So you think that's sharp...

[tosh]

I've seen numerous videos on youtube on so-called sharp blades.

But, they all seem to think if it cuts paper then it's sharp................

The edge of a piece of paper must show an enormous amount of resistence to any edged blade - implying anything that's remotely keen would possibly slice though.

I think it's time for a different approach?

I'd like to see a blade cut through a single piece of cotten thread hung from the air with no tension on the the thread it's self - just hung. The chosen blade is to cut upon contact in a VERY slow slicing motion - no flick of the wrist or simply slashing through the air.

Or we could be even more demanding.

How about cotton wool, again suspended with no tension applied. That would actually make for a VERY good test of sharpness - as any ragged edge no matter how small would simply snag the the fine fibres of the cotten wool and simply push it away as opposed to slicing through.

I've actually tried it tonight using a brand new razor blade - no luck, it simply pushed the cotten thread  away - but then, using a strong magnifying glass it's possible to see the ragged edge even on a brand new razor blade!!

Does anyone think it's possible - could an edge of steel be taken to such a microscopic level of sharpness??

Anybody care to rise to the challenge??

[Grant Lamontagne]

I'm no physicist, but I really don't think that's possible.  The only way you could possibly make it work is to use a downward angled cut with a very sharp knife moving very fast, but then that would get back to the tension issue.

This strikes me as one of those Kevon Costner Bodyguard type things, where he demonstrates how sharp the sword is bu dropping a sheer scarf on the blade and it cuts it.  Simply does not happen.  Anything that could be cut that easily simply would not be strong enough to survive in an open environment on the planet- and remember, thread may not seem like much, but for it's size it's quite sturdy- it has to be, as it's what holds out clothes together.

Paper is also surprisingly resistant, and the test isn't whether or not it can cut paper, but how cleanly.  Paper is fibrous- it's tiny strands of wood fiber going in all different directions stacked on top of eachother then heated and bonded together, similar to plywood.  When you tear paper you see lots of fibers, but when cut with a nice sharp blade, the edge of the paper should be very clean, and that is where the challenge lies.

Def

[Syph007]

For me its not just if it can cut paper, but if i can move the blade in tight curves while cleanly slicing.   Like cutting wavy spiral cuts.  At least that's what I always do to prove a SAK is sharp.  Most people also test against paper since odds are its easily at hand.

[tosh]

I'm no physicist, but I really don't think that's possible.  The only way you could possibly make it work is to use a downward angled cut with a very sharp knife moving very fast, but then that would get back to the tension issue.

This strikes me as one of those Kevon Costner Bodyguard type things, where he demonstrates how sharp the sword is bu dropping a sheer scarf on the blade and it cuts it.  Simply does not happen.  Anything that could be cut that easily simply would not be strong enough to survive in an open environment on the planet- and remember, thread may not seem like much, but for it's size it's quite sturdy- it has to be, as it's what holds out clothes together.

Paper is also surprisingly resistant, and the test isn't whether or not it can cut paper, but how cleanly.  Paper is fibrous- it's tiny strands of wood fiber going in all different directions stacked on top of eachother then heated and bonded together, similar to plywood.  When you tear paper you see lots of fibers, but when cut with a nice sharp blade, the edge of the paper should be very clean, and that is where the challenge lies.

Def

That is pretty much my own assumption, Def.

But I'm beginning to suspect the major problem is the bevel angle and wether the build up of steel to the secondary bevel actually creates a drag thus impeding the performance of the cutting edge. I'm thinking along the lines of a filleting knife but even thinner but gradually easing towards a stonger spine.

Basically, I'm  going to assume the secret is to do away with the secondary bevel, but to simply hone down the blade to an almost polished state...ouch   

[tosh]

Just found this:-

http://www.physicsforums.com/showthread.php?t=161956

http://en.wikipedia.org/wiki/Damascus_steel

Makes for interestin' reading.

[theonew]

I haven't played around with thread but this is one of my fine blonde hairs slivered twice while hanging solely under its own weight.



I consider that to be pretty sharp.

[Mike]

I'm no physicist, but I really don't think that's possible.  The only way you could possibly make it work is to use a downward angled cut with a very sharp knife moving very fast, but then that would get back to the tension issue.

This strikes me as one of those Kevon Costner Bodyguard type things, where he demonstrates how sharp the sword is bu dropping a sheer scarf on the blade and it cuts it.  Simply does not happen.  Anything that could be cut that easily simply would not be strong enough to survive in an open environment on the planet- and remember, thread may not seem like much, but for it's size it's quite sturdy- it has to be, as it's what holds out clothes together.

Paper is also surprisingly resistant, and the test isn't whether or not it can cut paper, but how cleanly.  Paper is fibrous- it's tiny strands of wood fiber going in all different directions stacked on top of eachother then heated and bonded together, similar to plywood.  When you tear paper you see lots of fibers, but when cut with a nice sharp blade, the edge of the paper should be very clean, and that is where the challenge lies.

Def

That is pretty much my own assumption, Def.

But I'm beginning to suspect the major problem is the bevel angle and wether the build up of steel to the secondary bevel actually creates a drag thus impeding the performance of the cutting edge. I'm thinking along the lines of a filleting knife but even thinner but gradually easing towards a stonger spine.

Basically, I'm  going to assume the secret is to do away with the secondary bevel, but to simply hone down the blade to an almost polished state...ouch   

Knocking that secondary bevel down a bit will keep your knife a nice slicer. That's the premise behind spyderco recommending use of the 30 degree angles every once in awhile. By knocking that shoulder down, it keeps the angle of the edge from becoming too obtuse. Now, you do need a certain amount of steel behind the edge to provide strength and keep the edge from rolling. This is best achieved by trial and error as it depends on the steel and heat treatment.

A very good book on sharpening is The Razor Edge Book of Sharpening by John Juranitch. Bear in mind that it's geared towards the sale of his products, but the principles are sound and easy to understand.

Knife edge grind reference link:
http://zknives.com/knives/articles/knifeedgetypes.shtml

Mike

[Grant Lamontagne]

I think they mostly just started cutting paper because their arms were bald.

Def

[Carlos]

That's no excuse, while they still have their legs available:

Faca da icel modificada

[Carlos]

But I agree that cutting general paper is a weak test. However cutting very soft paper is surprisingly a nice test, and not many blades can do it flawless. For instance, try to make one of those paper-cut tests on toilet paper instead: incredible hard.

[tosh]

But I agree that cutting general paper is a weak test. However cutting very soft paper is surprisingly a nice test, and not many blades can do it flawless. For instance, try to make one of those paper-cut tests on toilet paper instead: incredible hard.

I had actually considered the toilet paper test  - however, having once attempted to cut the stuff using a stanley blade - experiance now tells me it's almost impossible.

[OddFuture]

VR to knivesandstuff: Slicing Wet Paper Towel

What about a test like that.

[tosh]

VR to knivesandstuff: Slicing Wet Paper Towel

What about a test like that.

Hmm........Is that water on the Blade ?

Not entirely convinced that's authentic. Either the tissue was moistened or the blades were lubricated.

I could be wrong, but you can clearly see somethings running off the blade.

[OddFuture]

VR to knivesandstuff: Slicing Wet Paper Towel

What about a test like that.

Hmm........Is that water on the Blade ?

Not entirely convinced that's authentic. Either the tissue was moistened or the blades were lubricated.

I could be wrong, but you can clearly see somethings running off the blade.

Yes the paper towel was wet, so when you go to cut it. It want's to tear instead of cut, but if you get a clean cut then it's sharp.

[tosh]

VR to knivesandstuff: Slicing Wet Paper Towel

What about a test like that.

Hmm........Is that water on the Blade ?

Not entirely convinced that's authentic. Either the tissue was moistened or the blades were lubricated.

I could be wrong, but you can clearly see somethings running off the blade.

Yes the paper towel was wet, so when you go to cut it. It want's to tear instead of cut, but if you get a clean cut then it's sharp.

No denying those blades are sharp..ouch. much sharper than any I own.

But, surely water softens the fibres of the tissue.

Lets see those blades slice through cotten wool or as originally specified a single piece of  hanging thread.