Hamaguri Grind

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 progressivley 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.

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.

Convex Edge Slide Cut Seki City Steel Types

Related guide: Maintenance: Hamaguri vs Konvex

Sources

  1. Hair Scissors Complete Guide, Chapter 5: Sharpening stage (Stage 12) and Chapter 6: Blade Geometry
  2. KAMIU (kamiu.jp) hamaguri grind technical documentation
  3. Hayashi Scissors historical product literature

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