Sharpening Japanese Knives - what no one has ever told you.

There is a wonderfully romantic image associated with sharpening Japanese knives: an elderly Japanese craftsman sitting patiently at a bench, working a blade across a succession of whetstones, gradually moving through finer and finer grits until the edge is exactly as he wants it.

It is skilful, traditional and beautiful to watch. It has also helped create one of the biggest myths in knife sharpening -

Japanese knives must only be sharpened on whetstones.

This simply is not true.

Whetstones are one method—NOT the only method

Across internet forums, knife blogs and the websites of many Japanese knife-sharpening companies, you will repeatedly be told that whetstones are the best—or even the only—proper way to sharpen Japanese knives.

A skilled person can undoubtedly produce an excellent edge on a whetstone.

We are not disputing that.

However, the quality of sharpening is determined by the machinery or abrasive being used, the control of temperature and, above all, the knowledge and ability of the sharpener.

A whetstone does not automatically produce a good edge, just as a grinding wheel does not automatically produce a bad one.

Much of the opposition to machine sharpening comes from experience with the wrong type of machine or lack of awareness of what exists out there in the professional world of knife sharpening.

Not all grinding wheels are the same

Many sharpening businesses use low cost compact machines such as CATRA or Tormek systems. ( below )

Depending on the model, these may have grinding wheels only a few inches across or only up to ten inches in diameter at best.

These machines may have their uses in your shed, but they should not be confused with the enormous water-cooled grinding wheels traditionally used by our specialist professional sharpening workshops or knife manufacturing factories.

The smaller the diameter of a grinding wheel, the more pronounced its curve is at the point where it meets the knife. That curve can create a hollow or slightly concave bevel. On a thick European knife this may be less significant, but very thin Japanese blades require considerably more precision.

This is one reason people are frequently warned against having Japanese knives machine-sharpened.

That warning is understandable when the machine involved is a small, unsuitable grinder. Even worse, a belt sander without water! ( Knife Aid USA ? )

But it does not apply to every grinding wheel...

The difference is the size of the wheel

Blade & Butler uses enormous, extremely fine, water-cooled grinding wheels measuring approximately 28 to 36 inches in diameter—around the size of a car tyre. Similar to what is used in the Global ™ knife factory in Japan. ( see below )

At the point where a Japanese knife touches a wheel of this size, the grinding surface is effectively flat. This allows us to form a precise, controlled bevel suitable for extremely thin, or single bevel Japanese blades.

The principle is rather like standing on the Earth. We know that the Earth is round, but because it is so enormous in relation to us, the ground beneath our feet appears flat. It is the same relationship between the narrow bevel of a knife and one of our huge grinding wheels.

A small wheel presents a noticeably tighter curve. A wheel approaching three feet in diameter presents an almost flat working surface across the width of the bevel.

The larger the wheel, the flatter the contact geometry across the narrow width of the knife’s bevel.

Fine abrasives and water cooling matter

Wheel diameter is only part of the equation.

Our wheels use extremely fine abrasives and are continuously water-cooled. The water controls temperature at the cutting edge, carries away grinding residue and allows the sharpener to work gradually and precisely.

London knife maker Belnheim Forge also uses large water cooled grinding wheels as part of producing its exceptional blades. In our opinion, Blenheim Forge makes some of the most beautiful Japanese-style knives in the world. Take a look at their website—the quality and individuality of the blades are extraordinary.

So used correctly, a huge, fine, water-cooled wheel can remove remarkably little metal while producing a clean and accurate bevel. Used incorrectly, even an expensive whetstone can scratch a blade, round its edge or create an inconsistent angle.

It is the complete process that matters—not whether the abrasive happens to be flat or rotating.

This is not a new or experimental method

Blade & Butler’s sharpening heritage stretches back more than a century. We were servicing Japanese knives long before specialist Japanese knife-sharpening websites and social-media sharpening businesses appeared. Take a look at these vintage images of knife sharpening using the same wheels we use. Handed down from great grand father to the generations that followed.

Blade & Butler first started sharpening Japanese kitchen knives during the 1970’s. Their popularity continued to grow through each succeeding decade. Many businesses now advertising Japanese knife sharpening are comparatively new. Their relative limited experience and training may be centred almost entirely on whetstones. Consequently, whetstones become not merely their preferred method, but the only method they recognise as legitimate.

It speaks to a limited knowledge of the specialised machinery used by traditional professional grinding workshops and knife factories across the world.

The idea that powered grinding machinery is automatically unsuitable for Japanese knives is therefore demonstrably wrong. The real questions are:

• What type of machine is being used?
• How large and fine is the grinding wheel?
• Is the blade kept cool?
• Does the sharpener understand the construction and geometry of that particular knife to remove the correct amount of steel?

Why does this myth continue?

Because it makes for compelling marketing.

Once the same claim has been repeated across enough forums, blogs and sharpening websites, it begins to appear authoritative. Search engines—and increasingly AI —then reproduce that information because it is the version repeated most often.

The truth is more nuanced: Japanese knives should not be sharpened on unsuitable grinding machinery.

That is very different from saying they must only be sharpened on whetstones.

Below you can see close-up photographs of Japanese knives serviced in our workshop. Examine the bevels, the consistency of the edges and the tiny amount of steel removed.

Above is a £495 Mcusta Zanmai. Below, the three knives are collectively worth over £1000.

The evidence is on the blade.

Whetstones can produce beautiful results. So can the correct professional machinery. What matters is understanding the knife, controlling the process and knowing precisely what you are doing.

Japanese knives do not need sharpening mythology.

They need the perfect edge.