What is Hamaguri Grind (蛤研ぎ)?

Description

Hamaguri grind (蛤研ぎ) is a blade cross-section profile resembling a clamshell, originating in Japanese sword-making. Applied to hair scissors by Hikari Scissors in 1967, it creates the smooth cutting feel associated with premium Japanese shears. The grind refers to the shaping process; convex edge is the resulting edge type.

What is Hamaguri Grind (蛤研ぎ)?

Hamaguri grind (蛤研ぎ) is a blade cross-section profile resembling a clamshell. Named after 蛤 (hamaguri = clam), it originated in Japanese sword-making and was applied to hair scissors by Hikari Scissors in 1967. The grind creates the smooth cutting feel associated with premium Japanese shears. “Grind” refers to the shaping process; convex edge is the resulting edge type.

Why It Matters for Scissors

The hamaguri grind is the manufacturing technique that produces a convex edge — the two terms are intimately related but describe different things. Understanding this distinction is essential for evaluating scissor quality, because the quality of the grind determines the quality of the resulting edge.

A well-executed hamaguri grind produces a blade that tapers smoothly and symmetrically from spine to edge with no flat facets, abrupt transitions, or grinding marks. Under 10x magnification, the surface should show a continuous curve. When two hamaguri-ground blades close together, hair slides along the curved surfaces rather than catching on shoulders or irregularities.

Hikari’s 1967 innovation was not the hamaguri grind itself — Japanese swordsmiths had used it for centuries — but its specific application to hair scissors at angles and dimensions suitable for cutting hair rather than cutting through armor or flesh. The typical hair scissor hamaguri grind uses a much shallower curve than a sword, with the convex profile concentrated in the final 2-3mm near the cutting edge.

Technical Detail
In traditional Japanese sword-making (日本刀鍛冶), the hamaguri grind is one of several blade cross-section profiles, alongside shinogi-zukuri (ridgeline construction) and hira-zukuri (flat construction). The hamaguri profile was historically favored for cutting swords (as opposed to thrusting swords) because the convex surfaces guide material away from the edge during a cut, reducing friction and binding. Hikari Scissors (株式会社ヒカリ) of Niigata Prefecture adapted the hamaguri grind for hair scissors by modifying three parameters: the radius of curvature (much gentler than a sword), the grind width (concentrated near the edge rather than across the full blade), and the surface finish (polished to a mirror finish to minimize hair friction). The company's founder studied under a swordsmith before applying these principles to scissor manufacture. The hamaguri grind is performed on a rotating grinding wheel with a curved surface. The craftsperson holds the blade at a constantly changing angle as it passes across the wheel, creating the smooth convex curve. This is in contrast to a beveled grind, where the blade is held at a fixed angle against a flat surface. The variable angle is what makes hamaguri grinding so difficult to master — the craftsperson must maintain consistent pressure and angle changes across the full length of the blade. Modern CNC-equipped factories can approximate hamaguri grinds using multi-axis grinding machines programmed with the correct curvature profiles. However, hand-ground hamaguri remains distinguishable under magnification by the subtle organic variations that indicate human control rather than machine repetition. Premium brands like Mizutani, Hikari, and Naruto still use hand grinding for their top-tier models. The quality of a hamaguri grind can be assessed by placing the blade on a flat surface and examining the light gap between the blade face and the surface. A proper hamaguri shows a smooth, even crescent of light that narrows gradually toward the edge — any flat spots or irregularities indicate grinding errors.

Sources

Frequently Asked Questions

Hamaguri grind is the shaping process — grinding the blade to a clamshell cross-section. Convex edge is the resulting edge geometry. The grind produces the edge, but they describe different aspects: process versus outcome.

蛤 (hamaguri) means 'clam' in Japanese. When viewed in cross-section, the blade profile curves outward on both sides like the two halves of a clamshell before meeting at the cutting edge.

Related Glossary

Back to top