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TOPIC: What is "Sharp"

What is "Sharp" 4 months 2 weeks ago #16490

  • EamonMcGowan
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I think in the end, what is sharp, will have to be defined by the end user? When Clay made the sharp edge tester I made one at the same time. We both where running the same test on different edges.
As memory serves me we both came up with a 800 diamond stropped by 14/10 balsa gave the sharpest cut. The problem we found was the test only push cut and the medium to keep it standardized is 3m scotch tape.
Unfortunately the scale does not give real world data? It boiled down to the most "tooth" you can put on the edge is the best push cut.
A 10K chosera edge will not push cut as well as 10um balsa stop. So we are right back to where we started from. You can shave with a 10K chosera, but you can not cut tomatoes, bell peppers, ect. Take the same blade sharpen to 800 diamond, strop with 14/10um and it will cut through the veggies like there not even there!
So the answer in my opinion is the standard answer that Ken Schwartz or Tom Blodgett will tell you "it depends?"
If a list of the best knife sharpeners exist? I think you are going to find Ken Schwartz name in the top ten living knife sharpeners. He has answered with Tom on this forum many a time with " it depends?"
Maybe we will get lucky and the both of them will see this thread and chime in? I will send PM's to both and ask that they might add there .02?
The definition of insanity is to do the same thing over and over again and expect a different result?
An old Irish toast, May the wind always be at your back, may you always have work and may you be in heaven a half hour before the devil knows your dead. Cheers!
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What is "Sharp" 4 months 2 weeks ago #16492

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All this talk about sharping!!! Time to hit the WE and time to experiment!! Thanks again gentlemen !!
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What is "Sharp" 4 months 1 week ago #16509

  • wickededge
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Great topic, great comments! I think the ultimate definition for sharp begins with edge thickness because effective cutting starts with rupturing the surface of a material. A thinner blade means more concentrated force at the point of contact. There is a physical limit as to how thin an edge can be with steel. I believe it is around .4 microns when the steel has a very fine grain structure. Steels with larger grains cannot reach such a narrow edge thickness. Glass and obsidian can be fractured to much thinner widths. Having micro-teeth is another way to concentrate force at the point of contact such that the knife can still initiate a surface rupture even when it has a larger edge width. Once the surface has been ruptured, other factors like blade geometry come into play. As LeoNav points out, a thick blade with wide shoulders will quickly bog down inside of a cut, creating friction and requiring more force to keep cutting. Thinning and rounding the shoulders helps. I've noticed that I can get a knife with a super polished edge to do quite well with tomatoes and such as long as the blade is thin and I've sharpened the cutting bevel to a pretty low angle. My thicker blades don't do as well with a higher polish - they slide right off of zip ties and tomato skins. Thin knives that are highly polished can start a nice cut into a zip tie but don't have the strength to cut all the way through without significant edge damage.
--Clay Allison
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What is "Sharp" 4 months 1 week ago #16511

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That clarifies some questions one that I am not totally clear on is is a toothy blade more suitable for softer steels like European knives where as harder steels are possible likely to chip ; then also a polished edge on soft steel is possible more likely to roll would I be correct in this assumption?
I read and have refined most of my Japanese chef knives to 3-5K but as Eamon points out a western chef knife will be perceived as wickedly sharp at 600-800 grit.
My best Japanese chef knife an Honyaki Nakira is refined to 16K and slices well .
The deeper we go the more confusing it is .
Then it also struck me is to have a polished bevel with a more toothy bevel so I had a play on some cheap knives and combined a flat bevel asymmetric with a convex more polished bevel the results you can see below I need to play around a bit more and maybe polish the convex side a little more it is polished at the edge since the convex was steeper at the edge and polished that with 5K the other side is 1K
IMG_1700.jpg

it seems to cut quite well but I have just done it quickly.
IMG_1699_2014-03-10.jpg


ScreenShot2014-03-10at20.06.04.png
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Last Edit: 4 months 1 week ago by LeoBarr.
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What is "Sharp" 4 months 1 week ago #16513

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wickededge wrote:
Great topic, great comments! I think the ultimate definition for sharp begins with edge thickness because effective cutting starts with rupturing the surface of a material. A thinner blade means more concentrated force at the point of contact. There is a physical limit as to how thin an edge can be with steel. I believe it is around .4 microns when the steel has a very fine grain structure. Steels with larger grains cannot reach such a narrow edge thickness. Glass and obsidian can be fractured to much thinner widths. Having micro-teeth is another way to concentrate force at the point of contact such that the knife can still initiate a surface rupture even when it has a larger edge width. Once the surface has been ruptured, other factors like blade geometry come into play. As LeoNav points out, a thick blade with wide shoulders will quickly bog down inside of a cut, creating friction and requiring more force to keep cutting. Thinning and rounding the shoulders helps. I've noticed that I can get a knife with a super polished edge to do quite well with tomatoes and such as long as the blade is thin and I've sharpened the cutting bevel to a pretty low angle. My thicker blades don't do as well with a higher polish - they slide right off of zip ties and tomato skins. Thin knives that are highly polished can start a nice cut into a zip tie but don't have the strength to cut all the way through without significant edge damage.

Clay, You are the Master!! :woohoo:
The definition of insanity is to do the same thing over and over again and expect a different result?
An old Irish toast, May the wind always be at your back, may you always have work and may you be in heaven a half hour before the devil knows your dead. Cheers!
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What is "Sharp" 4 months 1 week ago #16523

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I am not a metallurgist and there is an awful lot of technical material to read on the subject; but for instance if I shear a piece of steel would I be correct in the assumption that the bigger the grain- crystalline structure the lower the quality of the steel ?

If this a correct assumption then I see why if the blade on a cheap steel is over refined the edge will soon be lost and a toothy edge with big grains will wear better since the grains breaking away will suit that toothy edge.
A superior steel will support a more refined edge since if pieces brake off the edge they will be so much finer that the edge will endure a not flatten or round as with a cheap knife.

If someone knows more about this I would love to know and I could be wrong in my current understanding perhaps Clay or Anthony could clarify this I am trying to understand the suitable grits for different steels for knives that are used for general purpose in the kitchen or even EDC.
As said in a previous posting I said my forged Honyaki Nakira seems to work well with maximum edge refinement .
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Re:Re: What is "Sharp" 4 months 1 week ago #16531

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Here's an example of edge geometry from my recent experience. I just thinned down several blades for a home chef... They should perform much better now! It went from around .040" thick to about .010". Even though you can't really see the bevel in the last pic :-)









Josh
Last Edit: 4 months 1 week ago by razoredgeknives.
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Re:Re: What is "Sharp" 4 months 1 week ago #16541

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razoredgeknives wrote:
.....It went from around .040" thick to about .010". .....

Josh

Very nice.

Just wondering.... do you (and others?) put the micrometer on every blade?
~~~~

For Now,

Gib

Φ

"Things work out best for those who make the best out of the way things work out."

"My goal is to be a good, practical knife sharpener. My dream is to polish molecules."
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Re:Re: What is "Sharp" 4 months 1 week ago #16542

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They should work beautifully for slicing not on crusty bread though they could roll on that .
What make is the western handled Japanese parer ?
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Re:Re: What is "Sharp" 4 months 1 week ago #16544

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I think the important instruments are the mark1 eye ball and the fingers just pinch a blade near the edge to tell what it is good for or whether it needs thinning I imagine Josh has given these measurements to pre-empt the questions that many would like to know.
I firmly believe that it is important to rely on touch and sight as much as possible the more it is used the more useful it becomes I find even with lines or nuts & bolts the more I estimate them the less time is needed and the better the estimation becomes.
Even looking at bevels can be reasonable accurate at least to be able to say if it is
10,15 or a little under 20˚ or under 10˚.
I do of course set bevels on the WE using the Angle cube but it is handy to be able to judge the bevels by sight.
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