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I keep oversharpening certain parts of my knife (with pics)

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oldm8

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I have this knife that I got in Japan, it is double-bevel. The blade is about 17cm. I was told the steel used is fairly soft and it was an entry level, all purpose knife.

The clerk at the store told me to sharpen at an angle roughly 2 yen coins high, I found a youtube from the store with those same instructions.
I have scratched up the sides plenty and ruined the decorative line that runs along it by being bad with the angle - however am slowly getting better.

After using sharpie to get some better feedback, I noticed that I really over-sharpen the bottom of the blade and also about half way up. Between those 2 points I have removed far less sharpie, it almost looks like a wave.

Today I found a great video by JapaneseKnifeImports which call this specific issue out and said the problem is applying pressure from the hand that maintains the angle, rather than the hand that is pushing down on the edge. Could that be a main cause? I do find that I place a lot of pressure on my thumb as I try and hold the angle.

Appreciate any general advice, I doubt you can give me much without watching me actually sharpen, I'll keep practicing because I like doing it, despite the frustration of being a newbie. Hoping to one day post a pic with a nice even line of sharpie :D

Screen Shot 2020-11-26 at 7.14.02 pm.png
 

jwthaparc

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It could be a few things. The grind on the knife could be uneven, leading to your edge bevel looking wavy like that. You could be inconsistent with your angle. Or like you said you could possibly be wearing the knife away in those spots.

For the first thing the solution would be to grind the wide bevel flat. I would not recommend you try this yourself if you are just getting into sharpening. It could be a big job.

For the second, just concentrate on keeping that angle consistent. It will get better with practice.

The third is the easiest to fix, if it is the problem. Just concentrate on the areas that aren't getting worn away as much.

You can figure out which of these is the issue, by process of elimination. I would start with 3, then 2, and finally if it's the 1st one then maybe see if you can find someone willing to help you fix it.
 

DHunter86

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Could be a number of things from my experience. Try to ensure that you hold the same angle across the blade when going up the curvature of the knife. Due to the knife being curved most of the way, you'll have to adjust for this. It is evident that the heel is over ground, might be due to your angle holding hand applying too much pressure (depending on your stance, probably the thumb).

Another thing to look out for is whether the knife had over/under grinds at the edge. To check this, put the edge down on a flat surface and see if light comes through where it shouldn't.

Finally, check whether the knife is indeed straight / flat on both sides. I own a cheap usuba, and it's evident the steel is wavy, not the blade (as the back is flat, but one side is wavy, meaning it wasn't ground properly). If the knife is wavy on one, there's nothing much you can do other than regrinding it flat. If it's warped, then you could have it straightened out.
 

M1k3

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Being newer at sharpening, I'd guess uneven angle is the problem. With a little spending to much time in some spots and not enough on others.

Followed by the knife being uneven.
 

ModRQC

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There's big recurve at the heel, explaining the bevel thickness there - however yours is still exaggeratedly thick which speaks mostly of inconsistent angle/too much pressure.

Check your fingers closely: I bet they're moving into and away from the edge as you go along the length, and if using a lot of pressure, when your fingers move too much away from the edge you are pushing the knife down, changing the angle.

From the "average" thickness of your bevel I would also assume you're sharpening the curve to tip section at a higher angle then the rest.
 

ian

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There are a lot of good ideas above. You might also pay attention to whether you’re mostly just putting your fingers on the spots of the blade where you’re seeing more steel removed. I think it’s possible to move your pressure hand up the blade in steps that are too distinct and predictable, in a way that leave some areas slightly oversharpened.
 

ModRQC

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There are a lot of good ideas above. You might also pay attention to whether you’re mostly just putting your fingers on the spots of the blade where you’re seeing more steel removed. I think it’s possible to move your pressure hand up the blade in steps that are too distinct and predictable, in a way that leave some areas slightly oversharpened.
In this light, too, it's very important that you use the longest strokes possible - the idea is that it works more evenly on a longer section of the edge, and it's easy to see when you mess up. Short strokes, sharpening on short sections at a time, can lead to over and under sharpening pretty fast when you've not "stabilized" your sharpening skills yet.

Sharpie, keep your knife clean, look at the bevel/sharpie removal, low pressure, long strokes, going slowly, until you build consistency. See Jon Broida videos on youtube about sharpening the tip, too. Lastly, listen very hard to your stone feedback: higher pressure, change of angle, change of pressure point away or into the edge, they all make a distinct sound.
 

HumbleHomeCook

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One thing you can do is go to high grit stone so you're not removing much, if any metal. Mark your bevel with the Sharpie. Make a couple passes as you normally would and then observe where the marker has been removed. Reapply it and this time, do something different, like changing your finger pressure or your control hand. The idea here is not to do any actual sharpening, but try to isolate the problem.

Understand that the bevel is already altered so you're not looking to take the marker off the entire bevel as it is now but just to see if you can get something fairly consistent at the edge.

At some point you're going to have to drop down to a low grit and reset everything but it would be good to have an idea of what is going on before that as you might just keep repeating the cycle.
 

oldm8

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Thanks for the advice! I did not realise that a knife might have not been ground properly - TIL!

Many great pointers! I will slow things down as I do tend to rush and take short strokes. Is it okay to take the blade complete off the stone and reset between strokes?

I had one theory about those over sharpened areas - I have been starting my grind heel-first, with my thumb on the heel applying a lot of pressure, as I move toward the tip, the heel is no longer the stone, so all of that thumb pressure is now pushing against air, then to compensate, I press even harder with my fingers to fight against the pressure from the thumb and keep the blade balanced.

I'll switch to my 6000 stone as I continue to practice - great idea!

Screen Shot 2020-11-27 at 6.24.53 am.png
 

ian

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Yea, try to lighten up with your thumb. I only press hard with my thumb when I'm sharpening the heel. Mostly I just try to keep a semi-firm pinch grip and focus on controlling more large scale body mechanics in order to keep the angle. It shouldn't actually require a bunch of pressure to keep the angle. I'm better at this with my dominant hand than my nondominant one, though.
 

Kawa

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Thanks for the advice! I did not realise that a knife might have not been ground properly - TIL!

Many great pointers! I will slow things down as I do tend to rush and take short strokes. Is it okay to take the blade complete off the stone and reset between strokes?

I had one theory about those over sharpened areas - I have been starting my grind heel-first, with my thumb on the heel applying a lot of pressure, as I move toward the tip, the heel is no longer the stone, so all of that thumb pressure is now pushing against air, then to compensate, I press even harder with my fingers to fight against the pressure from the thumb and keep the blade balanced.

I'll switch to my 6000 stone as I continue to practice - great idea!
In my limited experience, many cheap/crap knives (not saying yours is) have a wavy edge with low and high spots
 

RDalman

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Lots of good advice. Just want to add on the straightness part, you might have caused bend also if it's a thin blade with that technique the way I interpreted it.
 

oldm8

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Well, I got it pretty damn sharp, and also buffed out a lot of scratches with rust erasers.
Not sure how I can tell if its bent? If it is, I cant see it with my bad eyes.
It cuts ok with food, but does feel a bit crappy in certain spots - I think due to uneven blade.

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psfred

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You should be able to tell it it's bent by sighting down the edge -- hold it edge up with the edge level with your eye and pointed away from you. If you point it straight away from you only the choil (shape at the heel) should be visible. If you can see the sides of the knife "sticking out" it's bent. May or may not be fixable.

As far as the grind goes, inexpensive knives usually aren't perfectly ground, for obvious reasons. An uneven grind, which I suspect you have, will result in a wavy bevel although the knife is actually sharp. Worse case though, you will have "holes" in the edge where the edge, although sharp, isn't straight and won't touch the board. Bends and "overgrinds" were too much material was ground off the main bevel in manufacturing will result in high spots in the edge. Very annoying.

I would suspect you are not holding the knife flat while working on the heel, you need to apply some rotational force to work the whole edge. I found this out with straight razors, it's easy to let the weight of your hand rotate the knife handle down. It will take a long, long time to get the heel level, if it ever was. High is better than low, though, so concentrate on the belly, get that even and get the tip sharp for now.

I also suspect you are using far too much pressure -- a good stone will cut just fine with light pressure, and it's much easier to control the angle if you are not shoving down. Also results in less rotation the blade and less rounding of the bevel.

For the tip, because it's curved up some, you will need to lift the handle a little when sharpening the tip without changing the angle of the knife to the stone. It's easy, but you will have to learn it.

I'd also suggest using nothing coarser than a 1000 grit stone for a while, coarse grit stones will chew away far too much material when you don't have things quite right, and lead to spending much more time fixing an error!

Scratches on the sides are from allowing the blade to wobble up and down. Once you learn to hold a steady angle you won't have this issue any more (although I do, I have some involuntary muscle movements -- scratches on my knives and slices on my face shaving).
 
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