What is Ura-suki (裏スキ)?

Description

Ura-suki (裏スキ) is the concave hollow grind on the inner face of a scissor blade. This depression creates a gap between the two blades when closed, so they only make contact along the cutting edge line rather than across the entire surface. It is universally regarded as the most difficult step in scissor manufacturing.

What is Ura-suki (裏スキ)?

Ura-suki (裏スキ) is the concave hollow grind on the inner face of a scissor blade. This depression creates a gap between the two blades when closed, so they only make contact along the cutting edge line rather than across the entire surface. It is universally regarded as the most difficult step in scissor manufacturing.

Why It Matters for Scissors

The quality of ura-suki determines three critical performance characteristics: how smoothly the scissors open and close (friction), how cleanly they cut (blade contact precision), and how long the edge lasts (reduced wear from unnecessary blade-to-blade contact).

Japanese master sharpeners consider ura-suki “the soul of scissor-making.” Only a handful of craftspeople in Japan can perform it by hand to professional standards. The concave hollow must be ground to within tolerances of approximately 0.01-0.02mm to achieve proper blade contact.

When ura-suki is poorly executed, the full inner surfaces of both blades press against each other during every cut. This dramatically increases friction, causes premature edge wear, and makes the scissors feel heavy and sluggish in the hand. A well-executed ura-suki reduces blade-to-blade contact area by roughly 80-90%, concentrating all cutting force along the edge line where it belongs.

Technical Detail
Ura-suki is step 5 in the traditional 13-step Seki City scissor manufacturing process. V.ROAD (Yaoki Industry / 株式会社ヤオキ) of Seki City describes it as "the most difficult technique in scissor-making — only a few people in Japan can do it by hand." The company's published manufacturing process documents ura-suki as a separate specialist operation performed after initial blade shaping but before edge grinding. The depth and curvature of the hollow grind must be precisely matched between the two blade halves. If the hollow is too shallow, the blades experience excess friction and rapid edge wear from surface-to-surface contact. If the hollow is too deep, the blade loses rigidity and flexes during cutting, producing inconsistent results and an unreliable cutting line. The typical depth of ura-suki in a professional scissor is 0.1-0.3mm at the deepest point, measured from the blade's inner surface plane. The hollow begins approximately 1-2mm from the cutting edge and extends across the full width of the inner face. This geometry ensures that only the outermost edge line and the spine area make contact when the blades are closed. Machine ura-suki is standard in mass-production scissors, using CNC-controlled grinding wheels to cut the concave surface. While machine methods produce acceptable results for mid-range scissors, hand ura-suki remains the hallmark of artisan Japanese scissors. S2 Scissors of Seki City lists ura-suki quality as one of their primary differentiators when explaining their hand-finished process. Hand ura-suki requires the craftsperson to control grinding depth, curvature, and symmetry simultaneously while accounting for the specific steel's hardness and the blade's intended use. A thinner blade for slide cutting requires different ura-suki geometry than a thicker blade designed for blunt cutting.

Sources

Frequently Asked Questions

It controls friction, cutting precision, and edge longevity. Poor ura-suki causes blades to grind against each other across their full surface, increasing wear and making the scissors feel heavy.

Yes, but it requires a skilled sharpener experienced with Japanese scissors. Re-grinding the hollow on the inner face is a specialist service.

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