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If you’ve ever wondered how to grind a chef knife or what are the best culinary knife grinds this post should help dispel some of the myths and point you in the right direction in terms of geometry. It’s come about because I was asked by a few people if I would write a post on chef knife grinds and as the subject is as long as the proverbial piece of string, I thought I’d try my hand at it. As luck would have it, I also learned a whole lot more in the process and that’s a win/win in my books.
When I started making chef knives there weren’t many chef knife videos on youtube as there are now for makers to learn from (Mike Ekim of Ekim knives comes to mind). As such I’ve seen many a maker, myself included, start making kitchen knives with full flat grinds. Why not, because if you’ve read anything about the standard blade grinds, you’ll know that flat grinds are in many ways particularly well suited to kitchen knives. However, if you’re reading this post, you are aware that there are other grinds out there that can offer better cutting performance.
There is a natural evolution as a maker to hone and perfect one’s craft but I would still caution you not to try to incorporate all of the below information at once on your next blade. Each new addition requires a new set of skills or equipment and may take some practice to get right. It’s just a matter of mixing them until you find what works best for you. Just because I do something, a particular way doesn’t mean you should, and vice versa.
This post ended up being a bit longer than anticipated, so in part 2 I’ll deal with the ergonomics of chef knives.
- Thin vs Thick (The workhorse & laser)
- Distal Tapers
Thin vs Thick (The workhorse & laser)
My first chef knife was made from 3.2mm Bohler N690 because that was what the other knifemakers in my club recommended. Thereafter I went chasing “performance” and started using 2.5mm Bohler K110 (D2) because it was thin (and thinner is better after all), high level of carbon, good hardness (<63HRC) and edge retention. I’ve since moved onto Bohler Elmax (mainly due to its increased stain resistance and balanced properties) and after my initial misgivings about its 3.78mm, thickness has really come to love the ability to create bold tapers and unique geometries with the steel. I even emulated Don Nguyen’s style with a 5mm thick (spine) 1084 k-tip gyuto once.
Chris Anderson (Scorpion Forge) was one maker I followed early on and I was amazed at how he could flex the edges of his knives on his thumbnail. The idea that you could grind a knife that thin blew my mind. I worked at it and was eventually able to flex the edges of my own knives.
If you’re a fan/follower of Knife Steel Nerds (I’m sure you are), geometry (thickness behind the edge) plays a big role in cutting performance, especially in the CATRA cutting tests.
Japanese master sharpeners are reportedly stopping just at the point where the edge will start to flex under fingernail pressure. Not every knife needs to be that papery thin, just as not every steel will support such a “fragile edge”. Therefore as a maker, the heat treatment you use and the steel must be able to support your chosen edge geometry.
Especially in the beginning, one may feel unsure about how thin the blade is to be ground and how much material needs to be ‘left’ for the final surface finish (hand sanding) and one may easily end up with a blade that is too thick behind the edge.
Make the following measurements to assess your knife’s geometry.
- At the very edge (edge thickness)
- 10mm up the edge – from heel to tip
- 27mm up the edge on taller knives (end of jaws on my callipers) – from heel to about 2/3 of the blade forward
- Spine thickness at the handle, over the heel, 50mm from the tip, 10mm from the tip
- Straight edge against the side of the knife to gauge geometry (grind)
I use low grit ceramic belts (#36) to remove most of the material (post heat treat on hardened steel), then step up to #60/#80 and start refining the bevels before thinning the blade to 0.4mm (0,015″) with a #120 belt and finally a A160 Gator belt to prep the blade for hand sanding. I find this helps me “sneak up” on the final edge thickness (+- 0.25mm) and remove any of the previous grit’s scratches before the polishing.
The definition of a laser, workhorse or mid-weight knife is not one you’ll find clearly defined nor universally agreed on. It is mostly relative to the user and is therefore viewed in shades of grey. As topics go this is prone to starting arguments.
- One way to determine the style is the conventional “usage” of the word ‘workhorse’ – something akin to a hard-wearing, dependable tool that is designed for extended work. To this, we would assign a knife with some robustness, well balanced, comfortable and able to handle many different food items.
- The other usage is referring to specific “qualities” of a knife-like grind, thinness or weight, etc. Lasers for instance tend to be described as light, nimble and offer effortless cutting/low resistance.
For those who are into data, I found the following set of graphs which you may find interesting.
So which is better, the laser or the workhorse? The simple response is that neither is better than the other. It’s only in a tall, dense product like butternut that you first start to notice that a Workhorse may wedge while the Laser will struggle considerably less. On the other hand, the Workhorse should have excellent food release while the Laser occasionally slows down prep to remove stuck slices. These are typical tradeoffs of overall thickness, weight, cutting ability and food release.
Regardless of which style you go for, do consider the knife’s intended role. A laser cleaver for instance is probably not going to hold up incredibly well when attacking bone and a workhorse paring knife is best described as a butter knife.
When we talk about the shape of a blade, its profile is usually the first thing to spring to mind. The blade, however, has three other very important characteristics: the shape of its cross-section – the grind , the angles and shape of its cutting edge – the primary bevel and finally the thinning of the spine from heel to tip – the distal taper.
If we look at a knife from behind the handle towards the tip (choil), we see the cross-section of its bevels or the angles at which the blade surfaces have been sharpened from its spine to the cutting edge. The grind is therefore how the blade is thinned to result in the cutting edge. While a great indication of a knife’s overall setup, it doesn’t tell you the whole picture.
All types of grinds are great for variety and different applications. Regardless of grind or thickness at the spine, the main thing you should look for is the thinness behind the edge. Universally, if you get it thin enough just behind the edge, the knife will perform reasonably well in its primary task.
Primary bevels can be flat, concave, convex, or complex geometries like an s-grind, but for this article, we’ll exclude single bevel/chisel grinds as well. Those tend to be unique and specific to only a handful of knives.
THE HARDEST GRIND IS THE ONE YOU DO NOT REGULARLY DO, AND THE EASIEST WOULD BE THE ONE YOU DO ALL THE TIME.”JIM CROWELL
Full flat Bevel
Usually, you’ll see a full flat grind on production knives and while they are common (mainly due to ease of manufacture), the performance isn’t great as they tend to wedge in harder produce like sweet potatoes, butternut and exhibit a wonderful ability to collect food on the bevels (striction).
- Because of a very low angle of the primary grind which goes all the way down from the spine to the cutting edge, the knife requires often a 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 which interrupt cutting to clear the blade.
- A large contact area also means a larger drag effect when slicing – this can be very noticeable with raw meat.
Ultimately I’m not going to cover full flat grinds in-depth because they are quite common and most knifemakers can execute them reasonably well.
Before we go further, the below diagram will be helpful if you aren’t familiar with Japanese knife terminology.
Wide Bevel / Sabre Grinds
Wide double bevel knives are quite distinctive in that there is a discernible shinogi line, which is the abrupt corner between the flat “hira” where the maker’s stamps are usually found, and the bevel itself “kireha”.
The main purpose behind a wide bevel is so that the user can easily maintain the original geometry of the knife by “thinning” throughout the knife’s lifespan.
Nearly all blades with a Kurouchi (blacksmith finish), Nashiji (pear) or Tsuchime (hammered) finish to the flats of wide bevel knives. The face of the blade above the shinogi line is most often flat, but can be slightly convex or even concave (hollow).
It’s hard to say that the shoulder would negatively affect performance (wedging/resistance) because there are various factors that would change the properties of the blade quite a bit, such as thickness, taper and height of the blade. Some makers will gently convex the bevels (hamaguri convex) as well which will lessen the hard transition.
To grind a wide bevel knife with sufficient distal taper (more on distal tapers below), it is recommended that the taper be ground or forged in first, followed by the bevels (concave, flat, convex). The shinogi line should be even on both sides of the blade and run parallel to the edge. If you are using a san-mai blade, the core of the knife should be evenly exposed on either side of the entire cutting edge.
The width of the bevel can be anywhere between about 10 for a “low bevel”, or 25mm to 30 mm for a “standard bevel” and higher for a “high bevel”.
The grinding angle will naturally change from the heal, as you approach the tip. This is normal as the tip has a thinner cross-section due to the taper as well as a proportionally higher grind compared to the heel of the knife.
Convex grinds are already well known to knifemakers and are typically the first step away from a full flat grind. The main difference between Convex and the wide bevel is that there is no clearly defined shoulder/shinogi transition.
I examined my Japanese knives to see what was so different about them and when putting a ruler across the bevel it became immediately clear that they didn’t have perfectly full flat bevels.
The picture on the right is a great example of the lack of flatness.
Convex grinds offer good food release, the ability to get fairly thin behind the edge with enough backbone to still be robust enough to hold up to most tasks.
The amount of convexity varies quite a bit across different makers, some are quite “chunky” while others will have a very subtle convex from the edge all the way up to the spine. This may be impacted by the thickness of the stock, grind and distal taper.
In general, it needs to be noted that the convexity of the grind is subtle and should not be overdone. The blade may even look flat at first sight (looking at the choil from behind), even though it is convex.
The convexity of the grind is most pronounced first 20-30mm behind the edge which is much the same as a wide bevel. The curvature of the grind is not constant but changes over the height of the blade.
Don’t worry too much about the exact angles used as the different facets will or can be blended together and the focus should be primarily directed at the thinness behind the edge, with an end goal of good food release and minimal wedging. The overall bevel may remain convex up to the spine but often is almost flat or in some cases gently concave.
Most of the convex grinds will be finished with either a Migaki / Polished or Damascus (which is usually polished) finish to the blade. Some makers achieve an almost mirror-like polish while others do a cloudy/satin polished finish.
Western or production knives are predominantly evenly ground with a 50/50 or perfectly centred edge. The opposite is true of traditional Japanese knives, where it is very common to have an edge that is off-centre, usually with a right-hand bias (as most users are right-handed).
Alternatively, a knife that is ground with a 50/50 bevel, can also be referred to as asymmetrical should the bevels on either side be different (ie: concave/convex).
For our discussion purposes, an asymmetrical bevel refers to when the blade’s cutting edge is kicked off to one side or a non-centred edge.
Typical Offsets with examples:
- 100/0 (single bevel) – yanagiba, usuba, etc
- 90/10 (double bevel) – honesuki, garasuki, etc
- 80/20, 70/30, 60/40 (double bevel) – gyuto, nakiri, sujihiki, etc
- 50/50 (symmetric) – non-Japanese / production knives (Wusthof, Henkels, Shun, etc)
This results in one side having a steeper angle than the other and can in extreme cases (100/0 or 80/20) create steering issues that require a higher user skill to control. A good example would be a single-bevelled Yanagiba.
Rather than being a mistake or bad skill from a smith, this asymmetry is there for a reason. It is largely considered to contribute to better performance and promote food release (reduce striction). In reality, it was arguably a maker’s attempt to combine the cutting performance of a very thin blade (laser) with the more robust and enhanced food release of the wide bevel / convex blades so that the user enjoyed the best of both styles.
To this point, imagine a san-mai blade (hardened core with soft cladding on either side). In order for the edge to be equally revealed on both sides, the smith intentionally has to forge the core steel over to one side, otherwise, you’d end up with soft cladding at the edge all the way down to the edge on one side. (as per the below example)
For a typical double-bevel right-handed knife, the right side bevel is generally ground with greater convexity than the left side (when holding the knife edge down). The greater convexity of the right side improves food release by pushing the cut food away from the cut. The left-hand side due to the offset has a flatter profile.
A maker can combine either a flat, concave or convex grind to each bevel (eg, concave/convex, convex/convex). I’ve included a few choil shots below as examples. Given the thinness behind the edge of each knife, the geometry will be very subtle. Please click to view a larger image.
Sharpening becomes an important aspect of asymmetrical knives. Due to the potential for steering by the primary bevels, this can be compensated when you sharpen the blade edge.
To follow on from asymmetrical bevels, there are two rather important aspects in terms of sharpening the secondary bevel or edge. As mentioned above, extreme asymmetry can induce steering in the cut (the knife will veer off in a certain direction), so to avoid that, reduce wedging and have a razor-sharp cutting edge, you should sharpen it according to the grind or asymmetry. This creates the effect of “balancing” the forces.
Below is a diagram of my best understanding of the principle. Essentially in practice, and 50/50 bevelled knife will not steer to any side as the angles and bevels are exactly the same. As we increase the off-set / asymmetry, the bevel with the least material or shallower angle with experience less resistance from the food being cut and the knife would steer towards that side.
The second important aspect is to keep the apex of the edge centred where it should be. This is primarily of importance for laminated Ni-mai and san-mai blades as you want to keep the hardened core steel at the cutting edge. Mono-steel blades will still benefit by retaining the original relationship of the asymmetry.
By sharpening the knife with a complementary/inverse/asymmetrical edge some of that steerage can be mitigated enough that the knife will not steer at all. The idea is to match the edge angle to that of the opposite bevel.
Guided devices will be of little help with asymmetrical knives unless you plan for the different angles upfront and can allow for it. The easiest way to evaluate the blade’s asymmetry and then replicate it as best as you can:
- Lay a straight edge/ruler on the bevels and get a rough estimate of what you are dealing with.
- Lay the blade bevel on your water stone and take note of the height of the spine above the stone. Flip the knife over and try to keep the spine at the recorded height.
The modern take on s-grinds has been included as it is popular with many western knife makers. I already have an article on S-grinds (S-grinds are they worth it?) but we’ll cover the basics here as well.
S-grinds aim to provide good food release by creating an air pocket to reduce striction. The lack of material in the central portion of the blade also reduces drag and wedging.
The primary bevel is either convex or concave with the hollow occurring above the primary bevel and below the spine.
Some makers have really pushed this style to the extreme and created grinds that are unique to them alone.
To create S-grinds, knifemakers use either a very large diameter wheel or a 36″ radiused platten. I myself use a 30mm belt on a radiused platten as this gives me good stock removal rates and stops the heat from weakening the belt’s joint. That being said, there are examples where Japanese bladesmiths forge the flat “hira” of the blade to produce a slight hollow, which is essentially an s-grind as well.
This section isn’t so much about a particular grind but rather draws the makers’ attention to, shall we say differential blade geometry. I’ve alluded to this at various points above and while a maker can deliberately incorporate this concept, it also happens very naturally at the same time. So don’t sweat it too much.
The Japanese traditional art of swordsmithing has transformed into modern-day kitchen knives and as you would expect, many forging techniques and concepts were brought across. Hiraniku is an important characteristic of Japanese swords.
The Japanese concept of “Hiraniku” literally means “edge or surface meat” which refers to the amount of “swell”, or “mass”, left between the shinogi-ji and the very edge of the blade.
- A blade with “meat” (Niku) lower down, closer to the edge will have a robust and strong edge.
- Blades with little or no hiraniku near the edge or have the meat placed higher up around the shinogi-ji will have a weaker edge.
The placement of the “meat” also changes from knife to knife, sometimes a little closer to the edge (making the edge itself more convex) or a little further away (making the edge a little flatter).
As per the Kato v-grind example above right, the placement of the “meat” changes at various points along the blade. It has pronounced convexity mid-blade which tapers off toward the heel and tip. This enables the blade to perform delicate tip work and have excellent food release when push or roll cutting.
The concept of a distal taper is the thinning of the blade’s spine from the heel of the blade all the way toward its tip. Thin knives will have a less pronounced taper than thicker knives by virtue of having less material available to thin.
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, namely heal, middle and tip. A knife is with more mass at the heel will be heavier, stronger and more comfortable at the handle (we can exert more pressure with the heel), a good proportion middle will mitigate wedging and a thinner tip affords the user precision. This allows a knife to perform well at various tasks.
The other advantage is weight distribution which enhances manoeuvrability and allows for smooth and precise cuts. It’s very common for makers to point out where the “balance point” of a knife is in relation to the neck of a knife. In most cases, a knife that is equally weighted is prefered but in some cases like longer knives, a slightly forward weighted blade is desirable to aid in chopping and or powering through food items. Smaller knives like paring knives will almost always be handled heavy.
The way different makers create the taper can be quite different. Some makers will taper only in the last third, others will have a constant linear taper from heel to tip, others will have a concave or convex taper and then a few may employ a compound or mixture.
As will most things there are pros and cons to each implementation:
- Food separation – Thinner cross-sections will have better food separation but also introduce flexibility.
- Food release – thicker cross-sections will usually have better food release in combination with the grind.
- Flexibility – This may be fairly obvious but the less blade material or thinner the blade becomes the more flexible it will be. For some blades, this is a requirement while others will need backbone or rigidity.
- Balancing point – A blade that maintains its thickness over a longer distance will tend to be more tip heavy while extreme tapers will be more handle bias.
It’s worth noting that when you have an asymmetrical grind, especially extreme asymmetrical grinds, the tip placement can be altered. Since the edge has been kicked off to one side, what does that mean for the tip of the knife, is it too off-centre? Yes, it is.
The answer is in order to have the cutting edge of an asymmetric, distal tapered knife run parallel to the handle as it should, the tip of the knife needs to similarly be kicked off slightly left or right. That means that one side will have a stronger/steeper taper than the other. If not, you will introduce a twist in the knife which will throw off your bevel geometry and introduce steer, especially nearer the tip.
Test, Test, Test
Do consider the notion that popular youtube cutting tests like cutting paper, cardboard rolls, and shaving thin slices off tomatoes are ultimately a test of your sharpening skills and do not offer you or your customer a true insight into the cutting performance of the knife.
A good maker will often check his blades as he’s working on them. Once you got the blade ground close final dimensions, test it by cutting some food (that’s before you put an edge or handle on it).
If the performance is not as intended try to figure out where is the problem:
- is the blade too thick behind the edge (it will not want to even start the cut),
- is the blade too thick higher up the bevel (it will wedge),
- is the geometry of the grind too flat (food will stick & you feel resistance/drag in the cut),
- is the convex too wide behind the edge (edge will feel thick and cause wedging/cracking)
- Carrots (listen for cracking noises)
Food Release / Striction Tests
- Onions (double up with a tip test)
Chef knives are probably the most widely used knives in all corners of the world. As such they are subject to a lot of use, abuse and ongoing maintenance. As a knifemaker, you should pay specific attention to the construction of the knife so that it is ultimately fit for function not just out of the box but for the entire life of the knife.
Knives can be very specific to certain cuisine and or uses so it’s important to not adopt a one style fits all approach in your knifemaking but to match the knife to its intended purpose. The Japanese are infamous for having over 180 different styles, each with its own intended and specific use.
Talk to your clients upfront and investigate how they use a knife, what they want it for, what is their level of expertise and what are their expectations. The better you understand these things, the better you are able to dial in the geometries, profile and overall fit and finish to meet their expectations.
The design of a good kitchen knife isn’t a destination at all, it’s a journey, and likely you will chuckle at your first attempts if you continue down this road. And then when you hit on something you really like, you will start to see many minor variations that will make differences in ways you will only understand over time and through lots of feedback.
And above all, try new things. Dare to fail.