Putting a Good “Grind” On a Sticky Knife?!?

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TEWNCfarms

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Is this possible? Can I put a I guess it a convex grind on my flat ground k-tip gyuto Gekko? I got the Masashi Kobo SLD and it looks like the sides of the blade come out/bow out from the edge and spine? Is this correct? Could I thin out the edge of the Gekko to achieve a better grind? Now that I have this Masashi this Gekko is going to be my experimental knife. Any suggestions? I have no idea. Thanks
 
choil shot would be super useful
 
also, this..

http://www.kitchenknifeforums.com/s...n-of-Asymmetry?p=508178&viewfull=1#post508178


A Basic Explanation of Asymmetry

Way back when I began sharpening I remember reading through many forum threads about asymmetry in double bevel knives and having no idea what was going on. All this talk about 70/30 and 80/20, "You should be doing this and shouldn't do that", but no real explanation for what was actually going on. So I ignored the whole thing and went on sharpening in my 50/50 way.

A few years (and many knives) later, I realized after spending hours grinding further back behind the edge, I had developed my understanding on kitchen knives to the point where I could not only understand, but explain it in simple-enough terms. It really boils down to 3 general rules which, when understood individually, combine to explain the whole thing.

So we'll start off with a diagram of a crappy knife, then introduce one rule at a time and improve it till we get something which represents a good knife (the rules are in random order and only numbered for ease of reading).

JZOu0Y0.png

Figure 1. A huge, fat, symmetrical knife

Rule 1 - Food releases off a curved surface better than it does off a flat surface

Most cuts we do in the kitchen are flat, and when a flat surface on the food comes into contact with a flat surface on the side of your knife, the large amount of surface area in contact between them increases drag and can be enough to hold them together. This is known as stickage, and it's a pain in the ass to put up with. We can minimize this nasty effect with the use of a curve instead of a flat on the side of the knife, because there is less surface area shared between a flat and a curve (the same effect can be had with a multi-faceted compound bevel) when compared to a flat-on-flat.
dvhsqEz.png

Figure 2. A curvy, fat, symmetrical knife

Rule 2 - The thinner the knife, the easier it moves through what it is cutting

This is pretty much self explanatory. Thicker knives have to push more out of the way on either side as they pass through food.

But here's a problem: The thinner you make a knife, the less curve you can fit on either side. This compromises Rule 1, and so we have to balance how thin the knife is with how much stickage we are willing to put up with.
The heat-treatment and kind of steel will determine how thin you can get your knife before its strength becomes compromised.
rjrwW3d.png

Figure 3. A curvy, thin, symmetrical knife

So here we are at a nice compromise of thickness vs. curvature. Cut food falls off on either side of the knife and it's not so wide as to get wedged in the food all too often. Perfect, right?
It turns out there's another way to improve the shape even further, and it has to do with how we use kitchen knives.
When cutting food, we generally hold the knife in our dominant hand and the foodstuff in the other. Lets say you're right handed and the food is held securely in your left. Do you really need the ability for food to drop off the left side of your knife if you're already holding it down? We may as well sacrifice some of the curve on that side and make the knife thinner overall. Like so:
JZ5O4mq.png

Figure 4. A curvy, thin, asymmetrical knife

This flatter surface on the left also has the added benefit of helping your left hand guide the up/down movement of the knife in a more predictable fashion.
Of course, using this little trick introduces a new problem: Steer.

Rule 3 - Asymmetry in the grind will determine the amount of steer the user experiences

A blade pushing through foodstuff will turn if it's getting deflected more on one side compared to the other. This asymmetry we introduced in Figure 4 has increased the amount of deflection on the right side, and as such the blade will steer towards the left (of the user).
P7Z9Los.png

Figure 5. Different amounts of deflection on either side of the blade (green arrows) will cause the knife to steer off-center (red arrow)

We can counter-act this somewhat by sharpening the knife in such a way to make it want to steer in the other direction.
1roGHWs.png

Figure 6. Asymmetrical sharpening. Note the right bevel is both shorter and more acute to the blue line when compared to the left

If we zoom into the sharpened area you can see that the size and the angles of the bevels are uneven. This is done on purpose for two reasons: It helps steer the knife to the right, which in turn cancels out the existing steer to the left. And it also helps keep the sharp point closer in line to the middle of the blade (the blue line), which is very important in the case of clad/san-mai knives.
ML4LsWb.png

Figure 7. The differing size and angle of the bevels introduce deflection in the opposite direction of Figure 5, helping to cancel out any steering overall

So that's basically it! :)
Hopefully it's not too hard to understand and helps alleviate the confusion that some people have on the topic.
I should point out that while these general rules do apply to single bevel knives, the sharpening of them is done differently to what I've shown here. No correction is done to steering on a single bevel knife.
Let me know if I've missed something.
 

Thanks so much, I’ll take a picture tomorrow.

I had read this a week or so ago, you or someone else suggested it, really good read very informative.

I just tried out this Masashi, and it didn’t let the potato fall off like I hoped... it definitely has an attempt to, it’s on the verge but still sticks. I tried doing a 70/30 edge when I sharpened it up but i did forget to add a micro bevel... any suggestions? I’m going to cut some potatoes tomorrow at work and take some home and work on the sharpening maybe I can get it to just fall off. Because it’s hanging off on the top but the bottom half is sticking. This was russet
 
If you look at figure 4, it will show the the problem
as the one side is ~flat and the other side is convex.
its really hard to make the flat side convex,
as the metal is gone...unless the whole thing
is very thick to start out with.

Note that figure 4 is showing the L-R assymetry, but
the similar point more specifically
for the picture is you cannot make a righty
knife a lefty (=reverse the symmetry)
...basically for the same
reason...the asymmetry of the grind
is primary here for food release,
the assymetry of the edge is just
to correct for the assymetry of the
grind.

edge assymetry is ieasier to reverse,
because the amount of metal is larger
in proportion to the shaping ∆

You can howver usually tweak
some (low) convexity into the
edge if its thick, but this is usually
more about cut quality
than about food release,
as most of the action for food
release is up higher (grind vs edge)
 
If you look at figure 4, it will show the the problem
as the one side is ~flat and the other side is convex.
its really hard to make the flat side convex,
as the metal is gone...unless the whole thing
is very thick to start out with.

Note that figure 4 is showing the L-R assymetry, but
the similar point more specifically
for the picture is you cannot make a righty
knife a lefty (=reverse the symmetry)
...basically for the same
reason...the asymmetry of the grind
is primary here for food release,
the assymetry of the edge is just
to correct for the assymetry of the
grind.

edge assymetry is ieasier to reverse,
because the amount of metal is larger
in proportion to the shaping ∆

You can howver usually tweak
some (low) convexity into the
edge if its thick, but this is usually
more about cut quality
than about food release,
as most of the action for food
release is up higher (grind vs edge)

Ahhh! Thanks for helping with that, I’m starting to grasp it. Maybe I’m chopping the wrong way... maybe I should go left to right? I’m going to have to do some studying tomorrow and some practicing.

I’ll take a picture of both knives so you can get a look see at what I’ve got
 
Well I guess I’ll be holding off any sharpening or cutting for a day or two, got called into work because this one guy was being a baby thinking it was going to be busy and it wasn’t I left after 3 hours. But OF COURSE while I’m there within an hour I was cutting bacon and it slipped and took a Chunk out of my thumb!!! A good chunk, had to shove it in some coffee grinds to get it to stop bleeding, hurt like hell! I swear I’m not Ever cutting bacon again, last time I cut some a few months ago I cut myself but not nearly as bad. Thank GOD it wasn’t worse than it is though. I put this curse of this cut on my co worker being a baby convincing them to bring me in today! Bas tard!
 

This is what I get most of the time, now sometimes it releases good, but what am I doing wrong on my sharpening?!!? I rewatched the Korin video on 70/30 and realized for the past months I’ve been doing the sides reverse what they say. They have the 70 side on the right and 30 on the left...? This is the Masashi by the way
 
So I tried multiple sharpening techniques and then decided to revert back to a higher angle 50/50 instead of my low angled 70/30 and the food release was much better! Maybe I’m sharpening my edge to low?! I added Jons microbevel as well. I’m just trying to get it perfect and obtain the best food release!
 
maybe closeup pictures of your edge might help?

Here’s the edges as best as I could get them with my iPhone which is all I have... the top two are the Gekko I believe, that’s not that good of a grind, and the bottom two the Masashi with the good grind... you can’t really tell much but hopefully it’ll be enough for you all to help me out. Thanks!



 
So, obviously i cant tell much about cross sectional geometry from these, but i can see a lot of sharpening inconsistencies at the edge that would contribute to a lackluster cutting performance. You can see that light reflects all over the place with those edges... there are sections where your angle was too high, some where it was too low, and a lot of rounding over of the edges. Here are some pictures of what an edge should look like:

PfajncR.jpg


wMhZaHj.jpg


T1Hx0Cu.jpg
 
Tenn, I have to agree with Jon here. You've got a lot of bevels/angles going on so it's pretty safe to say that you're not going to be getting much in the way of performance.
 
Tenn, I have to agree with Jon here. You've got a lot of bevels/angles going on so it's pretty safe to say that you're not going to be getting much in the way of performance.
Cool I really appreciate it guys
I’m really glad I saw this now just left my farm house and I have the phone lens magnifier there, just turned around and got it, it’s 30 min from home. I kept forgetting to grab it, so now I’ll take a good picture of the bevels and let you all check them out and see what you say then. I really appreciate it!
So, obviously i cant tell much about cross sectional geometry from these, but i can see a lot of sharpening inconsistencies at the edge that would contribute to a lackluster cutting performance. You can see that light reflects all over the place with those edges... there are sections where your angle was too high, some where it was too low, and a lot of rounding over of the edges. Here are some pictures of what an edge should look like:

PfajncR.jpg


wMhZaHj.jpg


T1Hx0Cu.jpg
 
maybe closeup pictures of your edge might help?

Okay so here you go. I’m so stupid too I completely forgot about this wonderful little feature on my iPhone called Zoom and was able to take better pictures with it. So sorry I know this is a lot of pictures but I’ll keep them as linked thumbnails and this is basically both sides of both knives along the whole edge. Thanks for everyone’s input! Thanks Jon!
 
Also the Damascus is the Gekko the clad is Masashi that I just got. Sharpened only twice... also I tried to get the best lighting so you could see the bevel and not just light reflecting, so I hope they’re good
 
Jon and Dave answered your question, no?
 
Yeah... the new pictures show the same thing in better detail... same issues though
 
what is going on here?

https://ibb.co/fhGPNo

42_B37373_0_F1_D_43_DF_AF02_3_EF069513_BD2.jpg

Haha you mean how it’s high on one end and low on the other?! Yeah I had no idea I was doing. It’s so crazy how a couple months ago I thought I figured out Everything about sharpening and yeah I’d get it sharp, but now I’m entering this realm of insane detail about knives and sharpening, and the more I learn the more I learn I have No idea what I’m doing!
 
So, obviously i cant tell much about cross sectional geometry from these, but i can see a lot of sharpening inconsistencies at the edge that would contribute to a lackluster cutting performance. You can see that light reflects all over the place with those edges... there are sections where your angle was too high, some where it was too low, and a lot of rounding over of the edges. Here are some pictures of what an edge should look like:

PfajncR.jpg


wMhZaHj.jpg


T1Hx0Cu.jpg

Holy crap! That edge is insanely perfect! Did you do that yourself? With freehand?! I had no idea I was doing all that wonky work until you pointed I out, thanks!
 
Yeah... the new pictures show the same thing in better detail... same issues though

Cool thanks. What are some pointers to fix it? Just take my time and be more careful and accurate? How does the rolling of the edge exactly occur? Going to high when the edge was low from a few passes before?
 
Jon and Dave answered your question, no?

They answered questions I didn’t even know I had. And I guess the answer to the grind question is No I can’t really change the grind? Or can I from doing thinning?
 
That looks like the old thin behind the edge and put two bevels on the blade in one stroke method of sharpening. Don't ask me how I know....

Hahaha I was wondering if anyone would recognize this old technique, I brought it back from 1789
 
all this can be explained by one simple truth: you are not holding a steady angle, meaning you are wobbling up and down too much. we've all gone through this, just takes many hours more muscle memory and refinement through practice.
 
Cool thanks. What are some pointers to fix it? Just take my time and be more careful and accurate? How does the rolling of the edge exactly occur? Going to high when the edge was low from a few passes before?

Yup, what Panda said.

Pointer = try to keep your wrist and elbow locked. Rolled edge comes from raising the spine too high. Wavy bevel comes from putting the spine to low. Rolled edge + Wavy bevel comes from raising spine too much and not enough.

Rolled + Wavy bevel is probably a product of (1) not locking your wrist or elbow or both; (2) inconsistent angle during push/pull (edge-leading/edge-trailing)--lowering spine on away-stroke and pulling up spine on towards-stroke; and/or (3) fingers on the blade not consistent (too hard, too soft pressure) or putting different pressure in different places on the strokes.
Probably a combination of 1,2,3...

Solution = try the pointer about arm position; pay attention to 1,2,3 when you sharpen; watch Jon's videos A LOT. Every time I watch them I learn.

Last--KFF's "Search" feature is your friend--many of your problems are well-known issues and other threads have tackled them.
 
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