Knife sharpening-how fine?

[Porthos]

Frrom: http://forums.egullet.org/topic/26036-knife-maintenance-and-sharpening/

 

John Juranitch in his book “The Razor Edge Book of Sharpening” is emphatic that a polished edge is the answer, that micro-serrations are indicative of a dull knife. His experience comes from sharpening knives for the meat processing industry. Meat cutters go through knives faster than tissues in flu season, so Juranitch’s conclusions are hard to dispute.

However, Joe Talmadge, author of the Bladeforums “Sharpening FAQ;” Cliff Stamp, physicist and knife nut; Leonard Lee, president of Lee Valley Tools and author of “The Complete Guide to Sharpening;” and many others have come to the opposite conclusion: that micro-serrations, in the right context, can be a very good thing.

 

We are not alone in this debate over what makes for the best edge.

[dcarch]

"--"dished" stones - yup, they will not maintain a consistent angle. "

 

​I am not sure I understand. If you hold the knife at a consistent angle while sharpening, you will always end up with a consistent angle on the edge, regardless of the shape of the stone.

 

dcarch

 

 

 

 

[dcarch]

"----and many others have come to the opposite conclusion: that micro-serrations, in the right context, can be a very good thing.---"

 

I am surprised that no one talks about what kind of steel. With very brittle high Rockwell hardened steel, the broken edges can be as sharp as broken glass, which is one of the sharpest edges known.

 

dcarch 

Edited October 26, 2014 by dcarch (log)

[NEPolarbear]

"--"dished" stones - yup, they will not maintain a consistent angle. "

 

​I am not sure I understand. If you hold the knife at a consistent angle while sharpening, you will always end up with a consistent angle on the edge, regardless of the shape of the stone.

 

dcarch

 

It may take more work / time to keep that consistent angle even if the edge has contact with the stone..

 

 

[Porthos]

The tutorial I linked to above does discuss steel types. FYI: I found eGullet when I searched the Web for knife-sharpening info and found the tutorial.

[AlaMoi]

"--"dished" stones - yup, they will not maintain a consistent angle. "

 

​I am not sure I understand. If you hold the knife at a consistent angle while sharpening, you will always end up with a consistent angle on the edge, regardless of the shape of the stone.

 

dcarch

 

 

see your post

"2. Besides, if you look at the geometry, a highly curved stone will give you almost imperceptible angle change on the knife's edges."

and diagrams.

 

remember that for "jig" / mechanical approaches such as the EdgePro, the angle of the knife and the angle of the _back_ of the stone _do not change_

 

a knife moving parallel to the back/mounting plane of the stone will see a different "edge angle" depending on the degree of dish.

 

hand sharpeners spend hours "flattening" their stones to avoid this problem. 

hand sharpeners do not change the angle they hold the knife based on the degree of dish in the stone.

 

...."imperceptible"....

see: degree of knife nutiness.

[Hassouni]

I want just enough tooth for tomatoes to be a breeze.

 

 

Contrary to popular belief, a serrated or toothy knife is not better on tomatoes than a sharp one, but it is better than a dull knife.

 

Tomatoes are mindlessly easy to cut with a well sharpened knife.

 

Do you want to slice/draw cut or do straight up and down push cuts? I recently got a fairly new secondhand White #1 gyutou, which was sharpened prior to my receipt of it. It is a slicing DEMON, but it's not quite as good on a push cut, which to me implies the edge is still toothy. If you want to do up and down chopping, I'd recommend a highly polished edge, but for slicing, drawing or thrust-cutting, toothy works great.

 

Murray Carter sharpens on 1000 and merely strops on a 6000, and then again on newspaper. He does not sharpen (as in, back and forth) on the 6000. I suppose it gives tooth but polishes the teeth? On the other hand, it seems most sharpening enthusiasts would typically sharpen on the 6k or equivalent medium-high grit stone (say, 4k-6k), at least for a knife made of Japanese steel.

[dcarch]

see your post

"2. Besides, if you look at the geometry, a highly curved stone will give you almost imperceptible angle change on the knife's edges."

and diagrams.

 

remember that for "jig" / mechanical approaches such as the EdgePro, the angle of the knife and the angle of the _back_ of the stone _do not change_

 

a knife moving parallel to the back/mounting plane of the stone will see a different "edge angle" depending on the degree of dish.

 

hand sharpeners spend hours "flattening" their stones to avoid this problem. 

hand sharpeners do not change the angle they hold the knife based on the degree of dish in the stone.

 

...."imperceptible"....

see: degree of knife nutiness.

 

My point is not to compare hand sharpening with mechanical sharpening. My point is that I don't understand why spending hours to flatten a stone when a dish shaped stone can do no harm.

 

Hand sharpeners do change the angles they hold the knife based on that particular knife's edge angles. 

 

I suppose you can use the Sharpie method to determine the desired angle for that particular knife, then hold that angle when you grind, the dished stone should not be a problem to give you the desired sharpness, unless the very slight convex edge is not what you want.

 

dcarch

[AlaMoi]

hand sharpeners do not change the angle blade to stone based on where they are in "the dip" - 

 because they remove the dip/dish.

 

as the blade in your sketch moves right to left, it will contact the stone first at the trailing edge, then toward the left at the leading edge - effectively blunting the cutting edge angle.

 

now, for very shallow dishing does it matter?  well, for the knife types running into 20000 grit water stones followed by micron paste polishing on a glass block, yes.

[dcarch]

hand sharpeners do not change the angle blade to stone based on where they are in "the dip" - 

 because they remove the dip/dish.

 

as the blade in your sketch moves right to left, it will contact the stone first at the trailing edge, then toward the left at the leading edge - effectively blunting the cutting edge angle.

 

now, for very shallow dishing does it matter?  well, for the knife types running into 20000 grit water stones followed by micron paste polishing on a glass block, yes.

 

Let me see if I can be more clear, using a stone which is not flat:

 

Once the sharpener determines the desired angle for a knife, on the curved stone, lets say using the Sharpie method, he keeps the knife at that angle and starts to sharpen. Left-to-right, right-to-left, doesn't matter where the knife is on the dished stone, the only possible shape for the knife's edge to take is to conform to the profile of the stone, which will be a slightly convex edge. It has nothing to do with how fine or coarse the stone is.

 

Sharpening knives on a curved surface is done all the time on a belt sander, and to a lesser degree on a strop. Quality sharpening stone is very expensive, why waste a good part of it away by grinding it flat?

 

dcarch

[daveb]

Quite a tangent from the original question.

 

I freehand sharpen, mostly Japanese knives, some Germans.  I fllatten by putting pencil marks across the face of the stone then use a flattening stone to remove the pencil.  The face will then be flat on that plane.  It may not be flat relative to the base of the stone but that's ok.  I find that doing so prior to a sharpening session also gives me a little slurry to start with.

 

Sharpening on a dished stone is no good for thinning, no good for complex bevels, no good for the edge.  Other than that it's ok.  To the "wasting stone" argument I'll offer that the stones that dish the most are at the coarse end of the spectrum.  And the cheap end of the spectrum.   A Bestor 500 or Gesshin 400 or JNS 300 (my fav) will last several years with frequent use and regular flattening and cost less than 100 bucks.  Higher grit stones are used less and dish less.  "Waste" becomes noise.

 

To the OP's question the "how high" depends on knife hardness, steel, type of blade and other considerations.  For a mirror finish on a stainless (VG-10, AUS-8, AEBL, etc) Gyuto or Petty  I usually finish on a Suehiro Rika 5K.  3K to 6K  is a good balance of tooth and polish.   I also finish my Germans here but know the edge won't hold very long due to the softer steel.  The Rika are commonly available, one source is linked below.  Depending on your preferences you may want to take a Suji or Yani to an 8K+ finish, most stones in this range will leave a haze or mist finish at the edge.

 

http://www.japaneseknifesharpeningstore.com/Suehiro-Rika-5000x-5k-sharpening-stone-p/suerika5k.htm

 

 

Friends don't let friends use Edge Pros

Edited October 27, 2014 by daveb (log)

[Porthos]

.. Left-to-right, right-to-left, doesn't matter where the knife is on the dished stone ...

 

If you move the blade across the stone - yes, if you move the knife from one end of the stone to the other lengthwise then it matters. When I learned to sharpen free-hand I learned to go end-to-end lengthwise. The EP also goes lengthwise and so a dished stone would present a constantly changing angle through each stroke.

[rotuts]

"""   Friends don't let friends use Edge Pros  """

 

exactly.

 

they can't use my EP  but Ive let a few watch, and Boom !  off they are for their own.

 

the ones w a kitchen knife collection that is.

 

Ive done free hand on good quality water stones and enjoyed it for some time.

 

time however catches up will all of us sooner or later, and very fine motor skills just sometimes pass me right on by.

 

fortunately   methode rotuts only requires coarse motor skills.

Edited October 27, 2014 by rotuts (log)

[dcarch]

---------------

 

Sharpening on a dished stone is no good for thinning, no good for complex bevels, no good for the edge. 

 

I hear those statements all the time. I have not been able to find explanations why.

 

Other than that it's ok.  To the "wasting stone" argument I'll offer that the stones that dish the most are at the coarse end of the spectrum.  And the cheap end of the spectrum.   A Bestor 500 or Gesshin 400 or JNS 300 (my fav) will last several years with frequent use and regular flattening and cost less than 100 bucks.  Higher grit stones are used less and dish less.  "Waste" becomes noise.

 

To me, $100 is a lot of money, not to mention the time required to flatten stones.

 

--------------

 

If you move the blade across the stone - yes, if you move the knife from one end of the stone to the other lengthwise then it matters. When I learned to sharpen free-hand I learned to go end-to-end lengthwise.

 

For many people who do not have a huge collection of expensive knives, they tend to sharpen the same way for their knives.

 

The EP also goes lengthwise and so a dished stone would present a constantly changing angle through each stroke.

 

They changing angle will give you a convex edge, which I understand is very good for knives.

 

Interestingly, in astronomical lens making, when you grind two flat glass together, you will get one convex and one concave lens.

 

dcarch

Edited October 27, 2014 by dcarch (log)

[daveb]

Sharpening on a dished stone is no good for thinning, no good for complex bevels, no good for the edge. 

 

I hear those statements all the time. I have not been able to find explanations why.

 

 

 

If others have not been able to explain that to your satisfaction I doubt that I can either.  Will offer that "good" sharpeners flatten.  Professional (with Japanese Water Stones) sharpeners flatten.  I learned from people that flatten.  My sharpening is better with stones that have been flattened.  Some things are qualitative and thats good enough for me.

 

 

To me, $100 is a lot of money, not to mention the time required to flatten stones.

 

On this forum I enjoy the contrarian postitions you take to convential wisdom and the arguments you make are usually food for thought.  But.

 

This is absurd.  A $100 stone ($50 for the Bestor) to maintain knives over a several year period is noise.  I can't provide quantative numbers but my experience is less than 10% of a stone is lost to flattening.  (50/5) * 10% is a buck/yr with my calculator.  If it's a signicant amount to you then you're probably better served with periodic use of a grinding service. 

 

And a time argument is even more absurd.  It takes about the same amount of time to flatten a stone as it does to get it wet.

 

No where am I suggesting that everyone should know how to sharpen.  Not even cooking enthusiasts.  I teach knife skills with some food groups I belong to and most attendees do not know what a steel is for.  And that's ok.  Nor am I suggesting that everyone should have knives that benefit from sharpening on a whet stone.  Most don't.  And that's ok.

 

The OP did ask about sharpening on stones and I replied with my opinion to his(?) question.  If your response addressed his question it eluded me.

 

Edited October 27, 2014 by daveb (log)

[dcarch]

DaveB,

 

I apologize if you find it annoying and absurd about my curiosity regarding sharpening stone geometry and it's relationship to knife edges. I do want to point out, if you read the posts of this thread, that it is not I who started to talk about dished sharpening stones, and it is not I who said that it can take hours to flatten a stone.

 

While I don't have your knowledge on the various aspects of knives, I do want to learn about some of the details and mechanics about knives and sharpening systems. You see I do make my own knives. 

 

Since I suspect that EP uses thin and narrow stones and thin structural components, there may be a possibility that significant force might be placed on knife edges, especially on thin blades, causing uneven angles to happen while sharpening. So I made my own sharpening system, which using wider, thicker and longer stones as well as much sturdier components.

 

dcarch

 

 

[daveb]

dcarch - Not annoying at all.  The part I found absurd was your assertion (perhaps not the right word) that cost or time were significant factors when flattening stones.  WIthin the scope of the discussion the cost of the stone is a sunk cost.  The cost of the stone going down the drain as a result of flattening is noise.  The time required to flatten is noise.  There was no hostility in my reply and I hope it didn't come across that way.

 

The "system" vs freehand is a debate I try and avoid for the most part..   Like politics and religion, everyone has something to say and no one's mind ever gets changed.  People having sharp knives is a good thing however they get there.

[Shalmanese]

The lifetime of a stone is how long it takes for the center to completely wear away. This should be unaffected by flattening as the material taken away is the sides that get relatively less use.

Also, flattening by grinding two stones results in a concave/convex surface. Grinding with 3 stones against each other results in a perfectly flat surface. In practice, this ends up not really mattering that much. Alternately, you can just glue sandpaper to a sheet of glass and grind against that to achieve perfect flatness.

edit: Also, I've never known a home knife sharpener to completely use up a stone. Even if you sharpen every week, it takes a long time to wear away an entire stone.

Edited October 28, 2014 by Shalmanese (log)

[rotuts]

""  there may be a possibility that significant force might be placed on knife edges, especially on thin blades, causing uneven angles to happen while sharpening ""

 

actually the Ep works best w lots of water w a hint of liquid detergent and as light a pressure as you can stand.  the work being done is more in the horizontal plane than the vertical

 

the EP ( smaller version ) is sturdy enough for 90 % of its users once they understand the EP sharpening preinciples.

 

BTW d : nice knives and nice jig.

[dcarch]

Thanks Rotuts.

 

Regarding EP, the stones are 1 inch in width, my stones are about 3 inches wide. That works out to three times the pressure on the knife's edge.

 

In any case, if you hand sharpen your knives, I don't think there is a way not to end up with a convex edge, because there is no way to keep your movements absolutely constant. 

 

dcarch