sharpening the tip of a knife

[noj]

go for it

Look at my thought experiment. In picture 2, the wrist angle is wa = x > 0 (maybe 60 degrees with my plate) and the lift angle the handle above horizontal is la = 0. At the far extreme of a 90 degree belly is picture 4. The wrist angle is 0, and the lift angle of the handle above horizontal is la = x. In between (a more normal knife shape) involves both variables. I am feeling uninspired to come up with the model of a 5-axis milling machine. Sorry if that's not precise;-)

 

[noj]

My take on Jon's video is he is demo'ing laying back toward the spine on single or wide bevel knives. That's because he's trying to maintain the profile of the bevel up to the shinogi line.

In Peter's video he has a standard double bevel with just a narrow edge bevel. He doesn't have to roll that knife toward the spine because he isn't trying to raise a shinogi or alter the overall profile. He's simply sharpening the edge bevel so he can just lift and swipe.

You can't discount the knife types for each technique.

I could be wrong but that's what I see.

I actually spoke to Jon about this, and he is talking about the narrow edge bevel. He was even reading this thread;-) I stopped trying to figure out what Peter was saying, though not meant as a criticism.

 

[r0bz]

Look at my thought experiment. In picture 2, the wrist angle is wa = x > 0 (maybe 60 degrees with my plate) and the lift angle the handle above horizontal is la = 0. At the far extreme of a 90 degree belly is picture 4. The wrist angle is 0, and the lift angle of the handle above horizontal is la = x. In between (a more normal knife shape) involves both variables. I am feeling uninspired to come up with the model of a 5-axis milling machine. Sorry if that's not precise;-)

interesting did not understand tho

 

[MowgFace]

My take on Jon's video is he is demo'ing laying back toward the spine on single or wide bevel knives. That's because he's trying to maintain the profile of the bevel up to the shinogi line.

In Peter's video he has a standard double bevel with just a narrow edge bevel. He doesn't have to roll that knife toward the spine because he isn't trying to raise a shinogi or alter the overall profile. He's simply sharpening the edge bevel so he can just lift and swipe.

You can't discount the knife types for each technique.

I could be wrong but that's what I see.

I use Jon's method on all of my knives.

As the tip curves up, rotating the blade towards the spine reaches the area the same way as lifting your wrists. Take one of your knives to a stone without scrubbing and try to lay the bevel flat on the stone as you get to the tip.

Using a wide bevel knife just gives you a better visual than with a full convex knife. Technique is the same. Takes some getting used to, but even take out your folder and try to lay its bevel flat. When you get to the tip, your elbow moves closer to your hip, and the blade rotates toward the spine.

 

[HumbleHomeCook]

I use Jon's method on all of my knives.

As the tip curves up, rotating the blade towards the spine reaches the area the same way as lifting your wrists. Take one of your knives to a stone without scrubbing and try to lay the bevel flat on the stone as you get to the tip.

Using a wide bevel knife just gives you a better visual than with a full convex knife. Technique is the same. Takes some getting used to, but even take out your folder and try to lay its bevel flat. When you get to the tip, your elbow moves closer to your hip, and the blade rotates toward the spine.

Gonna have to try it!

 

[MowgFace]

If you want to use a wide bevel as a visual learning experience, take it and press the wide bevel flat against your table/desk. Continue to keep the wide bevel flat against a surface and move up towards the tip.

As you get towards the sweep and especially right at the tip, you will notice the handle of your knife change orientation. This is what you need to replicate when tip sharpening.

*This is similar to the plate excersize*

 

[noj]

interesting did not understand tho

My experiment, or the text? Picture 2 is on the flat or heel. Picture 4 is at the tip if it curved a full 90 degrees. An actual knife is probably a lot less than 90 degrees - somewhere in between. On the flat, the handle isn't lifted, and the wrist angle is whatever your bevel angle is. On the 90 degree tip, your wrist angle must be 0, and the handle angle is at whatever your bevel angle is. An actual knife is somewhere in between - specifically, the handle is elevated and the wrist angle is less than the bevel angle.

 

[superworrier]

My takeaway is for this type of thing, it's better to just think less mechanically and just think about following the curve of the knife. If you try and calculate the right amount to turn/lift it's gonna be a mess. Luckily, your brain and body are pretty good at this type of thing if you just try and do it naturally/visualize it. I'm pretty sure anybody (without any knife experience) would be able to understand swiping the knife along the edge and maintaining a more or less consistent angle.

 

[noj]

If you want to use a wide bevel as a visual learning experience, take it and press the wide bevel flat against your table/desk. Continue to keep the wide bevel flat against a surface and move up towards the tip.

As you get towards the sweep and especially right at the tip, you will notice the handle of your knife change orientation. This is what you need to replicate when tip sharpening.

*This is similar to the plate excersize*

Interesting, I thought that was a related, but maybe (just haven't thought about it until now) slightly different phenomena. Wide/single bevel are usually ground such that the shinogi is a constant height. Even with no belly curvature, the distal taper means you cannot achieve that using a constant angle. There was a nice video of this, specifically for single bevels that I saw somewhere on the forum.

 

[superworrier]

Also my understanding is that this is not actually sufficient: if you naturally do this you will make the tip bevel too wide/flatten out the tip profile because as the edge curves more, the pressure is more concentrated and you actually sort of deform the tip, which is why that sort of rocking technique exists. The other remedy I heard is to just use less pressure near the tip.

 

[superworrier]

Interesting, I thought that was a related, but maybe (just haven't thought about it until now) slightly different phenomena. Wide/single bevel are usually ground such that the shinogi is a constant height. Even with no belly curvature, the distal taper means you cannot achieve that using a constant angle. There was a nice video of this, specifically for single bevels that I saw somewhere on the forum.

Yes. This was a good video. Does anybody have the link to the thread? I remember he said there was a part 2 coming

 

[MowgFace]

Interesting, I thought that was a related, but maybe (just haven't thought about it until now) slightly different phenomena. Wide/single bevel are usually ground such that the shinogi is a constant height. Even with no belly curvature, the distal taper means you cannot achieve that using a constant angle. There was a nice video of this, specifically for single bevels that I saw somewhere on the forum.

I think that coming to terms that a "Constant angle" does not exist. Which is more or less why we do not buy in to sharpening systems.

"Keeping a steady angle" is a relative term.

 

[noj]

I think that coming to terms that a "Constant angle" does not exist. Which is more or less why we do not buy in to sharpening systems.

"Keeping a steady angle" is a relative term.

In the video, he meant putting the whole shinogi on a single plane is not possible if the blade has distal taper and constant shinogi height. That's what I meant by "constant angle", which might not have been the best term.

 

[noj]

Also my understanding is that this is not actually sufficient: if you naturally do this you will make the tip bevel too wide/flatten out the tip profile because as the edge curves more, the pressure is more concentrated and you actually sort of deform the tip, which is why that sort of rocking technique exists. The other remedy I heard is to just use less pressure near the tip.

I find the rocking technique or "smooth following of the curve to the tip" my preference. It seems to get all the angles right almost naturally. Plus, looking at the bevel, or magic marker says so.

 

[noj]

Yes. This was a good video. Does anybody have the link to the thread? I remember he said there was a part 2 coming

This thread! ;-)

www.kitchenknifeforums.com/threads/video-for-those-that-are-interested-in-sharpening-single-bevels.60538/#post-926394

 

[Blank Blades.]

i was confused about this also
i can just lift my elbow up and then the tip is touching the stone and ican sharpen it what got me confused is why do i need to lower the spine to the stone .....
do you know why does it happen geometrically ?

You don't need to. Some people are do sometimes change the angle going towards the tip to make the edge bevel a more acute angle. Though normally you really don't want to change the edge angle.

 

[superworrier]

You don't need to. Some people are do sometimes change the angle going towards the tip to make the edge bevel a more acute angle. Though normally you really don't want to change the edge angle.

No, this is to keep the edge angle the same. However, I think you don't need to consciously do it, it will happen naturally. In fact, it is very natural to rotate the spine/handle. You would probably only not do it if you're trying very hard not to/too mechanical

 

[superworrier]

I find the rocking technique or "smooth following of the curve to the tip" my preference. It seems to get all the angles right almost naturally. Plus, looking at the bevel, or magic marker says so.

Yes, it's super natural and intuitive. Overthinking is what causes people to be confused. Once you lift, you naturally rotate as well. The only thing I don't like about the rocking is I find it hard to do on the back side of the knife

 

[noj]

My experiment, or the text? Picture 2 is on the flat or heel. Picture 4 is at the tip if it curved a full 90 degrees. An actual knife is probably a lot less than 90 degrees - somewhere in between. On the flat, the handle isn't lifted, and the wrist angle is whatever your bevel angle is. On the 90 degree tip, your wrist angle must be 0, and the handle angle is at whatever your bevel angle is. An actual knife is somewhere in between - specifically, the handle is elevated and the wrist angle is less than the bevel angle.

Hope this helped conceptually. As someone already said, overthinking (or detailed math) probably won't help with freehand sharpening. I mean, would you be any further along if I said this? ;-)

 

[HumbleHomeCook]

Gosh damnit @JBroida! I don't know if I want to curse you or celebrate you.

This whole thing distracted my thoughts all day. I just couldn't visualize it and trying to simulate it with my Spyderco Endela on my desk at work just wasn't doing it. I know that John knows what he's talking about so I knew the issue was with me and @MowgFace added to my need to know.

So like every boy with an exciting new curiosity, I rushed home, did my chores, and gave it a shot. After four plus decades of doing the tip lift, it felt awkward but I managed it and damnit if it doesn't work.

And once I did it, it just seemed to make perfect sense and like all my previous consternations, even just hours before, were silly. I'm still not sure my brain grasps the geometry yet but it surely does work.

I don't know if I'll adopt it full stop but I will damn sure keep trying it.

Never stop learning. Never stop exploring. Never stop discovering! This is why I love sharpening so much.

 

[noj]

Yes, it's super natural and intuitive. Overthinking is what causes people to be confused. Once you lift, you naturally rotate as well. The only thing I don't like about the rocking is I find it hard to do on the back side of the knife

I just read this, notice the same, and after pondering for a bit, I think I know what can cause this. Keep in mind I tend to use my right hand to hold the handle regardless of sharpening on the left or right side of the knife. When using a sweeping motion on the right side, I have a strong tendency to move the handle to the side as I approach the tip. This creates a natural smooth lift and rotation - at least for me. On the left hand side, I have a strong tendency to move the handle more vertical as I approach the tip, and therein lies an issue. The lift is intuitive, but the rotation isn't - actually, it feels awkward. One method to combat this is to hold the knife handle with my left hand for the left tip. Just thought I'd share the observation.

 

[superworrier]

I just read this, notice the same, and after pondering for a bit, I think I know what can cause this. Keep in mind I tend to use my right hand to hold the handle regardless of sharpening on the left or right side of the knife. When using a sweeping motion on the right side, I have a strong tendency to move the handle to the side as I approach the tip. This creates a natural smooth lift and rotation - at least for me. On the left hand side, I have a strong tendency to move the handle more vertical as I approach the tip, and therein lies an issue. The lift is intuitive, but the rotation isn't - actually, it feels awkward. One method to combat this is to hold the knife handle with my left hand for the left tip. Just thought I'd share the observation.

That is a good point. It definitely feels less intuitive on the other side. I do find switching hands to be surprisingly natural, just because sharpening the other way is just weird.

 

[mpier]

On my off hand motion I tend to rotate my stone to a 45 degree angle, adjust my stance and approach it from the back side of the stone. In this way you can keep all the same motions and the tip feels more natural to sharpen. I’ve also been switching hands which seams to have good results it just feels so awkward at the tip.

 

[Miyamoto Musashi]

For what it’s worth, I had brought in a knife into JKI for choil and spine rounding/polishing (also just wanted an excuse to visit the store and crew there).

In addition to the knife I brought which was purchased elsewhere, I brought my regularly used Ginga (purchased from him) for him to refinish and sharpen (I figured I might as well bring it and it ended up being a big learning opportunity so I could see what Jon does).

I’ve taken a picture of what the tip looks like because I have had the same issues with you regarding tip sharpening and found what you said about not being able to gain a lot of information from the sharpie at the tip very compelling and relatable.

Here are two images of the tip of my Ginga after Jon’s work. I didn’t realize that tips could look like that when sharpened correctly and had associated this with the beginning of a bird beak forming out of my own ignorance and lack of knowledge.

Apologies if the photos are bad quality, lmk if you want me to send more.

As an aside, when Jon first handed me the knife (this was the first time I had had a knife of mine sharpened by someone else). I was immediately blown away at how even the bevels were. I wasn’t surprised in the slightest but it hit different seeing it in person.

I don’t remember what the tip looked like when it was new but I’m fairly confident that it didn’t look like that.

I think it fundamentally changed my preconceived notion of what the bevel at the tip of a knife should look like when sharpening.

 

[Blank Blades.]

Thats usually what a tip looks like when either the thickness behind the edge increases at the tip and the angle at the bevel stays the same . Or if someone changes their angle as they get to the tip (lowering the spine of the knife).

It could be either one if those.

 

[ReiHamono]

Just the tip…

 

[r0bz]

Here is a thought experiment, and pictures. First, as perhaps an
oversimplification, imagine your control of the knife is on just two
axis: your wrist (rotation angle along the axis of your knife handle),
and your wrist height. Of course, the human body is more complicated,
but let's focus on these because they are the primary ones involved.

Here is my model of a knife. Note the bevel angle is constant.
At any point along the curve of the "blade", the position of the
knife and handle isn't in question (assuming you want a constant
bevel angle).

View attachment 191934

Here is the position when grinding along (what would normally be) the
flatter part of the knife. Note the wrist angle and height.

View attachment 191935

Here is the position when grinding as you start getting into the curve
approaching the tip. Note the wrist angle and height. The angle is
decreased, and the height is increased. Again, by angle I mean
rotation angle along the axis of your knife handle, err paint stick;-)
The edge angle is constant (as determined by my junky plastic plate).


View attachment 191936

Still not sure? Let's push it to a (probably unrealistic) position
where the blade bends a full 90 degrees. The angle is now zero.

View attachment 191937

I conclude that under the assumption that we maintain a constant bevel
angle, and have two means of control (rotation angle along the axis
of your knife handle, and handle height), you must raise the handle
and rotate to a lower angle.

it seems from your experiment that it shows the opposite, that you need to rotate toward the blade in order to raise the angle between the spine and the stone because as you lift up it decreases the angle between the knife and the stone....
please tell me why am I wrong

 

[noj]

it seems from your experiment that it shows the opposite, that you need to rotate toward the blade in order to raise the angle between the spine and the stone because as you lift up it decreases the angle between the knife and the stone....
please tell me why am I wrong

As with many things in physics and engineering, measurements are dependent upon the observer. In the case in question, it's a little complex because of all the degrees of freedom. Imagine observing (and measuring) the angle* looking straight down the center of the handle, angle* = 0 parallel to the stone, and increasing in the counterclockwise direction (for right handed users). With the handle about parallel with the stone, the angle* is about what the edge bevel angle is. At least with the plate experiment, and you get into the curve, the rotation occurs clockwise (for right handed users). This is rotation is toward the spine (as I would describe it), and decreases the angle* as my observer sees it.

I may not be understanding your argument precisely. Keep in mind that in my experiment, I was letting the constant bevel angle dictate what the answer is, rather than any intuition.