Hamaguri Grind
Description
The hamaguri grind is the clam-shell edge geometry that defines premium Japanese scissors. Learn how this convex grind reduces friction and protects hair health.
Hamaguri Grind (蛤刃, hamaguriba)
Quick look
- What it is: A convex blade edge created through 7 sequential grinding angles on water-cooled stones
- Japanese name: Hamaguri (蛤), meaning “clamshell,” because the cross-section resembles two clamshell halves
- Distinct from: Generic “convex edge” and European Konvex-Schliff
- Key attribute: The edge forms an integral part of the blade mass, giving it greater rigidity and longevity than surface-only grinds
- Pioneer: Hayashi Scissors is widely credited with pioneering the hamaguri blade profile
Why it matters
The hamaguri grind is the defining edge geometry of Japanese professional scissors. Calling it simply a “convex edge” misses what makes it unique. The hamaguri is produced through a specific sequence of 7 grinding angles, applied by hand on water-cooled whetstones, with the master sharpener (研ぎ師, togishi) controlling pressure and angle through years of muscle memory. The result is a smooth convex curve from blade back to cutting edge that looks, in cross-section, like the shell of a clam.
This geometry matters for two reasons. First, the convex curve means the blade parts hair cleanly as it passes through. There is no flat bevel face to create drag or push hair sideways. This is why hamaguri edges excel at slide cutting and slicing. Second, the edge forms as part of the blade’s continuous mass. Unlike a secondary bevel ground onto a flat blade, the hamaguri edge is the blade. This gives it structural strength that holds up through thousands of cuts before resharpening.
How it is made
The 7 grinding angles are applied in sequence on progressively finer water-cooled stones. Each angle removes material from a slightly different zone of the blade face, building the convex profile layer by layer. Water cooling is essential. Dry grinding generates heat that can alter the steel’s temper and destroy hardness at the edge. The final angles produce a curve so smooth that the blade tip is finer than a human hair.
This is the most delicate operation in scissor manufacturing. A master togishi may spend years as an apprentice before being trusted with the final sharpening stages. Hand pressure, stone angle, water flow, and stroke speed all affect the outcome. Machines can approximate the hamaguri shape, but the highest quality examples are still finished entirely by hand.
Technical geometry
The hamaguri-ba profile is designed around a specific radius, typically approximately 800mm, though this varies by manufacturer and model. The cross-section transitions through multiple angle planes, from roughly 10 degrees near the cutting edge to approximately 42 degrees at the shoulder where the bevel meets the blade face. This compound geometry is what gives the hamaguri grind its characteristic “clam shell” shape and its smooth cutting action. Once this designed radius is removed by flat hone sharpening, it cannot be fully restored — which is why hamaguri-ba scissors require sharpeners trained specifically in convex geometry.4,5
Hamaguri vs. Konvex-Schliff
The European Konvex-Schliff (convex grind) is sometimes treated as equivalent to hamaguri. It is not. The two grinds use different stone types, different angles, and different finishing methods. Having Japanese hamaguri scissors sharpened by someone trained only in European convex technique can cause permanent damage to the blade geometry. The edge angles get flattened, the curve is destroyed, and the scissors lose their slide cutting ability. Always confirm your sharpener understands hamaguri technique before handing over Japanese scissors.
Related links
| Convex Edge | Slide Cut | Seki City | Steel Types |
Related guide: Maintenance: Hamaguri vs Konvex
Verified Sources
- Secondary 🇯🇵 SisRma — Scissor Information Portal (industry reference)
- Secondary 🇯🇵 Scissors Yamato — Sharpening Specialist (specialist service)
Frequently Asked Questions
The hamaguri grind is the clam-shell edge geometry that defines premium Japanese scissors. Learn how this convex grind reduces friction and protects hair health.
The hamaguri grind is the clam-shell edge geometry that defines premium Japanese scissors. Learn how this convex grind reduces friction and protects hair health. Edge type directly impacts cutting precision, hair damage, and the techniques you can perform.
Hamaguri Grind edges can be resharpened by a qualified professional. The sharpening method and frequency depend on the edge geometry, the steel type, and your cutting volume. Always use a sharpener experienced with this specific edge profile.