# Rambling thoughts on gyuto profiles



## Kippington (Sep 4, 2018)

I've been in a few conversations with people about gyuto profiles, and I've come to the conclusion that I envisage this topic slightly differently from most others. Perhaps my way of thinking is more efficient, or maybe not. I'd like to find out so please feel free to chime in with your thoughts.





In any conversation about profiles, the major measurements we start with are the length of the cutting edge and the height of the knife at the heel. With the tip of the gyuto being a point, we can use these measurements to draw a triangle.





Easy enough, but where do we go from here? The next point people like to bring up is the height of the tip relative to the heel, kind of like this:





But in the case of this triangle, how can we tell what angle to hold the knife in order to make this reading? You might think the answer is straight forward - to hold the cutting edge down before taking this measurement (like the one below, on the left), but even then there's a problem with the spine height, which I'll get to later.





So instead, I believe the next most important aspect after length is the combination of flat-spot and belly curve. These are the defining aspects on how the knife performs in either a rock or a chop - you don't even need to see the rest of the knife to get an idea of how it moves on the board.





I could give a more in-depth explanation on the flat-spot and belly curve, but that would go too far off this topic, and I think that most people here understand it well enough. If not, let me know.

Now that we have the cutting edge set, if we lay the flat spot down against the board the next important measurement should be the angle of the spine (as well as the handle, if the two are parallel) in relation to the board. The distance of your cutting surface to your elbow height is a major determining factor for this angle. Also, we actually need less heel height to get the same amount of knuckle clearance if the handle angle is steeper.





I'd like to point out that even though the two above have exactly the same flat-spot and belly curve (meaning they would behave quite similarly), they appear totally different if described by tip height alone.
You can hopefully see how I think it's wrong to describe one of these as "low tip" compared to the other: it isn't technically true. It's also a good time to bring up what I mentioned earlier - holding the flat-spot down doesn't change the illusion that one tip appears lower than the other.

Next I think of the choil shape - an important factor for comfort and safety. This probably should be higher up on the list in importance but it's easier to slot it in here.





Then the least important aspect and final thing to be modified would be how the spine curves into the tip. The Masashi gyuto cops a lot of flack for how they do this, but I honestly think it hardly matters.





So in a nutshell, it can be really confusing to talk about the profile of a gyuto in terms of tip height, as its relative position can be a bit of an illusion and relies on a couple of other more-important factors.
There are a few other points, but before I go into them - What do you guys think? Does this make sense, or have I lost the plot...


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## Gjackson98 (Sep 4, 2018)

Always a pleasure to read your write ups!


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## Mute-on (Sep 4, 2018)

Makes perfect sense. Having the spine more parallel to the edge always seemed more natural to me as it keeps the back of the handle a little lower, and closer to the board.

However, some upwards sweep of the handle (and therefore a lower appearing tip) is also necessary to help with glide. Naturally this will feel different to each user depending on their height, the work surface height, and personal preferences.

As far as choil shape, I vastly prefer a wider neck (emoto?) and a larger choil radius like on a Kato. However, unless the neck is very narrow, I probably wouldn’t notice after a few minutes.

Of course this might all just be a load of self indulgent BS and I’m deluding myself. Oh well ...

Cheers

J


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## RDalman (Sep 4, 2018)

yea good writeup! Slim tip a la KS can have some suji-like features and help it with release also. And there's the possibility of using a little recurve to the spine to mess with the profile and handling angle even more.


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## ecchef (Sep 4, 2018)

I love this type of thread. These topics really bring about the best discussions. 
Good point about spine recurve, Robin. I’ve been using a Sakai Takayuki Grand Chef lately and, although I don’t know the mechanics behind it, the slight spine recurve does seem ro make a difference.


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## Barmoley (Sep 4, 2018)

Great thread and write up. Matus should chime in, him and I were discussing this subject a few years back. It seems when people discuss blade height at the heel and knuckle clearance, what we really deal with is the angle of the handle vs the edge and also the height of the elbow over the cutting surface. So you could have a knife that is relatively low at the heel, but still gives a lot of clearance and is still comfortable plus the benefits of less drag, etc.

It also seems that some blade shapes are more visually appealing to most people. For example symmetrical, pointy shapes such as KS and Shig just look good even though the shape of the spine doesn't really affect performance as much as the other attributes of the profile.


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## HRC_64 (Sep 4, 2018)

Great post ...

On tip height, the "angle of attack" of the handle needs to be considered as you mention to me the concept of tip height is straigt forward...

1) the top of the blade (spine/handle) is paralell to the cutting surface, and
2) choil is at 90* ortogonal spine/handle and to cutting surface 






normally its pretty easy to sort it out and possible to evaluate most comparisons 
ie,...if you use photoshop, no problems...but sometimes maybe its a personal view,

(and sometimes maybe the maker puts the convex/grind indepently of either)


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## Interapid101 (Sep 4, 2018)

ecchef said:


> I love this type of thread. These topics really bring about the best discussions.
> Good point about spine recurve, Robin. I’ve been using a Sakai Takayuki Grand Chef lately and, although I don’t know the mechanics behind it, the slight spine recurve does seem ro make a difference.



Curious, how does it feel different?


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## HRC_64 (Sep 4, 2018)

Perhaps its worthwhile to think of the gind like an air-foil (cross section)
and then think of the chord which has the greatest width to the air-foil centerlind,
where that is vs the edge or spine is in part a function of where it is absolutely, 
but aslo proportionally ...ie, "in the middle" or "1/3 from the top" etc, so 
if the shape of the spine, and/or if the spine is not flat, the chord-
moves relatively to the spine along the cutting edge....i think. 
Or maybe I'm crazy.


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## valgard (Sep 4, 2018)

For me the angle of the cutting edge (longer section to the back) with respect to the handle/spine is a MAJOR factor, as well the angle between the handle and the board to be able to put the tip down. Those two determine a lot of what's comfortable for me.


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## JaVa (Sep 4, 2018)

Interapid101 said:


> Curious, how does it feel different?



IME It changes the balance of the blade significantly by adding more weight to the knife, making it more blade heavy as the added steel is right at the tip. The added surface area at the tip will make food release a bit worse and any task that requires puncturing will suffer too (like removing silver skin from meat) because the stubbier tip will have more resistance and the added drag doesn't help either.

Though with good taper and a thin tip some of those problems can be avoided to a degree.




Personally I like a semi pointy tip, long flat spot (like half the edge length) that progresses to a naturally rolling tip that's marginally lowered. I like the handle, spine and flat spot to be all in the same angle and paralell to the cutting surface.

Perfect height is for me is about 50mm. As I'm not that tall a taller blade and/or a handle that's curved up a bit will force my wrist in a slightly awkward position.

Edit.
Also a thinner neck feels better as it's more nimble for me. Though a tall neck feels more secure and powerful, but at the same time too cumbersome and slow.


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## McMan (Sep 4, 2018)

As always, cool points and super helpful images, Kip!
I think the different amount of meat above the tip also raises questions about weight and balance-point. Tip shape is (or at least could be) a factor here, no?…

Your tale of two tips is interesting, since both examples are pretty well known gyuto shapes…
(L) Left example = more weight above the tip (due to tip shape) but also behind the tip (since the spine is higher for longer and closer to parallel to the edge for longer)
(R) Right example = less weight above and behind the tip (due to a pointier tip and a more/sooner inclined spine). 




Of course, balance-point and weight are affected by several other factors (distal taper overall, how quick/severe the distal taper is, thickness at the neck, grind, etc.). But tip shape--and how it relates to spine slope--would seem to be one among multiple other factors. How impactful it is compared to other factors would be interesting to chase down… 

Assuming the two knives above also have the same grind, distal taper, and all that jazz, what we'd be left with is Left is heavier and more balance-forward, right is lighter and balance closer to the handle. Right?


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## gic (Sep 4, 2018)

Really interesting!


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## merlijny2k (Sep 4, 2018)

There is imo another factor where tip shape matters. Since you can only go so thin at the spine before the tip becomes too fragile, the left knife can have the primary grind bevel at a steeper angle in the tip area, therefore the tip may even outperform the tip of the right shape for some tasks like carrot cutting for example. I see this between my Kanso (left shape) and my sabatier (right shape).


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## merlijny2k (Sep 4, 2018)

I really enjoyed your writeup. Been mulling at the subject myself for a long time.

There are many productive thoughts in it but there is one thing about your system that I find less elegant. You start with a triangle but you eventually ditch... basically everything except the heel and the neck point. Makes me think you have a good system but could do with a more elegant start. I will try to do some drawings (and get them in here....) tomorrow. This discussion is too good not to join.


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## LucasFur (Sep 4, 2018)

Chiming in ...

(L) Left example = Takeda -- Large Santoku hybrid
(R) Right example = Masamoto KS -- short Sujihiki hybrid.



McMan said:


>




One thing I will say, is that I like when the handle is angled up ... towards me ... Like the left Photo. *But* Cutting board height makes a massive difference in what is preferable. (For me)


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## valgard (Sep 4, 2018)

LucasFur said:


> *But* Cutting board height makes a massive difference in what is preferable. (For me)



Huge point


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## HRC_64 (Sep 4, 2018)

Angle of attack for handle impacts also

hand clearance
push vs pull cut

etc


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## HRC_64 (Sep 4, 2018)

Here is a push-cutter example 
note the high tip, flat profile blade.

Guillotine à Saucisson





Whereas a standard suji has also has a flat profile, 
but combined with a low tip heigh, low heel height, 
and relatively flat angle of attack.


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## Kippington (Sep 4, 2018)

Some really good points here.

LucasFur, JaVa and merlijny2k rightly mention the influence the size of the tip has on balancing point, food release and thinness of the grind... I'd like to add flexibility/rigidity to that list.
I had the shape of the tip positioned near the end of my list of importance because of how dependent it is on other factors (spine and belly). But maybe I should reconsider my priorities.

Dalman and ecchef mentioned the recurve (sori) blade, so here's an image of one... and why not throw a K-tip in there for good measure! *All of these have exactly the same belly and flat-spot.*










merlijny2k said:


> There are many productive thoughts in it but there is one thing about your system that I find less elegant. You start with a triangle but you eventually ditch... basically everything except the heel and the neck point. Makes me think you have a good system but could do with a more elegant start. I will try to do some drawings (and get them in here....) tomorrow. This discussion is too good not to join.


Please do! Tell me more, I'd love to hear what you have to say - and anyone else for that matter. I put this up as a discussion for debate!

I'm glad some of you are talking about your preferences on the spine/handle angle of attack. The topic doesn't come up often in these kinds of conversations and I figured it was something people didn't really think about. Very happy to be wrong.


JaVa said:


> Personally I like a semi pointy tip, long flat spot (like half the edge length) that progresses to a naturally rolling tip that's marginally lowered. I like the handle, spine and flat spot to be all in the same angle and paralell to the cutting surface.
> Perfect height is for me is about 50mm. As I'm not that tall a taller blade and/or a handle that's curved up a bit will force my wrist in a slightly awkward position.
> Also a thinner neck feels better as it's more nimble for me. Though a tall neck feels more secure and powerful, but at the same time too cumbersome and slow.


Everything you say here makes me think you have a really high cutting surface, like you could knock your elbow on it walking past. Would that be right?
Either way, the closest knife I've used to fitting your description is a Shig 240mm, and ohmygosh it was fun to use on a high cutting board!


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## refcast (Sep 4, 2018)

To add more about tips:

A high tip angle allows me to cut with a higher angle. It's like the difference between the force when I poke myself with a straight finger (where the tip would be 90 degrees) versus with my fingerpad (a nakiri or kakugata usuba with no tip curve). I feel it gives more cutting force per user force input. This is obvious to me when peeling in hand. 

I prefer a pointy tip versus a super thin flat tip if I had to pick, but I enjoy and can use both. 

Lastly, the amount of downward curve from the top of the knife makes the knife more agile but less workhorsey. We can start angling down from the handle, which is good for heavier or taller knives to feel more nimble, or we can start near the tip to keep the workhorse feeling for thinner knives. Of course there is a trade-off in weight, and there are so many configurations that can be appropriate.

I like to think of the basic knife shape as going from nakiri to kamagata usuba to various tips and angles and spines.

Spine recurves make me want to hatchet-kind of chop. I like to imagine that the curve has a lowestmost point and I kind of swing from heel to that lowest point.

Lastly, sometimes the steel can be a bit undamped, which can be problematic when the tips are thin. I find some steel can feel "denser" but really they just are bit more damped when springing back from the super small left-right displacements that happen in cutting. I still like thin tips.


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## Kippington (Sep 4, 2018)

refcast said:


> Lastly, sometimes the steel can be a bit undamped, which can be problematic when the tips are thin. I find some steel can feel "denser" but really they just are bit more damped when springing back from the super small left-right displacements that happen in cutting. I still like thin tips.


There's definitely a sweet spot for springiness. I often hear complaints about blades being too flexible, but I think the reverse (a clunky thick tip) tends to be put up with more often.
__________________

Okay, here is something that hasn't been mentioned yet - I like to call it "the KS effect".
It turns out that the choil (or better yet, the emoto) - with all other things being equal - has a significant effect on how the overall knife behaves and can actually nullify a precise measurement of the heel height.
Take a look at this example:




These two profiles are identical in terms of the properties we've talked about so far. Blade shape, flat spot, the handle/spine angle relative to the board... all of these essentially duplicated. If we were to take each one and measure the height of the knife at the heel, the numbers would come out exactly the same. However it wouldn't give a good indication of how tall each knife feels on the board, as the shape of the emoto has caused the one on the left to be a "shorter" knife, while the one on the right is "taller". It's a difference of only a few millimeters, but it's enough to feel during use.

I first noticed this while looking closely at the Masamoto KS to work out why the blade looks so thin and slender, and I soon came to realize that their style of emoto raises the handle off the spine and gives them more space to work with. Other styles of emoto can cause handles to rest closer to the board, despite what an equivalent heel measurement might indicate.
Compare the following image to the one at the top of the thread - Could it be considered a KS clone?


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## JaVa (Sep 4, 2018)

Kippington said:


> Everything you say here makes me think you have a really high cutting surface, like you could knock your elbow on it walking past. Would that be right?
> Either way, the closest knife I've used to fitting your description is a Shig 240mm, and ohmygosh it was fun to use on a high cutting board!



Well, a Shig does have just about the perfect profile for me, that's very true. Wakui Kasumi (EE version!!!) is another one, as the profile is VERY close to Shigs profile, but the Wakui is thinner behind the edge and it has even slightly better cutting performance, but less food release. 

Great point about work space height, but my cutting surface at work and at home is the normal height, but as I'm 170cm tall, the effect would be about the same. I just went to measure and there's about 7,5cm clearance between my elbow and the cutting surface. 

Another reason I don't like too much belly and a high tip is because I'll knick my middle fingers knuckle easier with a knife like that. When I raise the blade and rest it on my finger, due to my height the tip will point just a tad bit too high and if I'm not paying attention, when I slice the blade backwards it can sometimes knick my knuckle ever so slightly. A taller blade will make the matter even more difficult as I need to lift it higher and as a consequence the tip will be angled higher still. So again it's the same effect as if the counter top would be too high.

Not a big deal at home, but at work when you need to plough through 20 to 30 kg of veg as fast as you can, it makes a world of difference for me. Also that's when a long flat spot shines for efficiency and more precise cutting.


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## JaVa (Sep 4, 2018)

Kippington said:


> There's definitely a sweet spot for springiness. I often hear complaints about blades being too flexible, but I think the reverse - a clunky thick tip - is put up with more often.
> __________________
> 
> Okay, here is something we haven't mentioned yet - I like to call it "the KS effect".
> ...


Those would be some of the reasons I like a thinner neck much more and why it feels so much more nimble.


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## refcast (Sep 4, 2018)

Thanks for pointing out blade height differences caused by neck thickness.

I didn't mention this earlier because we were focusing on the profile only -- but the way I use a knife changes when we consider neck thickness and the handle thickness in knuckle clearance.

I could describe it as how far the edge is away from the central axis of the handle, which tells me how nimble a blade is. I can idealize the most nimble shape of a knife as a stick. If I add weight further away from the stick, it requires a bit more effort for me to rotate the knife for motions like cutting horizontally, as well as move around. So a shorter knife emphasizes nimbleness in movement. But I gain a big advantage in being able to apply less user input force for a similar cutting output. This helps a ton. So I feel I gain nimbleness in cutting action.

We would add weight in the KS picture with the overlay if we added machi. This would add weight and make the knife heavier. It would change the weight distribution though, and may make it feel more nimble or predictable in some ways.

I also am not considering angle of handle attachment, and left-right displacement of the handle from center, which can do stuff, too, to feelings of nimbleness/instability versus feeling more locked in.


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## panda (Sep 5, 2018)

just combine edge profile of a KS with spine profile of Mizuno = perfect blade shape


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## HRC_64 (Sep 5, 2018)

Kippington said:


> Compare the following image to the one at the top of the thread - Could it be considered a KS clone?








That second outline is a "sakai 270" 

Only half-joking, as the 250 KS is an exact 270mm measured at the machi/insertion point. KS has not only a very narrow emoto, but its also longer than normal.

From another/design point of view, this puts the handle a bit further
back than normal and plays into the overall balance of the knife,
the handle acts like its a bit lever this way, and seems more nimble

I know the KS gets slagged on alot her at KKF but the overall design has alot going on
and all of these factors are what makes is 'work' a bit better


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## Kippington (Sep 5, 2018)

panda said:


> just combine edge profile of a KS with spine profile of Mizuno = perfect blade shape


...then stick a handle on it and call it the Panda Express!


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## Keith Sinclair (Sep 5, 2018)

Good thread
Head Gardemanger years liked the thinner tip of the Masamoto for decorative food work and slicing duties. For knocking out lots of banquet prep. like good flat & taller tip for forward push & chopping. One can not live with one style of gyuto alone.


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## Kozuka (Sep 5, 2018)

LucasFur said:


> Chiming in ...
> *But* Cutting board height makes a massive difference in what is preferable. (For me)



Interesting point, never thought of the actual work height in relation to the knife format / geometry.

Great thread alltogether, thanks for sharing and discussing guys!


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## Larrin (Sep 5, 2018)

I have nothing meaningful to add but I like the discussion.


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## panda (Sep 5, 2018)

Kippington said:


> ...then stick a handle on it and call it the Panda Express!


i support this idea 100%, and workpony grind! hehe


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## Migraine (Sep 5, 2018)

I fear there is a serious lack of conversation in here about one of - in fact probably THE - most important factors.

Does it look mad cool?


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## merlijny2k (Sep 5, 2018)

Personally I prefer a trapezoid as the basic shape when pondering profiles. I agree with most your steps but do a few of them differently:

First: flat spot to spine angle. Very important as it determines where on the nakiri/santoku-honesuki/garasuki spectrum you enter. Then also select heel height and length.

Next I offset the heel to neck line with the desired blade length. This gives me a line along which to put the tip. 

Then select tip height and try to make those curves look good. The last one I find surprisingly dificult. It quickly starts looking like a medieval peasant knife, which is probably why they looked like that back then, it's easy to end up there. Getting a distinctly Japanese, German or French profile without copying one I find quite challenging. Many smiths with a distinctive profile claim it took them a long time to develop. The devil is, as always, in the details.

Benefits of my own line of thought over Kip's I find is that I keep more of the starting geometry towards the end, and the term tip height gets a clear meaning. Advantage of Kip's system I find is that it is more ambitious and aims to work through the process in a progression of large and important decisions towards the minor ones while in my thinking I stay more with the math/geometry subject and don't link to desired effects for the user much.


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## merlijny2k (Sep 5, 2018)

Since many blades don't have a real flat spot but rather a curve with a radius that is lager near the heel than near the tip, I also propose to define belly as the max measurement from the heel-tip line. Devide by length to get dimensionless number if you will. Position of the top of the bellycurve can then serve as indicator for flatspot length. Can also be made into a dimensionless number.


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## Kippington (Sep 6, 2018)

merlijny2k said:


> Next I offset the heel to neck line with the desired blade length. This gives me a line along which to put the tip.


Can you explain this line at the heel in more detail? I'm not following what you're referencing off to find it.


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## merlijny2k (Sep 6, 2018)

I take a line perpendicular to the spine to the point at the corner of the heel. That is the striped line to the left. Then offset with blade length L to find the striped line to the right. Now I have a trapezoid consisting at the top of the spine, extending into the handle and extending the spine-line to the striped line to the right. At the bottom I have the line tangent to the heel, along the flat spot if the knife has one.

Basically on the left side I use the same two points you do for your triangle as vertices for the trapezoid.


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## Kippington (Sep 6, 2018)

Interesting... HRC mentioned measuring tip height off the spine, similar to you.
As ecchef and Dalman brought up, a sori can really throw a spanner in the works and I feel it strongly affects your method.




Would you consider this example to have a mid-height tip? Or instead would you draw a straight line from the two highest points on the spine and treat the re-curve like a gap, in which case the handle angle would be off-set from the spine.




I like your take on the flat-spot and belly measurement - I'm going to have to think about that one for a bit... maybe open a new can of worms!


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## quantumcloud509 (Sep 6, 2018)

Don’t see anyone talking about the inverted belly curves one can find for sale on the BST thread


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## ecchef (Sep 6, 2018)

Let’s throw another variable into this. The (for lack of a better term) progressive rate of distal taper and where along the spine it begins to break. Granted, this shouldn’t affect the profile, but it will the balance point which may be especially noticeable in longer, thinner blades. Maybe this is why I prefer a bit of recurve since I typically like 240+ blade lengths. Adds a touch of tip ‘presence’ in laserish blades.


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## merlijny2k (Sep 6, 2018)

Kippington said:


> Would you consider this example to have a mid-height tip?



Yes!

I never gave sori's much thought and certainly don't claim to have a system that elegantly accounts for them.

I don't have any knives that feature them. The locally popular knife from local celebrity chef Herman Den Blijker used to have one. He has a new model out and i'm not sure about that one.

Doing as you described makes most sense to me.


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## HRC_64 (Sep 6, 2018)

One idea for the belly discussion --

Put a line from the heel to the tip. 
Then take this line and copy it (cmd-c),
Move it over so its now tangent w/profile
Now marke orthogonal to the tangent line,
into the "front" of the curve, and the "back" behind the curve,
as our tangent point can "estimate" apex of belly

Since the tangent point can be further back 
or further forward to the tip,
its useful to know where it is
(ie, proportionatey along a relative continuum).

(This method may not be perfect but it
is I believe repeatable and comparable over many
different blade shapes.)


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## Larrin (Sep 6, 2018)

HRC_64 said:


> One idea for the belly discussion --
> 
> Put a line from the heel to the tip.
> Then take this line and copy it (cmd-c),
> ...


You lost me at orthogonal to the tangent line in front of the curve and the back behind the curve.


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## RDalman (Sep 6, 2018)

When I'm by the grinder, I typically roll the edge on a flat surface, that will typically tell me if I need adjustments my eye did'nt catch, works like a charm every time, repeatable and for every different size/model


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## LucasFur (Sep 7, 2018)

The way HRC was talking i would love to see some knife profiles that shapes of mathematical equations.





Fibonacci spiral. ... if you were to Un-coil it and see what happens with the edge.




Basically use the "GOLDEN RATIO" and apply it to a knife for the profile, spind and edge?
Its seen an insane amount in nature as the perfect ratio ...






















Ok, that last one is a joke


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## HRC_64 (Sep 7, 2018)

Larrin said:


> You lost me at orthogonal to the tangent line in front of the curve and the back behind the curve.




orthogonal means "line at 90*"








> "into the "front" of the curve, and the "back" behind the curve"



ie orange is "front".... assuming d=front/tip, and c=heel)
should be self explanatory w/ picture.

[edit: see below]






[or more precisey...]


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## merlijny2k (Sep 7, 2018)

Larrin said:


> You lost me at orthogonal to the tangent line in front of the curve and the back behind the curve.



Me too at the exact same line


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## RDalman (Sep 7, 2018)

I used to use the golden ratio for pin positioning on full tang handles. Works really well!


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## merlijny2k (Sep 7, 2018)

While we are rambling. Some thoughts on fun things that can ultimately be done with a mathematical model that translates knife shapes into a finite set of indicator numbers:

Computer analysis of profile pictures. Computer could then find similar profiles in a database. 

Computer aided profile design. You could play with the indicators and watch the knife shape evolve. Coupled with a laser cutter and CNC mill you could even design a shape and have the blank for it ready in about an hour. Of course you woyld still have to harden, finish, handle and dharpen but still.

You design your own profile and have the computer select closest profile shape from database.

I don't have all the skills necessary to pull it off but last year I coached a tech savvy student with his thesis. He built a parametric design model for an offshore jacket structure in Excell that then translated to a 3d graphic model. Of course he had some assistance from the company and he pulled a few smart tricks I probably would not have been able to come up with myself but it was nonetheless relatively straightforward. And having a good parametric model to start from really is key to success. 

I have seen other members say we should have a profiles database just like z's steel database. I really believe it can be done too. Having a vector image based on indicators is then highly desirable over just storing raster images.


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## Kippington (Sep 8, 2018)

HRC_64 said:


>


Oh wow, not only do you use the same tip height measurement technique as merlijn, but you use the same belly measuring method too, albeit a different way of wording it!
Does anyone else use this method? I hadn't thought of it like this.





---------------------------

Lucas, as beautiful as the Fibonacci spiral is, I really don't think it works in any way on the belly curve.
It's quite difficult to come up with an elegant and simple way of describing the dynamics of the curve. It's one of those more intuitive things, like throwing and catching a ball vs doing the math to work it out.

It won't stop us from trying though!


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## Mute-on (Sep 8, 2018)

By way of example, I have always found the Shigefusa gyuto profile instrinsically appealing. The angles, curves and proportions appear visually balanced to me.

Marko Tsourkan and Will Catcheside also produce similarly well resolved gyuto profiles. The Fibonacci proportions of the knife world, so to speak ...

Oh, and that Kippington bloke makes a pretty nice looking blade too ...


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## LucasFur (Sep 8, 2018)

I'm just thinking here...
might apply to handle length vs blade length. Vs height of blade? vs machi length? vs spine thickness? vs choil thickness? -- I don't know but is that why 240mm gyutos are so popular?
Length of the blade that you pinch vs the length of blade exposed
Average length of product cut vs length of blade available.
Length of flat spot vs length of curve/up sweep of the blade. ***kippington**
Circumference of handle vs length of hand.
Height of blade at heel vs mid & tip
Surface area of back third vs mid third vs last tip third. 
Ratio between ura and omote (single bevel)-- actually this one is probably true.

- there is a whole wackload of possibilities


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## panda (Sep 8, 2018)

Mute-on said:


> By way of example, I have always found the Shigefusa gyuto profile instrinsically appealing. The angles, curves and proportions appear visually balanced to me.
> 
> Marko Tsourkan and Will Catcheside also produce similarly well resolved gyuto profiles. The Fibonacci proportions of the knife world, so to speak ...
> 
> Oh, and that Kippington bloke makes a pretty nice looking blade too ...


i was not a fan of shig profile, and i had to alter the edge shape on my marko when i first got it cause it was too flat, kept digging into the board..


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## Matus (Sep 8, 2018)

You started a very interesting discussion Kippington! You (and others!) have made very interesting points. It also comes down to the fact, whether the person is looking at this as a knife user (who is trying to describe his/her preferences) or a knifemaker, who is trying to come up with a set of 'parameters' that will help him/her to somehow translate the wanted properties of a finished knife to geometrical parameters.

From my point of view (amateur knifemaker) most relevant parameters have been mentioned (inclusive very interesting & important user feedback) - like 'height of the tip', 'angle of the handle', 'shape (height) of the emoto v.r.t. knife height', 'shape of the tip' and also - the VERY important one - the relative height of the counter-top to the person. The last one has big impact on what knife shape will feel comfortable. For example - I am not particularly tall, but our counter-top is and so I tend to prefer knives that have a bit flatter profile and angle of the handle rather small. Otherwise the end of the handle will have tendency to hit my forearm (or it will require to hold the knife such that the handle will pass by my forearm).

One parameter that is directly influenced by the parameters already discussed and has big impact on how a knife feel in hand is weight and its distribution. If the blade profile is like on Masashi (or Wat or Toyama) - there will be a lot of steel close to the tip. Not only this shifts the center of mass away from the heel, but it also changes how the knife feels when moved (rotated - as cutting is partially a rotary movement) - that relatively large mass close the tip will make the knife feel less nimble, but cutting with more ease because of this weight. Of course - distal taper also can and does influence this. Knives like some of the Hide gyutos I have seen with not too pronounced distal taper will also have the center of mass further away from the heel.

Parameter that can be used to adjust the center of mass (at expense of additional weight) are handle length and materials. I find that for a Sakai-like knife (thing Konosuke, Ichimonji and similar) knife that is not too tall (usually around 48-49 mm) and relatively low weither of 180 - 200g a traditional HO wood WA handle works well and these knives feel very nimble. But with a knife like 240 Watanabe a bit heavier and longer handle helps to bring the centre of mass back a little and makes the knife fell more balanced. But that reflects my personal preference and not a universal truth.

The 'spine recurve' mentioned by Robin (this is something that tends to happen in quench) can allow the combination of large angle of handle AND taller blade closer to the tip.


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## merlijny2k (Sep 9, 2018)

So far we have four parameters for the blade curve: heel point, velly point and tip, and the angle at the heel. Gives you a fourth order polynomial equation. I'd say fourth order should be sufficient for a single curve if you have the correct parameters. I think these four should do fine but have been wrong and surprised too many times before. Not too recently been proven wrong by some guy known as kip....


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## Kippington (Sep 9, 2018)

This is my way of seeing it - not necessarily any better or worse than the ways above.




The fixed points represent the heel and the tip... simple enough. The yellow lines represent the starting angle of the curve between the points, and the length of each yellow line indicates the amount of weight, or influence, each angle has on the curve.
Even though both yellow lines say 'Weight and angle', in my mind the angle coming out of the heel is always a flat zero as if the flat spot were resting on the board. This gives me a reference with which I use to measure the angle of the tip. It also means that the spine or handle would always have a slight angle to be measured as well (I don't like using the spine as the reference point).


panda said:


> i had to alter the edge shape on my marko when i first got it cause it was too flat, kept digging into the board..


I'm guessing we all know that the angle of the tip is what causes this board-digging, but surprisingly the height of the tip has very little to do with it. For example, here would be a gyuto with hardly any belly (very flat) which could still be rocked high without digging the tip into the board:



*(but maybe it's not too surprising to some people)*
With looks only a mother could love, we won't be seeing this one in the stores any time soon. 

Actually I'm just reminded - A kitchen I used to work at has called me to fix up all their knives that were "professionally sharpened" by a dude with a belt grinder. He came on a closed day and rounded the tips (like the picture above) *and the heels* on every. single. knife... 
I'll take a picture in the next couple of days, its shockingly bad.


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## Matus (Sep 9, 2018)

Digging into the board was probably meant when the flat spot is ‘too flat’ and the either the heel itself or the geometrically straight flat spot catches on the unevenness of the cutting board. The important point is - flat spot should never be completely flat and there should be a tiny upcurve towards the heel.


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## Kippington (Sep 9, 2018)

Ah I see.
I agree with what you say about the tiny up-curve (many knives have it) but I don't think it's always necessary. If the transition from belly into flat spot is executed well (a very gradual transition), the knife can still move smoothly on a board without a small up-sweep at the heel. It's difficult to get right, though.
For example, I don't think the Shig photo in my post above has an up-sweep at the heel. I might be wrong though.


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## Matus (Sep 9, 2018)

The upcurve towards the heel is usually very subtle, I would see it more as a continuation of the very gentle curve most flat spots have. But as you say - different knives are ground differently.


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## Matus (Sep 9, 2018)

And to come back to the angle at the tip you mentioned above - that is an important, but also a rather complex topic as the curve towards the tip may have very different shape.


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## Kippington (Sep 9, 2018)

Absolutely. The length of the yellow lines determines the amount of curve in my style of doing things. With a bit of practice I can use it to recreate any profile, but I guess the problem is it might not be all that intuitive.


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## Kippington (Sep 9, 2018)

It was mentioned before that the height of your cutting board is important when considering the spine/handle angle (or flat-spot angle, the two being different sides of the same coin).




I find that (a) tends to be easier to use on a higher surface, while (b) is easier to use on a lower surface. Many of the pro chefs here would understand what it's like when someone is using your favorite spot in the kitchen and you have to go and find another bench to work on. I tend to use different knives depending on the height of the bench I'm working with.

To add to this, the profile shape will often influence the way I want to move my arm and wrist, depending on what I'm cutting of course.
On a higher table (a) will have more of a chopping wrist action with the lower arm moving up and down, pivoting at the elbow in a movement similar to a drummer. 240mm Shigs are amazing for this, and I'm sure many others are too.
On a lower table (b) tends towards a locked wrist push cut, and relies more on forward-and-down arm movements. Lifting the knife off the board is optional. This is my default style for most work, and so I personally like my knives to have more of a spine angle and prefer to work on lower tables.




Sori/re-curve spines are basically a mix of the two.



RDalman said:


> When I'm by the grinder, I typically roll the edge on a flat surface, that will typically tell me if I need adjustments my eye did'nt catch, works like a charm every time, repeatable and for every different size/model


I have a scrap cutting board next to my grinder for the same reason


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## merlijny2k (Sep 9, 2018)

There is to my knowledge no established mathematical method that can be applied to describing a curve that gives different weights to different tangent lines. You either know the angle at a point and can thus construct a tangent line and use that as a requirement for a curve equation or you don't. Nonetheless tangent at tip can be used as a boundary condition just like any other. May well turn out to be more successfull than the four I suggested but would have to check a few profiles to see.


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## ThinMan (Sep 9, 2018)

So for a truly bespoke knife you would to measure me, my kitchen counters and my cutting boards?


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## Kippington (Sep 9, 2018)

Well in the past I've asked people to send me a video of them working so I can tailor the knife to their needs, but it seems like maybe I'm asking too much. The easier option is just to ask for someone's favourite knife profile in a picture, and I can extrapolate plenty of information from it.


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## Kippington (Sep 9, 2018)

I should also mention that over many years of sharpening, blade (a) will gradually turn into (b) unless you make a conscious effort not to let it happen.

As I use my main knives over the years they start to feel flatter in the belly and more angled at the handle/spine - which in turn improves the feel and feedback as it slowly reaches my sweet spot.
Then one day it's suddenly too much, the knife handles like crap and needs re-profiling.

My Sukenari 240mm ZDP has reached the point of its life where it's gone over the sweet-spot for me and needs re-profiling.
As new profile:









My old faithful. She needs some loving.


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## Kippington (Sep 17, 2018)

As I mentioned earlier, here is one of my old workmates knives sharpened by some idiot going around with a grinder, charging money for sharpening.
It's the worst job I've ever seen without a shadow of a doubt. Of the twenty knives he worked on, ten of them are complete garbage now.

I'm still not sure how I'm going to salvage these... I mean, look at the knuckle clearance!







Matus said:


> The important point is - flat spot should never be completely flat and there should be a _*tiny upcurve*_ towards the heel.


Heh, not on these knives!


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## Nemo (Sep 17, 2018)

Kippington said:


> As I mentioned earlier, here is one of my old workmates knives sharpened by some idiot going around with a grinder, charging money for sharpening.
> It's the worst job I've ever seen without a shadow of a doubt. Of the twenty knives he worked on, ten of them are complete garbage now.
> 
> I'm still not sure how I'm going to salvage these... I mean, look at the knuckle clearance!



Make it a gyutohiki?

Would it even be worth the investment in belts?


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## ecchef (Sep 17, 2018)

Kippington said:


> *(but maybe it's not too surprising to some people)*
> With looks only a mother could love, we won't be seeing this one in the stores any



Actually, this looks remarkably similar to an older Takeda of mine.


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## Matus (Sep 17, 2018)

Kippington said:


> As I mentioned earlier, here is one of my old workmates knives sharpened by some idiot going around with a grinder, charging money for sharpening.
> It's the worst job I've ever seen without a shadow of a doubt. Of the twenty knives he worked on, ten of them are complete garbage now.
> 
> I'm still not sure how I'm going to salvage these... I mean, look at the knuckle clearance!
> ...



That looks aweful! The guy should pay the vaule of those knives back.


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## dreamwrx (Sep 17, 2018)

Holy... that's a lot of reading I just did. But you guys put lots of things in perspective. I agree that for me at home (not a pro) that the height of the food prep, board height, and my height does affect which knife is more comfortable to use. However in 99% of the time for home cooks.. I think we adapt to whatever is available (and complain that a knife is dull), more so then which knife profile is perfect. 

I think there is one I would agree I like more but I seem to be able to quickly adjust to whatever I have on hand. Obviously not going through 2o+ lbs of food though.


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## Kippington (Sep 17, 2018)

Yeah sorry, it was a bit of a disjointed ramble. I think about this kind of stuff a lot.


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## Nikabrik (Oct 10, 2018)

What you're doing here is very interesting. From a math/geometry/CAD standpoint, I think there are a couple things worth considering.

First, about nature of the curve/spline things you're using. They're known as Bezier curves - specifically, cubic Bezier curves. One nice thing is that they can be differentiated. This is useful because the second derivative of position is curvature (conveniently the inverse radius of curvature, ie curvature value of 0.1 equals a radius of 10mm).
Another characteristic - and you alluded to this earlier, but it’s somewhat relevant to this post - is that by definition, the curve arrives at the endpoints from the direction of the control points. This means that tip angle is equal to the angle from the tip control point to the tip point. As a result, placing that control point directly below the tip radiuses the tip.
It's also not difficult to calculate the belly similar to the method used by Merlin & HRC.

I've created a spreadsheet that takes the control point coordinates and generates the edge, the slope/angle along the edge, and the curvature along the edge. Each of those is plotted. It also calculates the belly point.
I think it also has potential use as a design generation/validation aid.
Also, I liked the idea mentioned earlier of some sort of knife profile database. By quantifying edge shape, you can filter and search more easily. For instance, if a maximum curvature or deviation from flat was defined, you could search for flat spot length.

Here's the spreadsheet - feel free to make a copy if you like, or I'm happy to add you as an editor if you're interested.
Edge Curve Analysis Spreadsheet


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## Nemo (Oct 11, 2018)

Your maths is starting to hurt my brain.


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## Barmoley (Oct 11, 2018)

Yam, fried brains......


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## Kippington (Oct 11, 2018)

Cubic Bezier curves, aye? Thanks for giving me the name, I wasn't aware.


Nikabrik said:


> Here's the spreadsheet - feel free to make a copy if you like, or I'm happy to add you as an editor if you're interested.
> Edge Curve Analysis Spreadsheet


Holy crap - This thing is awesome!
Did you have the spreadsheet before this thread, or was it something you created from my ramblings? It perfectly fits my way of thinking of profiles! 

I'm going to try and get my hands on a popular knife shape, an angle cube and a ruler to see how accurate a representation I can get using your spreadsheet and the measurements between the basic points.


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## Kippington (Oct 11, 2018)

For those of you with fried brains , this is how it works.
After filling in the seven boxes highlighted in red, the spreadsheet takes the coordinates of three points and - with the heel as a reference - uses them to calculate the flat spot and the belly curve, as well as some other information in the output.



If you resize the _Edge Shape_ graph 1:1 with a ruler on your screen, you'll get the edge profile in its real shape and size on your screen.
_Edge Slope_ represents the measurement a protractor would give you at any given point along the edge.
_Edge Curvature_ shows the strength of the curve, which exponentially increases as it travels towards the tip.




This would be an awesome way to start a knife profile database. It's not perfect though, as the control points (P1, P2) can be difficult to find on a knife. The rest is easy though.


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## Nikabrik (Oct 11, 2018)

I'm glad you liked the spreadsheet. I put it together after I came across this thread. If you check the column labeled "R", that's the equivalent radius of curvature at each point.

My hope would be to (eventually) create a simple enough interface that it's approachable to anyone with an interest, and make the math(s) part somewhat optional.

Finding the control point locations doesn't have to be too difficult, as long as you're comfortable making the curve match the edge. There are two fairly simple ways to get their locations.

The first is to create your curve in 2D CAD - Draftsight is a freeoption from Dassault. You could use NanoCAD or Creo Sketch, or even AutoCAD if you've got it. You'll insert the image, put the heel at (0,0), draw the curve, then scale to get the right length. Then, you can select the spline and look at the coordinates of each control point:




In this example, we're looking at the 3rd control point (P2). You can select the other control points to get their coordinates.

The other way to do it is to create the curve in a vector graphics editor, like Inkscape or Illustrator. You'll then export as SVG, and pop that open in Notepad (or your text editor of choice). Look for a line like this:


```
<path class="st0" d="M0,0c55.2,0,223,1.92,240-19.2"/>
```

Depending on the application, that could alternately look like this:


```
<path class="st0" d="M0,0 c55.2,0 223.2,1.92 240,-19.2"/>
```

In the above example, you can parse the following points:
p0: (0,0)
p1: (55.2,0)
p2: (223,1.92)
p3: (240,-19.2)

Note that because SVG is oriented for web use, its Y-axis is inverted, so you'll want to negate the Y-values.

While you're in notepad, you can manually change those coordinates as desired and save - and it'll still open.

One real upside to the SVG approach is that it's in relative coordinates - so the location of p0 (the heel) doesn't matter as long as the flat spot is horizontal. That means that for a database, a user could simply upload an SVG with their trace of the edge, and everything else is handled simply in the backend. I will say that rotating things horizontal is much easier in CAD.


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## Nemo (Oct 11, 2018)

I'm a little lost on what the controls are. Are they just points which are on a tangent to the curve at the heel (or tip)? Or is the distance from the heel (or tip) to the control important? If so, how do you determine this when tracing a profile?


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## Nikabrik (Oct 11, 2018)

Nemo said:


> I'm a little lost on what the controls are. Are they just points which are on a tangent to the curve at the heel (or tip)? Or is the distance from the heel (or tip) to the control important? If so, how do you determine this when tracing a profile?



They're a bit... Loosey-goosey, perhaps?
They do determine the direction at the point they're associated with, but their length determines the amount of informed they have beyond that point. Think of them like elastic bands - you pull farther, and they pull harder.
Generally speaking, placing the control points further from their endpoints results in more gentle, longer curvature near that point. For example, putting both control points close to the endpoints will result in tight radii on each end, with a nearly straight line running between them (a nearly triangular blade shape). Extending the tip control point gives a more gentle curve at the tip, but a more pronounced belly. Extending the heel control point yields a longer flat. If you extend both, you end up with a sharper transition from flat to tip, more like a sakimaru takohiki or an American tanto. I'll post some examples a bit later.

As to placing them - I drag them around until it matches. I set them at the correct angle, then extend or shorten them until the curve matches.


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## Nemo (Oct 11, 2018)

I think I see. So it's a bit of trial and error moving the controls around until the profile matches your sample knife's profile?


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## Nikabrik (Oct 11, 2018)

To a certain extent, yes - but it only takes a couple minutes.

For example, a 240 gyuto seems to generally have a heel control 50-60mm directly horizontal from the heel, and a tip control a couple mm below the heel (at the appropriate angle).

Bezier curves, while funky mathematically, are fairly intuitive to create with some practice.


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## Nemo (Oct 11, 2018)

Thanks. I think I get the concept now (if not the maths).


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## Nikabrik (Oct 11, 2018)

Nikabrik said:


> Bezier curves, while funky mathematically, are fairly intuitive to create with some practice.



I hope that didn't come off as arrogant, because I didn't mean it that way.

I think this GIF is illustrative of the actual role of the control points:

https://en.m.wikipedia.org/wiki/File:Bézier_3_big.gif


This actually makes me realize that placing P1 at Y=0 is often slightly incorrect - it would make the heel recurve bell-shaped if P2 is below 0. Therefore, P1 should actually point from P0 to P2. I think the easiest way is to put P1 on 0, then move it down once P2 is placed.


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## Nemo (Oct 11, 2018)

Nikabrik said:


> I hope that didn't come off as arrogant, because I didn't mean it that way..



Nope, it didn't come across as arrogant. I reckon it's interesting. And even pretty cool.


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## Kippington (Oct 11, 2018)

Nikabrik said:


> This actually makes me realize that placing P1 at Y=0 is often slightly incorrect - it would make the heel recurve bell-shaped if P2 is below 0. .


Can you give me an example of a bell-shaped recurve? I can't visualize what you mean by _"P1 should actually point from P0 to P2. I think the easiest way is to put P1 on 0, then move it down once P2 is placed".
_
I had P2 below 0 in this earlier picture with no such recurve:


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## Nikabrik (Oct 12, 2018)

Kippington said:


> Can you give me an example of a bell-shaped recurve? I can't visualize what you mean by _"P1 should actually point from P0 to P2. I think the easiest way is to put P1 on 0, then move it down once P2 is placed".
> _
> I had P2 below 0 in this earlier picture with no such recurve:


Hmm, yes, I suppose that was vague.
Take a look at my copy of the spreadsheet as it currently stands - at t=0 (also x=0), the control point forces the slope (dy/dx) to zero. Through t=0.06 (approx x=10mm), the slope becomes more negative - meaning the edge is concave there. If I hadn't used an absolute value in the curvature function, we'd have a negative curvature value, which indicates a curve being "concave down". I think that'll be useful to add.
From t=0.08 on, the negative slope levels off becoming fully flat around t=0.13, which means we've got a convex shape - as you'd expect a heel relief to be all the way to the very heel.

If, in contrast, you point the heel in the direction of the relief, you won't have any concavity. In the example in the spreadsheet now, I scaled the angle from P0 to P2 and put P1 along it. In particular:
Y(P1)=Y(P2)*X(P1)/X(P2)
In this example,
Y(P1)=(-2)*51.5/199=-0.51
Substituting that in for X at P1, I no longer have concavity at the heel.
I haven't yet done the overlay to see how much P2 will need to be corrected to compensate for overall shape changes.

All that said, it's quite miniscule. In the case currently shown, "heel relief" is only 30 microns.


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## Kippington (Oct 12, 2018)

I don't think it would be worth unlocking Y(P1) from zero as it would open up too many possibilities to throw the flat-spot off its reference plane. For example, what if we have a blade where P2 sits a few millimeters from P3? In this case, wouldn't your method (having P1 intersect the P0.P2 line) send P1 well into the positives? If this is the case, doing so opens up a can of worms when it comes to measuring any angles that were originally referenced off the flat-spot.

Also, I haven't found any gyuto profiles which require a negative Y(P2). In fact, today I borrowed some forum-popular knives off Marek07, and plan on taking some measurements to test out your spreadsheet over the next few days. I don't expect to find a knife that needs a negative Y(P2). but I'll let you know if I do.

And if all else fails, the 30 micron re-curve is easy enough to ignore. Consider that any particular run of knives will have far more than a 30 micron deviation throughout it's run to begin with, and many knives out there actually *do* have that damn re-curve at the flat. It's not done on purpose but it's there, and people ignore those re-curves all the time... much to my dismay!


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## Nikabrik (Oct 12, 2018)

Kippington said:


> I don't think it would be worth unlocking Y(P1) from zero as it would open up too many possibilities to throw the flat-spot off its reference plane. For example, what if we have a blade where P2 sits a few millimeters from P3? In this case, wouldn't your method (having P1 intersect the P0.P2 line) send P1 well into the positives? If this is the case, doing so opens up a can of worms when it comes to measuring any angles that were originally referenced off the flat-spot.


Yes, it certainly throws in some more variability, and may not be worth it - especially for 30 microns. What I meant, however, was only to move P1 down if P2 is below P0. Moving P1 above P0 isn't necessary. Here's an exaggerated example of that concavity:




Which won't be present if Y(P2) is positive (or P1 points to P2).



> Also, I haven't found any gyuto profiles which require a negative Y(P2). In fact, today I borrowed some forum-popular knives off Marek07, and plan on taking some measurements to test out your spreadsheet over the next few days. I don't expect to find a knife that needs a negative Y(P2). but I'll let you know if I do.



That's really exciting, and I'm curious to hear more! I nabbed a photo of a Kato workhorse 240, and it seemed to require P2 of (199,-2) - but that was a very quick and dirty run with a 2° clockwise rotation, and I'm currently running the image straight, with P2 at (205,3.3).



> And if all else fails, the 30 micron re-curve is easy enough to ignore. Consider that any particular run of knives will have far more than a 30 micron deviation throughout it's run to begin with, and many knives out there actually *do* have that damn re-curve at the flat. It's not done on purpose but it's there, and people ignore those re-curves all the time... much to my dismay!



Right, I think that's the ticket - I probably got overhyped before realizing the scale of the issue. I'm aware of the recurve on some knives - I thought I recalled in some cases it's intentional to help prevent heel sticking. I'd imagine it's more accurately represented as convex, which was my original point. It does complicate things unnecessarily, though. It's possibly worth considering for other knife types, but not really necessary on gyutos.


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## Kippington (Oct 12, 2018)

Nikabrik said:


> That's really exciting, and I'm curious to hear more! I nabbed a photo of a Kato workhorse 240, and it seemed to require P2 of (199,-2) - but that was a very quick and dirty run with a 2° clockwise rotation, and I'm currently running the image straight, with P2 at (205,3.3).



This is what I'm getting for the Kato workhorse after stealing a photo from Matus. 

It's amazing how much information we can get out of these three points.
I had to guess the scale of the picture, but the control points keep their relative positions if we change the ratio.


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## Nikabrik (Oct 12, 2018)

Interesting! It looks like you're using a lot more "weight" on P1, and less on P2 compared to what I've been doing. Yours definitely looks like a better fit than mine. My points were adding extra "tip belly" - drawing P2 closer to the tip reduces that, and P1 has a remarkably strong yet graceful impact way up there, filling out the rest of the belly.

FWIW, Matus has some additional specs on that Kato in this Gyuto design article.
Mucho Bocho's Kato 240 is 242 long x 52 at the heel.


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## Kippington (Oct 14, 2018)

I tried a Misono Dragon. Your spreadsheet deals with real life examples really well!
It's also a good way of discovering little nuances I had never noticed before. For example, the belly of this knife flattens out towards the tip. You can spot it a mile away in the _Edge Curvature_ graph.





I bought some 1mm spacing graph paper that helps accurately find the points.


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## Kippington (Oct 14, 2018)

And the whole shape gets neatly summed up as the following:
*Misono Dragon 240mm*
*P1 -* 143.3
*P2 -* 202.2, 1.9
*P3 -* 246.5, 21.5
*Heel Height -* 50.5
*Spine Angle -* 3.6°​


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## Kippington (Oct 15, 2018)

*Tojiro DP 240mm*
*P1 -* 171
*P2 -* 206.2, 6.9
*P3 -* 236.5, 18.9
*Heel Height -* 49.8
*Spine Angle -* 3.5°​
I wonder how many knives I'll end up doing...


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## Kippington (Oct 15, 2018)

A personal favorite of mine:
*Sukenari 240mm*
*P1 -* 141
*P2 -* 197.7, 1.5
*P3 -* 229.5, 18
*Heel Height -* 51.2
*Spine Angle -* 3.1°​
Can anyone that owns one of these knives test my measurements? I'd like to see how accurate this is against other knives from the same production run.
All you gotta do is punch in the numbers I've posted here into the spreadsheet, change the graph on your screen to the right millimeter scale then hold the knife up and take a picture.


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## merlijny2k (Oct 15, 2018)

Wow, bezier curves. Never heard of them but pretty cool stuff!. I was thinking of just taking a third or fourth order polynomial and solving the coefficients from the boundary conditions. This system is much more advantageous and easier to automate though. Wonder why they are in none of the mathbooks I know. Still got a couple of more advanced books on a harddrive somewhere. See if those get me anywhere.


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## Hanmak17 (Oct 16, 2018)

I'll be really impressed when you guy's can map the grind of a knife...


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## Nikabrik (Oct 16, 2018)

Hanmak17 said:


> I'll be really impressed when you guy's can map the grind of a knife...



We've seen a variety of reviews showing thickness at various points, but not typically a good representation of radius, depth of concavity - likely due to not having the right measuring instruments.

I've got some ideas, and I've been trying to analyze S-grinds from photos. There's an issue with pinhole effect, though, which needs to be sorted through.



merlijny2k said:


> Wow, bezier curves. Never heard of them but pretty cool stuff!. I was thinking of just taking a third or fourth order polynomial and solving the coefficients from the boundary conditions. This system is much more advantageous and easier to automate though. Wonder why they are in none of the mathbooks I know. Still got a couple of more advanced books on a harddrive somewhere. See if those get me anywhere.



Yeah, I think they're predominantly used in computer graphics, so there's probably some coursework somewhere that covers it. They're just a 3rd order parametric polynomial though, in this case - but yes, there are some real advantages.



Kippington said:


> I tried a Misono Dragon. Your spreadsheet deals with real life examples really well!
> It's also a good way of discovering little nuances I had never noticed before. For example, the belly of this knife flattens out towards the tip. You can spot it a mile away in the _Edge Curvature_ graph.
> 
> 
> ...



What a great idea with the graph paper! Interesting point about the tips. I'd be very curious to eventually see a comparison of the way the knives cut (subjective profile analysis) vs their curvature.


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## Nemo (Oct 16, 2018)

Hanmak17 said:


> I'll be really impressed when you guy's can map the grind of a knife...


CT scan, anybody?


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## HRC_64 (Oct 16, 2018)

Nemo said:


> CT scan, anybody?



normal CT resolution is 2.5mm slices


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## Nemo (Oct 16, 2018)

HRC_64 said:


> normal CT resolution is 2.5mm slices


Well, I'm not gonna put it in an MRI!


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## HRC_64 (Oct 16, 2018)

Nemo said:


> Well, I'm not gonna put it in an MRI!



its not like its magnetic, oh wait...


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## Nemo (Oct 16, 2018)

What was that movie, House of Flying Daggers?


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## Kippington (Oct 17, 2018)

House of Flying Gyutos, haha! 

I can think of a good method to classify cross sectional geometry. Maybe I should start another rambling thread on the grind...


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## RDalman (Oct 17, 2018)

The differences on grind that matters most for the cut (near edge geometry/relative assymetry and straightness) are so minute (from makers view) I actually think more they come down to execution than design these days.


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## Nemo (Oct 17, 2018)

Kippington said:


> House of Flying Gyutos, haha! [emoji14]
> 
> I can think of a good method to classify cross sectional geometry. Maybe I should start another rambling thread on the grind...


LOL.

The new thread could be interesting


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## RDalman (Oct 17, 2018)

But that's kindof my stance on profile too haha. They're connected though because they're a result of the final grind work.


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## Kippington (Oct 17, 2018)

RDalman said:


> The differences on grind that matters most for the cut (near edge geometry/relative assymetry and straightness) are so minute (from makers view) I actually think more they come down to execution than design these days.


I totally agree.


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## Kippington (Oct 17, 2018)

Nikabrik said:


> I'd be very curious to eventually see a comparison of the way the knives cut (subjective profile analysis) vs their curvature.


A quick thought:
The effect of any edge curvature within reasonable boundaries isn't so important if you lift the knife up off the board between cuts. However if you start using rocking cuts, the edge curvature begins to influence how the knife will move. The part of the edge in contact with the board becomes the fulcrum of a second class lever along the horizontal plane, the food is the load and the effort is supplied through the handle. A fulcrum on a rocking knife which changes its position in an intuitive fashion is easier to use.




Basically what I'm trying to say is: If you use a knife with two flat spots, it would be weird to rock chop. Similarly, walking the board is also affected.
None of this comes into play if you lift the knife off the board.


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## refcast (Mar 26, 2019)

Do you guys like profiles that sweep up abruptly at the tip like toyama or masashi?
Or do you prefer profiles with a more continuous, constant curvature like Hinoura, masamoto KS?

I kinda like more continuous curved profiles.


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## bahamaroot (Mar 26, 2019)

Kippington said:


> A quick thought:
> ...
> Basically what I'm trying to say is: If you use a knife with two flat spots, it would be weird to rock chop. Similarly, walking the board is also affected.
> None of this comes into play if you lift the knife off the board.


Bryan Raquin did a pass around about 2 1/2 yrs ago with a knife he made that had a "two tiered" profile or two flat spots very much like this. It wasn't met
with much enthusiasm. The transition from the one flat to the next gave it a weird feel on the board and made rocking and walking the board more uncomfortable
as Kipp pointed out. The added longer flat at the tip didn't seem to be of any real benefit either.


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## HRC_64 (Mar 26, 2019)

The KS has a nice forward cutting area and its not dead flat..
you don't want "flat spots" to be dead flat all the time...


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## Kippington (Mar 28, 2019)

refcast said:


> I kinda like more continuous curved profiles.


Me too, although they tend to be a little worse for chopping.
In the past I've tried to get the curve as close to a straight line that I can... but here's the problem, I can't account for the flatness of any given cutting board - and lets be honest - pretty much none of them are dead flat. So if I want to prevent the dreaded "flat-spot thud" on a slightly dished cutting board, I end up with more curve at the flat then I would otherwise prefer. The resulting shape looks like a continuous (but increasing) curve, much like the KS.


HRC_64 said:


> The KS has a nice forward cutting area and its not dead flat..
> you don't want "flat spots" to be dead flat all the time...


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## DitmasPork (Mar 28, 2019)

Kippington said:


> A personal favorite of mine:
> *Sukenari 240mm*
> *P1 -* 141
> *P2 -* 197.7, 1.5
> ...



Curious on why Sukenari is a 'personal favorite' of your's? I've never used one, but have handled a few in stores. What made you favor Sukenari over some of the other classic profiles like Mas KS, Shig, Watanabe, etc.


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## Migraine (Mar 28, 2019)

HRC_64 said:


> normal CT resolution is 2.5mm slices



CTs we do at work give us 1mm and 3mm slices.


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## HRC_64 (Mar 28, 2019)

Migraine said:


> CTs we do at work give us 1mm and 3mm slices.



AFAIK... I think we are talking nominal vs actual numbers
and probably saying the same thing...see, eg



> Automatic registration accuracy is greatest when 1.0 ≤ Δτ (mm) ≤ 3.0 is used. Contrast-to-noise ratio is optimal for the 2.5 ≤ Δτ (mm) ≤ 5.0 range. Therefore 2.5 ≤ Δτ (mm) ≤ 3.0 is recommended for kVCBCT patient registration where the planning CT is 3.0 mm.


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## Migraine (Mar 28, 2019)

I'm not sure what you're trying to tell me.


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## Matus (Mar 28, 2019)

Migraine said:


> I'm not sure what you're trying to tell me.



I actually think I follow, but let’s just get this thread back on the track and not continue a discussion on CT scanner parameters


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## Migraine (Mar 28, 2019)

Well I follow what he's quoted, but it doesn't change what the CTs I see actually are so I don't know what the intention behind the post was. But anyway.


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## Nikabrik (Mar 29, 2019)

CT scans notwithstanding, here are a few ideas I've had for digitizing grind:


A pantograph which draws on a smartphone screen using a stylus.
A pin contour gauge, which is photographed or scanned.
Project a laser line, photograph from an angle, and correct for perspective - inspired by this: https://hackaday.com/2013/05/15/3d-scanner-with-remarkable-resolution/
Draw a fine-tip sharpie line using a straightedge, and photograph similar to #3. I'm going to try that this Saturday, hopefully.
If #4 fails to produce useful results, I can get a line laser for about $10. I don't think #4 would work well with kurouchi, unless you applied tape first.


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## Kippington (Mar 29, 2019)

DitmasPork said:


> Curious on why Sukenari is a 'personal favorite' of your's? I've never used one, but have handled a few in stores. What made you favor Sukenari over some of the other classic profiles like Mas KS, Shig, Watanabe, etc.


It's more that I bought a couple of them which subsequently got me into knife making. Less to do with the profile itself.


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## Kippington (Mar 29, 2019)

Nikabrik said:


> I'm going to try that this Saturday, hopefully.


Let us know how it turns out! I'd be very interested to see how it works.


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## dan (Mar 30, 2019)

It seems like you all made a lot of progress with mapping the side profile of a knife. How do the cross-sectional profiles (spine to edge) vary along the length of a knife? I suspect this varies by maker but I've always wondered how, for example, the S-grind profile terminates at the tip. 

Looking at the choil shot is evident but I've found it harder to look at a tip and understand the grind. Fingers work decently well for the middle of the blade.


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## HRC_64 (Mar 30, 2019)

A good sense of touch will be useful up to about the belly/fwd sweet spot, 
after that is usually hard to discern as distal taper/thin-ness approach flat grind

The sticktion issue is alot less directly at the tip, In my experience


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## Nikabrik (Mar 30, 2019)

Kippington said:


> Let us know how it turns out! I'd be very interested to see how it works.


I folded a piece of gridded paper so that it would be perpendicular to the surface of the blade. I then used Snapseed (on my phone) to correct for perspective. Past a certain angle, the sharpie isn't really visible, but it's not too bad. The perspective makes that somewhat moot, except that more pixels in the curve are desirable. The sharpie line is normal to the edge curve (ie, perpendicular to the tangent).

I think a similar spreadsheet might be useful, in that we can look at a few things:

*Height of convexity (ie, is there a flat ground area near the spine
*Change in convexity from spine to edge
*Width, depth of concavity
*Radius of concavity

Or similar ideas.

I don't have anything particular interesting in grind, but I do have a Tosa knife (super thick at the spine) with a bit of upper concavity that I'd like to check out. That'll be a good extreme case for the technique. I'm concerned that the crepe texture on my painters' tape will interfere.


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## Kippington (Apr 2, 2019)

Interesting... I wonder how accurate that is. My head wont stop telling me that the perspective is skewed, and that the picture is no different from this kind of ruler picture (stolen from XooMG):




How would you account for the angle at the edge? So for example, on a flat grind knife where the line in your picture would come out completely straight, how would you find out thick the spine is using your method?


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## daizee (Apr 2, 2019)

This is an entertaining discussion for someone who can easily go off the rails with over-analysis. 

I agree with what seem to be the general conclusions about edge curves. When I profile a new kitchen blade, I continually check to make sure that rocking push cuts don't catch the tip too hard on rocking push-cuts. Of course that's all modulo the height of my workshop surfaces. 

And while I've made quite a number of knives from identical CAD drawings (bezier curves), they're all a tiny bit different in the end since they're all made by hand.

In factory knives, things like little flat sections of edge near the tip are well within re-sharpening reach for the home user. Just put it on your diamond hone before going back to whatever scented waterstone ritual you use for regular touch-up.

Re: belt-grinder ruination
I have nightmares about that sort of thing. My condolences.

Between this and another thread on santoku profiles, I wanted to mention my thoughts on spine/nose shape. I learned the hard way (surely because of bad technique, but that's probably quite common...) that the in-between profile between "pointy" gyuto and "severely Roman" santoku noses is a potential risk for cutting the support hand, if you're trying to cut through something tough, like a large melon or squash. If you are used to a pointy or K-tip profile, and put a bunch of pressure on the nose with your weak hand, you risk sliding down the nose and cutting your hand with the tip. I'm sure you don't need to ask how I learned this on the very first kitchen knife experiment I made... I don't know what that safety angle/curve is exactly, but I know it's dangerous when I see it.

Re: modeling existing blades - difficult to re-scan that stuff precisely, and even harder to reproduce precisely in 3D steel unless your CAM'ing your blades. Some empirical measurements with a best-fit curve might be an alternate approach. Sometimes you need to get the technology out of the way (says the computer scientist). Here's my transistor-free way of measuring thickness at various points on the blade.

Hmmm, looks like 0.110" to me:


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## Nikabrik (Apr 2, 2019)

Kippington said:


> My head wont stop telling me that the perspective is skewed, and that the picture is no different from this kind of ruler picture (stolen from XooMG):



The primary thing we have going for is the straight line (when viewed from above) - which allows us apply the principles of plane geometry and orthographic projection. If the shadow on XooMG is straight we could actually use that - if we could see the ruler markings to remove the perspective distortion. However, I did try some experiments with a ruler on the back side of my deba. I found that the light diffracted enough to make things fairly inaccurate, but it would be interesting to try a photo lot more like that one. The big issue is not knowing whether that curve lies on a plane perpendicular to the blade.



> How would you account for the angle at the edge? So for example, on a flat grind knife where the line in your picture would come out completely straight, how would you find out thick the spine is using your method?



You would have to measure it - for me, that's calipers or a mic like daizee mentioned but I know not everyone has them. Perhaps an additional photo of the spine with gridded paper or a ruler could provide sufficient accuracy - although rounded spines make things harder.

Essentially, we have a curve from each side, but they must be placed using an assumed thickness of zero at the very edge, and a measured spine thickness.

There's also the issue of how we define compound grinds (with non-smooth transitions) - perhaps choosing 1,2, or 3 segments would do the trick. I've looked at some graph digitizing software, but I think there's too much image processing in prep.



daizee said:


> Re: modeling existing blades - difficult to re-scan that stuff precisely, and even harder to reproduce precisely in 3D steel unless your CAM'ing your blades. Some empirical measurements with a best-fit curve might be an alternate approach. Sometimes you need to get the technology out of the way (says the computer scientist). Here's my transistor-free way of measuring thickness at various points on the blade.
> 
> Hmmm, looks like 0.110" to me:



Yeah, and that's something I'm happy to do also - but I'd like to come up with something simple wherein a knife enthusiast who isn't also metrology enthusiast can simply snap a couple pictures, tweak them a little, and share.


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## Nikabrik (Apr 2, 2019)

Processing images a bit further, I thought of a couple further considerations:
1) A contour gauge has no perspective to correct, but could scratch cladding or chip an edge.
2) The luminosity of a laser would be nice, because it would really stand out in the image. You could drop the exposure way down in a dim room. With a tripod, you could take two identical pictures, except the laser would be on for one - then subtract the laserless image to leave only the laser (although that's probably unnecessary).


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## daizee (Apr 3, 2019)

If you darken the room, you can usually segment out a laser pretty easily with a simple intensity threshold, or add spectral intensity for more reliability. But of course you run into issues using a laser on a highly specular surface like polished steel, which will be complicated by per-knife variations in finish direction or general scratched-uppiness. I would be concerned that you wouldn't be able to reduce the uncertainty in the laser segmentation below the threshold of accuracy you would like to achieve from the system.

The bugaboo in most computer vision systems is calibration. For many purposes, output that "looks good" is the goal, which is to say photos, basic structure with images wrapped on, mosaics, etc. But if you want to do actual metrology on an object, you have to control the setup substantially, account for camera distortion (possibly automatic in today's phone software? I haven't checked this decade), lighting, surrounding environment, etc.

Using a grid for calibration can work, if your segmentation of the grid can be precise enough to allow you to discern thousandths of an inch (pardon my units) from pixels - but resolution will be dependent on depth, remember, so the further the incident surface from the camera, the larger an angle subtended by any given pixel. You might be able to calculate that precision to learn within what depth of field you can expect a useful measurement. But if you're taking measurements across the image from left to right, you may also have a variation in expected precision. (again, variation per-camera)

There are similar algorithms that work with a moving shadow across a scene to get structure instead of a laser - I think the step function of the shadow on the shiny surface would be more precise, as demonstrated above, but again, the user will have to control the lighting. Not everybody "sees" what they're actually seeing, and that might take some training per-user.

Don't get me wrong, I think this is a very cool project which should be pursued! But representing it as "simple" for the end-user might be a stretch. 

While I did show a picture of a micrometer earlier, which I wouldn't expect most people to have (I have lots, but New England is littered with good used tools at flea markets), a good-enough set of ~$35 dial calipers is well within reach of any enthusiast willing to spend good money on fancy knives, and arguably a very informative accessory.


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## HRC_64 (Apr 3, 2019)

Agree with alot of the above...

raw digital capture files aren't inherently all that sharp and using SW layer edge-contrast filters
creates all kinds of problems....and this is assuming the distortion, chromatic abeerition, 
and specular highlights haven't created their own issues...but all of that is par for the course
whentryingt o capture high-contrast acute-angle shots like choil shots and /or 
\profile shots of thin-geoemtry knifes under artificial light

Oh, and then there is drop-shadow effects along profile edges..


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## Nikabrik (Apr 3, 2019)

Yeah, computer vision goes a bit further than I'd intended. And as you say, "simple" is perhaps an exaggeration. My thought of workflow would be:

Set up line and reference grid
Capture picture
Manually correct perspective in an image editor
Draw spline manually, similar to the side profile method.
As I alluded to earlier, splines won't really handle sharp cusps of compound grinds, so multiple spline segments are in order for certain types of grind.

It may be that measuring is actually simpler, and more intuitive; however, I think that a depth gauge measuring down from a bridge of sorts (think parallels across a pair of blocks) would handle asymmetrical shapes better. However, it requires layout of the measurement points, and recording each pair - which could be a bit fiddly. Ideally, it'd be nice to have data cables logging on two axis simultaneously to create data pairs as you drag the gauge - in essence, a digitizer/CMM. I'm not aware of any affordable ready-to-go options, though.

Perhaps the more accurate point is that regardless of fiddlyness, I'd like something that's easy for people to _contribute to_. If people were willing to draw a line, place a card, and take a photo I'd happily process them. 

That's assuming, of course, that the method is fairly accurate. My plan is to take my photos, stick the curves together, and check the thickness against real life. I'll also check the concavity depth of the ura on by deba to see how accurately that works. My hope is that it's accurate enough in the area of interest.

As to distortion - It's my understanding that modern smartphones do have lens profiles built in. Because the lenses aren't interchangeable, that won't vary over the life of the device. That's a upside over using my "real" camera, because I use vintage MF lenses, so I'd have to download/create the profiles for postprocessing. I did however notice a small amount of remaining barrel distortion in the grid spacing from my phone.


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## HRC_64 (Apr 4, 2019)

w/jpeg... you tend to see alot of low-information, high-contrast ege zones 
(ie w/ heavy jpeg artifacting)


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## CulinaryCellist (Apr 4, 2019)

Twas a great read Kippington, very educational


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## RDalman (Apr 4, 2019)

You guys are really going deep here.
Just a thought that rose. I don't intend to assume anyone is actually trying to copy, lets just play with the thought.
What is the purpose of this kind of detail precision mapping? Repeatability? Because imo that's not going to happen with any modern equipment actually. I don't believe even in this day, machines can work this hard steel accurately and consistently, as good as handground. Everything connects and impacts, for example the before and after hardening, if the steel moves in the process, adjusting profile and grind constantly throughout grinding and finishing.
So if someone (factory or handmade doesnt matter here) is producing a pretty good knife consistently. In order to be able to really repeat it, you need their full process, every trick and priorities they know, their skills, and a close study of all their tools. It's the interesting nature of hardened steel knives I think


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## milkbaby (Apr 4, 2019)

RDalman said:


> What is the purpose of this kind of detail precision mapping? Repeatability? Because imo that's not going to happen with any modern equipment actually. I don't believe even in this day, machines can work this hard steel accurately and consistently, as good as handground. Everything connects and impacts, for example the before and after hardening, if the steel moves in the process, adjusting profile and grind constantly throughout grinding and finishing.
> So if someone (factory or handmade doesnt matter here) is producing a pretty good knife consistently. In order to be able to really repeat it, you need their full process, every trick and priorities they know, their skills, and a close study of all their tools. It's the interesting nature of hardened steel knives I think



Totally agreed. The other thing I find interesting which happens here a bunch is when somebody posts measurements of one specific example of a knife and everybody basically thinks that if they buy one it will be the same. For sure there will probably be general trends when the same bladesmith and same sharpener work on a knife (in the case of Japanese knives), but I doubt the measurements will always be the same. That is one of the advantages of buying from a maker like you (Robin Dalman) because you test the performance of each knife individually and adjust it until you find it to perform the way you intend.


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## Chuckles (Jun 2, 2019)

What a thread. Thanks to everybody for contributing. FWIW when I joined this forum I was told there would be no math.

I find particularly interesting are some thoughts in the earlier pages on weight distribution and it’s relation to profile. It has helped me put some of my preferences in perspective.

It reminds me of a 270mm Kato I had. With a hefty knife you want to use the weight to your advantage. This knife just naturally wanted to fall exactly where the profile made the least useful board contact. It made you fight the substantial weight of the knife with every swing. It had such a unique spine to edge geo that I hadn’t even gone through the trouble of thinking through how to potentially add a faux full tang custom handle and even had Delbert Ealy lined up to make it but decided just to sell instead. Maybe the worst knife I have ever used for weight distribution in relation to profile. 

I appreciate the comments from makers regarding ways to address weight distribution without changing edge profile especially spine profile and distal taper. It has helped me understand why the particular characteristics of my favorites make them my favorites and hard to beat for my specific and quirky tastes.


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## Kippington (Jun 27, 2019)

Here's an interesting concept...

Over in the world of swords there's a highly regarded smith by the name of Peter Johnsson who likes to map out some points of interest under the blanket name of 'Blade Dynamics'. We all know of the balancing point, but there is also the pivot (rotational) points and vibrational nodes.
He can explain it better than I can, you can find it at the 48:15 mark of the following video. The relevant part takes about 10 minutes, but the whole video is pretty good.

So I'm wondering, do you guys think such points of interest apply to our knives?


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## HRC_64 (Jun 27, 2019)

mass and distance and rotational forces
uh oh...
here come newton meters


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## HRC_64 (Jun 27, 2019)

its an intersting question thinking about...
option 1) lever arms and force application (torque)
option 2) vs lever arms and mass distribution (balance)

what is more relevant to end users?

IMHO many of people use the 'balance' concept to describe a knife with good, neutral ergonomics.


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## McMan (Jun 27, 2019)

Very interesting stuff…
I don’t have anything to contribute beyond a question:
I wonder how the fact that the overall shape of a knife shape is asymmetrical (i.e. basically trapezoid with a tang) as compared to a sword which is symmetrical (i.e. cross-shaped) might matter?


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## Nikabrik (Jun 27, 2019)

I think it certainly could be a factor in the pleasure and ergonomics of using a knife - likely there's a role of balance and vibrational nodes when it comes to how a knife feels on the board, especially when chopping rapidly.


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## Kippington (Oct 31, 2020)

I've never seen anyone mention it yet, but it's kind of obvious. Longer knives need less belly.

As you all know, to stop the tip of a knife from digging into the cutting board during a rock-chop or a push/thrust cut, you need to have the edge sweep up at the tip.
To get the same height of handle lift, the belly on a short knife needs to be curvier than on a longer knife.





This helps to explain why we can get away with flatter profiles and a lower tip on longer knives.


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## captaincaed (Nov 1, 2020)

Salty had a video about ergonomics, where a longer knife needs less wrist angle to get over product than a short one. Just talking sides of a right triangle here. Longer hypotenuse with equal opposite side = smaller internal angle. 

Forget Newton meters, here come sines. Where's Ian?


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## Barmoley (Nov 1, 2020)

I've said it before somewhere that shorter knives need more belly and curvier profile to be used as a general purpose knife.


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## bbrooks008 (Sep 8, 2021)

captaincaed said:


> Newton meters...


aka Joules


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## memorael (Sep 8, 2021)

Kippington said:


> There's definitely a sweet spot for springiness. I often hear complaints about blades being too flexible, but I think the reverse (a clunky thick tip) tends to be put up with more often.
> __________________
> 
> Okay, here is something that hasn't been mentioned yet - I like to call it "the KS effect".
> ...


This is by far one of the most interesting posts ever in the knife community. Anyway, I wanted to ask you if there is such a thing as a santokuish gyuto like the takedas, with the masamoto KS style of emoto? I always have liked the masamoto KS profile a lot but I do find the 270 is harder to wield when it comes to precision cutting than other knives, after reading your post it makes me think that the closer the edge can get while holding the knife in the most natural position (that would be without having to lift your elbow higher in order to get the point closer to the board) the better the knife performs in terms of control.


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## bbrooks008 (Sep 9, 2021)

memorael said:


> Anyway, I wanted to ask you if there is such a thing as a santokuish gyuto like the takedas, with the masamoto KS style of emoto?


What about Watanabe? I wouldn't call his gyutos 'santokuish', but they have sort of a bullnose tip and no machi. They are widely considered to cut very well and might give you what you are looking for.


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## applepieforbreakfast (Sep 9, 2021)

memorael said:


> Anyway, I wanted to ask you if there is such a thing as a santokuish gyuto like the takedas, with the masamoto KS style of emoto?




Gihei's Blue 2 (Middle knife)


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## memorael (Sep 9, 2021)

applepieforbreakfast said:


> Gihei's Blue 2 (Middle knife)View attachment 141597


How would you describe the cutting action compared to the one on the left? This thread really got me thinking about the whole profile of a knife on like 10 different levels.


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## Jason183 (Sep 9, 2021)

The one in the middle is my current favorite profile, it’s suitable for most cutting motion, push/slice/rock chop.


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## applepieforbreakfast (Sep 9, 2021)

memorael said:


> How would you describe the cutting action compared to the one on the left? This thread really got me thinking about the whole profile of a knife on like 10 different levels.



Gihei is more suited to push cutting, having a flat spot that's at least half the blade.
Doi is nice for guillotine and glide, being basically all curve, albeit gentle.


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## baggyjorts (Sep 10, 2021)

memorael said:


> This is by far one of the most interesting posts ever in the knife community. Anyway, I wanted to ask you if there is such a thing as a santokuish gyuto like the takedas, with the masamoto KS style of emoto? I always have liked the masamoto KS profile a lot but I do find the 270 is harder to wield when it comes to precision cutting than other knives, after reading your post it makes me think that the closer the edge can get while holding the knife in the most natural position (that would be without having to lift your elbow higher in order to get the point closer to the board) the better the knife performs in terms of control.



At least in terms of profile, gesshin ittetsu is an interesting one that's a bit santoku-ish


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## memorael (Sep 10, 2021)

Jason183 said:


> The one in the middle is my current favorite profile, it’s suitable for most cutting motion, push/slice/rock chop. View attachment 141603
> View attachment 141664
> View attachment 141604
> View attachment 141605


Funny enough, this profile reminds me a lot of the knife I used to torture at work. This could be just me but it looks like what happened here is this knife is the one you sharpen the most? I remember having an INOX suisin honyaki and I sharpened that knife everyday, until it cut like I wanted it to. The funny thing is I remember it having a weird shape, after seeing this pic I can without a doubt in mind tell you my knife looked exactly like this. What's cool about this profile, other than looking horrible, is it is really versatile, the tip is easy to maneuver when you need to cut things like garlic or shallots, it push cuts really nice, it chope no problem cause the profile turns pretty flatish, IDK... it just works. LOVE THIS POST.


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## Jason183 (Sep 10, 2021)

memorael said:


> Funny enough, this profile reminds me a lot of the knife I used to torture at work. This could be just me but it looks like what happened here is this knife is the one you sharpen the most? I remember having an INOX suisin honyaki and I sharpened that knife everyday, until it cut like I wanted it to. The funny thing is I remember it having a weird shape, after seeing this pic I can without a doubt in mind tell you my knife looked exactly like this. What's cool about this profile, other than looking horrible, is it is really versatile, the tip is easy to maneuver when you need to cut things like garlic or shallots, it push cuts really nice, it chope no problem cause the profile turns pretty flatish, IDK... it just works. LOVE THIS POST.


The knife just looks liked that when I bought it new last year, haven’t changed anything to the profile. I was looking for KS style profile with extra heel height, although it’s not as pointy as the KS but after using it the first day, I knew this is a keeper, it just fits my cutting style perfectly, liked you said, really versatile.


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## Jeff (Sep 12, 2021)

ecchef said:


> I love this type of thread. These topics really bring about the best discussions.
> Good point about spine recurve, Robin. I’ve been using a Sakai Takayuki Grand Chef lately and, although I don’t know the mechanics behind it, the slight spine recurve does seem ro make a difference.


Tip height relative to the rest of the knife:

When discussing western chefs knives people often refer to 3 categories of tip heights.

1. HIGH TIP - Is generally equated with the classic German chefs knife.

2. MID TIP - Generally likened to the French style chefs knife (classic Sabatier tip)

3. LOW TIP - Asian style chefs knife (gyuto)

My question is discerning the belly or “roll” in a chef’s knife. D any Asian chefs knives (gyuto) have any belly to facilitate rock chopping etc.?


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## stringer (Sep 12, 2021)

Jeff said:


> Tip height relative to the rest of the knife:
> 
> When discussing western chefs knives people often refer to 3 categories of tip heights.
> 
> ...





You can rock chop with about anything with practice. Gyutos, nakiri, sujis, Chinese cleavers. Just gotta be careful of the tip. Upswept mid tip is best but not by any means necessary.


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## memorael (Sep 12, 2021)

Jason183 said:


> The knife just looks liked that when I bought it new last year, haven’t changed anything to the profile. I was looking for KS style profile with extra heel height, although it’s not as pointy as the KS but after using it the first day, I knew this is a keeper, it just fits my cutting style perfectly, liked you said, really versatile.


Wow, so this maker has the profile really down.


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## Jason183 (Sep 12, 2021)

memorael said:


> Wow, so this maker has the profile really down.


Carter does making all different kinds of profiles


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## Kippington (Sep 12, 2021)

Jason183 said:


> The one in the middle is my current favorite profile, it’s suitable for most cutting motion, push/slice/rock chop. View attachment 141603
> View attachment 141664
> View attachment 141604
> View attachment 141605





memorael said:


> Wow, so this maker has the profile really down.


It's quite similar to the knife I mentioned in *post #66*, which was one of the main reasons I started this rambling thread. It taught me a lot.


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## spaceconvoy (Sep 13, 2021)

Kippington said:


> It's quite similar to the knife I mentioned in *post #66*, which was one of the main reasons I started this rambling thread. It taught me a lot.


That's very nice, I imagine it took some time to get to that point. Here's my Sukenari 270 that I reprofiled over the course of a few days. I didn't have a particular profile I was aiming for, just knew I wanted to reduce the belly and make the tip flatter.


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## memorael (Sep 14, 2021)

Kippington said:


> It's quite similar to the knife I mentioned in *post #66*, which was one of the main reasons I started this rambling thread. It taught me a lot.


Maybe its just the perspective but it seems like the top knife has the point pointing down while the bottom one has a tip that is higher... I hope that makes sense. Anyway? how does one perform versus the other? I would imagine they perform similar but have you noticed any peculiar differences? like maybe a diminute ease when cutting garlic or something? Wrist's don't get as tired? IDK...


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## Kippington (Sep 14, 2021)

memorael said:


> Maybe its just the perspective but it seems like the top knife has the point pointing down while the bottom one has a tip that is higher... I hope that makes sense. Anyway? how does one perform versus the other? I would imagine they perform similar but have you noticed any peculiar differences? like maybe a diminute ease when cutting garlic or something? Wrist's don't get as tired? IDK...


I only own the Sukenari, so I can't compare them directly. The other one belongs to Jason.



spaceconvoy said:


> That's very nice, I imagine it took some time to get to that point. Here's my Sukenari 270 that I reprofiled over the course of a few days. I didn't have a particular profile I was aiming for, just knew I wanted to reduce the belly and make the tip flatter.
> View attachment 142183


So what did you think of your work? Did it turn out like you expected?


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## spaceconvoy (Sep 15, 2021)

Kippington said:


> So what did you think of your work? Did it turn out like you expected?


I'm pretty happy with it, especially the tip. IMO that flatish spot at the tip is the best feature of classic French/KS style profiles. I've said this in many other posts but I just don't get how people can stand the current trend of curvy tips (see: all the new hot Nakagawa-forged brands and every Sanjo maker except Mazaki). So much unnecessary elbow movement just to avoid accordion cuts.

If I had infinite time and energy I'd reduce the belly more, but as I'm sure you're aware it quickly becomes exponentially more work. I'll probably keep trying to knock of a few microns every sharpening session until it eventually looks more like yours. Also, I was worried the tip's spine profile would look odd, but I like the way it turned out like an elongated santoku. I probably removed the most material from this area just for aesthetics.


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