I'm frustrated, need your help !

[matc]

Okay so I've been hand sharpening for a while my knifes and especially more my chisels and handplane blades. However, I'm having issues with both my nakiri and gyuto, I seem to be creating a low spot along the flat part of the blade profile as I sharpen my knifes. I attached a picture so you can see what I'm talking about. My cutting board is truly flat so it's not the culprit, I also flatten my stones each time before using them with my atoma 140 so they're flat. One thing I noticed on both knifes is that the low spots occur right where the stones touch the blade when I sharpen with the knifes perpendicular to the stone to avoid hitting the handle (see the 2nd pic to get a better idea). I know it's a user error but what's causing this ? I always resharpen using my chosera 400-1000-3000 and 8000, that's it.

Last night I spent 30 minutes rubbing my nakiri vertically to the stone to flatten the blade, I got it near perfect but then after thinning and sharpening it, I created again a dip along the edge !! Im quite frustrated as this leaves a lot of accordeons and I wated 3h trying to fix the knife, your help would be appreciated !!

 

[HumbleHomeCook]

If you're starting off with flat blades, and this is happening in the same place on two different knives, it tells me you're sharpening too much and/or too hard in those spots. Or maybe you're sliding the spots over the corner of the stone.

 

[MSicardCutlery]

Unequal wear in one spot tends to mean unequal pressure or contact time in that area. One thing I was bad for in the beginning was flexing the blade over the edge of the stone, it doesn't take much on thin blades to make a divot with a corner. Try varying your approach angle and see if it stops happening or moves.

 

[matc]

how much pressure should I be using ? Sharpening the other side feels more natural, so maybe I'm flexing the blade and putting too much pressure. I tried "sharpening" my nakiri on my kitchen scale, the highest I got is about 5 lbs, felt like that was the max pressure I would use on my 400 stone to rapidly create a burr, is that too much ?

 

[matc]

edit : when you guys say sharpening too much at the same spot, let,s say I have a burr everywhere along the edge except near the heel, I tend to focus on that area until I get a burr. With what I just read above, it means it's wrong ? So for that case you just sharpen the whole blade until the burr gets to the heel ?

 

[refcast]

Yeah this sucks and I have had the same problem. Try changing hands while thinning, that helped reduce it a lot. And also less pressure during thinning. Or flattening more often. If you feel or see a burr develop more in one area, that area is being sharpened more.

You can get a flat piece of glass or something to keep on checking as you work on your knife, so you don't dirty your cutting board, then you can relate how sharpening affects the edge profile.

Alternatively, the knife might not be straight, or the grind behind the edge is a bit uneven and makes sharpening more uneven.

 

[M1k3]

Seeing as the hole is next to the heel, sharpen a little more at the very heel.

 

[ian]

I got it near perfect but then after thinning and sharpening it, I created again a dip along the edge !!

Yea, it can be a little frustrating if you do the vertical thing (it's often called breadknifing here, since you're trying to cut your stone with a sawing motion like you'd use when you were cutting bread) and get a great profile, and then the hole reappears when you sharpen. One reason this can happen is that when you're correcting the profile like that, you're not correcting unevenness in the grind, so you end up with an `edge' prior to sharpening that's thinner in some places than others, and then this doesn't sharpen evenly.

As to what's happening when you sharpen, my guess is that you're not moving up and down the blade enough when you sharpen, instead focusing too much on one section at a time. Over time this can create low spots near where the edge of your stone is contacting the knife. Sharpening with the blade perpendicular to the stone also can exacerbate this if you're not careful.

If you want, take a vid of yourself giving it a full sharpening and we can comment.

 

[Benuser]

Seeing as the hole is next to the heel, sharpen a little more at the very heel.

Excellent point. It is very common to have a heel section that's abrubtly thickening at some 1.5cm, 9/16" from the heel. As there is more steel to get abraded, it will take longer.
I wouldn't choose now for breadknifing but first thin behind the edge, and see if you can even out along the edge.

 

[matc]

okay so you guys recommend I first thin the knife and then resharpen it ? I'll try that

 

[Pie]

If the stone is flat it’s a pressure/technique thing. This has happened to one of my knives due to inexperience.

Ive seen mazaki flip the knife over so the handle is facing away from you at an angle and use the top right corner of the stone. It forces your blade to have more edge on the stone, stopping you from abrading too much where the hole is. It’s awkward but it works. You sort of hold the spine instead of the handle.

It’s sort of weird and may introduce other issues, but if all else fails give it a go.

Like this. Yeah, it’s weird.

And yes, I’d probably give them both a thin to take some of the extra fat off the edge.

 

[Desert Rat]

Yeah this sucks and I have had the same problem. Try changing hands while thinning, that helped reduce it a lot. And also less pressure during thinning. Or flattening more often. If you feel or see a burr develop more in one area, that area is being sharpened more.

You can get a flat piece of glass or something to keep on checking as you work on your knife, so you don't dirty your cutting board, then you can relate how sharpening affects the edge profile.

Alternatively, the knife might not be straight, or the grind behind the edge is a bit uneven and makes sharpening more uneven.

Judging from this picture it very well could be that the grind behind the edge is uneven. Just based on the damascus pattern.

 

[Desert Rat]

Just want to add it shows up in the bevel size also.

 

[natto]

Just want to add it shows up in the bevel size also.

Yep. Same thought here.

Some light strokrs without pressure will show the contact area.

 

[psfred]

Lotta possibilities here, including a bent or improperly ground knife. If it's a problem on more than one knife, it's likely your technique though.

You can get a "hole" in the edge from improper knife production where the initial grind is deeper in a spot, with the result that there is less metal there and as you shapen the edge "moves" sideways since there isn't any metal on one side. Usually takes a really bad grind though.

If the knife isn't straight, though, you will sharpen away material faster on the convex side while leaving the concave side untouched, and that will result in a "hole" in the edge. Found that out myself the hard way, luckily on a cheap knife and not an expensive one.

Most likely though, you are applying pressure at the heel improperly and over-grinding the hollow spot -- it's just about where I'd expect the edge of the stone to be when you are sharpening the heel. It's also easy to apply un-wanted torque to the blade from the handle, which results in excessive pressure on the side with more pressure (you and either lift to handle too much or push it down too much). I like to use the handle to guide the knife back and forth while applying pressure only with my fingers on the blade as I tend to torque the handle up and blade down. Just something you need to learn.

I think to fix the issue I'd make sure the knives are straight (you can just sight down the edge from the heel, should be obvious if there is a kink in the edge), then check for even thickness along the blade from top to heel. If the heel is fatter, not an uncommon issue, you may need to grind it down (thin it) on a coarse stone while staying well away from the edge so that you have similar contact down the whole edge. Apply pressure only with a couple fingers at the point you want removed and do NOT apply up or down force on the handle, only straight back and forth. Once you get that fixed it should be easier to sharpen.

You can also blacken the blade with a Sharpie and make a couple thinning passes to see if you have high or low spots behind the edge, and also make a couple passes on a normal sharpening stone at the edge and see where the blade is contacting the stone on both sides. That will tell you what you need to change in your sharpening motions to fix the issue I think.

 

[natto]

Apply pressure only with a couple fingers at the point you want removed and do NOT apply up or down force on the handle, only straight back and forth.

Good point, good post.

And I like to find the problem first, then look what I can do about it. so

You can also blacken the blade with a Sharpie and make a couple thinning passes to see if you have high or low spots behind the edge, and also make a couple passes on a normal sharpening stone at the edge and see where the blade is contacting the stone on both sides. That will tell you what you need to change in your sharpening motions to fix the issue I think.

+1
So far I am only guessing what might be the problem.

 

[Benuser]

Couldn't agree more. Except for the sharpie: I prefer a red one.

 

[Kawa]

Judging from this picture it very well could be that the grind behind the edge is uneven. Just based on the damascus pattern.

View attachment 175357

This was the first thing that crossed my, limited experienced, mind.
I can hardly imagine its a pressure thing, since you have a way broader part of the edge on the stone, so you have to seriously push hard and bend the steel locally to abrade that much more in that small area.

How is the left side of this blade at that same spot?
If the edge is completely gone at that point and not in front of and behind that low spot, it might be a bend knife at that spot?

Still can't figer out that hollow/recurved part as shown in picture 1. Only have seen that with soft steel which has been steeled for many years.

Interessting to hear what it was and how to counter.

 

[Ggmerino]

Possible culprit is that you are putting downward pressure on the blade with the hand holding the handle. The handle hand should only hold the angle and not put any downward pressure on the blade- otherwise you may flex the blade and create a low spot Where the blade edge hits the stone edge (like your pic when sharpening the heel area). The only pressure should come from 2 or 3 fingers of the other hand held directly over the center of the stone. The blade can move, but the downward pressure should always be centered on the stone. Hope this helps.

 

[VICTOR J CREAZZI]

Ha! To the people who make knives with 2" X 72" belt grinders this is known as the 2" notch.

It's very common among beginning knife makers. I have done the same thing with stones just like I think you have.