Blade Curvature (反り)

Description

Blade curvature (sori) is the deliberate bow in scissor blades that controls contact pressure from pivot to tip. Essential for smooth closing action and clean cuts.

Blade Curvature (反り, そり / Sori — also おがみ / Ogami)

Quick look

  • What it is: The critical lengthwise curvature along the inner face of each blade
  • Measurement: Approximately 0.03mm, roughly one hair’s width
  • Purpose: Forces blades to contact at a single moving point, creating true shearing action
  • Creation: Achieved by hammer forging by hand, with no measuring instruments used
  • Japanese terms: 反り (そり, sori) and おがみ (ogami)

Why it matters

Blade curvature is arguably the most critical and least understood element of scissor construction. This subtle lengthwise bow, measuring approximately 0.03mm (about the width of a single human hair), is what separates scissors that cut from scissors that merely close.

Without this curvature, both blades would contact each other along their entire length simultaneously. Hair would be trapped and folded between two flat surfaces rather than sheared. The curvature ensures that the blades meet at only one point at any given moment during closing, and that point travels progressively from the heel (near the pivot) to the tip. This moving contact point is what produces the clean shearing action that defines a quality cut.

Too much curvature and the blades press together too tightly. The scissors feel stiff, difficult to close, and fatigue the hand quickly. The excessive pressure also accelerates wear on the cutting edges.

Too little curvature and the blades fail to maintain contact. Hair folds between them instead of being cut cleanly. The stylist notices this as hair bending or pushing away rather than being severed.

What makes this dimension remarkable is how it is achieved. In traditional Japanese scissor making, blade curvature is created by hammer forging by hand. There are no measuring instruments involved. The craftsman judges the curvature entirely by eye and by the feel of the blade against a reference surface. This is a skill that takes years to develop and represents one of the clearest distinctions between handcrafted and mass-produced scissors.

Related: Touch Point Blade Spine Hollow Grind

Sources

  1. HSC Scissors (JP) — craftsman technical documentation
  2. Japanese scissor forging and blade-setting craft knowledge

Related Scissor anatomy