Nenohi's Dry Grinding Technology_Nenohi Record Vol_9
You are a professional steel craftsman at Nenohi, where we use only carefully researched and developed steel materials that we've studied over many years. We establish manufacturing methods (recipes) that maximize performance by thoroughly understanding the properties and characteristics of the steel we use. In this Nenohi Record, we'll spotlight the "dry grinding" technique used for rough shaping—transforming heat-treated steel into the basic knife shape.
What is Rough Shaping?
Rough shaping, as mentioned earlier, is the process of grinding heat-treated steel into a proper knife shape with 0.1mm precision. At Nenohi, during this rough shaping stage, we create the hollow flat and the hollow back for single-bevel knives (see our single-bevel structure explanation here). We also create the "taper" that gradually thins the knife from the heel to the tip, measuring each knife individually to ensure it follows our established proportions.
By the end of the rough shaping process, we grind the blade to approximately 0.2mm thicker than the final product, accounting for subsequent grinding processes.
If a knife has poor form at the rough shaping stage, it becomes extremely difficult to improve it in later stages. By pursuing exceptional precision even in what might normally be considered preparatory stages, we ultimately create knives of the highest caliber in both performance and beauty.
What is Dry Grinding?
Now, let's discuss dry grinding in detail.
As the name suggests, dry grinding is a method where the grinding stone is used without water in a dry state. Most conventional knife manufacturing employs wet grinding, which uses water-cooled grinding wheels.
Why Nenohi Adopted Dry Grinding
Nenohi's main products are "solid steel" (hon-yaki) knives, which require exceptionally high-precision processing. Precisely crafted knives are not only beautiful but also positively impact cutting performance more than most people realize. Nenohi's unique "dry grinding" technique was born from years of trial and error in our pursuit of perfecting the precision grinding of delicate, difficult-to-process steel materials.
As mentioned, Nenohi previously used water grinding. While maintaining a perfectly round grinding wheel is fundamental to grinding technique, with water grinding, the wheel gradually loses its true circular shape, causing "vibration." Despite numerous improvement attempts, water grinding inevitably produces a certain level of vibration. Additionally, as circular grinding wheels are repeatedly used, they naturally become smaller, decreasing in diameter and deforming, making it extremely difficult to create high-precision hollow flat and hollow back.
For these reasons, Nenohi determined that water grinding, with its inherent "vibration" and "changing wheel diameter," made it impossible to achieve our desired precision. We therefore decided to transition to dry grinding. After making this change, we incorporated various techniques and methods, such as improving "jigs (fixing devices)" to increase the reproducibility of knife processing angles and developing specialized machinery for hollow back and hollow flat processing.
By making possible what was impossible with water grinding, craftsmen who have mastered our rough shaping method can now consistently produce knives of the same high quality.
Overcoming Concerns with Dry Grinding
We sometimes receive concerns about whether the sparks shown in photos or the lack of water cooling might negatively affect the blade or damage the knife (steel material). You're right that excessive "heat" on the blade is one factor that can reduce a knife's performance, which is why we certainly don't recommend processing with ordinary grinders.
However, Nenohi has repeatedly researched the "heat" generated during processing, understanding it better than anyone, and we consider it with exceptional seriousness. Through various experiments, we've created an environment where frictional heat is less likely to transfer to the blade by using special ceramic abrasives. You can imagine it as "cutting away" the steel. By cutting away the steel material while generating sparks, we can achieve rapid, precise grinding while actually preventing the knife from heating up.
Additionally, our craftsmen perform the grinding process with "bare hands," allowing them to feel and monitor the knife's temperature directly, completely preventing any negative heat effects on the blade. We guarantee that Nenohi's unique "dry grinding" method has no adverse effects on blade performance.
Implementing Dry Grinding
To achieve high-precision grinding, Nenohi has spared no expense in equipment investment. As mentioned earlier, we use special abrasive materials optimized for grinding in every aspect. High-quality abrasives not only ensure processing accuracy but also faster grinding speeds, enabling high-precision, rapid grinding.
Furthermore, to overcome the weaknesses of water grinding—"vibration" and "changing wheel diameter"—President Sawada personally designed specialized machines exclusively for grinding hollow back and hollow flat. This equipment has eliminated unevenness in bevel depth caused by changes in grinding wheel size, enabling the creation of uniform, distortion-free bevels.
As explained in a previous Nenohi Record, creating uniform bevels (concave surfaces) contributes not only to aesthetic beauty but also to superior cutting performance (the blade enters ingredients smoothly), user-friendliness (ingredients are cut without catching), and ease of maintenance (easier to sharpen as the sharpening stone makes uniform contact). This level of attention to manufacturing equipment is characteristic of Nenohi's knife-making philosophy.
While this article has highlighted the machinery involved in blade processing, mastering knife production requires almost all work to be done by hand. However, craftsmen's handwork can reach an even higher level when equipped with precisely rotating "grinding machines," "jigs" that can reproduce the same angle consistently, and "jigs" that suppress vibration.
In knife manufacturing, while "individual craftsman skill" is certainly essential, a knife is completed through the combination of multiple elements, including the "tools," "machines," and "manufacturing methods" used by the craftsman. At Nenohi, we make knives without compromising on any aspect of knife production, with unwavering commitment to every detail.
Based on the traditions passed down through the long history of knife making, we continue to build upon these techniques and will never stop challenging ourselves to "deliver excellence" to our customers who use Nenohi knives.