Thoughts on designing a 240 WA gyuto

1. Introduction

Make yourself a nice cup of tea or a big coffee and find a quiet place, this is a 6.500 word article :)

Please read this first ...

I was pondering to write an article on a design of a gyuto (or chef's knife) since quite a while, but was (and still do) feeling uneasy about it. Indeed - my personal practical experience is still very limited and I most certainly do not want to make the impression that I have 'mastered' the topic.

In my view, the Japanese approach to kitchen cutlery with its focus on the function rather than 'looks' has yielded the best performing kitchen knives known to men. So contrary to numerous kickstarter projects I am not trying to 'reinvent' the kitchen knife here. Instead I am just trying to make to learn from Japanese kitchen knives and transfer those parts of the design and geometry that are accessible to my skills, tools and techniques.

What I try to share here is in the first place based on my observations (and discussions with people who have much more knowledge on the topic than me), rather than some kind of 'teaching'. Japanese craftsmen have been improving their processes and designs over generations. In comparison I spend a few hours in my 6 m2 workshop every now and than.

Since I do not posses neither the knowledge, not the practical experience of a skilled Japanese smith or a sharpener, all I can offer is in a sense a somewhat superficial description of what I understand that constitutes a well performing kitchen. So when executed well it may yield a pretty well performing knife that is a pleasure to use and a cut above the knives you can find in a local shop.

What to expect

This article is an attempt to 'analyse' Japanese kitchen knives from a perspective of an amateur knifemaker from central Europe. Since a design of a kitchen knife is first and foremost determined by the utility function of the knife, there is not a whole lot space for 'innovations' as you rather quickly end up with a cool looking, but not a very useful knife. 

So the main point is probably the attempt to understand what makes Japanese kitchen knives to stand out, rather than to give you a tool to design something completely different.

Limitations

Let's for the sake of simplicity talk about a particular type of a design, so that I can keep the number of variables down:

• Gyuto with a 240 blade length
• Blade made from single piece of steel via stock removal
• WA (Japanese) style handle with octagonal cross section
• Double bevel, symmetrical grind 

This topic can not be discussed without some hand drown sketches.  I even went as far as making a few short clips to show certain features of Japanese knives. please bear with me here, I am doing my best.

2. Japanese kitchen knives

Note: This is probably the most valuable part of this whole article as its contents were checked with a very experienced vendor and a professional sharpener of Japanese kitchen knives who helped me to correct my misconceptions and pointed out several details that would have otherwise escaped me.

There is little chance one is going to make a knife that could perform similarly to Japanese kitchen knife without using some and trying to understand how their design and execution relates to their cutting properties. I am using Japanese kitchen knives as a home cook since a few years and I am also lucky to have the chance to discuss the details about their grinds and geometry with people who have much more knowledge on the topic and have regular contact with Japanese craftsmen.

Grinds of Japanese kitchen knives

So if we go with the limitations as listed in the introduction, we are left with basically 2 different types of grind:

• Convex grind
• Wide Bevel grind (grind with a shinogi line)

• Knives with both convex and wide bevel grinds have several features in common:

• Very most of the knives have a distal taper - the thickness of the spine is larger at the handle than towards the tip. Obviously very thin knives will have less pronounced distal taper. Even beyond that - the distal taper can be quite different and there are differences across regions in Japan. In general though the distal taper is not linear from the handle to the tip. If the tang is forged thick (what has advantages when it comes to stiffness and prolongs the lifetime should the tang rust inside the handle), than the taper will be very pronounced towards the heel of the knife, than it will 'slow down' over the most of the length of the blade and will get again more pronounced towards the tip. If the taper is made linear over the length of the blade, than this results in a blade that is too thin towards the tip and thus also too flexible (what is usually not desirable in a gyuto).
• The distal taper also influences the grind of the blade as it dictates the thickness of the blade at the given position along the blade.
• Most knives also have taper of the thickness of the grind behind the edge, meaning that the grind is thicker at the heel and gets a bit thinner towards the tip. At 10 mm behind the edge this taper is usually between 0.1 - 0.3 mm, on a rare occasion more (usually only on generally thicker knives like Kato Workhorse). In general this will be less for thin knives and more for thicker knives.
• Talking about thickness of the blade, than at 10 mm behind the edge a thickness of 1.0 mm would be the middle ground - not too thin and not too thick. Including the distal taper one could think of a blade that has thickness of say 1.1 mm close to the heel and some 0.8 - 0.9 close to the tip. This would only be a rule of thumb for where to start - there are considerably thicker and also considerably thinner knives out there.

• The convex (hamaguri) grind:

• The convexity of the grind is most pronounced first 10 - 20 mm behind the edge, the curvature of the grind is not constant but changes with the distance from the edge. 
• Moving away from the edge the grind may remain convex up to the spine (like it seems to be the case on a Kato Workhorse), but often turns to flat (or gently concave) bevel, so the cross section of the grind would look like a very sharp 'V' where the last 10 - 20 mm at the tip are convex.
• There is often a pronounced transition (shoulder) between the convex and the near-flat grinds - like as if two bevels were merged into one (what may well be the case). This 'shoulder' would usually be found at around 15 mm from the cutting edge.
• Also, blades like the Gesshin Ginga, for example, are done in stages, so there are generally 3 distinct convex ranges- near the spine, middle of the blade, and near the edge (with increasing convexity moving towards the edge). 
• Towards to the tip the bevels above the convex grind may not have any horizontal taper left. This is mainly because the thickness of the spine tapers towards the tip and there is simply 'not enough thickness' left for it.
• In general it needs to be noted that the convexity of the grind is subtle (and I really mean SUBTLE) and should not be over done. The blade may even look flat at first sight (looking at the choil from behind), even though it is convex.

• The wide bevel grind:

• These knives have a sudden change in the angle of the grind which produces a distinct line that runs parallel to the cutting edge and is called shinogi. 
• The width of the bevel can be anywhere between about 10 to 30 mm.
• Nearly all knives with kurouchi (black finish after forging & HT that is left on finished blade) are of a wide bevel design.
• The wide bevel (part of the grind between the cutting edge and shinogi) is very near-flat, but is intended to be slightly convex (hamaguri) - in particular close to the edge. It can be also slightly concave like e.g. on Kochi knives, but this is a result of grinding process (grind being made on a very large grinding wheels - around 100 cm in diameter), not the final intended geometry. Overt time - with proper sharpening and blade maintenance (thinning) the concave grind will be turned to either flat or convex wide bevel. Here I would add - if you grind knives on a belt grinder with a platen (the typical grinding wheels for belt grinders are too small to grind a wide bevel on a kitchen knife), than you would not produce the concave grind to begin with.
• The bevels above the shinogi are most often flat (though on some knives like Takeda they are forged slightly concave), and similarly to what was said about the convex grind may show some vertical taper or be (usually only towards the tip) of nearly constant thickness.
• Advantage of a wide bevel grind is that it is a little easier for the user to maintain the geometry over time - in particular if the bevel is not too wide. Once the thickness behind the edge needs thinning, than the whole bevel will be equally thinned up to the shinogi line and the shinogi line would move a tiny little bit up.

3. Basic knife parameters

For this part I decided to use one knife as an example. It is actually a rather rare knife known in the community as 'Kato Workhorse' made by Yoshiaki Fujiwara (a.k.a. Kato) in size 240 mm. This particular one has a hand engraved Dragon on the left face and there were just a few made like that. This is a fairly thick & heavy knife for a Japanese gyuto with a WA handle at 250g and as such not to everyone's taste. Still - it is a great example of excellent design and execution.

Kato Workhorse Dragon 240 mm

Detail of the engraved dragon

Kanji

In my current view the basic parameters that have the main influence on how the knife will behave while cutting are the following:

• Weight

• Position of the center of mass

• Distribution of the weight

• Profile of the cutting edge

• Angle between the handle and the 'flat spot' 

• Height of the blade at the heel

• Grind / geometry

• Grind close to the cutting edge

• Hamaguri grind

• Neck design

• Handle type / design & materials

It should be noted that these are not completely independent from each other. If you make a significant adjustment of one of the parameters, most of the others will be affected too.

The weight

This is an obvious one - a lightweight knife will be more nimble and faster while a heavier knife will (with proper grind and weight distribution) be able to use its own weight to - as they sometimes say - 'divide instead of cut'. A 240 gyuto with a WA handle may weight as little as 130g or as much as 280g.

Important is that the geometry - in particular with lightweight knives - is tuned properly. While it is physically hardly possible to make a tick grind (like on Kato Workhorse) on a very lightweight knife, still - a lightweight knife that has grind on the thick side may require too much downward force when cutting. The same grind may be just optimal on a thicker knife. The other way round works though - a knife like for example Kochi (weight about 200g) has a very thin grind.

Position of the center of mass

With a small knife which weights very little (like 150 petty) the position of the center of mass is not that crucial (even though a heavy handle on a thin lightweight blade may still feel less comfortable), but with a gyuto it will make a large difference in how the knife will feel and handle. A knife that has centre of mass close to the handle (say on the heel or even the ferrule) may feel 'balanced' in a hammer grip, but potentially handle heavy with a pinch grip (which is the most common way to hold a gyuto). The further away the centre of mass is the more weight will there be on the tip in the use. This on one hand makes the knife a bit less 'nimble', but on the other hand makes cutting somewhat easier, as the weight of the knife means that one does not have to push down so much. This really is something one needs to experience. It is not about which is better or worse - it is mainly a question of a personal preference.

The distribution of weight

This should not be confused with a position of the centre of mass, even if in reality these two are related. Imagine a knife (A) which has a lot of weight located around the heel (tall blade at the heel with a thick neck), but tapers strongly towards the tip in both width and height, while having a simple and lightweight handle. Such a knife even if not super light will feel easy to move around. A knife (B) would have blade with little distal taper with a relatively tall blade towards the tip, but balanced with a more substantial, heavier handle. Both knives may have a centre of mass around the same position and may even have similar weight. The second knife however will feel less nimble or less easy to more around as any rotation of your wrist will have to move that much heavier tip around. Here again personal preference plays a large role.

The profile of the cutting edge

While there are some basic 'rules' that one should at least seriously consider when it comes to profile of the cutting edge, it needs to be recognised that many factors plays a role in what one may consider to be an optimal profile of the cutting edge - the most relevant ones would be cutting style of the user.

I personally find that about the best starting point for the profile of the cutting edge can be found on gyutos made by Konosuke, Ichimonji, Hide, Gengetsu, Itinomonn, Shigefusa, etc.

I will use the profile of the Kato Workhorse as an example (see the figure below).

So the 'rules' would be:

• There should be a flat spot (B in the figure) at the heel that would allow 'accordion-free' cuts when cutting vegetables. The length is hard to define exactly, but somewhere around 5-8 cm should work

• The flat spot should not be perfectly flat, more like a very large radius, deviating from a straight line just a fraction of a millimetre over its length. This curvature makes the knife less prone to get 'stuck' in a cutting board plus it allows for that minimal 'rocking' motion while chopping, which is sometimes wanted, but in reality can never be completely eliminated as it is part of the dynamics of the cutting movement by one's hand/wrist

• The flat spot should be integrated in the whole profile of the cutting edge without any 'bump' or sudden change in the curvature, otherwise it may disturb with push-cuts

• The profile at the very heel (last few millimetres) should have a slight up-curve (C). This serves to minimize the risk of the heel getting stuck accidentally in the cutting board (and possibly get damaged in the process)

• Once you move away from the flat spot towards the tip, the curvature of the profile should change continuously, but not linearly, so that the most curved part of the blade is close to the tip.
• I often use a 'height of the tip' - a position of the tip of the knife relative to the line defined by the flat spot (D). The higher the tip is, the more 'belly' the blade has. Indeed this parameter does not describe how exactly is the belly of the knife shaped, but it gives a first idea how much belly the knife has.

Profile of the Kato Workhorse 240 gyuto

Zoomed-in version of the figure above.

Personalizing the profile of the cutting edge:

• If one designs a knife for a certain customer, then one may try to tune the profile of the cutting edge to the customer's preferences and also external conditions. Here the relative height of the person and the height of the cutting surface play the most relevant role. A tall person working at a relatively low placed cutting surface may prefer blade with a more pronounced belly, while a smaller person working at higher placed cutting surface may prefer flatter blade profile. This is just a 'food for thought' and really needs to be discussed with the customer.

• Then of course comes the preferred cutting style. Someone who makes a lot of push cutting or cutting where most work is done close to the heel while the tip more-less rests on a cutting board, a too flat blade profile may make it too easy to 'stab' the cutting board and damage the tip. On the other hand someone who make a lot of pull cutting may prefer flatter blade profile, and so on.

The angle between the handle and the 'flat spot' 

This sounds strange at first but is actually pretty important. On my first knife I made the tang (handle) and the flat spot practically parallel and you notice it the moment you start to use the knife. It just does not feel right on a gyuto.

In general there should be a slight angle between the flat spot and the tang. This has direct impact on the profile of the spine and thus also on the weight distribution and position of the centre of mass of the knife.

In the drawing of the profile of the Kato Workhorse one can see that the slope of the spine of the knife is about 5 mm (height) over 90 mm (length) relative to the flat spot. Since I use paper with 5mm  dotted grit I am using this way to describe the slope of the spine, rather than the angle in degrees or radians.

Note: The axis of the tang should be parallel with the spine at the heel. This is not well represented in the figure above.

Height of the blade at the heel

This one is seemingly simple - if you want a taller knife you just, well, make it taller. But it also means you are adding steel at thickest part of the blade - the spine. So if you would like to keep the weight in check and not changing the grind behind the edge, than you may need to think how to adjust the blade grind higher up the blade or even making the knife a little thinner.

In general most users I have talked to seem to prefer 240 gyutos to be 50+ mm tall, so in my book a 'normal' height of a 240 mm gyuto would be around 51 - 52 mm, give or take.

In general - the height changes the way the knife handles rather significantly. While a taller blade (say 55 mm) gives you more room, it may quickly start to feel less 'precise' - in particular to a less experienced user than a blade 48 - 50 mm tall.

Note: as a general rule of thumb - for knives with a WA handle design one needs somewhere between 35 - 40 mm minimum height at the heel to allow enough clearance for you knuckles when cutting on cutting board, though the angle between the tang and the flat makes a difference too. 

The grind / geometry of the blade

This is in my view the most important ingredient of a well performing kitchen knife. No, a Full Flat Grind (FFG) is literally not going to cut it if you want to make a knife without obvious deficiencies in performance. I have described two main types of grind in the section 2, let's have a look at some examples.

I can not help but notice that in particular knifemakers that are coming to kitchen knives from general outdoor knives tend to make FFG knives. While with an outdoor or hunting knife such a grind make make sense, with a kitchen knife it is not the optimal blade geometry.

So what is wrong with a FFG than?

• Because of a very low angle of the primary grind which goes all the way down from spine to the cutting edge, the knife requires often larger edge bevel than optimal, as otherwise the edge would be way too thin and weak and would get damaged easily (rolled or chipped).
• Should the user attempt to maintain the blade geometry over time, he or she would have to regularly grind (sharpen) the whole surface of the blade, because otherwise the blade would quickly become too thick behind the edge and the knife will give more and more resistance of cutting hard vegetables (or even onions).
• Ingredients love to stick to the flat bevels what disturbs during cutting. Large contact area also means larger drag effect when slicing - this can be very noticeable with raw meat.

The following figure shows schematically a FFG. This grind on a kitchen knife is very thin - with a blade 3 mm thick at the spine and 50 mm tall would result in a bevel angle of only 1.72 degree per side or an inclusive angle of 3.44 degrees (Fig. A in green). Such an edge would be very thin and easy to damage. Normal edge thickness (thickness of the blade just behind the edge bevel - shown in red in the photo, the edge bevel would be produced with sharpening the blade at some 15 degrees per side) would be around  0.15 mm. On a blade with a said geometry this thickness is 2.5 mm from the 'geometrical edge' (Fig. B).

Note: Of course no maker grinds the FFG down to zero edge thickness as that would be next to impossible.

The Fig. B shows the problem the user will have to deal with over time. (1) shows edge on a new knife. As the knife will be sharpened over time, the edge will move up (2) and necessarily will become thicker and the knife will cut with more and more resistance. If the user wishes to maintain the knife geometry, than the only solution is to sharpen (thin) the whole blade (see the dotted line) up to the spine.

Not to scale: cross section of a FFG and zoom of the tip.

The Fig. C shows a cross section of a blade with a convex grind. Here I used each side of a blade to make a different example, I did not mean an asymmetrically ground blade.

The left side of the blade is meant to show a grind where there is a 'shoulder' in the grind (one would find this usually around 15 mm from the edge). Here the (1) in red would stand for a convexly ground bevel and then continuously going to (2) in green which might be convex, flat or even gently concave. In particular the concave grind higher up the blade (2) is sometimes found on asymmetrically ground Japanese kitchen knives (I personally worked on a Hide gyuto - see my Project #11).

The right side of the blade (3) is intended to show a blade with a continuous convex grind from the edge up to the spine. It is important to say that the curvature of the grind of course changes with the distance from the edge - it is NOT a single radius grind.

Not to scale: A convex ground blade

An example of a continuous convex grind is Kato Workhorse by Yoshikaki Fujiwara. This is a hefty gyuto with a 240 mm cutting edge length weights ca. 250g. This also means that it is thicker and the convex shape of the grind is more pronounced. I took a short video trying to show its grind.

Now we get to the wide bevel grind. In Fig. D one can see a sketch of a wide bevel grind. In general the main recognition feature is the shinogi line - in the photo below it would be where the green and red lines meet (at the dotted line). But wide bevel grind is much more than just a combination of 2 flat grinds. The (1) in red can be on a new knife convex, flat or even concave. As mentioned in the section 2, the concave grind is more of a result of the production process than the intended final geometry of the wide bevel. Over time this should be turned by the user to a hamaguri bevel - which would be best described as a very gentle convex grind (with most of the convexing happening first few millimetres behind the cutting edge).

The Fig. E shows a closer view of the wide bevel grind. As the knife is being sharpened (either by applying a micro-bevel at the edge or by convexing the cutting edge - none of these is shown in the figure) the knife will also need regular maintenance and to keep the geometry of the wide bevel the whole bevel will need sharpening. This is in a sense similar to what was mentioned at the FFG, but here the area that needs to be sharpened (thinned) is considerably smaller. One one wants to achieve is - as the cutting edge move upwards, so should also the shinogi line. This is represented by the red lines and small arrows.

Not to scale: wide bevel grind example

Here is a short video showing a nakiri with a wide bevel grind. I did some work on the wide bevel which as of now is practically 100% flat (which in spite of being fairly thin causes some issues when cutting that are similar to a FFG), but I will be giving it a hamaguri grind soon.

But how to get the grind (in particular close to the edge) right? You need to test it while making it. Once you got the blade ground close to a zero edge thickness just put a quick edge on it with a coarse stone and cut come potatoes, carrots and onions to get an idea where you stand. If the performance is not as intended try to figure out where is the problem - is the blade too thick behind the edge (will not want to even start the cut), or is the blade too thick higher up the edge (will wedge), or is the geometry of the grind too flat (sticking & resistance/drag) or is the convex too steep behind the edge (edge will feel thick and cause wedging).

Monosteel & san-mai 

There are many Japanese double bevel knives that are made from single piece of steel. Most of these knives are either rather thin blades (sometimes called 'lasers'), or honyaki knives (differentially hardened knives with visible hamon line - pinnacle of Japanese knifemaking). However most double bevel Japanese kitchen knives have 3-layered construction like san-mai or warikomi since this has several advantages for the maker and for the user.

Note: I am going to loosely use the term ´'san-mai' as a synonym for multi layered blade construction like san-mai or warikomi, where a hard steel in the center of the blade is clad on both sides with iron, soft steel or damascus.

From the maker's point of view there is indeed the need to master the skill of weld-forging 3 pieces of steel together (otgherwise delamination would destroy the knife later in the process) and of course to forge a blade out of it. However once the bladesmith has mastered that skill forging of a san-mai blade can actually be even faster than from a single piece of steel, because most of the blade will be formed by a soft iron or steel that is easier to forge. On top of that this blade construction allows the blade to be straightened also after heat treatment without risking damage to the blade. After HT the grinding of the blade is also easier than with a monosteel knife, as most of the material that will be removed in the process is again not hardened steel.

From the user perspective san-mai construction makes the knife less prone to larger damage or breaking in spite of the fact that the cutting core has 60+ HRC. Once the knife needs thinning as a part of geometry maintenance - this can be done more easily as again, most the material that will be removed in the process is the soft cladding.

However I assume that very most readers of this article are making knives via stock removal method from a single piece of steel and I think it is reasonable to consider the implications for the user. The main point here is to think of the knife maintenance and thinning over time - in particular if your choice of steel is some of the modern stainless steel with high resistance to wear and abrasion. In the first place the knife should be made thin behind edge - the user should not have the need to thin the knife out of the box. The next important point is that the knife should be reasonably easy to maintain (thin).

This is just something one may want to keep in mind when considering how to grind a blade, but not necessarily something that should be central to how the blade will be ground, since performance of the blade should be the primary objective.

Grind close to the cutting edge 

Especially at the beginning one may feel unsure about how thin the blade is to be ground and how much material needs to be 'spared' for subsequent surface finish (scratch removal) and one may easily end up with a blade that is too thick first few millimetres behind the edge.

Example: Think of an edge that on one hand has been brought to the intended thickness of say 1.0 mm @ 10 mm behind the edge, but is still 0.7 mm thick @ 5 mm behind the edge and 0.3-0.4 mm thick just right behind the sharpening (micro) bevel (or about 1 mm behind the edge). If you run the blade between your fingers from the spine to the cutting edge you will feel a sudden 'jump' very close to the edge. In use such a blade will give a lot of resistance when cutting anything dense. Do not get fooled by the fact that the edge will shave or push cut paper - that is just a testament to your sharpening skills, but it tells nothing about the edge geometry.

Once the knife will need thinning, the grind higher up the edge should ideally not require too much metal removal. So for example knife with a thick spine or very wide bevel would require more work to thin regularly than a thinner knife and/or a knife where the wide bevel is not quite as wide. The best example here that I can think of are knives by Robin Dalmann who makes a rather narrow wide bevel and then a gentle concave grind above and as a result maintenance of the blade only requires to sharpen a relatively small area behind the edge.

Hamaguri grind

I have mentioned above the hamaguri edge, but did not explain how to create it. Imagine that you have made a wide bevel grind that is 15 mm wide and you are in the stage where you brought the edge thickness close to the zero (say 0.2 - 0.3 mm) and at the moment the whole wide bevel is still perfectly flat as it came off the grinder.

What you want to do is to grind the first 3 - 5 mm behind the edge with a slightly larger angle, so that your wide bevel and then blend these two grinds together. You will end up with a wide bevel grind that is practically flat ~5 - 15 mm behind the edge and a gentle convex the first ~5 mm.

Neck design

Well, 'neck' is not exactly a proper term, but I will just stick to it :) I am using it to describe the part of the tang that is exposed when the handle is mounted. Or in other words it is the narrow part of the blade between the handle and the heel.

One possibly minor point is the design of the neck of the blade. On a hidden tang knife there are in general 2 ways to do this. the height of the tang is (near) the same as the height as the handle. That is the case on the Kato Workhorse in the photo above as well as the custom gyuto by Bryan below. This means that before the handle is mounted the tang has 'shoulders' which define where the handle will be mounted. There is one more option here - often on Japanese knives the handle is not mounted all the way to the 'shoulders' of the tang and a short (2-3 mm) part of the tang is exposed. This is then called 'machi'. 

The other option is that the tang has no 'shoulders'. The main practical difference is that the handle sits a few millimetres higher relative to the spine of the knife and thus making the effective blade height a little larger. This is not really relevant on a 50 mm tall gyuto, but would be on a small knife with less blade height that should still be tall enough to clear knuckles on a cutting board.

Left: custom 195 gyuto by Bryan Raquin
Right: 165 nakiri by Masakage 

Taking a closer look

Handle type & design

WA handle is a fairly easy to make (I show the details of my approach in several other project related articles), but when designing one it should be seen as a part of the knife, rather than a separate component. For me as a maker the large advantage of a WA (basically a hidden tang) handle is that I can make it separately until it is 100% finished before mounting in on the knife. This allows me to test it in hand (given that blade is fully ground and thus is shape and weight is final) and should I make a fatal mistake while making the handle I do not have to figure out how to remove if from the blade without damaging the finish of the blade.

The relevant features of a WA handle are:

• The handle is taller than wider
• The handle is both taller and wider at the end than at the ferrule. In other words the handle tapers in both vertical and horizontal direction along the length of the handle. This improves the grip considerably over a handle without any taper.
• One may want to apply additional taper under larger angle on the sides of the ferrule - this will make the front of the handle narrower and allow it to sit more comfortably in your hand when using a pinch grip, while the rest of the handle retains enough thickness.
• Length of the handle can be used to adjust the weight of the handle and thus the position of the centre of mass, but both too short and too long handle is going to look strange on a gyuto.

Check out the article on the Project #25 for an example.

When it comes to materials and design I would recommend to start with a simple handle made of 2 materials for ferrule and body of the handle. Add a spacer if you feel the 'need', but avoid metal spacers at the beginning. You can use natural or stabilized woods, buffalo horn, micarta, etc. In general natural woods tend to be lighter than stabilized ones. I would recommend not to get 'scared' by using non stabilized woods. There is great variety of them and apart from very soft woods are mostly suitable for handle. It may make sense to use either a more dense and oily wood for the ferrule (which will have in general more contact with the food and its juices) - african blackwood is a great example. I sometimes use stabilized wood for the ferrule and natural for the rest of the handle. Water buffalo horn (comes in rolls and is usually black) is also a great material for the ferrule.

When choosing the handle materials do not only think about the aesthetics, but in the first place about how heavy you want the handle to be and where the centre of mass of the knife should end up. Indeed - this is not easy to judge upfront and will require some experience. 

Note on metal spacers: These can look great on a handle and provide very strong optical separation, but once the whole handle is glued together it should be power-sanded very carefully. The metal heats up very quickly and if you are not careful it may and will cause the epoxy to over heat and the handle will fall apart. I have a first hand experience on more than 1 handle. Also - the thicker the sparer the higher the risk. I have read a tip where one knifemaker while power-sanding the handle dips it regularly to ice water (obviously only applicable with stabilized or very oily woods) to keep the epoxy safe. Also - working in parallel on 2-3 handle and rotating through them would allow one to cool down while the other is being worked on.

4. Putting it all together

A very experienced knife user and vendor often uses a term than a knife or its design should 'make sense'. With that he means that the basic parameters (as loosely discussed above) plus heat treatment should follow the same philosophy (or simply purpose) so the knife can be used to its full potential. What exactly that means can be best understood from first hand experience with Japanese kitchen knives.

Well made knife that suits the style of its owner largely 'disappears' in use - it will simply do its job without getting in the way and without requiring 'workarounds' to be used efficiently. One often hears the term 'prolongation of one's hand' - that is basically what I am trying to achieve (even if it is a bit of an over-statement)

Once you made a knife - how are you going to know if it is any good? The best you can do is try to find a few pro chefs who themselves use Japanese kitchen knives at work and ask them to test your knives. You will most likely get a very to-the-point feedback that will help you to improve. Of course - every user has different 'sweet spot' and it will be the same here. Not even a 'perfect' knife will please everyone, mainly because a perfect knives do no exist.

5. Summary

This brought me to the end of this lengthy article. I hope you found it interesting or maybe even helpful. I would very much appreciate your feedback, so please do not hesitate to leave a comment, question or a critique.