thinning questions (yet another thread)

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noj

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I have been reading a lot on this forum, and some of Jon’s (JKI) videos on thinning, and have some questions and observations. I only wish to discuss double bevel knives here. I have some, but limited experience thinning, and want to learn more before jumping to something more expensive, preferably before they need major thinning. A couple may need major thinning, mentioned below. I don’t have, or plan to have any motorized equipment. I am interested in maintenance thinning. Despite collectability, all knives will be put to work in the kitchen, and have to work well;-)

A. The first topic is about measurements and cutting observations.

A.1 Thickness behind edge (or 1 mm back)

I own a good micrometer. I don’t think I am capable of measuring the thickness behind the edge (or 1 mm behind) with any accuracy; there’s simply too much guesswork for me. That said, if I sharpen around 15 degrees, it turns out if your bevel is 1 mm deep, it’s 0.5 mm wide (and just behind the edge). That seems a lot more than some have recommended, and a 1 mm bevel doesn’t seem excessive after a handful of sharpenings.

A.2 Measurements (5 and 10 mm back), and knives that do and don’t cut well

First, I understand different knife makers, or styles, will have different geometries, and there’s no one right answer. I own a Konosuke FM I like a lot. I have two others that don’t cut well. One is a Mizuno which came new very thick and convex, and I haven’t sharpened it much. The other is a 15 year old famous maker (not going to mention here) I got used, I haven’t sharpened, and also a convex grind. Measurements (in mm) at midpoint follow:

Konosuke FM 0.6 1.0
Mizuno 1.2 1.7
15 year old 1.0 1.4

B. Recommendations for help thinning

I don’t think I am capable of thinning the two thick ones above. A lot of work, and too valuable to me to get wrong. Any suggestions? I would want someone that won’t change the makers character and geometry too much (like someone that doesn’t do convex bevels).

C. Maintenance thinning

C.1 Convex grinds
Jon’s (JKI) has a video on thinning wide bevel, but very little on thinning convex grinds. Any good threads or suggestions? I am having a hard time understanding how to comfortably and accurately maintaining a 5 degree angle, if that is an example of what’s required. There’s no obvious feedback like what one might get with a shinogi. I am looking for a lot of detail. Plus pitfalls I don't need to experience first hand;-)

C.2 Blade anomalies
I know there will be some. Low spots, high spots, etc. I am looking for the most common, and what to do with them. My guess is anything that gets to the cutting edge needs to be "fixed", less sure about the thinning area, and some are cosmetic (or will go away as the thinning progresses).

Thanks in advance, suggestions on this forum are always great!
 
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tostadas

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A.1 Thickness behind edge (or 1 mm back)

I own a good micrometer. I don’t think I am capable of measuring the thickness behind the edge (or 1 mm behind) with any accuracy; there’s simply too much guesswork for me. That said, if I sharpen around 15 degrees, it turns out if your bevel is 1 mm deep, it’s 0.5 mm wide (and just behind the edge). That seems a lot more than some have recommended, and a 1 mm bevel doesn’t seem excessive after a handful of sharpenings.
This assumes that the blade thickness gets down to 0.0mm at the very tip, which is not the case. In reality, the thinnest part of the knife (at 0mm) still has measurable thickness when sharpened. Too thin and the steel will literally fall apart.

Here are some measurements I posted in a separate thread that may be helpful to you.
 

noj

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This assumes that the blade thickness gets down to 0.0mm at the very tip, which is not the case. In reality, the thinnest part of the knife (at 0mm) still has measurable thickness when sharpened. Too thin and the steel will literally fall apart.

Here are some measurements I posted in a separate thread that may be helpful to you.
I don't know how to get a measurement at 1 mm. It would be pure guesswork, I don't know or can't see whether it's .75 mm or 1.5 mm with a tool that had a 5 mm surface.

My calculation assumes the final bevel is 1 mm deep, and has a 15 degree angle. Yes, a tiny fraction may be rounded due to some natural convex-ing, but I don't imagine it affects the calculation.

|\ <----- 14 deg
| \
| \
| \
+-----+

------> picture hard to draw with this editor, hope u can figure it out

The vertical line is the depth 1 mm. The horizontal ( +----+) is thickness behind edge (divided by 2) t2.
tan (14 deg) = t2/1 = t2 = .25, so thickness behind edge is 0.5. This is what was called "Distance behind edge at midpoint" in the referenced thread. This is the case anywhere the edge is ground flat. Obviously, this assumes your edge grind is at least 1 mm deep.

I don't understand the reference to the very tip.
 

HumbleHomeCook

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So, understand this is coming from someone with a fair bit but still limited experience and who is function-over-form oriented...

I don't measure. Maybe I should just to get a real understanding of measurements correlating to my experience but I don't and doubt I ever will.

I think a lot of people would be amazed how much of a difference even just mild easing and smoothing of the edge bevel shoulders can make. That's where I think everyone should start, just smoothing things up a little.

I just go and let the knife tell me how it's going. I've yet to work on a blade that didn't have variation along the length to at least some degree. That gets revealed pretty quick on a higher grit stone and can help guide you. This is especially true if you want to focus on aesthetics.

Anyway, I'm a big believer in the old adage that you can always take away, but you can never put back on so my thinning is generally slow and takes place over time and multiple sessions. Do a little, sharpen everything up and use it for a while.

How do I like it? Adjust and repeat.

I'm also not really great at closely replicating the maker's original grind. I mean, that can be pretty challenging with flat stones anyway. Sure, you can add in convexity and such but you're only ever gonna get so close. I do know there are folks on the forum that are very good at targeting and accomplishing very specific profile outcomes but I'm not one of them.

In other words, my advice is to not stress the technicals too much and let feel and experience guide you.
 
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tostadas

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By "tip" i meant to say "edge." The thickness at the very edge is never going to be 0, but at the very least probably around 0.1mm

Here's a sketch based on actual measurements of one of my blades (the red line). As you can see, the thickness at 0 is not 0.0, actually closer to 0.2mm. In any case, the actual distance, whether it's 0.75mm, 1.5mm behind the edge is not that significant. What you will know is that it's thinner than the thickness @5mm, and thicker than @0mm. Essentially what I'm trying to get at is the thinnest point behind the edge that you can reasonably measure. Digital calipers with a small measuring surface are a more helpful tool here. But I think if you try to get the smallest non-zero measurement with your tool, it should be kinda close.
1670184880665.png
 

noj

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By "tip" i meant to say "edge." The thickness at the very edge is never going to be 0, but at the very least probably around 0.1mm

Here's a sketch based on actual measurements of one of my blades (the red line). As you can see, the thickness at 0 is not 0.0, actually closer to 0.2mm. In any case, the actual distance, whether it's 0.75mm, 1.5mm behind the edge is not that significant. What you will know is that it's thinner than the thickness @5mm, and thicker than @0mm. Essentially what I'm trying to get at is the thinnest point behind the edge that you can reasonably measure. Digital calipers with a small measuring surface are a more helpful tool here. But I think if you try to get the smallest non-zero measurement with your tool, it should be kinda close.
View attachment 212299
I am afraid to measure anything like that for fear of breaking off a piece of metal. I only have a micrometer.

My argument though is about the thickness 1 mm back from the edge. The part I assume is zero is the final edge itself, which would be pretty un-sharp at 0.2 mm. I think your diagram doesn't include this final edge, but I could be wrong. My diagram was only of the very final edge, and not including the main bevel being thinned. I am not sure your diagram is depicting this, as the very last bit to the left should abruptly change from 5 degrees (or whatever) to 15 degrees (or whatever). My argument was only discussing that very last bit to the left, and based on my observation/guess that bevels are probably 1 mm wide after a few sharpenings.
 

tostadas

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I am afraid to measure anything like that for fear of breaking off a piece of metal. I only have a micrometer.

My argument though is about the thickness 1 mm back from the edge. The part I assume is zero is the final edge itself, which would be pretty un-sharp at 0.2 mm. I think your diagram doesn't include this final edge, but I could be wrong. My diagram was only of the very final edge, and not including the main bevel being thinned. I am not sure your diagram is depicting this, as the very last bit to the left should abruptly change from 5 degrees (or whatever) to 15 degrees (or whatever). My argument was only discussing that very last bit to the left, and based on my observation/guess that bevels are probably 1 mm wide after a few sharpenings.
It includes the final edge. It would be less than 0.2, but not by a lot, and certainly not 0.

edit: and clarification, the 0.2 was actually measured @1mm, so yea you can assume it kinda narrows down a bit to the edge. If you do the trig and assume a 12deg angle, that puts the thickness of the very edge approx 0.16mm
 
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noj

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Better than a micrometer? I still have little confidence I could hit 1 mm back with much accuracy. My measurements at 5 and 10 mm may be enough to look at my other questions.
 

tostadas

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Better than a micrometer? I still have little confidence I could hit 1 mm back with much accuracy. My measurements at 5 and 10 mm may be enough to look at my other questions.
Yes, because you said that you are unable to get closer than 5mm accuracy with your micrometer that has a 5mm surface.

I think it's important to know what the edge is like on your blade before recommending some sort of thinning. But if you're looking for a general recommendation, the numbers in my table are how I categorize thickness behind the edge. So you can thin a bit, check your work, test some cuts, and maybe compare.

If the measurements you list for your thick knives are actually correct at 5mm and 10mm, they're incredibly thick. And any sort of thinning by definition will alter geometry. If you're concerned about that, then reach out to a professional, like Jon, and see if they're accepting work.

Jon has a video on hamaguri grinds. You might want to check that one out.

And I dont think you need to worry about low spots or anything at this point until you get to actual thinning and figure out what you're after. The high/low spots are more related to aesthetics than performance.
 

noj

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Here's the math with your geometry though. The acute angle is say 14 degrees. The middle vertical line is a model of your final edge. For sake of calculation, if the bevel edge is 0.1 mm, then it's (middle vertical line) is 0.05 mm. There is 1 mm of ground final edge at 14 degrees. The additional distance to zero (if there was metal there) is x. Half the width at 1 mm behind the edge is y.

x = .05/tan(14) = 0.2
y = (1 + 0.2 ) * tan(14) = 0.3

This yields a width 1 mm behind the edge of 0.6.

The same calculation with a bevel edge of 0.2mm yields a width 1 mm back of 0.7.

The answer without the model of the bunted edge was 0.5.

So I acknowledge the interesting idea, but doesn't yield dramatically different results.



Untitled.jpg
 
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noj

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Yes, because you said that you are unable to get closer than 5mm accuracy with your micrometer that has a 5mm surface.

I think it's important to know what the edge is like on your blade before recommending some sort of thinning. But if you're looking for a general recommendation, the numbers in my table are how I categorize thickness behind the edge. So you can thin a bit, check your work, test some cuts, and maybe compare.

If the measurements you list for your thick knives are actually correct at 5mm and 10mm, they're incredibly thick. And any sort of thinning by definition will alter geometry. If you're concerned about that, then reach out to a professional, like Jon, and see if they're accepting work.

Jon has a video on hamaguri grinds. You might want to check that one out.

And I dont think you need to worry about low spots or anything at this point until you get to actual thinning and figure out what you're after. The high/low spots are more related to aesthetics than performance.
Sorry what I said wasn't clear. What I was trying to say was the measuring heads of the micrometer are a 5 mm disks. The instrument is graded in 1 mil (1/1000 inch) or 0.0254 mm. The problem is my guessing where exactly 1 mm is by visual guesswork, imperfect kinesthetics, and not taking a piece out of my knife;-)

Oh, and thanks much for the rest of the comments. I think the measurements are pretty accurate. Those are easy when the instrument head is a 5 mm disk. I welcome a thinner geometry, I just didn't want someone to grind a convex blade dead flat.

I think those extra-thick ones are beyond me, but I'd still like to learn how to maintain my others. They are newer, and working fine, so I am in no hurry. I'd just like to get good at it before they need major work.
 
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noj

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My micrometer. The black material on the ends of the disk are electrical tape I used to prevent scratches. Yes, I subtracted the extra width from the calculations, and re-checked that there was no measurable deformation (of the tape) at the end.

20221204_183046[1].jpg
 

M1k3

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So, understand this is coming from someone with a fair bit but still limited experience and who is function-over-form oriented...

I don't measure. Maybe I should just to get a real understanding of measurements correlating to my experience but I don't and doubt I ever will.

I think a lot of people would be amazed how much of a difference even just mild easing and smoothing of the edge bevel shoulders can make. That's where I think everyone should start, just smoothing things up a little.

I just go and let the knife tell me how it's going. I've yet to work on a blade that didn't have variation along the length to at least some degree. That gets revealed pretty quick on a higher grit stone and can help guide you. This is especially true if you want to focus on aesthetics.

Anyway, I'm a big believer in the old adage that you can always take away, but you can never put back on so my thinning is generally slow and takes place over time and multiple sessions. Do a little, sharpen everything up and use it for a while.

How do I like it? Adjust and repeat.

I'm also not really great at closely replicating the maker's original grind. I mean, that can be pretty challenging with flat stones anyway. Sure, you can add in convexity and such but you're only ever gonna get so close. I do know there are folks on the forum that are very good at targeting and accomplishing very specific profile outcomes but I'm not one of them.

In other words, my advice is to not stress the technicals too much and let feel and experience guide you.
An example of taking care of those bevel shoulders.
PXL_20221205_003919676.jpg
 

M1k3

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A picture worth 1000 words, thanks!

On a convex grind, is that done with just finger pressure, or do you maintain some very low angle?
I tried to barely lift the knife, while also placing my fingers near the edge. Where you put pressure makes a big difference in where you grind.
 

noj

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No need to measure. If your edge bevel is 1mm wide, thin until it is a hairs breadth thick.

You can even thin until you feel a burr "zero grind". Then put a new (and super narrow) 15 degree edge bevel on it.
I guess that is where I was sort of headed. If it's 1 mm, then just behind the bevel it's somewhere between 0.5 and 0.6 (0.7) mm, as long as the assumptions behind my calculations hold. How to tell if the edge is 1 mm not clear, again guessing, and hard to measure.
 
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You can even thin until you feel a burr "zero grind". Then put a new (and super narrow) 15 degree edge bevel on it.
When I read Tutorial on how to thin european knives I thought, that’s clever, setting the edge bevel before the bulk of the thinning makes it less likely to run into deformation difficulties vs setting the edge bevel against a zero grind. In practice I do the latter, as you wrote :)
 

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When I read Tutorial on how to thin european knives I thought, that’s clever, setting the edge bevel before the bulk of the thinning makes it less likely to run into deformation difficulties vs setting the edge bevel against a zero grind. In practice I do the latter, as you wrote :)
I tend to go to a zero grind, then add a new edge bevel.

But.

1) I use the existing edge bevel to inform me about how my thinning is going.

2) I avoid using anything coarser than around 500 grit as I approach a zero grind (i.e.: once the original edge bevel is very small, I move up to 500 grit so that I don't reach the edge with anything coarser than 500).
 

M1k3

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I tend to go to a zero grind, then add a new edge bevel.

But.

1) I use the existing edge bevel to inform me about how my thinning is going.

2) I avoid using anything coarser than around 500 grit as I approach a zero grind (i.e.: once the original edge bevel is very small, I move up to 500 grit so that I don't reach the edge with anything coarser than 500).
Honest question. Why would you not using anything coarser than 500 grit on the edge?
 

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Honest question. Why would you not using anything coarser than 500 grit on the edge?
I guess it's a mostly theoretical concern of wasting steel refining that edge with a 500ish coarse stone (and I guess thus thickening the edge a little and undoing some of my good thinning work) before moving to a medium and fine stone.

Edited to add: As metioned in @ian 's subsequent post (#32), removing very much metal when creating a zero grind risks mucking up the profile.
 
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I tend to go to a zero grind, then add a new edge bevel.

But.

1) I use the existing edge bevel to inform me about how my thinning is going.

2) I avoid using anything coarser than around 500 grit as I approach a zero grind (i.e.: once the original edge bevel is very small, I move up to 500 grit so that I don't reach the edge with anything coarser than 500).
I do the same. I use the existing bevel as I guide, starting with a #200-220 stone, then when it's thin like a hair or two I move up to a #500 stone. A sharpie also works well. In my case I'm thinking I'll jump to a #500 in any case to remove the #200 scratches and must not forget it also removes metal, not only polishes... so I leave a little bit of "fat" there to be ground by following stones.

Learning from mistakes I guess. More than once I did all the thinning job on the #200 and forgot about the obvious fact that following stones, even if intended only for polishing, also remove metal (specially a 300 or 500). Then I ended up with thinner edges / behind the edge than I had planned.

Another mistake learned - be careful with the tip. Usually I work on it only slightly with the #200 stone (maybe 1/10 of the effort dedicated to the other areas) and leave most of the job for the #500 stone.
 

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Thanks *everyone* for your posts; very helpful. I haven't started with the stones, yet.

I did try to get some 1 mm measurements. While there is a big caveat about the accuracy of 1 mm, I took several measurements to perhaps offset the issue.

__________________ 1 mm, 5 mm, 10 mm
Konosuke FM____ 0.23, 0.6, 1.0
Mizuno___________ 0.5, 1.2, 1.7
15 year old_______ ??, 1.0, 1.4

On the 15 y/o I could not get consistent measurements. I had a closer look at the edge (not ever sharpened by me), and it looks very convex as well as wide. Someone couldn't hold an angle. Anyhow, the BTE and 5 mm measurements explain why my carrots kept exploding;-)

I might need to get a junker knife to learn on. I have an old Sab I already thinned, but it's a pain because it bends (and stays bent easily). I also like it on the thick side because it's the softest metal I have seen. I have a junker I did some work on, but it's solid stainless and heavy, and was taking forever to thin, though I think I was he**-bent on removing low spots at the time for some reason.
 

noj

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This is where a microscope complements the micrometer: here are mm rules at a certain magnification, and the edge at the same magnification.
View attachment 212388
View attachment 212391

Thanks for the idea. I could use something better than a magnifying glass for other reasons too. Last I looked, there were a dizzying number of microscopes on sale. Which one are you using, or perhaps more key is what are key features for this application? I imagine focus range, magnification (not including pure digital, which I can do easily later on computer), and pixel resolution.
 
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If you are looking for a practice knife, I really like Forgecraft for this.


For measuring 1mm behind the edge, I put a mark on my calipers at 1mm. Line up the edge with the mark and consistent 1mm measurement all along the edge.

You’ll usually get the biggest performance benefit with thinning in the area just behind the edge. I usually take it down to 0.2-0.3 at a minimum.
 
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If you are looking for a practice knife, I really like Forgecraft for this.


For measuring 1mm behind the edge, I put a mark on my calipers at 1mm. Line up the edge with the mark and consistent 1mm measurement all along the edge.

You’ll usually get the biggest performance benefit with thinning in the area just behind the edge. I usually take it down to 0.2-0.3 at a minimum.
How is the grind on Forgecrafts? Convex or wide / flat bevel?

edit: sorry, totally off-topic
 
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