What's the sharpest knife on earth?

  • #1

Main Question or Discussion Point

I was thinking about the principle of energy density and how sharp knives cut so easily because their surface areas are tiny and thus any force applied to them is imparted on this tiny area.

So my question arises, does anyone know just how sharp the sharpest knife/ sword is? Lets no discuss microscopic knives, but rather macroscopic cutting instruments such as samurai swords. I would make a wild guess at a surface width of 10 microns, am I crazy?

** Mod note: there are now modern nanoblade surgical knives that cost hundreds of thousands of dollars.
 
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Answers and Replies

  • #2
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laser knife count?
 
  • #3
nope. no lasers.
 
  • #4
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I've heard a titanium alloy knife that is the sharpest. It's very hard. But if that's the case, a diamond knife should be number one.
 
  • #5
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As mentioned, a diamond knife should be number one. And I'm sure you can get pretty freaking sharp, but at the expense of the knife's durability. Sharper knives tend to be more brittle.
 
  • #6
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Maybe this is what you're looking for:

http://en.wikipedia.org/wiki/Damascus_steel" [Broken]

Microns? Pff. Think nanometers =D Who knew we actually managed to produce and use nanomaterials 1000 years ago? They still aren't sure if its properties can be attributed to the nanotubes, but still, that seems to be very sharp for a weapon.
 
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  • #7
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Maybe this is what you're looking for:

http://en.wikipedia.org/wiki/Damascus_steel" [Broken]

Microns? Pff. Think nanometers =D Who knew we actually managed to produce and use nanomaterials 1000 years ago? They still aren't sure if its properties can be attributed to the nanotubes, but still, that seems to be very sharp for a weapon.
Wikipedia saves the day yet again. :approve:
 
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  • #8
Danger
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It's hard to believe but the sharpest knives that have ever been used in recent years were mounted with stone flakes made of obsidian. A company called Aztecnics was manufacturing and selling surgical scalpels mounted with different sizes and shapes of obsidian blades. Good quality obsidian fractures down to single molecules which can produce a cutting edge 500 times sharper than the sharpest steel scalpel blade ("American Medical News", Nov. 2, 1984:21). On the cellular level an obsidian knife can cut between cells rather than tear the cells as a steel knife will do. A sharper cut will allow a wound to heal more rapidly with less scarring. High magnification of a steel scalpel blade edge looks like a serrated saw blade but an obsidian edge looks smooth.
I'm not sure of the accuracy, but the guy certainly seems to know his stuff.
http://lithiccastinglab.com/gallery-pages/2001julykanzichimp.htm" [Broken]
 
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  • #9
Thanks guys, most interesting posts.
 
  • #10
Synthetic diamond scalpel blades are commercially available and well liked by surgeons. Contrary to what you might think they stay sharp much better than steel and chipping doesnt seem to be a problem. Quoted sharpness is 3 nm and achieved with plasma polishing. This is like 30 atoms wide at 1 angstrom per atom.

Outside diamond, cracked glass edges have been used for years as ultramicrotome blades for cutting sections as thin as 200angstroms for electronmicroscopy. These would be similar sharpness to the obsidian blades quoted above by Danger. However the glass blades can cut less than 100 sections before geting blunt even on soft tissue. cutting bone is not possible. 40 yrs ago there were expensive diamond blades available that lasted well and would cut bone ok, but the glass ones were sharper and would cut the thinnest sections. The latest diamond blades are obviously sharper than glass if the 3 nm is correct.
 
  • #11
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I saw something on Discovery channel where eye surgeons are using flint (obsidion)blades because they are sharper then any steel.
 
  • #12
Synthetic diamond scalpel blades are commercially available and well liked by surgeons. Contrary to what you might think they stay sharp much better than steel and chipping doesnt seem to be a problem. Quoted sharpness is 3 nm and achieved with plasma polishing. This is like 30 atoms wide at 1 angstrom per atom.

Outside diamond, cracked glass edges have been used for years as ultramicrotome blades for cutting sections as thin as 200angstroms for electronmicroscopy. These would be similar sharpness to the obsidian blades quoted above by Danger. However the glass blades can cut less than 100 sections before geting blunt even on soft tissue. cutting bone is not possible. 40 yrs ago there were expensive diamond blades available that lasted well and would cut bone ok, but the glass ones were sharper and would cut the thinnest sections. The latest diamond blades are obviously sharper than glass if the 3 nm is correct.
Very nice post. 3nm is very impressive.
 
  • #13
Obsidian Is one of the sharpest things there is.......it can be up to 5 times sharper than steel.....An Obsidian blade can reach almost molecular thickness
 
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  • #14
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sharpest Knife

I'd say Wootz should be pretty close.

Diamond of course but you'd need to need to find a big enough diamond.

My guess is a carbon nanotube edge might be worth a try.

I wonder which non-steel superalloy might be as sharp or sharper than wootz while being possible to actually make (forge, grind or laser cut...) and not too brittle.
 
  • #15
stewartcs
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Come on guys, eveyone knows the http://en.wikipedia.org/wiki/Ginsu_knife" [Broken] is the sharpest! :rofl:
 
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  • #16
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When talking about the sharpness measured in atomic widths, you have to look at the molecular structure.

Diamonds are cubic. This means two things
1. They have distinct 90 degree cleavage (look it up if you think breasts. Check out the geology related cleavage article if you want to know more) in all 3 dimensions. This means that the edge will be flat because a large number of layers will just slog off of the cutting edge.(if you have a big diamond in your/your spouse's ring, you will want to be careful not to knock it on anything hard. It's easier to break in two than a piece of glass the same size. If the atoms are jolted just slightly out of place, the atomic repulsion will do the rest and your diamond will cleave.)

2. The two sides of the blade will always want to be 90 degrees from each other, but you may be able to grind it down to around 45. The repulsion of each carbon atom to each next will keep you from getting a stable edge.

Obsidian is a glass. Glasses being amorphous, do not have any cleavage so easy to shatter along. It does however have conchoidal cleavage, though its comparatively weak.
This actually works to a glass knifes advantage. If you take some obsidian and knap off two sides, you can get the two sides to be around 33 degrees or even less depending on how fast the glass cooled and what minerals it is made up of. The concoidal cleavage means a smooth cutting surface, and the amorphous, but bonded structure, means that you can get down to a molecule thick. These blades are actually MORE durable AND SHARPER than a diamond blade. Try it. Break a peace of glass and see how easy it is for that glass to cut you. Some man made glass is specifically designed NOT to have these edges, so get a non shatter proof glass. Im not liable when you get cut or worse, you were warned.

Obsidian, specifically, has been used for a very long time in the medical profession and was the prized tip for spears. We have had the sharpest knives on earth since before we could write. Now days they are used in ocular surgeries when lasers are not available. As far as the famed diamond blades are concerned, its their HARDNESS (mineralogical term. look up Mohs hardness scale) that gives them their notoriety. If your mineral is harder on Mohs scale than mine, you can cut mine. If mine is harder, your just going to blunt your edge. Now days, we harvest non jewler grade diamonds and artificial diamonds to COAT blades with. To cut glass, jewels or just anything you want a precise cut on, you use diamond because it will keep its edge the longest, seeing as its the hardest. There's also nothing it cant cut, while glass which can be sharper, is only a 5.5 on this scale to 10 (diamond). Glass will loose its edge on about anything.

It'd make a wicked blade till you hit something other than flesh though!
 
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  • #17
turbo
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I learned how to knap obsidian blades from an instruction set and some materials and basic tools gotten from an anthropologist. The flakes are incredibly sharp. He sold flakes to a company that mounted them in autoclave-able SS handles. Those scalpels were very popular with plastic surgeons. They cut cells rather than tear them like metal blades can do, so there was a lot less scarring and swelling, and shorter recovery-times. All very good things when you are cutting up movie stars and millionaires for a living.

Edit: Necroposting can be fun!
 
  • #18
mgb_phys
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People doing dissections on insects used to make their own blades by snapping a steel wire in a flame, but it had to be old fashioned town-gas (CO) it doesn't work with methane.

You can make tips for scanning electron microscopes by just cutting a brittle wire.
 
  • #19
I learned how to knap obsidian blades from an instruction set and some materials and basic tools gotten from an anthropologist. The flakes are incredibly sharp. He sold flakes to a company that mounted them in autoclave-able SS handles. Those scalpels were very popular with plastic surgeons. They cut cells rather than tear them like metal blades can do, so there was a lot less scarring and swelling, and shorter recovery-times. All very good things when you are cutting up movie stars and millionaires for a living.

Edit: Necroposting can be fun!
That is very interesting turbo. One can even cut a single cell in two, and cleanly!
 
  • #20
Come on guys, eveyone knows the http://en.wikipedia.org/wiki/Ginsu_knife" [Broken] is the sharpest! :rofl:
:) funnyyyyyyyyyyyyyyy and trueeeeeeeeeee.
 
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  • #21
Can't they use aggregated diamond for the blades? I'm pretty damn sure that they will literally SEVER the crap out of any blade, more than the floppy damascus steel.
 
  • #22
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this site is super informative and scientific in its approach, event to the level of steal analsis graph, and why some steals have there place while other's have other places, by the way this is my first post :D

http://zknives.com/knives/articles/knifesteelfaq.shtml
 
  • #23
I have found through personal experience that hand forged, folded carbon steel blades are superior in longevity and "staying power"

The "sharpest" knife would be the one that is sharpened to the finest edge/point, But once you get anything past razor "sharp-ness" you begin to lose strength in the blades fabric and layers.

The `sharper you grind a blade or cut a blade edge the more Brittle it becomes, Using dense tough metals like tungsten is a bad idea, this metal is not good to work with on the Anvil, it also chips alot and fractures. A combination of soft metals and hard metals is needed to produce a "perfect" blade, you need shock absorbance and a hard edge that can also become flexible when tension is applied to prevent breakage.

Research into the Art of Sword "Smithing", they have it down to a science and have since fuedal japanese era. Diamond edge cutting tools have been around for a long time though obviously.


Regards.
 
  • #24
SteamKing
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That's easy. The sharpest knife on earth is Occam's Razor.
 
  • #25
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Hello there,

In my biophysics research days at UC Berkeley, I was trained to use a transmission electron microscope and to prepare biological specimens for that technique. The ultramicrotome is the thinnest sectioning instrument that I have used, producing ultrathin sections of epoxy-embedded cellular microstructures that are only a few molecules thick. It can cut even down to a single molecule thick though that was too thin for our purposes. It used either commercially produced diamond knives which lasted a long time but were horrendously expensive or we could prepare our own glass knives with a special tool used to break thick glass pieces in a predetermined way. Those edges were actually the sharpest that could be made but would have a limited lifespan before needing replacement. My answer to you is that glass actually fractures conchoidally into the sharpest edges around.
 
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