# How to keep blade curve/belly after repeated sharpening



## Boynutman (Jun 17, 2014)

This topic may have been addressed before - but I was unable to find any references. Sorry if I missed a thread on this.

I have noticed that there seem to be 2 ways of sharpening that can roughly be described as follows:
1.) sharpen the blade in lengthwise sections by moving the blade back and forth over the stone (perpendicular to the edge direction) and then moving to the next section when the first section is done,
2.) make a slicing motion across the stone with the entire length of the blade.

I once saw a remark that suggested that method 1 would eventually reduce curve of the blade (i.e. Make it less curved). Considering the geometry of things (flat stone, curved blade) it is easy to see how this can happen - or at least in theory (things may work out differently in practice). When moving a curved blade back and forth over a flat stone at an angle the curve will be ground away until it achieves the same flat profile as the stone.
In 'an edge in the kitchen' method 2 is suggested, which I follow with improving results. So that's good.

Still I frequently see videos of people using method 1 on what appear to be curved blades such as gyutos. And they seem to get razor sharp results - something that I am only approximating for now.

So... Is method 1 any good, or will it eventually ruin the blade geometry? Or does it depend on the blade type? Or is the less than perfect flatness of the stone combined with the less then perfect consistency of manually moving the blade sufficient to maintain the curve with method 1?

I would appreciate your thoughts!


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## LKH9 (Jun 17, 2014)

Boynutman said:


> This topic may have been addressed before - but I was unable to find any references. Sorry if I missed a thread on this.
> 
> I have noticed that there seem to be 2 ways of sharpening that can roughly be described as follows:
> 1.) sharpen the blade in lengthwise sections by moving the blade back and forth over the stone (perpendicular to the edge direction) and then moving to the next section when the first section is done,
> 2.) *make a slicing motion across the stone with the entire length of the blade.*



This thing always gets on my nerves!:knife: Totally misguiding, I just finished talking about this in the previous topic.


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## rami_m (Jun 17, 2014)

Oops please ignore


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## echerub (Jun 18, 2014)

You can definitely maintain the curve on a knife with method 1. You are moving the knife so that when you sharpen each section in order to accommodate the curvature. You can also "slide in" (or going the other way, slice) the tip against the stone in order to hit the tip and follow the curvature of the belly right behind it.

Pay attention to what's happening and adjust accordingly. If you are holding the knife handle in your right hand and putting the fingers of your left hand on the blade when sharpening, then you are going to extend out your right hand a bit further away from you in order to accommodate a bit of curvature. As you get to the really curved part near the tip, you might then choose to change your technique to accommodate the tip - whether you do the slide-in/slice way or Jon Broida's "wave" motion.

Sorry for the really vague word-description. It's easier to show than to describe!


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## Von blewitt (Jun 18, 2014)

To maintain the curve toward the tip, lift the handle up when you reach that section, and try and follow the curve laterally while the knife is in contact with the stone.
+1 to checking out Jons video on tip sharpening


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## chefcomesback (Jun 18, 2014)

+2 on Jons video , it has been a revelation for me .


Sent from my iPhone using Kitchen Knife Forum


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## Yamabushi (Jun 18, 2014)

Definitely method #1! I would imagine, while not impossible, it would be extremely difficult to hold a consistent angle using method #2.

And, I also would add my recommendation for Jon's videos. They are all excellent! That being said, what most stood out for me was the method he shares for sharpening tips. It has finally allowed me to consistently produce quality results in the area that had formerly been my bane.


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## Boynutman (Jun 19, 2014)

Thanks guys, I appreciate your feedback!

So far I have been following the advice in Chad Ward's book. I think I am achieving a pretty consistent angles this way, judging by the reflections of a spot light and judging by the width of the achieved bevel. And I am not unpleased by how my skills are improving.

But this difference in methods really got me intrigued. I will watch Jon's videos and use one knife to try this out. I was (am!) a bit apprehensive about mixing sharpening techniques - but there's only one way to find out I guess.

Thanks!


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## Benuser (Jun 20, 2014)

Welcome, by the way!


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## Boynutman (Jun 22, 2014)

Ha, thanks, I see that we are practically neighbors!


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## Benuser (Jun 24, 2014)

Indeed!


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## DDPslice (Jun 24, 2014)

I prefer method 1 because my knife feels like a large single bevel with a large belly, I think I would prefer method 2 if I had a primary and secondary bevel. In which case, I would do method 2 on the cutting bevel than a couple strokes of method 1 on the upper bevel (the purpose would be to make teeth on the primary and smooth the secondary bevels respectively) Also I noticed that when I do a small back and forth saw-like method (only with the jnats) I pull out a lot more character out of my higane. Sorry no pics yet, my phone should be in a museum.....miz > phone.


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## Boynutman (Jun 24, 2014)

Well, you all certainly got me started thinking about this.

I figured that with method 2 I couldn't go wrong; if you do a consistent motion the edge and burr development should be equal along the entire edge (assuming consistent pressure and maybe some other parameters I haven't even started to consider...). And it is very easy to very gently move the knife which should help in deburring I thought.

And I figured that with method 1 (moving up and down) this would be less the case (because it is easier to over-do or under-do some local spots) so it would require more frequent and detailed checking of the edge at multiple spots to see how things are developing. But maybe this is a good idea anyways and it is just me being lazy... 
To help out I just bought one of those 5 dollar iphone clip-on microscopes to take a look at my edges; it showed there is definitely some more deburring work to be done, which was what I kind of expected based on feeling with my finger tip.

From what I read above it sounds like that with method 1 one can ultimately achieve a better edge then.


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## DDPslice (Jun 27, 2014)

Oh I see. I do not like moving the blade up and down as you've described. Because 1) repeated motion over the same area can cause an uneven grind 2) creates larger flat spots along the belly. I think a better solution would be to place the blade lengthwise and then move up and down so the blade is perpendicular to the stone staring the contact point a the shinogi and ending at the cutting edge. I have read in razor sharpening to use this method and I have achieved exceedingly sharp results. I think because doing it lengthwise will create more tangent points along the belly making a smoother rounded belly.


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## Boynutman (Jul 1, 2014)

Thanks DDPslice. Your concern about the flat spots was exactly what I was wondering about so that makes sense to me.

I am trying to visualise what you are saying about the razor sharpening method you picked up but I cannot really figure it out. Could you provide some more clues or a reference?


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## DDPslice (Jul 1, 2014)

Boynutman said:


> Thanks DDPslice. Your concern about the flat spots was exactly what I was wondering about so that makes sense to me.
> 
> I am trying to visualise what you are saying about the razor sharpening method you picked up but I cannot really figure it out. Could you provide some more clues or a reference?



I will try and find the reference but in the meantime google sword polishing, that's how I came across it. I believe that the sword and the kitchen knife are almost one of the same and learning the art of sword polishing will help bring about a sharper/stronger edge and a less reactive blade. 

As to try and clarify the polishing technique I mentioned in the previous post. Lay the blade flat and lengthwise down the polishing stone with nagura slurry/or on a nagura stone if you have a whole one. The majority of the blade is touching the stone. Now with just the edge (higane) touching move the blade up and down in diliberately small strokes (millimeters) checking your work after every couple of seconds, keeping the slurry clean.

Now to clarify, this should be done with Jnats I doubt you can get the same results with synthetics, I would love to try a coticule or escher stone to see a difference. Also this polishing technique is used to bring out the contrast of the higane to the jigane. My knife is iron clade so I am having a tough time not nicking the iron and cause a scratch. 

Question, was your knife sharpened before you got it? Is the bevel face smooth?

For me I did not have it sharpened before I got it(terrible idea for a beginner) so the bevels have high and low rivets, and it took a couple polishing sessions to realize I needed to go back and even out my bevel with my DMT diamond plate so I don't scratch my jigane. I think the natural posture of the knife will always be there so don't be afraid of smoothing the bevels if you think it needs it.


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## DDPslice (Jul 1, 2014)

Wow I think I may have completely misunderstood your question. When you mention belly are you talking the edge or the bevel? If your worried about loosing the curvature of the blade I would follow the blades' shape as your grinding and you will maintain its curvature. Similar to putting on a new tip that's been chipped. 

What I thought is that your jigane/secondary bevel was becoming more concave due to the fact when you are sharpening/polishing the cladded steel is much softer than the core causing a dimple in the kiriba?


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## ThEoRy (Jul 2, 2014)

I haven't "ruined" a knife yet. :dontknow:


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## Benuser (Jul 2, 2014)

DDPslice said:


> Wow I think I may have completely misunderstood your question. When you mention belly are you talking the edge or the bevel? If your worried about loosing the curvature of the blade I would follow the blades' shape as your grinding and you will maintain its curvature. Similar to putting on a new tip that's been chipped.
> 
> What I thought is that your jigane/secondary bevel was becoming more concave due to the fact when you are sharpening/polishing the cladded steel is much softer than the core causing a dimple in the kiriba?


A soft clad steel may be much more abrasion resistant than a harder core steel.


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## Seth (Jul 2, 2014)

There was a youtube, which I can't find now, demonstrating like this: take a stone or similar object and put it at about 20 degrees tilt and hold your knife with the face of the blade parallel to the ground. As you move around to the tip you will more easily see the amount of lift you would need to come around the tip of the blade to maintain an even bevel. I always thought this was a good graphic way to get a sense of this. The trick then is to translate this to actual sharpening.


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## DDPslice (Jul 2, 2014)

@Besuner 
Not in my case, it is a soft cladded iron, I cant think of any others steels stronger than Japanese Blue #2 (my core). And for the most of what I've been reading most blacksmiths wrap a softer material around a harder material.

@Seth
I think I have seen it too but SaltyDog has some great videos and there are others with decent music to boot. 

@theory
Oh brother....neither have I, but if I did, I'll just have to get another:biggrin:


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## cazhpfan (Jul 2, 2014)

I might be wrong, but is this video you're referring to: https://www.youtube.com/watch?v=JFhUXgYS0Os



Seth said:


> There was a youtube, which I can't find now, demonstrating like this: take a stone or similar object and put it at about 20 degrees tilt and hold your knife with the face of the blade parallel to the ground. As you move around to the tip you will more easily see the amount of lift you would need to come around the tip of the blade to maintain an even bevel. I always thought this was a good graphic way to get a sense of this. The trick then is to translate this to actual sharpening.


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## DDPslice (Jul 2, 2014)

Not what I was thinking of but this video is perfect! Thanks


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## Benuser (Jul 2, 2014)

cazhpfan said:


> I might be wrong, but is this video you're referring to: https://www.youtube.com/watch?v=JFhUXgYS0Os


This voice sounds somewhat familiar.


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## ThEoRy (Jul 2, 2014)

DDPslice said:


> Not what I was thinking of but this video is perfect! Thanks



Do NOT listen to good ol' Kenny. He's a shyster and a schill.


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## DDPslice (Jul 4, 2014)

ThEoRy said:


> Do NOT listen to good ol' Kenny. He's a shyster and a schill.



That's pretty harsh for not contributing anything, do you have anything of value to say?


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## Yamabushi (Jul 4, 2014)

DDPslice said:


> That's pretty harsh for not contributing anything, do you have anything of value to say?



Uhhh...? No offense intended, but you appear to be pretty new here. Theory on the other hand is a proven, quality long term member of KKF. He has contributed far more here than most ever will. Perhaps you should dig through the forums a bit before having a go at him?


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## DDPslice (Jul 4, 2014)

Yes I am new, can you tell? Do I care? I'm looking to gain useful information not call some guy a shill or whatever and run my mouth with no explanation nor taking the time to find a better video to explain why theory's 2ND! rude comment was justified. Are you serious? I'm trying to help myself and boynut find the correct answer to his question which i hope was accomplished. Do you expect someone to comb through years of posts to find some sort of semi-relevant info when I can start a new thread and ask the question I want so I can move on with my life, when the searches are a bit vague (no offense to Dave). And I have done that and have been lurking for almost a year (now questioning that choice). There were others on this thread who had no problem answering the question at hand. Also just because you say something a thousand times doesn't mean it was worth saying the first time (irony).


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## Benuser (Jul 4, 2014)

ThEoRy said:


> Do NOT listen to good ol' Kenny. He's a shyster and a schill.


Even if the terms might appear unusual, they are rather appropriate when applied to this personage. See it as a warning.


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## labor of love (Jul 4, 2014)

DDPslice said:


> Yes I am new, can you tell? Do I care? I'm looking to gain useful information not call some guy a shill or whatever and run my mouth with no explanation nor taking the time to find a better video to explain why theory's 2ND! rude comment was justified. Are you serious? I'm trying to help myself and boynut find the correct answer to his question which i hope was accomplished. Do you expect someone to comb through years of posts to find some sort of semi-relevant info when I can start a new thread and ask the question I want so I can move on with my life, when the searches are a bit vague (no offense to Dave). And I have done that and have been lurking for almost a year (now questioning that choice). There were others on this thread who had no problem answering the question at hand. Also just because you say something a thousand times doesn't mean it was worth saying the first time (irony).



C'mon dude, relax  I dont think Theory was trying to offend you, atleast I dont think.


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## Seth (Jul 4, 2014)

Not the video I was thinking of but similar idea. Poor Ken; he needs a voice transplant. (Just joking....)


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## cazhpfan (Jul 4, 2014)

I did not mean to start an argument by linking to the video.

My apologies if it came across that way. I was just trying to recall something that I'd seen some time ago...

@ DDPSlice and the OP:

Sharpening the belly is something that comes with practice and will get especially easier once you learn how to sense the feedback given by your waterstones.

My humble suggestion would be to continue watching Jon Broida and Theory's videos--it'll click, eventually.

For the belly, Theory's videos were particular useful because the POV is on the same plane as the flat surface of the waterstone that he's using.

You'll be able to clearly see him lifting the knife's handle, and twisting the knife towards the spine, in order to maintain the plane of the bevel at just the right angle to the stone.

Jon's channel: https://www.youtube.com/user/JKnifeImports

Theory's channel: https://www.youtube.com/user/PCCkitchen



Seth said:


> Not the video I was thinking of but similar idea. Poor Ken; he needs a voice transplant. (Just joking....)


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## DDPslice (Jul 4, 2014)

No it was my bad, my apologies for derailing the thread.


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## ThEoRy (Jul 5, 2014)

DDPslice said:


> That's pretty harsh for not contributing anything, do you have anything of value to say?



Both of my comments in this thread have added value to the topic at hand. 1st I commented on how after years and years of sectional sharpening I have yet to "ruin" a knife. This comment directly relates to the OP as to assuage his fears. Secondly I posted a warning about listening to the advice of good ol Kenny Schwartz. He is a known schillster with magical abilities that can sharpen even the impossible "Black Steel". On the other hand you have personally attacked me twice in this thread which I've chosen to ignore.


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## DDPslice (Jul 5, 2014)

Yea, my bad, I misunderstood what you were trying to say. But they did seem off-handish. Also colloquialisms are confusing, as well as you said to "NOT" to listen to him, and maybe saying you've never ruined a knife after someone posts a novella and not saying something along the lines of "don't worry" or "you'll be fine" would have been more reassuring of your actual intent. Once again please accept my apology.


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## Boynutman (Jul 14, 2014)

Everybody, thanks for all your feedback, it certainly provides a new perspective for me (and provides some reassurance!).
Just be be complete I looked up the article that brought this issue to my mind:

http://www.richardblainesezcooking....sharpen-a-large-curved-blade-a-butchers-knife

For newbees like myself it can be hard to distinguish between poor and good advice, and to detemine whether certain techniques are appropriate for certain knife types. The above link came up during earlier searches. So this is in part what drove my question - I thought it contrasted with all the section by section sharpening videos i saw so that it made me wonder which was right. I figured that (at least in theory) there is no principal difference between a mildly or strongly curved blade and that with a mildly curved blade it would be even less desireable to loose the curve. Hence my concern.


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## Lizzardborn (Jul 14, 2014)

Hmm - just by the amount of ads on that lights a lot of warnings. Also I remember seeing him in the knuckleheads tread.


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