Custom Kitchen Knife Design
How To Make A Great Kitchen Knife
From the knife profile to the handle design to the steel chosen and overall balance, every element comes together to create beautiful custom knives you love to use. OR NOT!
Each part of a knife must work in harmony with all the others and be pleasing to look at! Whether For Professional Chefs Or Home Cooks, The 8" Chef's Knife, Cleaver, Or A Simple Paring Knife Needs To be Made Right! Steel choice, the right profile, and the handle design can make the knife a dream or a nightmare!
What Makes A Good Custom Kitchen Knife?
How to Design a Great Kitchen Knife
Let's Explore The Possibilities
I like thin knives. All other things being equal thin blades cut better, feel sharp longer, and are easier to sharpen when dull. These statements remain valid regardless of the steel the knife is made from.
Because I make thin kitchen knives, the steels I choose and the heat treatment protocols I apply must result in a matrix of carbides and ferrite that are tough enough to support thin blades. Acute sharpening angles require great strength and toughness.
Due to these requirements, AEB-L is my stainless steel of choice for kitchen blades. It is the toughest stainless I have seen test results for, offers high hardness and excellent grain structure. AEB-L has good machinability, polishes well, is easy to sharpen, has good stain resistance, and doesn't break the bank when restocking.
For high-carbon steel in the kitchen, I offer 52100, 80CRV2, or 26C3. These are relatively simple steels with low alloying and high carbon. They have a fine grain and carbide structure, offer outstanding toughness, high hardness, ease of grinding, sharpening, and machining, and a comparably low restock cost.
It always feels good when you pick up a knife, and it falls into the curves of your hand as if it were made for you. Custom Knives deserve custom knife handles! Home cooks and professionals alike appreciate a well thought out, fine wood handle.
The handles here at Keith Nix Knives are designed and built exclusively by Keith Nix Knives. I build my handles from stabilized wood, G10, or Micarta, in a pattern similar to a soft drink bottle. These handles have no straight edges other than at the spine, have a light swell in the middle to fit in your palm, and two smaller diameter areas to guide in the placement of your front and rear fingers.
Wood handles are sanded as high as 3000 grit and finished with a durable blend of oils and varnishes developed for gun stocks, called Tru Oil. Handles can be customized to fit your hand and style of holding!
PRO TIP: The finish on your handle will withstand many hand washings. It WILL NOT survive a single trip through the watery hell of the dishwasher! Please hand wash and dry your fine knives! Also, don't use any abrasive scrubber or oil/chemical you wouldn't use on your best piece of wood furniture.
The profile is the outside dimensions of the knife we're making. The profile includes the amount of "belly" in the edge, how the edge and spine meet at the tip, the handle's shape, and the blade's overall height.
All those factors must play well together to make the knife practical, functional, and easy on the eye. If you like to rock your 8" chefs knife when chopping, you'll need enough belly to allow that to happen. If you chop by lifting your blade from the cutting board (like me), you probably prefer a bit more "flat" toward the heel to accommodate the guillotine chop!
Paring knives mostly peel veggies, so their profile is less critical.
Opinions can vary, and some folks favor either German profiles, French knives, Japanese styles, or a modern western style. There is no right or wrong, just what's right for you.
Take a look at this western-style all-carbon Deba!
The edge is the business side of the profile, where the actual cutting takes place. And there are dozens of ways to put the final edge on a knife. The method I employ resembles the fifth in the picture to the left, the compound bevel, though my edges are far more acute than those shown, and there are three angles.
The first angle forms the "cheeks" of the blade itself and is usually 2-3 degrees, depending on the height and thickness of the blade. This angle extends from the spine to an edge thickness of 0-.005 at the heel and .005-.010 at the tip to provide a little more strength.
The second angle down toward the edge is 10 to 11 degrees per side and forms an apex at the edge. The final angle is 15-17 degrees per side, applied by hand on a fixed angle sharpener, and is finished to 3000 grit, stropped to shaving keenness, and delivered to you.
So to summarize, the steel, profile, handle, and bevel angles must all work together and support your slicing or chopping efforts. The steel must be tough and strong enough to support the thinner edge geometry of a kitchen slicer. The handle needs to fit the hand and provide a firm grip. Finally, the profile has to be functional as well as eye-pleasing!
First, let's clear up a common misconception- in steel, hardness has nothing to do with stiffness and vice versa. A steel part may have a high or low hardness, but it will always have the same stiffness. To make a knife more flexible, it is necessary to thin the blade, so we're actually bending less steel.
Hardness is a measure of the relative strength of a material. This is a little counterintuitive for me; my mind thinks the Charpy toughness test is about strength. But, the definition says hardness is directly related to a steel's "ability to resist permanently deforming." So I believe hardness is a contributor to edge stability.
Hardness also increases wear resistance, so let's remember that too. There are several ways to measure the hardness of an already hardened steel, but the Rockwell C test and scale are the most common. This test measures the depth of penetration of a diamond cone under 150 kg (330.693 lbs) load.
While I know what hardness my heat-treating recipes should produce, testing the hardness of every blade guarantees that human error and failure of my ovens or cryogenic quench have been eliminated. That hardness translates to more strength and better edge holding for you. To a point.
All knives must be "tempered" in their heat treatment protocol. When first hardened, they are quite brittle and under tremendous internal stresses. The blades must be reheated to some lower temperature to relieve these stresses and slightly soften the knife. Many mass producers of knives temper their blades to be much softer than they should be for kitchen use.
At Keith Nix Knives, we aim for 62-63 HRc most of the time, while those other guys are mostly in the upper 50s. We use a digitally controlled convection oven for tempering, accurate to plus or minus 2 degrees at 400F.
So temper we must! Only then will it be a trustworthy kitchen companion!
Toughness is a measure of a steel's ability to resist catastrophic fracture. To the left is a chart of various stainless steels and D2 tool steel. The vertical graph labeled 5, 10, 15, etc; lines represent toughness as measured by the foot pounds of force required to break a standard sub-size Charpy sample. The horizontal lines labeled 58, 59, 60, and so on represent the hardness of the piece as measured on the Rockwell C scale.
One of the first things I noticed is that the harder a steel is, the lower its toughness. So two desirable properties generally negatively affect each other. However, we need as much hardness/strength AND as much toughness/fracture resistance as possible when it comes to edge stability. Looking at the chart above, you'll see why I chose AEB-L for my "House Stainless."
Carbides and Edge Stability-
We've established that edge stability is at least partially dependent on hardness and toughness, but there is another property at play in the game: carbide size. Carbide size and volume negatively affect toughness and edge stability, but POSITIVELY affects edge RETENTION. Here's why:
Carbides are combinations of carbon and one or more other elements found in the steel. There are iron carbides, Chromium, Tungsten, Vanadium, etc. These carbides are MUCH harder than the steel matrix surrounding them, but they're also quite brittle. In the images above, you'll see a steel cracking at and then through a carbide particle (Steel matrix is darker gray, and carbides are lighter gray-blue). So we have another conundrum here. More carbides lead to better edge retention but poorer toughness.
We can work around that a little by processing steels to have very small carbides. Testing has proven that smaller carbides are less detrimental to toughness, and therefore edge stability, while still being in the composition for edge retention. So we want a steel with extremely fine carbides. Again, AEB-L.
Here are SEM images of D2 on top and AEB-L at the bottom.D2 has very poor toughness, and the carbide size reflects that, while AEB-L has tiny carbides and excellent toughness. While other factors contribute, the carbide size in D2 makes it test so poorly in toughness while also being a solid performer in edge retention.
Steel selection is a tightrope walk, trying to balance the properties we've discussed. There are compositions of steel out there that look for toughness ONLY, or others willing to sacrifice all other properties for the best edge retention, stain resistance, or some other trait. My approach in knife design is to find the steel with the best BALANCE of properties, including the ones we haven't discussed, sharpenability, affordability, and ease of manufacture.
All those tangible and intangible properties contribute to making you the best, most affordable knife I am capable of making. When backed by the Keith Nix Knives Guarantee and unmatched customer service, I don't know why you would want another brand!
Take a look at "The Norton" Fillet/Boning/Camp Kitchen Knife
Other FREE Learning Articles:
See the Mini Cleaver!
Learn To Care For Custom Knives