Grind
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- This article is about tools and weapons with sharp edges. For other uses, see grinding. For the music style, see grindcore.
Blade_grinds.JPG
When speaking of Japanese edged weapons, the term niku (meat) refers to the grind of the blade: an edge with more niku is more convex and/or steep and therefore tougher, though it seems less sharp. Katana tend to have much more niku than wakizashi.
Decisions about the grind of a blade are based on what it will be used for, since a tradeoff exists between a blade's ability to take an edge (enhanced for more shallow or concave grinds) and its ability to keep an edge (enhanced in steeper or more convex grinds).
A sharp object works by concentrating pressure, but high pressures can nick a thin blade or even cause it to roll over into a rounded tube when it is used against hard materials. An irregular material or angled cut is also likely to apply much more torque to hollow-ground blades, due to the "lip" formed on either side of the edge (figure, part d). More blade material can be included directly behind the cutting edge to reinforce it, but during sharpening some proportion of this material must be removed to reshape the edge, making the process more time-consuming. Also, any object being cut must be moved aside to make way for this wider blade section, and any force distributed to the grind surface reduces the pressure applied at the edge.
One way around this dilemma is to use the blade at an angle, which can make a blade's grind seem less steep, much as a switchback makes a trail easier to climb. Using the edge in this way is made easier by introducing a curve in the blade, as seen in sabers, scimitars, and katana, among many others. Some old European swords (most memorably Hrunting) and the Indonesian style of kris have a wavelike shape, with much the same effect in drawing or thrusting cuts.