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 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

See Also

Best cobalt steel shears →

Verified Sources

1. Secondary 🇯🇵 SisRma — Scissor Information Portal (industry reference)
2. Secondary 🇯🇵 Scissors Yamato — Sharpening Specialist (specialist service)

Frequently Asked Questions

What makes the 7-angle grinding sequence different from standard convex grinding? +

Standard convex grinding approximates a curved edge using one or two abrasive passes at different angles. The hamaguri sequence applies seven distinct grinding angles, each on progressively finer water-cooled stones, building the curve from the blade back toward the cutting edge in stages. Water cooling is required because dry grinding at this level of precision generates heat that alters the steel’s temper at the edge. The result is a cross-section profile that transitions smoothly from roughly 10 degrees near the cutting line to approximately 42 degrees at the shoulder — a compound geometry that single-pass convex grinding cannot replicate.

Why can the hamaguri profile not be restored once a flat-hone sharpener has worked on it? +

Flat-hone sharpening removes material from the curved face and replaces it with a flat secondary bevel. That flat surface is now part of the blade’s metal; there is no way to put the removed curved steel back. Re-grinding a new hamaguri profile from the flat bevel would require removing significant additional material from the blade, which shortens the scissor’s service life considerably and can only be done by a togishi with the correct water-stone sequence. Most sharpeners who are not trained in hamaguri technique either cannot or will not attempt this restoration, which is why Japanese scissor manufacturers treat factory sharpening as the only service option for their premium convex scissors.

How does hamaguri-ba differ from the European Konvex-Schliff used in Solingen scissors? +

Both are convex grinds, but the stone type, grinding sequence, and finishing method differ. Solingen Konvex-Schliff is produced on dry-wheel grinding machinery with precision-controlled angle fixtures. Hamaguri is produced by hand on water-cooled stones, with the togishi controlling angle and pressure through muscle memory rather than mechanical fixtures. The resulting cross-sections are similar in shape but differ in the smoothness of the curve transitions. A sharpener trained only in European convex technique cannot correctly service hamaguri scissors — the angle increments and stone progression are different enough that the wrong approach damages the geometry.

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