen to be. I imagine a bigger factor is the frequency that you are exciting it at, i.e., making it vibrate. If you are sharpening then the knife will be receiving an excitation over a range of frequencies, with the range depending on factors such as velocity of stroke, coarseness of surface, and where you are gripping the handle and how hard. When you are hearing your blade sing after a sharpening stroke, then I would imagine you have just the right knife blade on just the right surface in a good grip...and it sings! Some factors are much more important than others, but I bet you could kill the singing by gripping it hard in a different place, such as halfway down the blade. Experiment, especially with a very light grip at just the right place, and you may just make it hit a high-C. Incidentally, its the exact same concept (I imagine) as a singing wine-glass..

Of course, it may just be excited :p

(PS - I hope someone totally planes me on this and invalidates my last 6 years of working on a PhD in structural dynamics... no seriously..)
 
if it's anything like wine glasses, would how clean the blade is have an effect?
making wine glasses sing is fun.
 
I have an RTAK (1095) that had no noticeable sound qualities until I stripped the coating, cut the clip to an edge and made other modifications and now it has a sweet "ring" to it even when just removing it from the sheath. I would guess the coating was suppressing this quality. I have a Fixed Blade in D2 that also rings.
 
Im glad you guys have experienced this with certain blades as well.

Ive noticed that by pinching an unfinished blade at the balance point and flicking it, it will ring long and clear. (No hande)

Im interested in what contributes to blade ring post handle.... ie - what is making it ring in use.

Both of the blades I have heard this on were handled with cutlers rivets.... no glue involved. One has a 10 inch blade, the other 15. Both are fairly thin, they appear to be ~1/8 inch stock.

I only have one of the two in hand, and it has no plunge cut or real ricasso. I cannot remember if the other did or not (15 inch tram machete)

Id really like to be able to duplicate this behaviour in a camp knife. It might not be useful, but I sure do like it.
 
My Shun santoku makes a pleasant resonant sound when I run my finger along the blade. As others have said may be the thinness of the blade is a factor.
 
I should add to my initial post that the blade shape and stiffness (material property of the metal) are the most important factors, followed by how much damping is present both in the system (especially the handle) and in how it is held (boundary conditions in technical speak). To get a sweet ring the blade will have to be shaped such that it has low natural frequencies, or resonant frequencies, well defined in a frequency range that sounds sweet. It then needs to have low enough damping that it will continue to vibrate like a bell. HOWEVER, none of this matters much if you can't find a way to make the thing vibrate at those sweet resonant frequencies. That is why you'd probably find that it rings sweet after contact with certain materials,e.g. its sheath or a certain stone, while not so much with others, e.g. you pant leg. Higher frequency vibrations tend to damp out much faster even if the damping is low, so short and fat blades will probably not ring as sweet or as long, since their resonant frequencies are higher.

Btw, pinching the knife at the balance point helps because that point probably coincides with the first resonant frequency nodal point, which is a point that doesn't move when the knife vibrates at that frequency. By holding it there you greatly decrease the effective damping that your hand introduces, allowing it to vibrate for longer. :thumbup::thumbup:
 
Interestingly, my father-in-law has a short-and-thick bladed skinner with a large handle that I sharpened for him, and it sang no matter what I tapped it with, and no matter where I held it, other than the blade. Can't remember the brand, but it was a heavy beast for it's size.
 
My old Collins machete sings when drawn from the sheath and when cutting vegetation.
 
^^ Yeah, machetes make awesome ringing sounds. In my experience, the longer and thinner the blade, the more it rings. Condors have holes cut in the blades that supposedly cause them to ring a certain way when you're hitting properly.
 
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