Blade Fuller--Blood Groove

A Fuller is a rounded or beveled groove on the flat side of a blade. Although 19th century romantic fancy referred to them as "blood grooves", their purpose is to strengthen or lighten the blade, rather than to allow blood to flow from a stabbed person.

A well made blade will have a forged Fuller to increase the strength in the spine of the blade. If the Fuller has been cut or ground out of the blade, the spine is weaker.Many blades use fullers even when they are so short that the physical effect is negligible; in this case, the purpose may be to make the weapon resemble larger blades.

The basic design principle is that bending causes more stress in material near the edge or back of the blade than material in the middle, due to leverage.

The stress distribution in an ideal blade with a rectangular section, with only a small amount of shear stress present at the neutral axis of the blade. Fullers remove material from near this neutral axis, which is closer to the blade's spine if only one edge is sharpened. This yields stiffer blades of a given weight, or lighter blades of a given stiffness.

In Japanese bladesmithing, fullers have a rich tradition and terminology, enough that there are separate terminologies for the top (hi) and bottom (tome) ends of the feature. A listing follows:

• Hi






• Bo-bi: A continuous straight groove of notable width, known as katana-bi on tanto. With soe-bi, a secondary narrow groove follows the inner straight length of the main one. With tsure-bi, the secondary is similar but continues beyond the straight length.



• Futasuji-bi: Two parallel grooves.



• Shobu-bi: A groove shaped like the leaf of an iris plant.



• Naginata-bi: A miniature bo-bi whose top is oriented opposite from the blade's, and usually accompanied by a soe-bi. Seen primarily on naginatas.



• Kuichigai-bi: Two thin grooves that run the top half of the blade; the bottom half is denoted by the outer groove stopping halfway while the inner one expands to fill the width.



• Koshi-bi: A short rounded-top groove found near the bottom of a blade, near to the tang.





• Tome






• Kaki-toshi: The groove runs all the way down to the end of the tang.



• Kaki-nagashi: The groove tapers to a pointed end halfway down the tang.



• Kaku-dome: The groove stops as a square end within 3 cm of the tang's upper end.



• Maru-dome: Similar to the kaku, except with a rounded-end.